JP5031335B2 - X-ray CT system - Google Patents

Description

  The present invention relates to an X-ray CT apparatus.

  The X-ray CT apparatus includes an X-ray source and a two-dimensional X-ray detector arranged to face each other with the subject interposed therebetween, and the X-ray CT device is arranged around the subject with the X-ray source and the two-dimensional X-ray detector facing each other. In this case, the cross-sectional image of the subject can be reconstructed from the output data from the two-dimensional X-ray detector obtained by receiving the X-ray from the X-ray source through the subject.

  Here, as the two-dimensional X-ray detector, for example, a flat panel detector (FPD) or an X-ray image intensifier incorporating a television camera is used.

  In this case, since the imaging rate of the two-dimensional X-ray detector is configured to be about 30 per second, when performing X-ray imaging with an imaging time of about 10 seconds using the cone beam X-ray CT apparatus, As a result, the number of shots is limited to about 300. .

  For example, as disclosed in Non-Patent Document 1 below, a method of performing X-ray imaging that compensates for a shortage of the number of radiographs by using a so-called filtered back projection method has been known. However, when the filtered back projection method is used in this way, a radial false image (streak artifact) centered on the rotation center or high absorber is generated in the cross-sectional image due to lack of projection angle information. End up.

As a method of compensating for the inconvenience of X-ray imaging when the number of images is small as described above, for example, as disclosed in the following Patent Document 1 or Patent Document 2, the adjacent projection data is added and averaged. A method is known in which interpolated projection data is generated and then the filtered backprojection method is performed.
Japanese Patent No. 3583836 JP 2001-286462 A Practical Cone-Beam Algorithm; LAFeldkamp, et al .; J. Optical Society of America, A / Vol. 1 (6), (1984), pp.612-619

  However, in the cone beam X-ray CT apparatus that performs X-ray imaging using the interpolation projection method disclosed in Patent Document 1 or Patent Document 2, the number of interpolation data generated by interpolation is the number of imaging data (the number of projection data). 2) to 3 times, but the calculation time also increases by that amount (2 to 3 times), and the increase in the calculation time cannot be avoided.

  An object of the present invention is to provide an X-ray CT apparatus that obtains a cross-sectional image in which radial artifacts are reduced while avoiding an increase in calculation time.

   Of the inventions disclosed in this application, the outline of typical ones will be briefly described as follows.

(1) An X-ray CT apparatus according to the present invention includes, for example, an X-ray source that irradiates a subject with X-rays,
A two-dimensional X-ray detector that is disposed opposite to the subject and detects transmitted X-rays of the subject;
Rotating means for rotating the X-ray source and the two-dimensional X-ray detector around the subject while facing each other;
Image reconstruction means for generating an X-ray CT cross-sectional image from X-ray image data from the two-dimensional X-ray detector;
Adding means for adding the generated first X-ray CT cross-sectional image and a second X-ray CT cross-sectional image obtained by rotating the rotating means by a predetermined angle;
Display means for displaying the added X-ray CT cross-sectional image.

(2) The X-ray CT apparatus according to the present invention is based on, for example, the configuration of (1), and the rotation of the second X-ray CT cross-sectional image at a predetermined angle is the first and second X-ray CT cross-sectional images. The X-ray absorption distribution is performed around the center of gravity.

  In addition, this invention is not limited to the above structure, A various change is possible in the range which does not deviate from the technical idea of this invention.

  In such an X-ray CT apparatus having a small number of radiographs, it is possible to obtain a cross-sectional image in which the increase in calculation time is avoided and radial artifacts are reduced. Thereby, it is possible to realize an X-ray CT apparatus with excellent so-called CT value uniformity and improved low contrast resolution.

  Embodiments of an X-ray CT apparatus according to the present invention will be described below with reference to the drawings.

  First, FIG. 2 is a schematic configuration diagram showing an embodiment of a sitting-type cone beam X-ray CT apparatus to which the present invention is applied.

