JP4236666B2 - X-ray tomography equipment - Google Patents

Description

  The present invention relates to a medical X-ray tomography technique, and in particular, a tomographic image of an arbitrary slice plane can be obtained simply by adding a plurality of frames of projection data obtained by multiple exposure of an X-ray to a subject. The present invention relates to an X-ray tomography apparatus capable of

  Conventionally, as medical modalities capable of obtaining a tomographic image, various types such as an X-ray CT scanner, an X-ray tomography apparatus, a magnetic resonance imaging (MRI) apparatus, and an ultrasonic diagnostic apparatus have been used.

  Among them, the X-ray tomography apparatus has been used in the past as an apparatus that can obtain a tomogram relatively easily. However, due to the development of X-ray CT scanners and magnetic resonance imaging apparatuses, In the past it was almost distant. However, in recent years, it has begun to attract attention again due to the simplicity of image processing.

  As this X-ray tomography apparatus, an analog type and a digital type are known. In an analog X-ray tomography apparatus, an X-ray film is mainly used as an X-ray detector. An X-ray tube (X-ray focal point) and an X-ray film are placed facing each other with the subject interposed therebetween, and the X-ray beam exposed from the X-ray tube always includes an arbitrary cross section of the subject. Both are moved relatively sequentially. Various trajectories such as a straight line and an 8-shaped curve are selected as the movement trajectory of the X-ray tube. As a result, it is possible to blur image information other than the slice plane through multiple exposure of X-rays, and to focus on the information only on the slice plane to form an image.

  In this analog X-ray tomography apparatus, every time a slice plane is set, the X-ray film needs to be replaced and the trajectory of the X-ray tube needs to be changed. For this reason, while the trouble of replacing the film is required, the exposure of the patient increases. In addition, since the patient is required to stop breathing for each scan, the more the slice plane is set, the more disturbed breathing stops, the more likely the phase shift occurs, and the more easily the artifact appears in the image.

  In order to solve this problem, for example, a digital X-ray tomography apparatus known from Japanese Patent Application Laid-Open No. 57-203430 has been proposed. As with the analog type, this X-ray tomography apparatus moves the X-ray tube and the digital X-ray detector in the opposite directions, detects the movement position of both, and removes the X-ray detector from the X-ray detector. Image information is stored in association with each movement position, and an image of an arbitrary slice plane is obtained from this image information. Thereby, an image of an arbitrary slice plane can be obtained with one X-ray scan data.

The digital X-ray detector used in this digital X-ray tomography apparatus includes an imaging plate (IP), I.I. I. -Indirect conversion type planar detector having a TV system, an X-ray / light conversion layer (for example, an intensifying screen, a ceramic scintillator, etc.) and a light / charge conversion layer (for example, a liquid crystal such as a TFT, a photodiode, etc.), X A direct conversion type flat panel detector that performs line / charge conversion is known.
JP-A-57-203430

  There are still the following unsolved problems in both types of analog and digital X-ray tomography apparatuses.

  First, there is a situation where it is technically very difficult to control the X-ray tube and the X-ray detector to move synchronously. The accuracy of this synchronization control is very sensitive to the image quality of the tomographic image. The higher the accuracy of synchronous control, the more complicated the control mechanism and control circuit, and the higher the manufacturing cost of the apparatus.

  Secondly, there is a problem regarding the positional deviation of the X-ray tube (focus). Since the conventional tomographic apparatus does not take any measures against this point, there is a problem that the image quality is deteriorated, for example, an artifact is generated due to such a displacement.

  Third, there is a problem related to the movement trajectory of the X-ray tube. The conventional tomography apparatus does not take any special measures in this respect, and there is a problem that artifacts associated with the movement trajectory are conspicuous on the image. For example, in the case of a linear trajectory, noticeable linear artifacts appeared in the image.

  Fourth, there is a problem with contrast resolution. Since this type of X-ray tomography apparatus is basically a method of obtaining an image of a slice plane by blurring a structure other than the target slice plane, the contrast resolution is low. Even in the above-mentioned digital type device, of course, there is a similar problem because it is not configured in consideration of this point.

  Fifth, there is a problem regarding the enlargement ratio of the image. The conventional tomographic apparatus does not perform imaging taking into consideration the image enlargement ratio for each slice plane. For this reason, for example, when a tomographic image such as a coronal image having different slice positions is displayed as a moving image, a difference in enlargement ratio for each image becomes conspicuous. As a result, there is a problem that the interpretation work is affected, for example, the visibility of the affected area is lowered.

  Sixth, the collected image data of the slice plane is not fully utilized. For example, in the case of the digital X-ray tomography apparatus described above, it is possible to obtain, for example, image data of a plurality of coronal surfaces by one scan, but in the case of a conventional apparatus, the coronal image is displayed to the extent. Only image data is used.

  Further, seventhly, in the digital X-ray tomography apparatus disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 57-203430, the scan trajectory in which the X-ray tube and the detector are moved in the opposite directions relatively. In addition to the above limitation, there is a limitation on data processing in which image information from the detector is associated with each movement position and stored in the memory. Limitations on the scan trajectory and data processing have had the problem of reducing the degree of freedom related to device layout and image processing procedures in designing the system.

  Eighth, in the digital X-ray tomography apparatus, the process for obtaining a tomographic image when the X-ray tube or the detector is moved two-dimensionally or three-dimensionally is not particularly specific. No proposition has been made.

  The present invention solves the problems associated with the conventional apparatus described above and has the following objects.

  The main object of the present invention is to reduce or eliminate the difficulty associated with the conventional synchronous movement control of the X-ray tube and the X-ray detector, and to control the movement of the X-ray beam necessary for scanning. It is to be able to simplify the configuration.

  Another object of the present invention is to improve or improve the tomographic image quality by preventing or suppressing the occurrence of artifacts due to the positional deviation of the X-ray tube (focal point).

  Another object of the present invention is to prevent a state in which artifacts due to the movement trajectory of the X-ray tube are conspicuous on the image and improve the image quality of the tomographic image.

  Yet another object of the present invention is to improve contrast resolution.

  Still another object of the present invention is to prevent the occurrence of a difference in enlargement ratio for a plurality of tomographic images having different slice positions, and to improve display ability and interpretation ability.

  Still another object of the present invention is to alleviate or eliminate conventional restrictions on the scanning trajectory and restrictions on the image processing process and increase the degree of freedom of the system design and the image processing process.

  Still another object of the present invention is to obtain a tomographic image of an arbitrary slice plane even when the scan trajectory of the X-ray tube or detector is not limited to one dimension but is moved in two or three dimensions. It is to provide a highly functional system capable of data processing.

  In order to solve the above-described problems, according to the X-ray tomography apparatus of the present invention, the top plate on which the subject is placed, the bed that supports the top plate, and the X-ray from the focal point toward the subject. The relative position relationship between the focal point and the subject is changed by moving at least one of the focal point and the top plate. A driving means; a contrast medium injecting means for injecting a contrast medium into the subject in a pulsed manner; and a means for taking an X-ray image transmitted through the subject; and the relative positions of the focal point and the subject are different. X-ray detection means for capturing an X-ray image, second support means for supporting the X-ray detection means, and a positional relationship for obtaining a relative positional relationship between the focal point and the X-ray detection means during the X-ray image capture Based on the outputs of the detection means and the X-ray detection means and the positional relationship detection means. An image processing unit for obtaining a tomographic image of the subject; and a display unit for displaying an image processed by the image processing unit, wherein the driving unit performs a predetermined movement at a cycle different from the contrast agent injection cycle. The apparatus is configured to repeatedly perform the operation, and is characterized in that it is means for creating a tomographic image by selecting and combining X-ray images having the same pulse-shaped injection cycle.

  This X-ray tomography apparatus has the following advantages as compared with conventional analog and digital apparatuses.

  In the X-ray tomography apparatus of the present invention, the detector is not necessarily moved, but is installed in a fixed state, and it is sufficient to move only the tube. Alternatively, it is sufficient to move only the subject without moving the detector and the tube. For this reason, it is not necessary to perform the synchronous movement of the detector and the tube, which are difficult to control as in the conventional case. Therefore, it is possible to avoid the deterioration of the image quality of the tomographic image due to the synchronous control, while the complicated control mechanism and control circuit for the synchronous control become unnecessary, and the manufacturing cost of the apparatus can be reduced.

  In addition, this X-ray tomography apparatus is equipped with a function for improving the contrast resolution, which tends to be sacrificed on the principle of imaging, so that the contrast resolution is dramatically improved and improved, and the visibility is high. Can provide a tomographic image with excellent diagnostic ability.

  Furthermore, this X-ray tomography apparatus is equipped with a function for fully utilizing the collected slice plane image data, as compared with a conventional digital X-ray tomography apparatus. Thereby, it is possible to provide a high-performance X-ray tomography apparatus that effectively utilizes the collected data and meets various needs desired at the treatment site.

  Unlike the conventional digital X-ray tomography apparatus, this X-ray tomography apparatus eliminates the restriction on the scanning trajectory of moving the tube and the detector in the opposite directions. In addition, the limitation on data processing in which image information from the detector is stored in the memory in association with each moving position is also eliminated. The image can be recombined even if the tube (or tube and detector) is arbitrarily moved two-dimensionally or three-dimensionally. In this way, restrictions on scan trajectory and data processing have been significantly eliminated, greatly increasing the degree of freedom in equipment layout and image processing procedures in system design. Therefore, it is possible to provide an X-ray tomography apparatus that is highly versatile, easy to use, and low in cost.

  First, definitions of important terms used in the present invention and its embodiments will be described.

  As a coordinate system coordinate system, for convenience of explanation, as shown in FIG. 1, the longitudinal direction of the top plate 10a of the bed 10 is Z-axis (usually the patient's body axis direction), and the top plate 10a orthogonal to this is An orthogonal coordinate system is introduced in which the horizontal direction is the Y axis and the vertical direction perpendicular to the Z and Y axes is the X axis.

  A series of operations of X-ray exposure performed to obtain projection data of a plurality of frames necessary for generating a scan tomogram and movement of the imaging system (X-ray tube 12, X-ray detector 14, and subject P). To tell.

  Projection data Two-dimensional projection data formed by transmitting an X-ray beam through the subject P in one view. To obtain a tomographic image of a slice plane, projection data of a plurality of frames is required for the same slice plane.

This refers to a cross section of the body of the slice plane subject P.

Volume data Three-dimensional data consisting of tomographic image data of a plurality of slice planes.

One pixel of voxel three-dimensional data.

This is a process for obtaining a tomographic image of the image recombination slice plane, specifically, a process of adding the positions of the projection data of a plurality of frames together.

(Embodiment that covers features applicable to the present invention)
First, features (functions) that can be applied to the X-ray tomography apparatus of the present invention are listed by category, and embodiments that cover them are described. The X-ray tomography apparatus according to the present invention can be implemented (mounted) by combining any one or a plurality of such features (functions).

  First, FIG. 1 shows a schematic overall configuration of the X-ray tomography apparatus according to the present embodiment.

  The X-ray tomography apparatus includes a bed 10, an X-ray tube 12, an X-ray detector 14, a support mechanism 16, and a control / processing device 18. An input device 19 and a display device 20 are connected to the control / processing device 18.

  The bed 10 includes a top plate 10a that is slidable in the longitudinal direction. The subject P is usually laid on his / her back on the top board 10a and is photographed in this state. The X-ray tube 12 and the X-ray detector 14 are supported by a support mechanism 16 so as to face each other with the subject interposed therebetween. In the support mechanism 16, at least the X-ray tube 12 is supported so as to be movable three-dimensionally.

  The X-ray tube 12 emits X-rays toward the subject P. The X-ray detector 14 functions as X-ray detection means, and detects X-rays transmitted through the subject P. The control / processing device 18 includes necessary elements such as a memory (including a collected image memory 18a and a three-dimensional data memory 18b) and a CPU, and is responsible for control and data processing of the entire imaging apparatus. A tomographic image of an arbitrary slice plane is also obtained. Further, the X-ray tomography apparatus is provided with a contrast medium injection device 141 for injecting an X-ray contrast medium into the subject and an electrocardiogram data measurement device 142 for obtaining electrocardiogram data of the subject.

  In correspondence with the present invention, the control / processing device 18 functionally configures the drive means, part of the X-ray detection means, positional relationship detection means, image processing means, storage means, and alignment means of the present invention. ing. Each of these means functionally accomplishes various means for control and calculation described later.

  The imaging principle of the X-ray tomography apparatus of the present invention will be described with reference to FIG. As shown in the figure, a slice plane SP is assumed in the subject P, and the slice plane SP is formed by a large number of voxels V. Focusing on one voxel V, it is assumed that one X-ray path Xp passes through the voxel V from the focal point S of the X-ray tube 12. Actually, the X-rays emitted from the focal point S are cone beams, and there are innumerable X-ray paths in the cone beams. Between the X-ray tube 12, the X-ray detector 14, and the subject P (specifically, the top plate 10a of the bed 10) so that the angle θ of the X-ray path that passes through one voxel V changes for each view. The positional relationship (geometry) is controlled, and projection data for each view is obtained by the X-ray detector 14. The projection data of the plurality of frames are moved by an amount corresponding to the amount of change in the positional relationship and added. As a result, only the assumed slice plane is focused and projection data of each frame is added to form image data, and the image data of other slice planes SP is blurred. A tomographic image of the slice plane SP is obtained by the relative difference in blur of the image.

  The mechanical and electrical features and examples of the X-ray tomography apparatus are classified into categories, and the features, configurations and / or operations of the examples are described in detail below. In addition, when explaining each characteristic, the variation is also demonstrated collectively. These features, examples, and variations thereof can be implemented in combination with each other as appropriate, or can be implemented alone as appropriate.

2) Mechanism 3) Detector and tube 4) Scan trajectory 5) Data collection 6) Data selection 7) Data processing before image recombination 8) Image recombination 9) Image processing Image extraction / correction, 10) multi-modality, 11) overall system operation, and 12) other features will be picked up and described in this order.

1. System design Features related to the system design of the entire X-ray tomography apparatus are as follows: 1.1. -1.4. Each item can be listed up to and can be selected and implemented as appropriate. In the following description, the X-ray tube 12 may be called a tube, and the X-ray detector 14 may be called an abbreviated form as needed.

1.1. Attachment angle / position of tube and detector The X-ray tube 12 and the X-ray detector 14 can be arranged at various attachment angles / positions with respect to the subject P (that is, the top 10a). In the X-ray tomography apparatus according to the present invention, in principle, it is sufficient that the X-ray detector 14 can receive transmitted X-rays when X-ray irradiation is performed while moving the X-ray tube 12. It may or may not be moved. Various examples of this arrangement are shown below.

1.1.1. This is a system that will be referred to as a “detector horizontal system”. As shown in FIG. 3, this detector horizontal placement system is arranged in a horizontal position on the left and right sides in the Y-axis direction so that the X-ray tube 12 and the X-ray detector 14 face each other with the subject P interposed therebetween (subject When P is on its back, they are arranged on the left and right sides of the subject. For this reason, the X-ray tube 12 and the X-ray detector 14 are lateral to the floor.

  Employing this horizontal detector system has the advantage that the operator can easily access the affected area of the patient from above during the operation.

  Note that the X-ray tube 12 and the X-ray detector 14 may be placed diagonally to the left and right of the subject P.

1.1.2. Detector Underlay System Another example relates to a system that will be referred to as a “detector underlay system”. As shown in FIG. 4, the detector placement system makes the X-ray tube 12 and the X-ray detector 14 face each other with the subject P interposed therebetween, and the X-ray tube 12 is located below the subject P in the X-axis direction. And the X-ray detector 14 is arranged on the upper side of the subject P in the X-axis direction.