  In FIG. 2, the sitting-type cone beam X-ray CT apparatus includes an imaging unit 10, a control calculation unit 20, and a display device 80.

  The imaging unit 10 includes a chair 7 on which the subject 2 is placed, an X-ray source 11 that irradiates the subject 2 placed on the chair 7 with X-rays, and the X-ray source 11 that is disposed facing the subject 7. A two-dimensional X-ray detector 12 that detects X-rays transmitted through 2 and outputs X-ray image data, a swing arm 5 that fixes the X-ray source 11 and the two-dimensional X-ray detector 12, and the swing arm 5 And a fixed base 8 for holding the column 6 and the chair 7. The X-ray source 11 comprises an X-ray tube 11t and a collimator 11c.

  The X-ray source 11 and the two-dimensional X-ray detector 12 are rotated around the subject 2 (around the vertical axis 4) while facing each other, and at that time, the X-ray from the X-ray source 11 passes through the subject 2. The two-dimensional X-ray detector 12 receiving the X-ray image data outputs the X-ray image data. As the two-dimensional X-ray detector 12, for example, a flat panel detector (FPD) using a TFT element is used. In this case, the two-dimensional X-ray detector 12 includes an X-ray image intensifier that converts an X-ray transmission image into a visible light image, and a television camera that captures a visible light image by the X-ray image intensifier. It may be configured.

  The control calculation unit 20 includes an imaging unit control unit 100 that controls the imaging unit 10, an imaging system rotation control unit 101 that is driven by the imaging unit control unit 100, an X-ray irradiation control unit 103, a chair position control unit 105, An image collecting unit 110 that collects and stores X-ray image data obtained from the imaging unit 10 through the detection system control unit 107; Reconstruction means 200 for reconstructing a three-dimensional X-ray CT image based on X-ray image data, and image display means 120 for guiding the cross-sectional image data obtained from the reconstruction means 200 to the display device 80 are provided. Configured.

  Here, the reconstruction unit 200 includes a preprocessing unit 210, a filtering unit 220, a back projection unit 230, and a rotation addition unit 240.

  The pre-processing unit 210 converts the X-ray image data from the image collecting unit 110 into a distribution image of X-ray absorption coefficients. In this embodiment, first, a natural logarithmic conversion operation is performed on each pixel data of an X-ray transmission image of air that has been imaged in advance without the subject 2 and the bed 17 being placed in the field of view, and then the subject. The natural logarithm conversion operation is performed on each pixel data of the X-ray transmission image taken with 2 placed on the bed 17 and the difference between the two X-ray transmission images is taken to obtain the X of the subject 2 and the bed 17. A linear absorption coefficient distribution image is obtained.

  The filtering unit 220 performs a filtering process in the X-ray CT image reconstruction, and the back projection unit 230 performs a back projection operation on the X-ray image data after the filtering process (for example, the method described in Non-Patent Document 1). A three-dimensional X-ray CT image is generated by performing a back projection operation comprising: Here, the three-dimensional X-ray CT image is generally grasped as a stack of a plurality of axial cross-sectional images.

  Further, the rotation addition means 240 is a characteristic component together with the rotation addition angle input means 300 described later in this embodiment, reads the axial cross-sectional image output from the back projection means 230, and this axial cross-sectional image. An image rotated by a predetermined angle is generated, and the generated image is multiplied by an integration coefficient and added to the original axial sectional image. Here, in the rotation adding means 240, the setting of the rotation angle at the time of generating an image rotated with respect to the read axial sectional image and the setting of the integration coefficient to be applied to the generated image are rotation addition. It is made through the corner input means 300.

  The configuration and operation of the rotation addition means 240 and the rotation addition angle input means 300 will be described in detail later.

  Here, in the above-mentioned cone beam X-ray CT apparatus, the distance between the X-ray tube 11t and the rotation center axis 4 is, for example, 800 mm, and the distance between the rotation center axis 4 and the X-ray incident surface of the two-dimensional X-ray detector 12 is. The distance is 400 mm, for example, and the size of the X-ray incident surface of the two-dimensional X-ray detector 12 is a rectangle of 400 mm × 300 mm, the image size is 2048 × 1536, and the image pitch is 0.2 mm, for example. ing. When X-rays are incident on the two-dimensional X-ray detector 12, the light is converted into light by a light emitter such as CsI disposed on the X-ray incident surface, and the optical signal is converted into electric charge by a photodiode. It has become. The accumulated charge is converted into a digital signal by a TFT element, for example, at a constant frame rate and read out. In the rotation shooting mode in this case, the rotation speed of the swivel arm 5 is 36 ° per second, for example, and the scan time is 10 seconds. For example, two-dimensional image data is read out at 30 frames per second, for example, image size 1024 × 768. It has become.

  FIG. 3 is a schematic configuration diagram showing an embodiment of a C-arm type cone beam X-ray CT apparatus to which the present invention is applied.

  In FIG. 3, the imaging unit 10 c of the C-arm type cone beam X-ray CT apparatus includes a bed 17 that lies on the subject 2, and an X-ray source 11 that irradiates the subject 2 lying on the bed 17 with X-rays. A two-dimensional X-ray detector 12 installed opposite to the X-ray source 11 and detecting X-rays transmitted through the subject 2 and outputting X-ray image data; and the X-ray source 11 and two-dimensional X-ray detection A C-type arm 13 for fixing the container 12, a C-type arm holding body 14 for holding the C-type arm 13, a ceiling support 15 for fixing the C-type arm holding body 14 to the ceiling, and the ceiling support 15 Is provided with a ceiling rail 16 that moves the two-dimensionally in the front-rear and left-right directions, and an injector 18 that injects a contrast medium into the subject 2. The X-ray source 11 comprises an X-ray tube 11t and a collimator 11c.

The X-ray source 11 and the two-dimensional X-ray detector 12 are rotated around the subject 2 (around the horizontal axis 4) while facing each other, and at that time, the X-ray from the X-ray source 11 passes through the subject 2. The two-dimensional X-ray detector 12 receiving the X-ray image data outputs the X-ray image data. As the two-dimensional X-ray detector 12, for example, a flat panel detector ( FPD ) using a TFT element is used. In this case, the two-dimensional X-ray detector 12 includes an X-ray image intensifier that converts an X-ray transmission image into a visible light image, and a television camera that captures a visible light image by the X-ray image intensifier. It may be configured.

  The control calculation unit 20c includes an imaging unit control unit 100c that controls the imaging unit 10, an imaging system rotation control unit 101, an imaging system position control unit 102, and an X-ray irradiation control unit 103 that are driven by the imaging unit control unit 100c. , Injector control means 104, bed control means 106, and detection system control means 107. Similarly to the sitting-type cone beam X-ray CT apparatus, the image collecting means 110 for collecting and storing X-ray image data obtained from the imaging unit 10 through the detection system control means 107, and the image Reconstructing means 200 for reconstructing a three-dimensional X-ray CT image based on the X-ray image data collected by the collecting means 110, and for guiding the cross-sectional image data obtained from the reconstructing means 200 to the display device 80. The image display means 120 is provided. As shown in FIG. 2, the reconstruction unit 200 includes a preprocessing unit 210, a filtering unit 220, a back projection unit 230, and a rotation addition unit 240, and the rotation addition angle input unit 300 performs the rotation addition. Information on the rotation angle and the integration coefficient can be input to the means 240.

  The configuration and operation of the rotation addition means 240 and the rotation addition angle input means 300 will be described in detail later.

  Here, in the C-arm type cone beam X-ray CT apparatus, the two-dimensional X-ray detector 12 has the direction of the left hand of the subject 2 lying on the bed 17 by the imaging system rotation control means 101 (− 100 °) passes through the ceiling direction (0 °) and moves to the left hand direction of the subject 2 (+ 100 °). Accordingly, the X-ray tube 11t passes from the right hand direction (+ 100 °) of the subject 2 to the ceiling direction (0 °) and is moved to the left hand direction (−100 °) of the subject 2, for example, a projection of 200 ° A two-dimensional X-ray transmission image of the subject 2 is taken over an angle. The rotational speed of the C-arm 13 is, for example, 40 ° per second, and the scan time is, for example, 5 seconds.