1.1.3. Detector-mounted system Yet another example relates to a system that will be referred to as a "detector-mounted system". As shown in FIGS. 5 and 6, the detector placement system makes the X-ray tube 12 and the X-ray detector 14 face each other across the subject P, and the X-ray tube 12 is in the X-axis direction of the subject. In this system, the X-ray detector 14 is arranged on the upper side and on the lower side in the X-axis direction of the subject. In this detector mounting system, two embodiments can be proposed as follows.

1.1.3.1. A system having a mechanism for moving the X-ray tube 12 As shown in FIG. 5, this detector placement system places the X-ray tube 12 positioned below the subject P in a predetermined space below the subject P. A movable moving mechanism 22 is provided. Thereby, the X-ray tube 12 can be moved one-dimensionally, two-dimensionally or three-dimensionally within the predetermined space.

1.1.3.2. System having portable X-ray detector When this detector mounting system is employed, the X-ray detector 14 is positioned above the subject P. Therefore, in the detector mounting system of another embodiment, the X-ray detector 14 is attached to be suspended from the tip of a portable device 24 with casters, as shown in FIG. Is supported below the subject P by a support mechanism separate from the portable device 24. That is, the X-ray tube 12 and the X-ray detector 14 are supported by support mechanisms that are independent of each other. The mechanism for supporting the X-ray detector 14 is not necessarily limited to the portable device 14 and may be another separate support mechanism.

  Thereby, the convenience at the time of setting the X-ray detector 14 improves. For example, the portable device 24 can be moved to the lateral position of the top plate 10a after the subject P is turned upside down on the top plate 10a, and the X-ray detector 14 can be set to a predetermined height above the subject P. As a result, the subject P does not get in the way when getting on and off the bed.

1.2. Detector Fixation System Another feature of the system design is a system that will be referred to as a “detector fixation system”. This system is a system for holding the X-ray detector 14 in a fixed state.

1.2.1. A system for inserting the detector into the bed As a preferred example of the detector fixing system, as shown in FIG. 7, the X-ray detector 14 is formed as a cassette, and the cassette is detachably inserted into the body of the bed 10. Constitute. When the cassette is inserted, the X-ray detector 14 is mounted in a fixed state at a predetermined position below the subject P, for example.

  In this case, if the cassette for loading a film for normal X-ray photography and the cassette for mounting an X-ray detector can be used in common, the convenience can be improved.

1.3. Covered system system Another feature of the design is the system we will call "covered system". In this system, as shown in FIG. 8, for example, predetermined space regions in which the X-ray tube 12 and the X-ray detector 14 move are surrounded by protective covers 26a and 26b, respectively. As a result, it is possible to prevent a situation in which the X-ray tube or the X-ray detector moves and involve other objects, and the subject P can be given a sense of security.

  This system with a cover may be employed only for the X-ray tube 12 and the X-ray detector 14 that are moved during imaging. Further, the system with a cover may be used not only for the detector horizontal installation system described above but also for either the detector lower system or the detector upper system. Further, the X-ray tube 12 or the X-ray detector 14 may be movably accommodated in the bed main body so that the bed main body itself functions as the cover.

1.4. System for moving the couch top (subject) Another feature is that the couch 10a of the couch 10 is slid in the Z-axis direction, for example. At this time, the X-ray tube 12 may be moved asynchronously to the slide of the top plate 10a, or the X-ray tube 12 and the X-ray detector 14 may be moved together asynchronously to the slide of the top plate 10a. Alternatively, the X-ray tube 12 and the X-ray detector 14 may be fixed, and only the top 10a, that is, only the subject P may be scanned while sliding in the Z-axis direction, for example. As a result, the subject P moves relative to the X-ray beam.

1.5. Tube / detector removable / retractable system Further features of the system design will be described with reference to FIG. This feature relates to removal or evacuation of the X-ray tube and / or X-ray detector. Below the top plate 10a of the bed 10, a moving mechanism 28 such as a rail and a motor mechanism that can move the X-ray tube 12 is installed. For this reason, the X-ray tube 12 is linearly moved along the Z-axis direction by the moving mechanism 28, for example. The X-ray tube 12 is connected to the high pressure generator 30. The X-ray tube 28 can be removed and attached according to the purpose of imaging. For example, the above-described portable device 24 can be used to position the X-ray detector 14 so as to be retractable above the subject P placed on the top 10a. This system can cope with switching between a plurality of photographing modes.

1.5.1. Shooting mode switching (1)
One of the typical imaging mode switching is switching between the simple imaging mode and the tomographic mode. First, assume that simple shooting is performed. In this case, the X-ray tube 12 is attached to the moving mechanism 28 (see FIGS. 9A and 9A). Next, the X-ray detector 14 ′ attached to the portable device 24 ′ is carried to the bed side, and the X-ray detector 14 is placed at a predetermined position above the subject P (FIG. 9B, ( b ')). As the X-ray detector 14 'in this simple imaging, one having a high spatial resolution is usually selected. In this installation state, simple imaging (acquisition parameters are, for example, spatial resolution 0.05 mm, acquisition size 17 ″, still image). At this time, console-side parameters (dynamic range, etc.) are also used for simple imaging. Adapted.

  When this simple imaging is finished, the operation shifts to tomography in the tomography mode. As a preparation for this, the X-ray detector 14 ′ so far is retracted together with the portable device 24 ′ (or placed in an unobstructed place (side)), and the X-ray detector 14 ″ for tomography is used. Are transported together with the portable device 24 ″ and installed (see FIGS. 9C and 9C). As the X-ray detector 14 ″ in this tomography mode, one having a large (fast) acquisition rate is suitable. In this state, tomography (acquisition parameters are, for example, spatial resolution 0.2 mm, acquisition size 10 ″, The collection rate is 30 frames / sec).

  Also, when returning from tomographic imaging to simple imaging, the procedure is performed in the opposite procedure to that described above.

1.5.2. Shooting mode switching (2)
Another typical imaging mode switching is switching between an angiography mode and a tomography mode. In this case, angio-perspective imaging is performed at the imaging steps of FIGS. 9B and 9B ′.

  Since the X-ray tube and / or the X-ray detector can be easily removed or retracted in this way, another inspection can be easily performed at the same place before and after tomography, which is very versatile. A system with excellent performance can be provided.

2. Various features that can be classified into the “mechanism” category of the mechanism X-ray tomography apparatus will be described with reference to the drawings.

2.1. In the present invention, for example, scanning is performed while moving the X-ray tube 12 and the X-ray detector 14, or the X-ray detector 14 is fixed and only the X-ray tube 12 is moved. Scan while moving. When the X-ray tube 12 and the X-ray detector 14 are moved, it is desirable to move both in synchronization. That is, in order to simplify post-processing of X-ray transmission data, it is necessary to recognize “at which position” the transmission data irradiated with X-rays is detected at “at which position”. Two examples of the synchronous movement of the tube and the detector are as follows.

2.1.1. Electrical synchronization In this embodiment, the synchronous movement of the X-ray tube 12 and the X-ray detector 14 is performed electrically. As shown in FIG. 10, the X-ray tube 12 and the X-ray detector 14 are respectively attached to moving sub arms 30 a and 30 b at both ends of a support arm 30 called a U arm formed in a U shape, for example. The moving sub-arms 30a and 30b are movable with respect to the support arm 30 by moving mechanisms 32a and 32b. The moving mechanisms 32a and 32b include a servo mechanism, for example. The same drive signal P1 is given from the synchronous drive circuit 34 to the moving mechanisms 32a and 32b. For this reason, both the moving mechanisms 32a and 32b move in response to the drive signal P1, and the X-ray tube 12 and the X-ray detector 14 move in synchronization. Position sensors 34a and 34b such as encoders are attached to the moving mechanisms 32a and 32b, respectively. The actual positions at which the X-ray tube 12 and the X-ray detector 14 have moved are detected by the position sensors 36a and 36b, respectively, and taken into the synchronous drive circuit 34. For this reason, the synchronous drive circuit 34 can recognize the positions of the X-ray tube 12 and the X-ray detector 14 in real time.

2.1.2. Another example will be described with reference to FIG. In this embodiment, the tube 12 and the detector 14 are mechanically synchronized. The X-ray tube 12 and the X-ray detector 14 shown in FIG. 11 are movably supported by a support arm (U arm) 30 configured in the same manner as the support mechanism in FIG. Drive transmission means 38a such as a shaft and an arm from the synchronous drive mechanism 38 are mechanically coupled to the moving mechanisms 32a and 32b at both ends of the support arm 30. The synchronous drive mechanism 38 includes elements such as a motor and gears, and is driven in response to a command signal from the control circuit 40. For this reason, the X-ray tube 12 and the X-ray detector 14 are mechanically driven by the synchronous drive mechanism 38 and move in synchronization.

2.2. Another feature in the category of slip ring mechanisms is the use of slip rings. As described above, in the present invention, since scanning is performed while moving at least the X-ray tube 12, it is desirable to use a slip ring so that the power supply line and the signal line are not entangled. It is particularly suitable when the X-ray tube 12 is moved in a two-dimensional or three-dimensionally complicated locus.

2.2.1. Low pressure slip ring A low pressure slip ring 42 is used as one example of this slip ring. As shown in FIG. 11, a low-pressure slip ring 42 is inserted in the middle of the power supply line reaching the X-ray tube 12. The AC 100V power is supplied to the tube side through the low-pressure slip ring 42. On the tube side, a generator 44 attached to the support arm 30a is provided. This generator 44 generates a high pressure from a low pressure and supplies it to the X-ray tube 12.

2.2.2. High Pressure Slip Ring Another example of a slip ring is the high pressure slip ring 46. As shown in FIG. 10, a high-pressure slip ring 46 is interposed in the middle of the power supply line reaching the X-ray tube 12. For example, a high voltage power supply of 120 kV DC is supplied to the X-ray tube 12 through the high pressure slip ring 46.

  The slip rings 42 and 46 are not limited to being used for the U arm, but can be suitably implemented for the C arm described later.

2.3. Non-slip ring system As another feature, a tube moving mechanism that does not use the above-described slip ring can be provided. An example of this is shown in FIGS.

  The moving mechanism shown in the figure is configured such that the X-ray tube 12, that is, the lead wires 12a and 12b, does not rotate but only reciprocates in a circular arc and reciprocates linearly. Specifically, the X-ray tube 12 is fixedly supported by a slide member 100 having a shoulder, and the slide member 100 is fixedly supported by a support rod 102. The support rod 102 passes through the ring 104a at one end of the arm 104 so as to be rotatable. The other end of the arm 104 is connected to the output shaft of the motor 106. For this reason, when the motor 106 rotates as indicated by the arrow AR1, the arm 104 rotates as indicated by the arrow AR2, and the support rod 102 is also rotated in the direction of the arrow AR2 by being urged by this rotation.

  As shown in the drawing, the slide member 100 is slidably engaged with a groove 108a formed along the longitudinal direction of the strip-shaped support plate 108 via its shoulder. One end of the support plate 108 is rotatably attached to the fixed shaft 110 as shown. For this reason, when the motor 106 rotates in the direction of the arrow AR1, the slide member 100 also tries to rotate in the same direction as the rotation (see the arrow AR3). At this time, the arm 104 is not fixed to the support rod 102, that is, the slide member 100, and the support plate 108 can freely rotate about the fixed shaft 110. Therefore, the slide member 100 is moved (rotated) in the direction of the arrow AR3 and is also converted into a linear movement along the groove 108 by rotating the support plate 108 in the direction of the arrow AR4 (see the straight arrow AR5). That is, the slide member 100 only moves linearly in the groove 108.

  For this reason, when the motor 106 is continuously rotated, the position and orientation of the slide member 100 (that is, corresponding to the position and orientation of the X-ray tube 12) change as shown in FIG. The X-ray tube 12 itself continuously rotates 360 degrees as the motor 106 rotates, but the direction of the X-ray tube 12 only changes by the arc-shaped opening angle of the support plate 108. Therefore, since this arc-shaped movement can be absorbed by the flexibility of the lead wires 12a and 12b itself, it is not necessary to install a slip ring in the middle of the lead wires 12a and 12b.

  On the other hand, an X-ray collimator 112 is installed below the X-ray tube 12, and a support rod 114 of the X-ray collimator 112 is connected to an output shaft of the motor 106 via, for example, a C-shaped arm (not shown). Mechanically coupled. For this reason, the X-ray tube 12 and the X-ray collimator 112 move in synchronization, and the X-ray beam exposed from the X-ray tube 12 can always be narrowed by the X-ray collimator 112.

2.4. Another feature in the category of U-arm mechanism is the use of U-arm 30. As shown in FIGS. 10 and 11, the U arm 30 can control the length of its arm support (see arrow A in the figure). By this length control, the image enlargement ratio can be freely controlled within a predetermined range.

2.5. Another feature that falls into the category of C-arm mechanisms is the use of C-arms.

2.5.1. System for Direct Attachment to C-arm As an example of the C-arm, the configuration shown in FIG. 12 is provided. That is, the X-ray tube 12 and the X-ray detector 14 are respectively attached to both ends of the conventionally known C-arm 50. The C-arm 50 can be slid and rotated along the circumferential direction of the arm (see arrow B1), and can be rotated around the arm support shaft 50a (see arrow B2). Thereby, the X-ray tube 12 and the X-ray detector 14 can be moved.

2.5.2. Method of Extending Child Arm from C-arm As another example of the C-arm, the configuration shown in FIG. 13 is provided. According to the configuration of this embodiment, the moving / rotating mechanisms 52a, 52b are respectively attached to both ends of the C arm 50, and the child arms 54a, 54b are respectively attached from the moving / rotating mechanisms 52a, 52b. The X-ray tube 12 and the X-ray detector 14 are attached to the child arms 54a and 54b, respectively. The movement / rotation mechanisms 52a and 52b receive movement / rotation command signals from a control circuit (not shown), and are driven independently or synchronously.

  Therefore, for example, even when the C arm 50 itself is fixed, the X-ray tube 12 and the X-ray detector 14 are provided by giving commands to the moving / rotating mechanisms 52a, 52b and moving / rotating the child arms 54a, 54b. Can be moved (see arrows C1 and C2). Further, as described above, the movement of the child arms 54a and 54b is added to the movement of the C arm 50 itself in the circumferential direction of the arm and the rotation around the arm spindle (see arrows B1 and B2). You may make it raise the freedom degree of movement of the X-ray tube 12 and the X-ray detector 14. FIG. For example, as shown in FIG. 14, when the child arm 54a having the same length is changed from the solid line Di to the imaginary line Dj, the movement range of the X-ray tube 12 even if the C arm 50 moves in the same way. Changes, so the shooting range can be controlled.

  On the other hand, to simplify the control of the motion, the X-ray detector 14 can be held in a fixed state, and tomography can be performed by moving only the X-ray tube 12.

  In the support configuration of FIG. 13, the X-ray detector 14 may be directly fixed to the C arm 50 without providing a moving / rotating mechanism.

2.5.2.1. System for Adjusting Length of Child Arm As a modification of the embodiment using the child arms 54a and 54b, a mechanism for adjusting the length of the child arms 54a and 54b can be provided. For example, at least the tube side of the moving / rotating mechanisms 52a, 52b described with reference to FIG. 13 is configured so that at least the length of the child arm 54a can be adjusted (see FIG. 13, arrows D1, D2). Thereby, for example, the radius of rotation when the child arm 54a is rotated can be changed, and the photographing range can be easily controlled only by adjusting the length of the child arm 54a (FIG. 13, arrows E1, E2). reference).

  Thus, in the U arm and the C arm, the apparatus alone has a support mechanism for the tube 12 and the detector. For this reason, as seen in the conventional analog X-ray tomography apparatus, the X-ray tube is suspended from the ceiling, and the X-ray tube is moved along a rail provided on the ceiling surface. There is no need for large-scale devices.

2.6. Drive mechanism A servo motor is mounted on the drive source of the drive mechanism of the various support mechanisms, whereby the electrical control amount is suitably converted into the mechanical movement amount. However, it is not necessarily limited to a servo motor, and an arbitrary one can be used.

3. In the category of detector and tube “detector and tube”, X-ray detector 14 and X-ray tube 12 applicable to the X-ray tomography apparatus of the present invention are exemplified.

3.1. Fluorescent plate and readout means As an example of an X-ray detector, a detector comprising a fluorescent plate that converts X-rays into light and a readout means such as a high-sensitivity camera that reads out the light can be used.

3.2. I. I.
As another example of an X-ray detector, I.I. I. (Image Intifier) can be used.

3.3. Planar Detector As yet another example of an X-ray detector, a planar detector can be used. This flat detector may be either an indirect conversion type or a direct conversion type.

  The various detectors described above are preferably two-dimensional detectors having a large two-dimensional X-ray incident surface size. If the size of the two-dimensional detector is large, X-rays from all focal positions when the tube is moved can be made incident even when the detector is fixed.

  In addition, it is desirable that the above-described various detectors include or add an A / D converter to finally output the read X-ray transmission data in a digital amount.

3.4. Fixed anode X-ray tube As an example of an X-ray tube, a fixed anode X-ray tube can be used. When using a slip ring, the fixed anode X-ray tube may be a low-pressure slip ring, and the focal spot size can be reduced, so that the resolution is improved.

3.5. Rotating anode X-ray tube As another example of an X-ray tube, a rotating anode X-ray tube can be used. The rotary anode X-ray tube becomes a high-pressure slip ring when a slip ring is used.

4). In order to perform scan orbit tomography, it is generally necessary to perform a scan while moving the tube and detector or the tube. In this scan, the trajectory for moving the tube and detector or the tube is called a scan trajectory. In principle, photographing is possible by moving only the tube, but in many cases the detector is also moved to increase the field of view.

  This scan trajectory is usually preset. At the time of imaging, the movement of the tube and detector or the tube is controlled based on the set scan trajectory. The scan trajectory is one of the important factors that determine the shooting time and the quality of shooting.

4.1. Scan trajectory The scan trajectory of the tube and detector or the tube may be a straight line as shown in FIGS. 15 (a) to 15 (c), and may be the same plane as shown in FIGS. 16 (a) to 16 (c). It may be a two-dimensional curve, or may be a three-dimensional curve as shown in FIG. That is, any trajectory is possible.

4.2. Scan trajectory of detector When the detector is moved, it may be moved in parallel (two-dimensional or one-dimensional) in the coordinate system, or may be moved in a three-dimensional shape such as an arc. Movement by rotation is also possible. That is, any trajectory is possible.

4.3. Face-to-face detector tube One example of the scan trajectory is that the detector 14 is always faced to the tube 12 (the detection surface is perpendicular to the X-ray exposure center direction). There is movement control. As shown in FIG. 18, for example, it is assumed that the X-ray tube 12 has moved in an arc from a state F1 shown by a solid line to a state F2 shown by an imaginary line. In response to this, the X-ray detector 14 changes from the state F1 shown in the solid line (in this state, the X-ray incident surface of the X-ray detector faces the X-ray tube) to the state F2 shown in the phantom line. To move the X-ray detector 14 to the X-ray tube 12 again.

  Thereby, even when the X-ray tube 12 moves using, for example, a three-dimensional curve as a trajectory, the direct relationship between the X-ray incident surface of the X-ray detector 14 and the X-ray tube 12 can always be maintained. As a result, unlike the conventional analog X-ray tomography apparatus, the field of view of the X-ray detector 14 can always be utilized to the maximum.

4.4. Closed curve scan trajectory Another example of a scan trajectory is a closed curve scan trajectory. For example, the scan trajectories shown in FIGS. 16B and 16C are closed curves in which the start point and the end point coincide. If this scan trajectory is adopted, the scan end position becomes the scan start position, so that the scan can be executed a plurality of times continuously without interruption.

  Further, intermittent scanning may be performed using the scanning curve of the closed curve. For example, after the scan is executed once, the scan is paused for a predetermined time, and the scan is executed again after the pause. This is suitable for dynamic acquisition in which a contrast medium is injected into a blood vessel and its spread is imaged.

4.5. Non-Closed Curve Scan Trajectory Yet another example of a scan trajectory is a non-closed curve scan trajectory. For example, in the scan trajectory shown in FIG. 16A, the starting point and the ending point do not coincide with each other, and are open curves. However, intermittent scanning is possible by returning the scan position from the trajectory end point to the trajectory start point each time one scan is completed. This intermittent scan is suitable for dynamic acquisition.

4.6. Peripheral motion scan trajectory Yet another example of a scan trajectory is perihelical motion. For example, this scan orbit is the orbit of a satellite orbiting around the sun. In order to achieve this scan trajectory, for example, as shown in FIG. 19A, the X-ray tube 12 is supported by two rotatable axes. The child arm 64 is supported by the support arm 60 via the rotation support mechanism 62 so as to be rotatable on the YZ plane, and the grandchild arm 68 is also supported by this child arm 64 via another rotation support mechanism 66 so as to be rotatable on the YZ plane. Has been.

  Thus, by rotating the grandchild arm 68 while the child arm 64 is rotated, a scan trajectory of the circumferential sky motion is obtained as shown in FIG. In contrast, in order to realize this scan trajectory, information such as the rotation speeds of the child arm 64 and the grandchild arm 68 may be set in advance. Due to this circumferential orbital scan trajectory, a large imaging range can be obtained even if the amount of movement of the tube itself is small and the X-ray incident surface of the detector is relatively small.

4.7. Scanning trajectory for moving the imaging field of view As yet another example of the scanning trajectory, there is a scanning trajectory for scanning a plurality of times while moving the imaging field of view. For example, as shown in FIG. 20, the scan trajectory is a circle of the tube and the detector that is synchronously drawn on the YZ plane. When this circular trajectory is completed, the tube and the detector are moved in the Z-axis direction. Then, a circle is again drawn synchronously on the YZ plane, and this is repeated a plurality of times. In order to obtain this scan trajectory, for example, in FIG. 19 described above, the entire support arm 60 may be moved linearly intermittently while only the grandchild arm 68 is rotated.

  As a result, a circular scan trajectory can be formed, for example, in the Z-axis direction, and the field of view can be shifted in the Z-axis direction for removal. The direction in which the field of view is shifted may be other than the Z-axis direction, and the trajectory of each scan may be a shape other than a circle, for example, an ellipse. This scan trajectory is advantageous when the focal trajectory and the detector size are relatively small, and provides a wide imaging range across multiple scans.

  In FIG. 20, the tube and the detector may be rotated and both may be linearly moved continuously. As a result, a scan trajectory in which circular trajectories are linearly connected is obtained.

4.8. Scanning trajectory in which the period of the tube and the detector is shifted As another example of the scanning trajectory, there is a trajectory for scanning while shifting the period of the tube and the detector. This scan trajectory is illustrated in FIG. In the case of this example, while the tube is continuously rotated n times (n> 1, for example, 10 times, each cycle being for example 1 sec), and the circular scan trajectory is drawn at the focal point, the detector Are moved linearly from position a to position b in the figure every predetermined time (for example, every second) or continuously.

  Thereby, in the same desired slice plane S, the cycle (time) of the tube and the detector is shifted from each other depending on the position. For this reason, it is suitable for observation of the blood flow BD flowing along the slice plane S, and images other than the desired slice plane can be favorably blurred.

  The scan trajectory of the tube is not circular, and may be a scan trajectory that performs a circumferential sky motion. The scan trajectory of the detector may not be linear.

4.9. Scan trajectory by two-axis movement of tube and one-axis movement of detector As another example, the tube is moved by two axes 64 and 68 as described above in 19 (a), and the detector is moved by one axis. There is a scan trajectory when moving. Depending on how both the tube side and detector side axes are moved, for example, a scan trajectory combining a scan trajectory due to the circumferential motion of the tube and a scan trajectory due to the linear motion of the detector can be formed.

4.10. Selection of scan trajectory, trajectory radius Yet another example involving scan trajectory involves selection of scan trajectory and / or trajectory radius. In the conventional X-ray tomography apparatus, the shape of the scan trajectory and the trajectory radius are fixed in advance, and only the determined scan trajectory and trajectory radius can be used. However, in this embodiment, as described above, it is possible to use a U arm or a C arm that supports the tube and the detector with multiple degrees of freedom (not supported from the ceiling) by the apparatus itself. Therefore, data for instructing a plurality of scan trajectories and trajectory radii is stored in advance in the control device for driving the arm so that the operator can select the scan trajectories and trajectory radii. As a result, a scan corresponding to the field of view and the region to be imaged can be commanded accurately and quickly.

4.11. Combination of mechanisms for a plurality of scan trajectories Yet another example is to arbitrarily combine mechanisms capable of realizing a plurality of scan trajectories. For example, there is a combination in which a support mechanism that draws a scan trajectory of any one of a circumferential sky motion, a circular motion, and a linear motion is adopted on the tube side, and a support mechanism that draws a scan trajectory of the linear motion is adopted on the detector side.

4.12. Numerically Arbitrary Scan Trajectory Yet another example relates to a technique for providing an arbitrary numerical value and drawing a scan trajectory along that numerical value. In order to obtain the scan trajectory, as described above, the tube / detector support mechanism unique to the device itself is provided, and the support mechanism has a plurality of support shafts, so the motion of the support shafts is controlled numerically. For example, an arbitrary sine wave scan trajectory can be obtained.

5. Data Collection Next, the characteristics classified into the “data collection” category of the X-ray tomography apparatus according to the present invention will be described.

  In this X-ray tomography apparatus, at least each tube is moved continuously or intermittently, and X-rays that have been exposed from the tube focus and transmitted through the subject are detected by a detector. X-ray projection data (frame data) at the time of shooting is collected. This exposure / detection is repeated a plurality of times to achieve one scan. As will be described later, based on projection data of a plurality of frames obtained by performing at least one scan, image recombination of arbitrary slice planes is performed to obtain a tomographic image of the slice planes. The scan is performed multiple times if necessary.

  The characteristics related to the category of “data collection” represent various characteristics at the time of scanning. This example will be described in detail below by item.

5.1. One example of a variable resolution feature of the image intensifier (I.I.) is the I.I. I. When using. I. I. The resolution is made variable by electronic enlargement. Thereby, the resolution can be easily controlled.

5.2. Data collection in line with the scan trajectory Another example is to adapt the timing of data collection to the scan trajectory, in particular the shape. For example, as shown in FIG. 22A, it is assumed that an elliptical scan trajectory is adopted for both the tube and the detector. In the case of a scan orbit having such a shape, the orbital motion speed may be lower in the elliptical arc portion having a small curvature than in other portions. In such a case, assuming that the projection data collection timing of the detector is temporally uniform as shown in FIG. 5A, the spatial collection density in the arc portion having a small curvature is equivalent to another portion. Higher than. As a result, an artifact AF similar to the shape of the arc portion having a small curvature may appear in the recombined image as shown in FIG.

  In order to prevent this, as shown in FIG. 5C, the projection data collection timing of the arc portion having a small curvature is made rougher in time than the other portions. That is, the density of data collection is set according to the shape of the scan trajectory. In this timing control, the control device may recognize where the current tube and detector positions are on the scan trajectory, and control the collection timing in accordance with the recognition result. As a result, the scan as a whole is spatially uniform by setting data with a spatially uniform period, that is, by setting the time unevenly.

  This data collection timing is not only the data detection timing by the detector but also the exposure timing of the tube when the tube is exposed to pulsed X-rays.

  Instead of the method of changing the data collection timing, the moving speed on the scan trajectory may be controlled relatively, for example, the moving speed is slower as the curvature increases (lower as the curvature decreases).

5.3. Use of Pulse X-rays As another example, X-rays exposed from a tube may be set to pulse X-rays. In this case, the timing of data detection by the detector also follows this.

5.4. Control of Dynamic Range Based on Projection Data Yet another example is to control the dynamic range of a detector using projection data (frame data) of transmitted X-rays detected by the detector. This embodiment has the following two modes.

5.4.1. Control of dynamic range by adjusting output of tube For example, a pixel value of projection data is determined, and the determination result is fed back to the tube. For example, when the pixel value indicates an overflow of the dynamic range, an adjustment for decreasing the tube output is automatically performed to prevent the overflow.

5.4.2. Dynamic range control by detector gain adjustment Another example is detector gain adjustment. Since the A / D converter is mounted on the X-ray detector as described above, the gain (sensitivity) of the integrator of the A / D converter is adjusted according to the determination result of the pixel value of the projection data. . For example, when the pixel value indicates an overflow of the dynamic range, the adjustment for decreasing the gain is automatically performed to prevent the overflow.

5.5. Use of continuous X-rays Another feature is that the tube is operated in continuous X-ray mode.

5.5.1. Data collection timing (position) is defined as a point In the continuous X-ray mode, X-rays are continuously emitted from the focal point of the tube in time. Therefore, as shown in FIG. 23, the detector accumulates (integrates) transmitted X-ray energy (charge) with time every frame data collection period, and accumulates it at an appropriate point position timing in the frame period. Detect energy. There are the following two modes for setting this point position.

5.5.1.1. In this example, if the collection period of a certain frame data is t1 to t2 (positions on the scan trajectory L are L1 to L2) as shown in FIG. It is determined by the position of the center of gravity, that is, the center time. For example, the acquisition timing for one frame is determined by (t1 + t2) / 2.

  The acquisition timing in this mode is calculated in advance from the frame data acquisition times t1, t2, t3,..., And the acquisition command is given to the detector along the acquisition timing calculated at the time of scanning. That's fine.

5.5.1.2. According to this example, the centroid (distance) of the scan trajectory for each frame is calculated in advance, and the detector is instructed of the collection timing at which the centroid position as this point position is reached. In the case of FIG. 23, for example, the collection timing for one frame is determined by (L1 + L2) / 2.

  Note that the collection timing based on the centroid of the collection time coincides with the collection timing based on the centroid of the scan trajectory only when moving on the straight scan trajectory at a constant speed.

5.6. DSA with multiple scans
As another feature, DSA (Digital Subtraction Angiography) can be performed by scanning the same part of the subject a plurality of times. This is suitable for detecting the movement (change) of a contrast medium injected into a blood vessel or examining changes in a certain part before and after surgery.

5.6.1. Difference in projection data As an example, there is a difference between projection data. Projection data obtained in each view in the first scan is stored as mask data. The difference between the mask data (projection data) and the collected projection data is calculated for each view in the next and subsequent scans. In the recombination of images described later, a tomographic image is obtained by adding difference data of a plurality of frames.

5.6.2. Differences in tomographic image data or voxel data Another example is two-dimensional tomographic data of a slice plane obtained by recombination or three-dimensional volume data obtained by recombining a plurality of slice planes. A difference may be taken according to the state. Also in this case, for example, the tomographic image data or volume data obtained in the first scan is used as a mask image, and the difference from the tomographic image data or volume data obtained in the subsequent scan is calculated for each pixel. Thereby, change with time can be examined.

5.6.3. Collection timing of mask image data The timing of collecting the mask image is not necessarily limited to the first scan, and is an intermediate scan of the plurality of scans depending on the nature and state of the amount of change to be observed. It can be set at any time such as scanning.

5.6.4. Nonlinear Processing After Difference Further, nonlinear processing can be performed as a processing example after the difference calculation.

5.6.4.1. Nonlinear processing is threshold processing As specific nonlinear processing, there is threshold processing. The data obtained by the difference calculation is further discriminated by a predetermined threshold value, and the difference data below the threshold value is forcibly set to zero. As a result, the background contrast can be compressed and the overall data amount can be reduced.

5.7. Installation of Compensation Mechanism As yet another feature, a compensation mechanism such as a wedge filter implemented in a water bed or an X-ray CT scanner may be provided. Thereby, a dynamic range can be expanded.

5.8. Strobe photography Another feature is strobe photography using pulse contrast enhancement.

5.9. ECG-synchronized scan As yet another feature, an ECG-synchronized scan may be performed. As an alternative to the pulse contrast cycle, the heartbeat cycle is used.

6). Data Selection Next, features and examples classified into the category related to “data selection” of the X-ray tomography apparatus according to the present invention will be described.

  Image recombination in this X-ray tomography apparatus performs a process of “selecting data” from projection data of each frame and adding the data to each voxel on the slice plane. The “data selection” process at this time is the simplest process when the tube and the detector are moved in parallel with each other.

  That is, the positions of the focal point (tube) and the detector are detected, the shift amount of the projection data of each frame necessary for image recombination is calculated, and the shift amount is appropriately corrected. That is, instead of determining the shift amount from the beginning, it is possible to calculate the shift amount after performing a scan by appropriately moving the focus and detector or the focus. Since the shift amount can be freely calculated in this way, it is possible to facilitate the setting of the scanning conditions, such as widening the selection range of the focus at the time of scanning and the movement pattern of the detector.

6.1. Use of position detection means One feature is the method of detecting the focus and detector or the position of the focus by the position detection means. In this case, position information at the time of detecting transmission data of each view is stored, and projection data of pixels that match the position information is selected for each frame.

6.1.1. Position Detection Means Provided Inside As an example of the position detection means, first, position detection means such as an encoder and a potentiometer provided in the moving mechanism 16 may be mentioned. This position detection means is constituted by the position sensors 36a and 36b shown in FIGS. 10 and 11, for example.

6.1.2. Position Detection Unit Provided Outside Another example of the position detection unit is a unit provided outside the moving mechanism 16 of the apparatus. An example of this is an infrared detector that detects the focal position from the heat of the focal point. What is necessary is just to fix this infrared detector toward the moving space range of a focus.

6.2. Use of Markers Another feature of position detection is a technique of attaching a marker having a different X-ray transmittance from that of the subject. Thereby, a marker is also reflected in each projection data. By calculating the position of this marker for projection data of a plurality of frames, position information in the projection data necessary for data selection for image recombination can be obtained.

  As a specific example, as shown in FIG. 24, markers M1 (x1, y1, z1), M2 (x2, y2, z3), and M3 (x3, y3, z3) are set as focal points S (x, y, z). It gives between detectors 14. By solving nine simultaneous formulas for the coordinates of the markers M1, M2, and M3 from the projection data, the position of the focal point S can be determined, and the relative movement amount of the focal point can be determined. That is, in the case of FIG. 24, since there are three markers, the six variables of the detector 14 can be solved, and the positions of the detector 14 and the focus S can be known. If the position of the detector 14 is known, there are three variables, so one marker may be used.

6.2.1. Giving a marker to a subject As an example, a marker may be attached to a subject.

6.2.2. The marker may be attached to the bed. The marker may be attached to the bed (top plate).

6.3. Correction of stationary positional deviation using a marker As another feature related to data selection, stationary positional deviation can be corrected using a marker. For example, as shown in FIG. 25, a plate body 62 is provided on the front surface of the X-ray tube 12 moving within the cover body 70, and pin holes M1 to M3 as markers are formed in the plate body 62. Prior to scanning, position correction data may be collected using the pinholes M1 to M3, and projection data at the time of scanning may be corrected with the position correction data. As a result, it is possible to correct stationary positional deviation such as mechanical rattling.

  The markers M1 to M3 may be attached to the bed side.

7). Data Processing Before Image Recombination Next, an embodiment (feature) classified into a category related to “data processing before image recombination” of the X-ray tomography apparatus according to the present invention will be described. In principle, this category of data processing need not be implemented. However, in order to improve the quality of tomographic images to be recombined later, it is desirable to implement one or a plurality of features (processing) exemplified below as appropriate.

7.1. Scattered ray correction One feature is the implementation of scattered ray correction. In principle, this scattered ray correction may be performed by any method or mechanism. It is desirable to remove or correct X-rays scattered by the subject or bed.

7.1.1. Physical removal by grid or the like As a specific example of the scattered ray correction, there is a method of arranging a blocking body 76 (hereinafter referred to as a grid) such as a grid in front of the X-ray incident side of the X-ray detector 14 as shown in FIG. This physically blocks the scattered radiation from entering the detector.

7.1.1.1. Grid is always fixed As an example of a suitable grid arrangement, the grid is fixedly arranged. Although the trace of the grid is shown in the projection data detected by the detector, the position of data selection from the projection data changes for each view. Therefore, the trace of the grid automatically disappears from the recombined tomogram.

7.1.1.2. Moving the Grid As another example of the grid arrangement, the entire grid 76 may be moved during scanning (see FIG. 26). At this time, preferably, the grid itself is moved so as to erase its own mark.

7.1.1.2.1. Specific Trajectory Specific trajectories for moving the arranged grid 76 include, for example, a circular trajectory, an 8-shaped trajectory, and a reciprocating trajectory.

7.1.1.3. Example of Grid Shape As another example of the grid, as shown in FIG. 27, each blade forming the grid 76 may have a cone shape so as to face the focal point S (X-ray tube). Thereby, transmitted X-rays can be made incident efficiently, and scattered X-rays can be blocked efficiently.

7.1.1.4. As another example of the movable grid, as shown in FIGS. 28A and 28B, a structure in which each of a plurality of blades forming the grid 76 is movable can be given. The plurality of blades may be controlled so as to always face the focus S during scanning.

7.1.2. Mathematical removal of scattered radiation Another example of scattered radiation correction is to mathematically remove scattered radiation by computation. This mathematical removal may be used in combination with the above-described physical removal based on the grid, or may be performed alone.

As a specific method of this mathematical removal, for example,
・ "A technique of scatter-glare correction using a digitalfiltration" Michitaka Honda et al., Med. Phys. 20 (1), Jan / Feb 1993 pp.59-70
It has been known. For this reason, at the stage when the projection data is collected, before the image recombination, these appropriate mathematical removal operations (PSF and the like) may be performed using, for example, a computer in the control / processing device 18.

7.1.3. Calculation of Scattered Dose Still another example relates to a configuration that calculates a scattered dose and corrects collected data with this calculated value. This scattered dose is calculated based on information such as scan parameters. Scan parameters include beam energy, subject thickness, field size, distance between subject and detector, and the like. For example, the following documents are known as examples of this calculation.

・ "Method for controlling the intensity of scattered radiation usinga scatter generation model" Michitaka Honda et al., Med. Phys. 18 (2), Mar / Apr 1991 pp. 219-226
7.2. Nonlinear Processing Another feature is that each pixel data of the collected projection data is subjected to nonlinear processing to improve contrast.

7.2.1. Gamma Conversion A specific example of nonlinear processing is nonlinear gamma conversion, which can be processed by, for example, a lookup table.

7.2.2. Filter Processing Another example of non-linear processing may be appropriate filter processing such as threshold processing or median filter.

7.3. Logarithmic processing Yet another feature is that a logarithmic operation is performed on each pixel data of the collected projection data. As a result, the range of pixel data can be compressed, and image data for recombination that directly reflects the linear absorption coefficient can be obtained.

7.4. Correction of Beam Spread / Detector Tilt Angle Yet another feature is the correction of the X-ray beam spread and detector tilt angle with the “cos term”.

7.4.1.
As a specific example, as shown in FIG. 29, the path in the thickness direction of the slice surface of the subject is corrected. When the angle of the pencil beam X-ray with respect to a certain voxel (the swing angle from the vertical line passing through the focal point S) is θ, each pixel data of the projection data is multiplied by “cos ₃ θ”.

7.5. Filter processing before recombination As another feature, various filter processing may be performed before recombination. This filter processing is implemented by software by the control / processing device 18, for example.

7.5.1. Isotropic filter processing As an example of this filter processing, there is filter processing in which the processing direction of the filter is isotropic.

7.5.2. Anisotropic Filter Processing Another example is filter processing in which the processing direction of the filter is anisotropic.

    7.5.2.1. As a processing direction of this anisotropic filter processing, a method of matching with the moving direction of the focal point is suitable. This eliminates artifacts that may occur along the focal direction.

7.6. Removal of motion components (other slice components) This feature relates to the removal of motion components for projection data of a plurality of frames on the same slice plane. This removal calculation is performed by a computer of the control / processing device 18, for example.

In this case, “movement” means that, in addition to photon noise, the projected position of the structure on the slice plane other than the target slice plane (other slice planes) is in the direction and distance corresponding to the moving direction and moving distance of the focal point. Say a changing state. For example, as shown in FIG. 30, the motion M of the structure of X = X2 on the slice plane of X = X1 is
[Equation 1]
M (X1, X2) = B (X2, A (n))-B (X1, A (n)) (1)
It is represented by A (n) represents the movement of the focal point. When A (n) is a two-dimensional quantity, the structure motion M is naturally also a two-dimensional quantity, but when a motion is detected for each frame with a pulse X-ray, it becomes a straight line.

  For example, when adding (recombining) 100 frames of projection data, the data of the target slice plane is added 100 times to the same pixel position, but the structure data of other slice planes is 1 at the same pixel position. It is added only once. As a result, the signal of the structure on the other slice plane becomes relatively lower than the signal on the target slice plane, and an image of the target slice plane is generated (recombination). This is also the imaging principle of the present invention. However, from the opposite viewpoint, the signal of the structure on the other slice plane is always added to 100 places on the target slice plane. This is a fate of the image principle of the present invention, but reduces the contrast resolution.

  Therefore, the other slice plane components (herein referred to as motion components) added to the target slice plane are removed.

7.6.1. Motion Detection Based on Data Difference As an example of the motion component removal process, a motion component is detected by calculating a difference between frames. For example, as shown in FIG. 31, when there are two frames of projection data A and B, the difference of “A−B” is calculated for both corresponding pixels. This difference data (frame data) becomes a motion component.

  When this motion component “A−B” is obtained, the motion component is calculated by, for example, calculating “A + B− | A−B |” for the projection data A of the first frame using the absolute value | A−B |. Remove. By repeating this calculation of motion component removal between adjacent frames, for example, the motion component is favorably removed from each frame. Therefore, recombination processing described later can be performed using only high-quality projection data having almost no other slice plane components.

7.6.2. Detection of motion component with threshold As another example of motion detection, there is a method in which threshold discrimination is added to the difference calculation. That is, as shown schematically in FIG. 31, after calculating the difference of “A−B”, a predetermined threshold value process is performed (see the example of the variation of the difference data in FIG. 32). If this threshold value is set to a value that can remove a noise component, for example, motion detection and noise component removal can be performed together.

7.6.3. Motion component detection between non-adjacent data As another example, the above-described motion component detection is performed between non-adjacent frames, for example, between frames in which one or several frames are skipped, such as between the first frame and the eleventh frame. The motion component may be detected by. This makes it possible to detect minute motion components that cannot be detected between adjacent frames.

7.6.4. By the way, this motion component (components of other slice planes) moves in a direction opposite to the moving direction of the focal point and does not move in other directions. Therefore, as another example of motion component detection, the detection direction of the motion component may be limited to a specific direction to facilitate detection.

7.6.4.1. Direction Dependent on Focus Movement Direction Specifically, it is preferable to detect a motion component in which the detection direction is limited to only two ± directions along the focus movement direction. For example, processing for tracking the moving direction of the focus is performed for each frame, and motion component detection is performed only in two directions ± along the direction.

7.6.5. Stopping Motion Component Detection Processing This example relates to an aspect of forcibly stopping motion component detection processing. For example, when a contrast medium is injected into a subject and the contrast medium is tracked for each frame, such as when performing DSA, the movement of the contrast medium itself is an observation target. In such a case, the motion component detection process described above is forcibly stopped. For example, the control / processing device 18 may perform such a stop in response to information from the operator.

7.6.6. Motion Component Detection After Adding Multiple Frames Yet another example of motion component detection relates to variations in the number of frames at the time of detection. The above-described detection example assumes the case of detecting one frame at a time, but in this example, a plurality of frames can be combined and performed in the same manner. For example, the projection data of the first to third frames are added to each other, the projection data of the fourth to sixth frames are added to each other, and the same as described above between the added projection data of both groups. A difference calculation, a difference calculation with a threshold value, a difference calculation with a detection direction restriction, and the like are executed.

  Thus, the S / N ratio can be improved by using the addition of a plurality of frames as a base.

7.6.6.1. Variable of threshold value When performing a difference calculation with a threshold value, the threshold value can be changed according to the number of additions.

7.6.7. Another method for detecting a motion component Another method for detecting a motion component is the expression of A + B−ω | A−B | (ω: weighting coefficient) for each pixel when there are two frames of projection data A and B. It is possible to obtain the difference based on the weighting based on (including the threshold value).

7.7. Correcting distortion inside the detector Yet another feature that falls into this category relates to correcting distortion inside the detector. The inside of the detector means I.I. I. The entire path from the X-ray incident surface of the detector to the internal D / A converter. When this distortion exists, for example, even if an X-ray representing a straight line is incident, a phenomenon that a signal representing a curve is output occurs. As a result, distortion occurs in the recombined tomographic image.

  Therefore, markers having different X-ray transmittances are attached to the X-ray incident surface of the detector, correction data is collected, and distortion inside the detector is corrected based on the correction data. This correction calculation can be performed by the control / processing device 18. An example of the marker M is shown in FIGS.

7.7.1. Correction at the same time as scanning As an example of this distortion correction, for example, as shown in FIG. 33, a plurality of dot-like markers M can be attached to the incident surface of the X-ray detector 14 so as to be two-dimensionally distributed. In the case of this dot-like marker, even if it is reflected in the actual projection data, the data content is hardly affected. Therefore, correction data can be collected at the same time as scanning to perform correction calculation dynamically.

7.7.2. Correction Data Collection Before Scanning As another example, as shown in FIG. 34, for example, a lattice-like marker M can be attached to the incident surface of the X-ray detector 14. In this case, since it is difficult to collect correction data at the same time as scanning, correction data is collected and calculated and stored before scanning. Then, at the time of scanning, the stored correction data is read out, and the projection data collected according to this correction data is subjected to correction calculation.

7.7.2.1. Matching with scan trajectory When correction data is collected before scanning, it is desirable to match the scan trajectory for collection with the scan trajectory for collecting projection data.

7.8. Removal of structures on other slice planes Another feature is to calculate and remove structure data on other slice planes from the re-production data.

8). Image Recombination Further, features, examples, and variations classified into the “image recombination” category of the X-ray tomography apparatus according to the present invention will be described. This image recombination is a process for obtaining a tomographic image of an arbitrary slice plane by adding projection data of a plurality of frames collected in a plurality of views. Specifically, data corresponding to each voxel of the slice plane is selected from the projection data of each of the plurality of frames according to the tube focus for each view, the slice plane, and the geometric relationship (geometry) of the detector, and added. It is processing. That is, in order to perform image recombination, data selection information indicating which data of projection data of each frame should be selected for a desired slice plane is necessary.

  This data selection information can be expressed as a shift amount in the linear direction when the tube and the detector move in a straight line relatively in parallel, for example. The basic feature of the present invention is that the tube / detector can be recombined so that it can cover up to any three-dimensional movement as well as the one-dimensional movement. One.

8.1. Generalized representation of image recombination processing In the present invention, as described above, as a scan, it is sufficient to project a plurality of views while moving at least the focal point of the tube relative to the subject and / or the detector. . In other words, the movement of components associated with scanning includes the movement of only the tube (focal point), the movement of the tube and the detector, the combination of these movements and the movement of the top plate (subject), and the top plate (subject). (Sample) only. The trajectory of movement of the tube and detector can be up to any three dimensions.

  Therefore, first, an image recombination process implemented in the present invention is extended to three dimensions, and a generalized expression of image recombination so as not to depend on the tube focus or the movement trajectory of the detector will be described. In the present invention, it is essential to perform this image recombination in any tomographic imaging. This image recombination processing is performed by the control / processing device 18.

Now, as shown in FIG.
Tube focus coordinates: S (sx, sy, sz)
Voxel coordinates of desired slice plane: V (vx, vy, vz)
Normal vector of the plane representing the position of the detector plane or projection data:
(E1, e2, e3)
A point contained in the detector plane or plane representing the position of the projection data:
(Pl1, pl2, pl3)
Then, the equation of the straight line connecting the focal point and the voxel is

Is obtained.

Data used for image recombination of the voxel V (vx, vy, vz) exists at the intersection of the linear equation (2) and the detector. Therefore, in general, the intersection of the detector plane or the plane (plane or curved surface) representing the position of the projection data and the straight line may be obtained. If the detector surface or the surface representing the projection data is a plane (even if such a surface is a curved surface, it can be recreated once it is resampled, so that such a surface is a plane)
[Equation 3]
el · (x−pl1) + e2 · (y−pl2) + e3 · (z−pl3)
= 0 (3)
Is obtained. The coordinates (x, y, z) satisfying the expression (3) are present in a plane including the coordinates (pl1, pl2, pl3) with the vector (e1, e2, e3) as a normal line. The intersection may be obtained by solving the simultaneous equations of the equations (2) and (3). That is, substituting equation (2) into equation (3),

Is obtained, the coordinates P (x, y, z) of the intersection point are obtained by substituting Equation (4) into Equation (2). That is, the coordinates P (x, y, z) are the position coordinates in the absolute coordinate system of the projection data selected for image recombination.

  In the image recombination processing, projection data at a pixel position corresponding to the coordinate P of the absolute coordinate system may be selected from the projection data of a plurality of frames moving for each frame and added to the voxel V. The projection data is selected using information on the relative movement of the tube focus, subject (bed), and detector geometry. This addition is performed for all voxels in the slice plane.

Incidentally, since the coordinates (x, y, z) of the point P described above is an absolute coordinate system, as shown in FIG. 36, a relative coordinate system p based on a position pc (xc, yc, zc) where the detector is located. The conversion to (i, j) makes it easier to specify the elements of the detector (data selection). For this,
[Equation 5]
p (i, j) = projection data of i rows and j columns detected by the detector in a certain view i = F [P (x, y, z) −pc (xc, yc, zc)]
j = G [P (x, y, z) -pc (xc, yc, zc)]
F, G: Conversion function
...... (5)
Calculation based on

Since the projection data p (i, j) of the intersection point P (x, y, z) obtained in this way may be sequentially added, the final expression of the generalized expression is

It is represented by When adding a plurality of views, a weighting process such as increasing (or decreasing) the weighting coefficient may be used in combination with a specific view.

  When there is no detection element of the detector at the calculation position p (i, j), the projection data detected by the detection element closest to the calculation position p may be used as the projection data, or in the vicinity of the calculation position p. The interpolation data may be adopted by interpolating projection data detected by a plurality of detection elements.

  Further, as described above, the detector surface is not necessarily a flat surface. For example, the detector surface may be a part of a cylindrical shape as shown in FIG. 37 (a), or an arbitrary shape such as a convexly expanded surface as shown in FIG. 37 (b). Good. In addition, rotation within the detector plane is also possible. On the other hand, since the recombination calculation is performed for each slice surface on a voxel basis, the slice surface is not limited to a plane and may be an arbitrary curved surface. Of course, this slice plane may be a plane inclined at an arbitrary angle (corresponding to making an MPR image directly in section 9.1 described later).

8.1.1. Example of trajectory for image recombination (Part 1)
The moving trajectory of the tube (focus) for image recombination is not limited to a one-dimensional trajectory that is a linear trajectory in a slice plane parallel to the floor surface (considered to be horizontal), but a two-dimensional trajectory including rotation, or A three-dimensional trajectory may be used. Or a track without a predetermined track may be used.

8.1.2. Example of trajectory for image recombination (Part 2)
The moving trajectory of the detector for image recombination may be a one-dimensional or two-dimensional trajectory parallel to the floor, a three-dimensional trajectory (such as an arc) or a rotational trajectory.

8.1.3. Example of image recombination This example relates to an example of image recombination processing for obtaining a tomographic image from acquired projection data of a plurality of frames. In the X-ray tomography apparatus shown in FIG. 1, the control / processing device 18 constitutes an image processing means for image recombination according to the present invention. A processing example of image recombination based on the software processing shown in FIG. 67 performed by the control / processing device 18 in accordance with the above-described generalized expression will be described below.

8.1.3.1 Processing example (1)
For example, based on input information from the input device 19, the control / processing device 18 sets a plane as a slice plane including at least a part of the subject as a display plane (step S31). The inclination of the plane with respect to the subject can be changed and can be set to a desired inclination. That is, an arbitrary angle slice plane including at least a part of the subject can be set. Next, each coordinate included in the set plane is determined (step S32). Next, projection data to be added is selected from the projection data of each view based on the relative positional relationship between the focus and the detector (step S33). This selection of projection data is performed in accordance with the principle described above (Section 8.1). Next, the selected projection data is added to the determined coordinates (step S34). This selection and addition of projection data is repeated for each coordinate of each view and plane (step S35).

  In FIG. 67, the process of step S31 corresponds to the setting means of the present invention, the process of step S32 corresponds to the coordinate determining means of the present invention, and the processes of steps S33 to S35 correspond to the tomographic data creating means of the present invention. .

8.1.3.2 Processing example (2)
For example, based on input information from the input device 19, the control / processing device 18 sets a curved surface as a slice plane including at least a part of the subject P as a display region (step S31). That is, an arbitrary curved slice surface including at least a part of the subject can be set. Next, each coordinate included in the set curved surface is determined (step S32). Next, projection data to be added is selected from the projection data of each view based on the relative positional relationship between the focus and the detector (step S33). This selection of projection data is performed according to the principle described above (Section 8.1). Next, the selected projection data is added to the determined coordinates (step S34). This selection and addition of projection data is repeated for each coordinate of each view and plane (step S35).

8.1.3.3 Processing example (3)
The control / processing device 18 sets an ROI having an arbitrary three-dimensional shape including at least a part of the subject based on, for example, input information from the input device 19 (step S31). Next, each coordinate included in the set ROI is determined (step S32). Next, projection data to be added is selected from the projection data of each view based on the relative positional relationship between the focus and the detector (step S33). This selection of projection data is performed according to the principle described above (Section 8.1). Next, the selected projection data is added to the determined coordinates (step S34). This selection and addition of projection data is repeated for each coordinate of each view and plane (step S35).

  As described above, the above 8.1.3.1 to 8.13.3. If any of the processing in the section is performed, the image recombination operation is performed only for the necessary cross section specified by the operator, that is, each coordinate in the slice plane or each coordinate in the three-dimensional ROI of the required volume. Therefore, there is an advantage that the calculation of image recombination becomes faster and the capacity of the memory provided in the control / processing device 18 can be reduced.

8.1.4. Image Recombination of Multiple Slice Surfaces This example relates to image recombination that obtains a plurality of tomographic images from projection data of a plurality of frames collected in one scan. In other words, when this recombination method is used, it is not necessary to repeat the scan multiple times. First, the scan is performed only once, and a plurality of slice plane positions are specified in the process of recombining the projection data. Those tomographic images can be obtained.

Specifically, in the formulas (2) to (4) or (2) to (6) described above,
(I): Image recombination of slice planes with vx = specified value, vy, vz = variable is performed. Then
(Ii): vx = vx + Δx (distance between slice planes: see FIG. 38), vy, vz
= Change the image of another slice plane to be variable. Thereafter, the process (ii) is repeated for an arbitrary number of slice planes.

  Thereby, a plurality of tomographic images at arbitrary positions can be obtained from the projection data of one scan.

8.1.5. Data Selection Method from View Projection Data Another example of image recombination relates to a method of selecting data from projection data of a (each) view.

  In this embodiment, as shown in FIG. 39 (a), regions in a plane slice plane designated by four voxels V1, V2, V3, and V4 are recombined. Specifically, first, 8.1. The recombination process described in the section is repeated four times for each of the voxels V1, V2, V3, and V4 to calculate the corresponding positions P1, P2, P3, and P4 on the detector surface or the plane representing the position of the projection data. To do. Next, an arbitrary voxel in the slice plane is uniquely expressed using four voxels V1, V2, V3, and V4. For example, the position of an arbitrary voxel is represented as a point with respect to a grid that internally divides the region in the voxels V1 to V4 as shown in FIG. Next, the position of the projection data for the arbitrary voxel is expressed using positions P1, P2, P3, and P4. For example, as shown in FIG. 39 (c), it is easily calculated as the position with respect to the grid that internally divides the areas P1 to P4.

  In this way, by designating projection data using the positions of four voxels V1, V2, V3, and V4 given in advance, an enormous amount of calculation of solving the simultaneous equations for all the voxels can be avoided, and high speed can be achieved. There is an advantage that processing is possible.

  Although an example of a region where four points are connected by a straight line is shown here, the combination of the shape of the region and the given coordinate position is arbitrary, such as giving an elliptical region by giving a center position, a major axis, and a minor axis.

8.1.6. Image Recombination with Resampling Yet another embodiment of image recombination relates to a technique with resampling.

  When a plane slice plane is reconstructed, if a detector plane or a plane representing projection data is non-planar, a straight line is not projected even if it is projected. Since the projection of the straight line is non-linear, it is very difficult to calculate the intersection point P described above and to specify the projection data to be added, and it is necessary to perform a large amount of complicated calculations, which may be difficult to put into practical use. . In particular, when recombining a plurality of slice planes, this tendency is considered to be remarkable. On the other hand, the situation is the same when the detector surface is flat and the slice surface is non-planar, but there is a similar problem.

  Therefore, the object is to recombine images as if they were projected on a straight line, and to increase the speed by calculating complicated calculations at a time so that complicated calculations need not be performed.

  In this embodiment, for example, as shown in FIG. 40, when the detector surface is non-planar and the slice surface is planar, a planar resampling surface (resampling surface) is prepared. This resampling plane is a virtually set plane in the memory, and the distance between the tube focus and the resampling plane is maintained at a constant value in all the views being scanned, and the slices are recombined. Set parallel to the surface. It is more desirable to set the voxel row on the slice plane and the resampling row on the resampling plane in parallel. In addition, this resampling surface matches the shape of the slice surface. For example, when the slice surface is a plane as shown in FIG. 40, the resampling surface is also set to a plane. As shown in FIG. 41, if the slice surface is a curved panorama, the resampling surface is also matched to the shape.

  In the case of FIG. 40, the projection data collected by the non-planar detector is once resampled onto a planar resampling surface. Next, using the resampled projection data on the resampled surface, data selection (sampling) for image recombination is performed, and addition calculation of the projection data is performed. In sampling the projection data on the resampling plane, the sampling pitch is set smaller than the original (detector plane) data sampling pitch. Thereby, the error of interpolation is suppressed.

  By this resampling process, it is possible to always recombine tomographic images of a plurality of slice planes without depending on the shape and / or moving direction of the detector.

  FIG. 42 shows the state of resampling when the slice plane and the detector plane are both planar, but the inclinations do not match. The resampling surface in this case is also set based on the principle described above.

8.1.7. Data translation and image recombination when the detector moves in parallel, the focal point moves three-dimensionally In this embodiment for image recombination, the detector is placed on the floor as a typical mode of movement of each component. A description will be given of image recombination when the tube focus is moved in a three-dimensional manner while moving in parallel with the (horizontal plane in the coordinate system of the apparatus).

  As shown in FIG. 43A, it is assumed that the focal point S has moved three-dimensionally from S1 to S3. The movement amount of the focal point S is decomposed into a parallel movement component and a vertical movement component. That is, the focus S is considered to have moved from S1 to S2 in parallel, and then moved vertically from S2 to S3.

i) First, a shift position P2 (px2, py2, pz0) from the focal position S2 moved from the following equation (7) is obtained for an arbitrary voxel V on the slice plane with respect to the parallel movement component.

  The second term on the right side of Equation (7) is the shift amount (in this case, the vector amount).

  In this example, an arbitrary voxel V has been described. However, as described above with reference to FIG. 39, several reference voxels V1 to Vn (V1 in the example of FIG. 39) are used to limit a certain area in the slice plane. ~ V4) The shifted position may be obtained by applying equation (7) to each.

ii) Next, the shift position relating to the vertical movement component of the focus from S2 to S3 is obtained. From the intersections RV (sx2, sy2, vz) and RD (sx2, sy2, pz0) of the perpendiculars dropped from the focal positions S2 and S3 to the slice plane and the detector plane, the shift position (px3, px3) is calculated according to the following equation (8). py3, pz0) are obtained, and data selection at that position is performed.

  In the second shift position calculation, as in the first shift, several reference voxels V1 to Vn (V1 to V4 in the example of FIG. 39) for limiting a certain area in the slice plane are used. ) It is also possible to obtain the shifted position by applying the formula (8) to each, and calculate the remaining voxels using the position of the reference voxel.

8.1.8. Data selection when translating the tube and detector together
(When scaling is required)
In order to perform image recombination, it is necessary to select (data selection) data to be added to the target volume on the slice plane from the projection data of each frame in some form. The mode of movement in which the data selection position can be calculated most simply is when both the tube and the detector are moved parallel to the floor surface (horizontal plane in the coordinate system of the apparatus).

  In the present embodiment, this will be described. When scanning by moving the tube and the detector in parallel, the projection data of each view is added by changing the amount of shift in the translation direction for each desired slice plane, and the images are recombined.

  However, the number of sampling pitches in the projection data (for example, a pitch of 400 pixels × 400 pixels) is the same throughout all slice planes. Therefore, if the addition is performed as it is, as shown in FIG. 44, spatial sampling of each slice plane is performed due to the geometric relationship (geometry) between the plurality of slice planes, the tube focus S, and the detector plane D. The pitch is different. Therefore, the slice images recombined by addition have the same sampling pitch on the memory, but have different spatial sampling pitches (enlargement ratios) as shown in FIG. When a plurality of slice images having different sampling pitches are three-dimensionally processed or displayed in cine, there is a problem that distortion occurs in position, shape, and the like.

  Therefore, in this embodiment, a plurality of slice images that have been recombined are resampled at equal pitches (spatially) on the slice plane, for example, as shown in FIG. 44 (a) to FIG. 44 (b). The sampling pitch is adjusted (that is, enlargement / reduction processing). At this time, any one pitch among a plurality of slice images is adopted as the equally spaced pitch. Thus, the above-mentioned inconvenience can be avoided by adjusting the sampling pitch.

  Before the image reconstruction process, the projection data of each view is resampled, the sampling pitch is adjusted on the memory so that the spatial sampling pitch is equal, and then recombination is performed. Also good.

8.1.9. Data selection when translating the tube and detector together
(When scaling is not required)
This embodiment relates to another data selection technique when the tube and detector are both translated and scanned.

  (I) Using the projection data of the first view, the above-mentioned 8.1.4. The processing of the item (see FIG. 38) is performed. Thereby, projection data used for image recombination is specified for each voxel of each slice plane. (Note that the processing described in Section 8.1 may be performed to specify all voxels).

(Ii) For the projection data of the next view and subsequent views, the shift amount with respect to each slice plane is obtained from the equation (6). Data at a position shifted by the shift amount obtained from the data used for image recombination in the previous view is used for image recombination of each voxel of the current view. (Alternatively, the shift amount of the target slice surface may be obtained from the shift amount with respect to a certain slice surface based on the geometric relationship.)
In this way, if the pitches (intervals) of voxels are set to be equal in all of the plurality of slice planes, data can be selected and recombined regardless of the problem of enlargement ratio.

8.2. Enlargement / reduction (enlargement ratio) process As another feature related to the image recombination process, it is possible to provide a process for adjusting the enlargement ratio by enlarging or reducing the slice image. The magnification of the slice image (voxel image) is larger on the focus side slice image than on the detector side. That is, since the enlargement ratio of the slice image differs depending on the height X of the slice surface, it is necessary to match these. This processing is performed based on the following formula, for example.

[Equation 9]
S2 (X, Y0, Z0) = S1 (X, aY, bZ)
Coefficient a = a (X), coefficient b = b (X) (9)

  Note that the image recombination described above in 8.1. When processing based on the expression of the generalized expression of the term, the processing for adjusting the enlargement ratio is unnecessary.

8.2.1. Perform image recombination and enlargement ratio adjustment in a single process When adding (recombining) projection data, specify (select) the data to be added, but there is no pixel at the position that matches the specified position at that time In this case, for example, neighboring four-point interpolation is performed. This substantially increases the pixel size. If further adjustment of the enlargement ratio is performed on the interpolated data as described above, the spatial resolution of the data is reduced (blurred). In order to avoid this, a plurality of slices with the same enlargement ratio are obtained by the following equation. Processing to obtain images at once is desirable.

[Equation 10]
S3 (X, Y, Z)
= Σ (P {n, aY, b (Z + B [X, A (n)])}) / N (10)

  As a result, the interpolation calculation is performed only once, and the spatial resolution is not deteriorated.

8.3. Cutting out slice image at arbitrary angle from volume data As another feature, it is possible to provide a process of cutting slice image at arbitrary angle from volume data. This process is performed, for example, by the control / processing device 18 in an interactive process with the operator. By creating a plurality of slice images by changing the designated position on the slice plane, three-dimensional volume data can be obtained. By specifying an arbitrary angle for the volume data and performing MPR (cross-sectional transformation) processing, a slice image at the arbitrary angle can be obtained. Thereby, for example, an oblique image, an axial image, and a sagittal image can be arbitrarily created from the volume data of the coronal image.

  In the present invention, in order to obtain a slice image at an arbitrary angle, as described above, it is not always necessary to perform cutting using a method of cross-sectional transformation. In the present invention, image recombination processing generalized to three dimensions is performed and added in units of voxels on the slice plane. For this reason, if an oblique surface having an arbitrary angle is designated at the time of image recombination, projection data is added to each spatially inclined voxel forming the oblique surface. As a result, an oblique image of a slice plane at an arbitrary angle can be generated directly from the projection data.

8.4. Image recombination at the same time as acquisition In the various aspects described above, it was assumed that image recombination was performed after projection data was collected, but the timing of image recombination of the present invention is not necessarily limited to this. . In other words, as another feature related to the timing of image recombination, the collection of projection data and the image recombination (addition of projection data) may be performed simultaneously (in parallel). Specific examples are shown below. This can be realized by the control and processing of the control / processing device 18.

8.4.1. Specific Example of Simultaneous Recombination To perform this simultaneous recombination, the scan trajectory and the projection data collection timing are determined in advance. That is, in order to generate a slice image, data selection information indicating which pixel value at which position in the projection data of each frame should be added to which voxel on the slice surface is known in advance. Thereby, as schematically shown in FIG. 45, when projection data of a certain view is collected, the projection data is immediately added to each voxel data of the slice plane. Collect projection data of another view during the addition. Hereinafter, by repeating this over a predetermined view, image recombination processing can be performed simultaneously (in parallel) with the collection of projection data, and a slice plane tomogram can be obtained quickly.

8.5. Weighted addition processing As yet another feature, it is possible to provide a method of performing weighted addition depending on the projection data collection position (ie, scan trajectory). This addition processing is also selectively performed in the image recombination processing by the control / processing device 18.

  For example, assume that the tube draws an elliptical scan trajectory on the two-dimensional YZ plane as shown in FIG. In this case, the projection data collected in the view of the part having a small radius of curvature is multiplied by a weighting coefficient smaller than that collected in the view of the part having a large radius of curvature. By smoothly changing the weighting coefficient according to the radius of curvature, it is possible to suppress or prevent the occurrence of artifacts due to the local deviation of the trajectory. Furthermore, 5.2. There is an advantage that it is not necessary to perform complicated control such as adjusting the collection timing and the moving speed on the track according to the shape of the track described in the section.

8.6. Large field of view (1)
When obtaining a tomographic image, it is of course necessary that the tomographic image includes a region of real medical interest, but on the other hand, the region around the region of interest is imaged as widely as possible. It is often convenient to have been done. In other words, a wider field of view is more convenient.

  For this reason, a large field of view larger than the detector size is provided as another feature of image recombination. This large-field imaging can be realized as data processing by the control / processing device 18 at the stage of image recombination. For example, as shown in FIG. 46A, when the X-ray tube 12 and the X-ray detector 14 perform data acquisition while moving along a circular scan trajectory, the end portion through which the X-ray path passes even once. The space area is designated as a slice plane area, and image recombination is performed on the entire slice plane. However, it is desirable to employ addition averaging as the recombination processing to eliminate or suppress the shading of the image due to simple addition.

  As a result, the recombined tomographic image of the large field slice plane has a field of view wider than the detector size. In this tomographic image, the number of additions increases toward the center, and the definition and resolution as an image increase, and an image region with a low definition and resolution with a small number of additions is arranged in the vicinity. The region of real interest may be aligned with the center of the slice plane. As a result, it is possible to provide a tomographic image having a wide field of view as much as possible surrounding the region of interest.

8.7. Large field of view (2)
Another aspect related to large-field imaging will be described. In this large-field imaging, scanning is performed a plurality of times while moving the imaging field of view, and the recombined images of the respective scans are aligned and overlapped. This imaging method can be achieved by post-processing by the control / processing device 18 after data is collected by scanning a plurality of times and a recombined image is generated.

  For example, as shown in FIG. 47A, both the tube and the detector are scanned a plurality of times along the body axis direction of the subject P while drawing a circular scan trajectory. Markers M,..., M are attached to the couch top. The scan trajectory is determined so that each scan always includes the marker copied in the adjacent scan. As a result, as shown in FIG. 47 (b), recombined images IG1, IG2,... Are obtained corresponding to each scan, so that the recombined images IG1, IG2,. . As a result, as shown in FIG. 47C, a large-field tomographic image that is long in the body axis direction is synthesized. Thereby, for example, the running state of blood flow can be easily grasped.

  In addition, as a marker in the case of overlap-combining recombined images, the marker is not necessarily attached to the top board, and an observation target itself such as a blood vessel may be traced and used for positioning.

  Also, in this large-field shooting, the overlapping portions of each image are weighted and added, and the weighting coefficient is smoothly changed as shown in FIG. 47 (d) so as to suppress the influence on the images at each joint. It may be.

8.8. Adoption of addition averaging Further, a feature at the time of image recombination is that addition averaging may be used as recombination processing. If this addition average is used instead of simple addition, variations in pixel density due to differences in the number of additions can be suppressed.

8.9. Range reselection (restriction) image recombination method As yet another feature, it is possible to provide a technique for selecting or limiting the range of projection data to be recombined in one image. This feature is derived from the fact that in order to perform image recombination according to the present invention, it is sufficient to have projection data for a plurality of frames with different angles of the X-ray path passing through each voxel on the slice plane. This feature is also effective for dynamic shooting. This feature can be implemented in the course of image recombination processing after data collection by the controller / processor 18.

8.9.1. Using a part of collected data FIG. 48 shows an example of image recombination of this range selection (limitation). For example, it is assumed that the scan trajectory of the X-ray tube and the detector is elliptical as shown in FIG. 48A, and scanning is performed while rotating around the same scan trajectory a plurality of times to perform one imaging. It is assumed that one round takes 1 second, for example.

  In this case, for example, as shown in FIG. 48B, one image is recombined from the projection data of a plurality of frames obtained during each round of scanning. That is, the first round scan (time t = 0 to 1 second), the second round scan (time t = 1 to 2 seconds), the third round scan (time t = 2 to 3 seconds), and so on. A tomographic image is obtained.

  Further, as shown in FIG. 48C, the images may be recombined in the same manner by changing the time pitch between the images. That is, after one image is recombined in the first round scan (time t = 0 to 1 second), the pitch is changed and the projection data from time t = 0.1-1 to 1 second is changed to the next. Recombine the images. Further, the next image is recombined from the projection data at the time t = 0.2 to 1 to 2 seconds by changing the pitch. Thus, the time resolution can be changed between images by changing the time pitch between images.

  Further, as shown in FIG. 48D, the images may be recombined in the same manner by changing the time pitch in the image. That is, for example, a single image is first recombined from projection data of a plurality of frames collected during a time t = 0 to 0.3 seconds, and then the pitch is changed to a time t = 0.4 to 0, The next image is recombined from the projection data for 6 seconds. Further, the next image is recombined from the projection data at time t = 0.8 to 0, 9 seconds by changing the pitch. Thus, the time resolution of an image can be changed for each image by changing the time pitch used for recombination. This time pitch may be arbitrarily changed.

8.9.1.1. Use of Some Views The example of FIG. 48 (d) described above uses multiple frames of projection data collected in some views during scanning. This situation can be schematically represented as shown in FIG.

8.9.1.2. Use of Some Projection Data As another aspect, for example, as shown in FIG. 50, when a tube and a detector move and take a predetermined scan trajectory, an obstacle (for example, a tube) A structure such as a sphere or an arm end of a support mechanism of a detector, or a bone) may be included. In this case, the projection of the obstacle is partially reflected in a part of the projection data detected within the predetermined range of the detector trajectory, but there is a portion where the obstacle is not reflected (the non-hatched portion in the figure). NH part). Therefore, if recombination is performed using only a portion NH of the projection data, a tomographic image can be obtained without being affected by the obstacle.

8.9.2. Change according to slice position As another example, the range selection (limitation) used for the recombination described above may be changed according to the slice position.

8.9.3. Shift recombination As another example, the same slice plane is recombined while shifting the position on the time axis little by little when collecting projection data used for recombination, or volume regions (multiple slices) Surface) may be recombined (see FIG. 48C).
8.9.3.1. Variable time resolution During this recombination, the time resolution between images may be variable (see FIGS. 48C and 48D).

8.10. Iterative Convergence Method It is another feature of the image recombination process that an iterative convergence method can be provided. This iterative convergence method repeats a series of processes leading to reprojection (reprojection) by difference values, recombination processing, difference of each voxel (that is, artifact), or reprojection (reprojection) by difference values, This is a technique in which a series of processing up to voxel difference and recombination processing is repeated, and a recombined image is obtained as a true image when each difference value converges to a predetermined value or less.

8.11. Subtraction with movement correction This feature is a subtraction method suitable for, for example, comparing tomographic images of slice planes before and after surgery. The slice plane described above has been specified in the absolute coordinate system. However, in the subtraction method with movement correction according to this feature, the slice plane is considered centering on the subject. For that purpose, the amount of movement and / or torsion of the subject in the body axis direction is detected, or the amount of movement is specified by using the marker attached to the subject or the feature position of the bone as a landmark. The slice plane is moved, and the projection data is recombined with the slice plane. If the difference for each pixel of the two images recombined in this way is calculated, a change between the two images such as before and after the operation can be easily imaged.

9. Image processing, image cropping, and post-correction Further, features and examples classified in the category of “image processing, image cropping, and post-correction” of the X-ray tomography apparatus will be described. The features and examples of this item are executed by the control / processing device 18.

9.1. Cutting out voxel data at an arbitrary angle This feature is to cut out a tomographic image secondarily at a cross section at an arbitrary angle. As described above, for example, if a plurality of slice planes as coronal planes are designated and images are recombined with each slice plane, three-dimensional volume data is created. An image of an arbitrary cross section such as an oblique image can be obtained by performing a cross section conversion (MPR) process by specifying a cross section of an arbitrary angle in the volume data. An axial image and a sagittal image can also be obtained depending on how the cross-sectional angle is set.

9.2. Panorama development This feature relates to a cross-section in which the cross-section is panoramic rather than flat. 9.1. When specifying an arbitrary cross section in the volume data obtained in the section, information such as curvature, the center of curvature, and the arc angle at the center of curvature is specified to specify a panoramic curved surface. By applying a cross-section conversion process to this curved surface, a panoramic curved tomographic image is obtained (panoramic development). This is useful, for example, in medical practice such as dental gums.

  In addition, 9.1. Term and 9.2. The image processing related to the feature of the term is not directly performed as post-processing, but directly from the projection data by selecting such an arbitrary cross section or panoramic curved surface as a slice plane when recombining projection data of a plurality of frames. It can also be created.

9.3. Tracking cut-out of an object This feature cuts out an image along a free surface on which an object is tracked, for example, a blood vessel in a lung. Also in this case, by setting such a free surface and converting the cross section to volume data formed by recombination with a plurality of slice surfaces, a tomographic image along that surface is created secondarily. be able to.

    9.4. Image Extraction by Dialogue / Plan Processing This feature relates to processing an image extraction process based on MPR on demand or with a plan. For example, when an operator issues a command “adjacent surface” while observing an image cut out from volume data by MPR, an image of an adjacent slice surface that is slightly translated in a predetermined direction is generated by MPR, or “ When a command “rotate several times” is issued, an image of the slice plane that is finely rotated in a predetermined direction is generated by MPR. Alternatively, a series of image generation processes may be performed in advance by a plan process.

9.5. Removal of DC Blur Component Still another feature relates to a technique for removing a so-called DC blur component that is thinly and averagely superimposed on the recombined image.

  Since the tomographic image generation processing of the present invention is based on the addition of projection data as described above, it is inevitable that components of other slice planes always enter the target slice plane as DC blur components. . Since the DC blur component lowers the contrast of the target image, the present invention aims to remove this as much as possible.

  Therefore, a reference slice surface having a known component, such as a slice surface in the air before and after (up and down) the subject and a slice surface of the bed, is designated, and images of the reference slice surface are recombined. One or a plurality of slice planes in the air are set, such as N1 to N5 and M1 to M5 shown in FIG.

  A DC blur component of the target slice plane is estimated from, for example, X-ray intensity distribution data at a predetermined position (one or a plurality of positions) of the recombined image of the reference slice plane, and a correction value is created. For example, if the X-ray intensity distribution in the one-dimensional X-axis direction at a certain two-dimensional position (Y, Z) estimated from a plurality of reference slice planes in the air is as shown in FIG. 51B, for example. The intensity I = I1 corresponding to the position X = x1 of the target slice plane corresponds to the DC blur component of the target slice plane. Such an X-ray intensity distribution may be obtained and stored in advance, or may be obtained each time a DC blur component is removed. Further, instead of obtaining such an X-ray intensity distribution, a DC blur component may be obtained by performing a correction operation directly from the recombined image data of the reference slice plane.

  Then, the DC blur component is removed by subtracting this correction value from each pixel on the target slice plane. An outline of the flow of this series of processing is shown in FIG. This processing can be performed in the control / processing device 18 as processing after collecting projection data and recombining images.

  The correction value may be formed for each pixel on the target slice plane and the removal calculation may be performed for each pixel, or one correction value may be obtained for each image.

9.5.1. Use of a plurality of reference slice planes As a specific example, as described above, it is desirable to obtain a correction value of a DC blur component using a recombined image of a plurality of reference slice planes. Thereby, the reliability of DC blur component correction is improved.

9.5.1.1. Use of Nonlinear Interpolation When using recombined images of a plurality of reference slice planes, correction values may be obtained by nonlinear interpolation of these image data.

    9.5.2. The use of two front and rear reference slice planes and a preferred example are the front and rear sides of the subject, that is, in the example of FIG. 51A, the upper and lower reference slice planes N1, M1 (or N2, M2, N1, M2, etc.).

9.5.2.1. Linear Interpolation When two slice planes before and after the subject are used in this way, the recombination data is linearly interpolated and the X-ray intensity distribution in the X-axis direction (correction value of the DC blur component of the target slice plane) Or the correction value of the DC blur component of the target slice plane can be easily estimated.

9.5.2.2. Multiplication of coefficients A coefficient that takes into account the position of the target slice plane and imaging conditions is added to the X-ray intensity distribution in the X-axis direction generated by linear interpolation as described above or the correction value of the DC blur component of the target slice plane. Multiplication may be performed to obtain a final correction value.

9.5.3.1 Use of One Reference Slice Plane Further, as an example that can simplify the correction calculation, there is a method of using only one reference slice plane. In this case, the reference slice plane is one before and after the subject, for example, in the case of FIG. 51A, one front N1 (N2,...) Or one rear M1 (M2,...). .

9.5.3.1. Use of Reference Slice Plane Data One Specific Embodiment in this case is to employ the obtained recombined image data of one reference slice plane as a correction value. At this time, the correction value may be formed for each pixel, or may be integrated into one value for the entire image.

9.5.3.2. Coefficient Multiplication Another specific example in this case is to multiply the obtained recombined image data of one reference slice plane by a coefficient that takes into account the position of the target slice plane and imaging conditions, and finally A correction value may be obtained. At this time, the correction value may be formed for each pixel, or may be integrated into one value for the entire image.

9.6. Three-dimensional image filter processing The above-described feature is removal of the DC blur component, but the feature of this section is to remove the whole blur component with the three-dimensional image filter.

9.6.1. Enhanced filter (Bokeh recovery filter)
From the principle of main imaging, it can be considered that the component of each voxel on the slice plane protrudes along the X-ray path direction, thereby blurring in the X-ray path direction. For example, as shown in FIG. 53, when both the focus and the detector draw a circular scan trajectory, the component of the voxel V having the slice surface is in a funnel-like oblique direction (oblique direction NN in FIG. 53). Blur along. Therefore, a filter for correcting this blur is applied. Therefore, an enhanced three-dimensional filter (blur recovery filter) is applied.

9.6.2. Filter isotropic As this enhanced three-dimensional filter, for example, an isotropic filter can be used.

9.6.3. Filter is anisotropic Further, the enhanced three-dimensional filter may have an anisotropic filter characteristic that filters only in a specific direction.

9.6.3.1. Filtering is performed in one direction. For example, the vertical direction VT in FIG. 53 is selected as a direction representative of all X-ray paths, and this direction is filtered to remove the blur.

9.6.3.2. Filtering is the direction of the X-ray path. Further, as an example of such a specific direction, for example, filtering may be applied to each of the directions of the oblique X-ray path NN shown in FIG. 53 to remove the blur more reliably.

9.7. Three-dimensional image processing Further, in the image processing of the present invention, there are various 3 processing such as volume rendering, MIP (maximum intensity projection), surface rendering, and reprojection (reprojection) processing. Dimensional image processing / display can be performed.

10. Multi-modality Further, characteristics and examples classified into the category of “multi-modality” will be described. The “multi-modality” mentioned here means systematic coupling of the X-ray tomography apparatus according to the present invention with other modalities such as an X-ray CT scanner and an MRI apparatus. The purpose of this multi-modality is to respond to various needs in the clinical setting while making use of and complementing the characteristics of individual modalities.

10.1. Coordinate system alignment with other modalities The X-ray tomography apparatus according to the present invention is characterized in that alignment can be performed very easily. Therefore, scanning is performed with markers having different X-ray transmittances attached to the subject. As a result, the marker is reflected in the recombined image, and the position of the marker in this image may be used for alignment with the coordinate system of another modality. Specifically, the coordinates of the subject are uniquely determined by the marker position in the image, and the recombined image is rotated and moved so as to match the marker in the image captured with another modality, for example, a plurality of You can align images collected with different modalities.

10.1.1. Number of markers As a specific example, there is an example in which the number of markers is adjusted to the number of unknown variables. Usually three markers are used.

10.1.2. Marker position As another example, when attaching a marker to the subject, the marker is placed at the edge of the recombined image and the marker is attached so that it does not appear at the center of the image. Rejoin in view.

10.1.3. Use of alignment Further, such alignment is used for a surgical plan, a radiation treatment plan, and an intraoperative navigator.

10.1.4. Alignment of the coordinate input device In particular, it is possible to align with the pointer (pen etc.) of the coordinate input device of the intraoperative navigator. An area including the surgical portion of the subject is imaged in advance with the X-ray tomography apparatus of the present invention, and recombined image data or volume data thereof is obtained. At the time of surgery, the marker portion of the subject is indicated once with such a pointer, and the marker position (absolute position) is stored. In this state, during the operation, a spatial position to be known in the subject is indicated with a pointer. As a result, the distance and direction between the designated position and the absolute position are calculated, and based on the calculated value, the designated position is displayed superimposed on the recombined image or volume data image captured in advance. Thereby, for example, when performing an operation of digging the head using a scalpel, if the operator observes the display image, the current operation position (the position pointed by the pointer of the coordinate input device) can be visually confirmed. it can. Thereby, information for assisting the operation, such as whether or not to dig further, can be easily obtained.

11. System Overall Operation Further, features and examples classified into the “system overall operation” category of the X-ray tomography apparatus according to the present invention will be described.

11.1. Stroboscopic imaging by pulse contrast enhancement A feature described first is a technique in which a contrast medium is injected in pulses (pulse contrast (or pulse injection)) and stroboscopic imaging is performed to make it appear that blood flow is slowly running.

  This strobe photography is suitable for imaging blood flow in a region where the blood flow velocity is relatively fast, such as the head. As shown in FIG. 54, a contrast medium and physiological saline are alternately injected into a blood vessel in a pulsed manner. When this pulse injection cycle (phase) is Tp, scanning is continuously performed at a rotation cycle Ts slightly deviated from this cycle. An example of this situation is shown in FIG. From the projection data obtained as a result, data at the position where the pulse injection cycle is the same, for example, scan phase data corresponding to the pulse injection cycle φ = φ1 in FIG. 55 is selected. By recombining only the selected data, volume data at each phase of the pulse injection period is obtained.

11.1.1. Calculation of blood flow velocity As an example using this feature, blood flow velocity can be calculated from the contrast agent position at each time (each phase).

11.1.2. Pulse Contrast As an example suitable for pulse contrast, there is a configuration in which a contrast medium and physiological saline are alternately packed in a thin tube (see FIG. 54), and this is sent out at the aforementioned pulse injection cycle.

11.2. ECG-synchronized scanning Another feature relates to ECG-synchronized scanning. If the scan trajectory is circular, an electrocardiographic waveform signal obtained by ECG can be superimposed on the scan trajectory as schematically shown in FIG. Only data having the same heartbeat period (for example, data in the diastolic period) is selected from the electrocardiographic waveform signals and recombined. In other words, this is a technique of replacing the pulse injection period in the above-described strobe imaging with a heartbeat period and recombining images only with the same heartbeat period data.

11.3. Intraoperative navigator / intraoperative monitor Yet another feature is the use as an intraoperative navigator or intraoperative monitor suitable for stereotactic brain surgery and the like. In an intraoperative navigator and an intraoperative monitor, it is important which image of the slice plane is recombined and shown to the operator.

  Therefore, in the X-ray tomography apparatus implementing this feature, a cross section of a plane including the needle (plane H1 in FIG. 57) and / or a plane passing through the tip of the needle and perpendicular to the needle (plane H2 in the figure). Generate and display an image. This image generation may be a method of directly recombining the above-mentioned plane images from projection data obtained by performing an intraoperative scan, or a plurality of projection data obtained by performing an intraoperative scan once. The slice planes may be recombined and the plane image may be cut out from the volume data by cross-sectional transformation. This makes it possible to easily and quickly determine what is slightly ahead of the tip of the needle. That is, with this intraoperative navigator or intraoperative monitor technique, accurate position information such as whether or not the needle can be further advanced can be provided to the surgeon in a timely and visual manner.

11.4. Quantification by volume ROI As another feature related to the overall operation of the system, it is possible to provide a method for quantifying the lesion state using the volume ROI.

  When this method is implemented, 1) Image recombination is performed on a plurality of slice planes from projection data obtained by scanning a region including a lesioned part of the subject in advance, and volume data is obtained. 2) In this volume data, as shown in FIG. 58, a three-dimensional region of interest (ROI) is set as the volume ROI. Next, 3) a three-dimensional region including the volume ROI is scanned a plurality of times while a contrast medium is injected into the lesion of the subject. 4) For each of the plurality of scans, the acquired projection data is recombined with a plurality of slice planes to obtain volume ROI data. As a result, a plurality of sets of blood flow concentration (voxel value) data forming the volume ROI are obtained over time. 5) From this data, information such as the time density curve of the volume ROI or the average transit time of the contrast agent is calculated.

  Thus, by setting the ROI as a solid rather than a plane, only the time-concentration information of the entire lesion can be easily obtained, and the dynamic observation of the lesion becomes possible in a more quantitative state. .

11.5. Filter processing Another feature is filter processing. This is a combination of the above-described method of processing projection data with a two-dimensional filter and the above-described method of processing voxel data obtained by image recombination with a one-dimensional filter.

11.1.5.1.1 Filtering direction of the one-dimensional filter The filtering direction of the one-dimensional filter is preferably set to, for example, the tube-detector direction.

11.6. Threshold processing Still another feature is a method of recombining images after discriminating projection data by a threshold value. This feature is the same as that described in 5.6.4. It can also be understood as an evolution of nonlinear processing of terms. Image compression is performed by setting a predetermined threshold value to the projection data and performing processing to discard pixels with low density.

12 Other Lastly, “others” features and examples of the X-ray tomography apparatus according to this embodiment will be described.

12.1. Adoption of various technologies of X-ray diagnostic equipment Various techniques (gamma correction, image compression, automatic brightness control (ABC) techniques, etc.) adopted in X-ray diagnostic equipment are fundamental to this X-ray tomography apparatus. Can be used to improve functionality.

12.2. Confirmation of X-ray Irradiation Range Another feature relates to a technique for confirming in advance the X-ray irradiation range associated with scanning.

  As shown in FIG. 59, a mirror 82 that transmits X-rays but reflects light is installed in a path through which the X-ray beam irradiated from the X-ray tube 12 propagates through the X-ray collimator 80. . A light source 84 is installed at a position geometrically targeted with the focal point S of the X-ray tube 12, and the light emitted from the light source 84 reaches the mirror 82 through the optical collimator 86. The opening area of the optical collimator 86 and its position are always matched with those of the X-ray collimator 80. For this reason, the light emitted from the light source 84 is reflected by the mirror 82 and projected onto the subject. The projection position and area are the same as those when the X-ray is irradiated.

  Thus, by emitting light from the light source 84 at the position of each view before scanning, the X-ray irradiation range at the time of scanning can be confirmed with only light, and the position of the view can be corrected according to the confirmation result. As a result, it is possible to confirm the movement range of the X-ray irradiation range when moving the tube or detector along with the scan trajectory, and scan positioning considering exposure such as not irradiating X-rays to important organs. Can do.

  The optical system for checking the X-ray irradiation range may be set integrally with an X-ray irradiation mechanism including an X-ray tube and an X-ray collimator, or may be set separately.

  Features and embodiments that can be implemented in the X-ray tomography apparatus of the present invention are configured and function as described above.

Example of Procedure for Imaging and Image Processing FIG. 62 shows an example of the procedure from imaging to image processing for the X-ray tomography apparatus described above. Here, “system design”, “mechanism”, “detector and tube”, “scan trajectory”, “data collection”, “data selection”, “multi-modality”, “overall system operation”, It is assumed that features and examples related to “others” are selected in advance.

  In step S1 of FIG. 62, the operator first controls / processes scan conditions such as a slice region, slice thickness, number of slices, tube voltage, tube current, scan trajectory, and data collection method via the input device 19. Give to 18. Next, the process proceeds to step S <b> 2, and the operator causes the control / processing device 18 to set an X-ray irradiation field via the input device 19. This irradiation field can be confirmed by, for example, the aforementioned 12.2. It is made based on the method of the term.

  Next, in step S3, the control / processing device 18 starts scanning in response to the scan command signal from the input device 19. This scan is performed by moving at least the X-ray tube 12 or at least the subject P (that is, the top 10a) along the scan trajectory. Thereby, projection data is collected from the X-ray detector 14 in a plurality of views on the set scan trajectory, and is temporarily stored in the memory of the control / processing device 18.

  When this data collection is completed, the control / processing device 18 shifts the processing to step S4 and executes “data processing before image recombination”. In this process, the aforementioned 7.1. Item to 7.8. One or a combination of some of the features (examples) described in the section may be executed together.

  Next, in step S5, the control / processing device 18 sets one or a plurality of slice planes from the information given from the operator via the input device 19.

  Next, in step S6, the control / processing device 18 selects projection data to be used for image recombination of each voxel of each set slice plane from each frame of the stored projection data of a plurality of frames, and adds (recombines). ) This addition process is the same as described in 8.1. Implementation is based on the preferred embodiment of the paragraph. Further, in the “image recombination” process, the above-described 8.2. Item to 8.11. One or some of the features (examples) described in the section may be combined.

  Thereafter, the control / processing device 18 proceeds to step S7 and executes “image processing, image cropping, and post-correction”. In this process, the aforementioned 9.1. Item to 9.7. One or several of the features (examples) described in the section are executed in combination.

  The above-described “data processing before image recombination” in step S4 and “image processing, image cropping, and post-correction” in step S7 can be omitted as necessary.

  Next, the process proceeds to step S8, and the control / processing device 18 displays the tomographic image recombined in step S6 or the tomographic image processed, cut out, or corrected in step S7 on the display device 20.

  For this reason, this X-ray tomography apparatus has the following advantages over the conventional analog and digital apparatuses.

  First, the detector is not necessarily moved, but is installed in a fixed state, and it is sufficient to move only the tube. Alternatively, it is sufficient to move only the subject without moving the detector and the tube. For this reason, it is not necessary to perform the synchronous movement of the detector and the tube, which are difficult to control as in the conventional case. Therefore, it is possible to avoid the deterioration of the image quality of the tomographic image due to the synchronous control, while the complicated control mechanism and control circuit for the synchronous control become unnecessary, and the manufacturing cost of the apparatus can be reduced.

  Second, since a function for correcting the displacement of the tube (focal point) is mounted, the occurrence of artifacts due to this displacement can be prevented or suppressed, and the image quality can be significantly improved.

  Thirdly, the function of removing or correcting the occurrence of artifacts related to the tube scan trajectory pattern (for example, in the case of a linear trajectory, the linear artifact in the image) is incorporated, so that the image quality is improved. It can be further improved.

  Fourth, because it has functions to improve contrast resolution (scattering correction, motion component removal, non-linear processing, DC blur component removal, etc.) that tend to be sacrificed due to the principle of photography, contrast resolution is higher than before. It is possible to provide a tomographic image that is dramatically improved and has high visibility and excellent diagnostic ability.

  Fifth, image recombination processing is performed in consideration of the image enlargement ratio and generalized to three dimensions. For this reason, for example, even when a coronal image at a plurality of different slice plane positions is displayed as a moving image, an image that contributes to improving the visibility of the affected area and improving the efficiency of the image interpretation work can be provided.

  Sixth, a function for fully utilizing the collected slice plane image data is installed even compared with a conventional digital X-ray tomography apparatus. For example, image extraction at an arbitrary angle, image extraction on a curved slice surface, strobe photography, electrocardiogram synchronization scan, superimposed display with position information input from a coordinate input device, intraoperative navigator, intraoperative monitor, and the like. Thereby, it is possible to provide a high-performance X-ray tomography apparatus that effectively utilizes the collected data and meets various needs desired at the treatment site.

  Seventh, unlike the digital X-ray tomography apparatus described in the above-mentioned publication, the restriction on the scanning trajectory of moving the tube and the detector in the opposite directions is eliminated. In addition, the limitation on data processing in which image information from the detector is stored in the memory in association with each moving position is also eliminated. The image can be recombined even if the tube (or tube and detector) is arbitrarily moved two-dimensionally or three-dimensionally. In this way, restrictions on scan trajectory and data processing have been significantly eliminated, greatly increasing the degree of freedom in equipment layout and image processing procedures in system design. Therefore, it is possible to provide an X-ray tomography apparatus that is highly versatile, easy to use, and low in cost.

(Another embodiment)
Next, another embodiment of the present invention will be described with reference to FIGS. This embodiment relates to an X-ray tomography apparatus that simplifies the movement of a tube and a detector and can easily perform image recombination processing.

  The X-ray tomography apparatus shown in FIG. 63 is configured so that the detector and the subject are fixed, and only the tube is moved. Specifically, the X-ray detector 14 is composed of a direct conversion type large digital detector, and this detector 14 is installed under the top plate 10a to constitute a detector lowering system. Here, the term “large” refers to a two-dimensional size that allows detection of transmitted X-rays of all views with a fixed detector when the X-ray tube 12 is moved to detect transmitted X-rays in a plurality of views. That means

  The X-ray detector 14 collects and outputs projection data at a predetermined interval (for example, 100 times / second). The output side of the X-ray detector 14 is connected to a CPU 122 as a control / processing device via a memory 120. For this reason, the digital projection data collected by the X-ray detector 14 is stored in the memory 120.

  The X-ray tube 12 is positioned above the subject P in the X-axis direction, and is supported by the moving mechanism 16 so as to move, for example, linearly on a plane parallel to the slice plane to be set. The X-ray tube 12 can be switched between pulse X-ray irradiation and continuous X-ray irradiation modes. The X-ray tube 12 is connected to the CPU 122 via a high pressure generator 124 and an X-ray controller 126. The CPU 122 plays a central role in the control and processing of the entire apparatus, and the control and processing procedures are stored in the built-in memory. Thereby, transmission of X-ray control information to the X-ray controller 122, bed control, image recombination, and the like can be executed in a predetermined procedure. The CPU 122 is connected to the input device 128 and the display device 130 for information transmission with the operator.

  The operation of this X-ray tomography apparatus will be described.

  X-rays are continuously irradiated while the X-ray tube 12 (focal point S) is moved along a predetermined scan trajectory (for example, a straight scan trajectory as shown in FIG. 64). During this period, a plurality of N frames of projection data P (N, X, Y) are collected by the X-ray detector 14. The projection data of a plurality of N frames is stored in the memory 120 for each frame.

The CPU 122 reads the projection data of a plurality of N frames stored in the memory 120 and calculates the shift amount of the projection data for image recombination for each frame. As shown in FIG. 65, when the shift amount B with respect to the n-th frame is a focal movement amount A (n), a distance X between the focal movement plane and the slice plane (slice position), and a distance L between the focal movement plane and the detector,
[Equation 11]
B (X, A (n)) = − (L−X) / X · A (n) (11)
It can be calculated according to the following formula. The focal movement amount A (n) is a different value for each frame. For example, a certain point in the coordinate system (for example, a focal position (for example, an initial position) at the time of collecting the first projection data or an arbitrary position of coordinates), a subject, An image position of the marker attached to the body surface of P is set as a reference position, and a deviation from this reference position is obtained by calculation. In addition, in order to obtain the focal amount, a detector such as an infrared focus detector or an encoder can be added to the apparatus.

After this shift amount calculation, the CPU 122 shifts the projection data of a plurality of frames according to the shift amount B, and adds the projection data to each other (see FIG. 66) or averages. When the shift amount B changing for each frame is not an integer multiple of the pixel size, the projection data may be interpolated to create new projection data. As a result of the addition or averaging, the tomographic image data S1 recombined at the slice position X is
[Equation 12]
S1 (X, Y, Z)
= Σ (P {n, Y, Z + B [X, A (n)]}) / N (12)
As required. Thereby, a tomographic image at the slice position X is obtained.

  Thus, when the X-ray detector 14 is fixed and the X-ray tube 12 is moved on a plane parallel to the slice plane, a slice image can be provided by a simple recombination process. Further, since the X-ray tube 12 is merely moved along, for example, a linear scan trajectory, the movement control is simple, and the difficulty of synchronization accuracy when controlling the tube and the detector in synchronization is reduced. Can be avoided.

  In addition, although another embodiment mentioned above acquired one slice image by one scan, when obtaining a plurality of slice images from one scan data, the calculation of the shift amount described above is performed. In the equation (11), X = X + ΔX is calculated for each of a plurality of slice positions and for each frame. Then, as described above, the projection data is shifted for each frame according to the shift amount and added to each slice position. At this time, the enlargement ratio of the focus-side slice image is large, and that of the detector-side slice image is small. That is, since the enlargement rate of the slice image differs depending on the slice position, it is desirable to perform the process for adjusting the enlargement rate described above. From the data (volume data) of a plurality of slice images (for example, coronal images) in a certain direction generated in this way, images in other directions, for example, an axial image, a sagittal image, and an oblique are converted by a method of cross-sectional transformation (MPR). cut. As a result, a plurality of slice images can be obtained simultaneously from projection data obtained by one scan, and other slice images obtained by cross-sectional conversion can be obtained together.

  In addition, in the configuration of the above-described another embodiment, it is possible to further simplify processing and speed up image recombination. This method is particularly effective for group screening. Specifically, this is a method in which the focal scan trajectory, detector data collection timing, slice position, and the like are determined in advance, and the projection data shift amount is determined in advance based on these values. While the scan is executed in this state, the projection data is collected in each view, and immediately after that, the projection data is shifted, and if necessary, interpolated and added. This enables image recombination at the same time (in parallel) with acquisition. The recombination process is simple, and scanning to recombination completion can be performed at high speed.

  This X-ray tomography apparatus has the following advantages as compared with conventional analog and digital apparatuses.

  First, the detector is not necessarily moved, but is installed in a fixed state, and it is sufficient to move only the tube. Alternatively, it is sufficient to move only the subject without moving the detector and the tube. For this reason, it is not necessary to perform the synchronous movement of the detector and the tube, which are difficult to control as in the conventional case. Therefore, it is possible to avoid the deterioration of the image quality of the tomographic image due to the synchronous control, while the complicated control mechanism and control circuit for the synchronous control become unnecessary, and the manufacturing cost of the apparatus can be reduced.

  Second, since a function for correcting the displacement of the tube (focal point) is mounted, the occurrence of artifacts due to this displacement can be prevented or suppressed, and the image quality can be significantly improved.

  Thirdly, the function of removing or correcting the occurrence of artifacts related to the tube scan trajectory pattern (for example, in the case of a linear trajectory, the linear artifact in the image) is incorporated, so that the image quality is improved. It can be further improved.

  Fourth, because it is equipped with a function that improves contrast resolution, which tends to be sacrificed due to the principle of radiography, it dramatically improves contrast resolution compared to conventional methods, and produces a tomographic image with high visibility and excellent diagnostic ability. Can be provided.

  Fifth, image recombination processing is performed in consideration of the image enlargement ratio and generalized to three dimensions. For this reason, for example, even when a coronal image at a plurality of different slice plane positions is displayed as a moving image, an image that contributes to improving the visibility of the affected area and improving the efficiency of the image interpretation work can be provided.

  Sixth, a function for fully utilizing the collected slice plane image data is installed even compared with a conventional digital X-ray tomography apparatus. Thereby, it is possible to provide a high-performance X-ray tomography apparatus that effectively utilizes the collected data and meets various needs desired at the treatment site.

  Seventh, unlike the digital X-ray tomography apparatus described in JP-A-57-203430 described above, there is a limitation on the scanning trajectory that the tube and the detector are moved in the opposite directions. Eliminated. In addition, the limitation on data processing in which image information from the detector is stored in the memory in association with each moving position is also eliminated. The image can be recombined even if the tube (or tube and detector) is arbitrarily moved two-dimensionally or three-dimensionally. In this way, restrictions on scan trajectory and data processing have been significantly eliminated, greatly increasing the degree of freedom in equipment layout and image processing procedures in system design. Therefore, it is possible to provide an X-ray tomography apparatus that is highly versatile, easy to use, and low in cost.

1 is a diagram showing a schematic configuration of an X-ray tomography apparatus according to one embodiment of the present invention. The figure for demonstrating the imaging | photography principle of this invention. The figure explaining a detector horizontal installation system. The figure explaining a detector installation system. The figure explaining a detector placement system. The figure explaining a detector placement system. The figure explaining the system which inserts a detector in a bed. The figure explaining a system with a cover. The figure explaining the system which can remove or retract a tube / detector. The figure explaining the mechanism for taking electrical synchronization with a tube and a detector. The figure explaining the mechanism for taking mechanical synchronization with a tube and a detector. The figure which shows the attachment to the C arm of a tube and a detector. The figure which shows attachment of the tube and the detector using the child arm extended from C arm. The figure explaining a movement of a child arm. The figure explaining various one-dimensional scanning orbits. The figure explaining various two-dimensional scanning orbits. The figure explaining a three-dimensional scan orbit. The figure which shows the mode of the facing to the tube of a detector. The figure for demonstrating the scanning orbit of a circadian circle motion. Explanatory drawing of the scanning orbit which moves a photography visual field. The figure which illustrates the scanning orbit which shifts the cycle of a tube and a detector. The figure explaining control of the data collection timing according to the scanning orbit. The figure explaining the setting method of the data collection timing when using a continuous X-ray. The figure explaining utilization of a marker. The figure for demonstrating correction | amendment of the stationary position shift using a marker. The figure which shows the arrangement | positioning condition of a grid. The figure which shows direction of the blade | wing of a grid. The figure which shows direction control of the blade | wing of a movable grid. The figure for demonstrating correction | amendment of the projection data by a COS term. The figure explaining a movement component. The figure explaining an example of the detection of a motion component. The figure explaining the detection of the motion component with a threshold value. The figure which shows an example of the marker attached | subjected to a detector front surface for distortion correction inside a detector. The figure which shows another example of the marker attached | subjected to a detector front surface for distortion correction inside a detector. The figure for demonstrating the process of an image recombination with the generalized expression. Explanatory drawing for converting the generalized expression of image recombination from an absolute coordinate to a relative coordinate. The figure which shows the variation of a detector surface. The schematic diagram for demonstrating the process of the image recombination of a some slice surface. The figure explaining an example of the data selection from the projection data of each view. The figure explaining an example of image recombination accompanied by resampling. The figure explaining another example of the image recombination accompanying resampling. The figure explaining another example of the image recombination accompanying resampling. The figure explaining another example of data selection and image recombination. The figure explaining another example of data selection and image recombination. The figure explaining the flow of a process of image recombination simultaneous with collection of projection data. The figure explaining an example of large-field imaging | photography. The figure explaining another example of large-field imaging. The figure explaining an example of the image recombination method of range selection (limitation). The figure explaining another example of the image recombination method of range selection (limitation). The figure explaining another example of the image recombination method of range selection (limitation). The figure explaining removal of a DC blur component. The flowchart which shows the outline | summary of the flow of a removal process of a DC blur component. The figure explaining the direction of filtering for performing a blur recovery process. The figure which illustrates typically the pulse injection of the contrast agent in strobe imaging | photography. 6 is a timing chart for explaining the relationship between a contrast agent pulse injection period and a scanning period in strobe imaging. The figure explaining the data collection timing in an electrocardiogram synchronous scan. The figure explaining the surface of an image generation when performing an intraoperative navigator or an intraoperative monitor. The figure which illustrates the mode of setting of volume ROI. The figure explaining the outline | summary of the mechanism for confirmation of the X-ray irradiation range by light. The perspective view explaining the moving mechanism of the X-ray tube which does not use a slip ring. FIG. 61 is a plan view illustrating the movement of the moving mechanism illustrated in FIG. 60. 3 is a schematic flowchart showing procedures of imaging and data processing of the X-ray tomography apparatus according to the embodiment. The figure which shows schematic structure of the X-ray tomography apparatus which concerns on another embodiment of this invention. The figure explaining the scanning system which fixes a detector and moves a tube. The figure explaining the shift amount in this another embodiment. The figure explaining addition of the projection data in this another embodiment. 6 is a schematic flowchart showing an example of image recombination processing.

Explanation of symbols

10 Bed 10a Top plate 12 X-ray tube (focus, tube)
14 X-ray detector (detector)
16, 24, 30, 30a, 30b, 32a, 32b, 38, 38a, 38b, 40, 50, 52a, 52b, 54a, 54b, 60, 62, 64, 66, 68 Support mechanism 18 Control / processing device 19 Input Device 20 Display device 120 Memory 122 CPU
124 High-pressure generator 126 X-ray controller 128 Input device 130 Display device 141 Contrast medium injection device 142 Electrocardiogram data measurement device

Claims (1)

A top plate on which the subject is placed;
A bed supporting the top plate;
An X-ray tube that emits X-rays from a focal point toward the subject;
First support means for supporting the X-ray tube;
Drive means for moving the position of at least one of the focal point and the top plate to change the relative positional relationship between the focal point and the subject;
Contrast medium injection means for injecting a contrast medium into the subject in a pulsed manner;
X-ray detection means for capturing an X-ray image transmitted through the subject and capturing an X-ray image having a relative position between the focal point and the subject;
Second support means for supporting the X-ray detection means;
A positional relationship detection means for obtaining a relative positional relationship between the focal point and the X-ray detection means at the time of X-ray imaging;
Image processing means for obtaining a tomographic image of the subject based on outputs of the X-ray detection means and the positional relationship detection means;
Display means for displaying the image processed by the image processing means,
The driving means is configured to repeatedly perform a predetermined movement operation at a cycle different from the contrast agent injection cycle,
An X-ray tomography apparatus, which is a means for creating a tomographic image by selecting and combining X-ray images at the same pulse-shaped injection cycle.

Images