  FIG. 4 is a schematic configuration diagram showing an embodiment of another type of cone beam X-ray CT apparatus to which the present invention is applied.

  The X-ray source 11 and the two-dimensional X-ray detector 12 disposed opposite to the X-ray source 11 are fixed, and the object to be disposed between the X-ray source 11 and the two-dimensional X-ray detector 12 is fixed. For example, the specimen 2 is placed on the turntable 19 in an upright state.

  The subject 2 is rotated by driving the turntable 19, and at this time, the two-dimensional X-ray detector 12 receiving X-rays from the X-ray source 11 through the subject 2 outputs X-ray image data. It is like that.

  Although not shown in the figure, similarly to FIGS. 2 and 3, the control calculation unit 20 and the display device 80 are provided. The image forming apparatus includes a configuration unit 200, a rotation addition angle input unit 300, an image display unit 120, and the like.

  FIGS. 5A to 5C are explanatory diagrams conceptually showing the processing in the rotation adding means 240.

  First, FIG. 5A shows an axial cross-sectional image 40 that is input from the back projection unit 230 to the rotation addition unit 240 because the number of radiographs is small in a cone beam X-ray CT apparatus. It is shown that radial streak artifacts 42 are generated around the high absorber 41 due to the shortage.

  Here, the streak artifact 42 is generated at a projection angle interval. In a CT apparatus having a large number of projections, such as about 1000, compared to the CT image matrix size, radial streaks fill the CT image matrix and no artifacts are generated, but the number of projections is limited to about 300, for example. In the case of the cone beam X-ray CT apparatus, the streak artifact 42 as described above is generated.

  FIG. 5B shows an axial cross-sectional image 50 when the axial cross-sectional image 40 is rotated by, for example, b / 2 around its center 41 (a portion corresponding to the rotation center axis 4). Here, b is the projection angle interval. By this rotation, the streak artifact 42 moves to the position indicated by reference numeral 52 in the figure. The b / 2 value is a value set by the rotation addition angle input means 300.

  FIG. 5C shows an axial sectional image 60 obtained by adding the axial sectional image 40 shown in FIG. 5A and the axial sectional image 50 shown in FIG. 5B to each other. . In the axial cross-sectional image 60, streak artifacts are formed as disappeared, and even if the axial cross-sectional image 50 rotated at a slight angle with respect to the original axial cross-sectional image 40 is added to the cross-sectional image, Thus, an axial cross-sectional image 60 that is not affected by the above is formed.

  The rotation adding means 240 operates according to the procedure shown in FIGS. 5A to 5C, and the flowchart is shown in FIG.

  That is, in FIG. 1, first, as shown in step S241, the axial sectional image 40 that has already been calculated by the back projection unit 230 is read.

  Next, as shown in step S242, the read axial sectional image 40 is rotated by the rotation angle (b / 3 to b / 2) set by the rotation addition angle input means 300 around the center of the image. The axial image 50 is created. Here, b is the projection angle interval. The axial cross-sectional image 40 is rotated in both clockwise and counterclockwise directions to generate images, respectively. However, only one rotation image is generated, and subsequent addition processing is performed. May be.

  Next, as shown in step S243, the axial cross-sectional image 50 is multiplied by the addition coefficient set by the rotation addition angle input means 300 and added to the original axial cross-sectional image 40. By adding the rotated images, as shown in FIG. 5C, the shades of the radial cross streaks of the axial cross sectional images 40 and 50 are filled up, and a uniform axial cross sectional image 60 is obtained. After the addition, the pixel value is normalized so that the image level is the same as the original axial sectional image by dividing by the addition coefficient.

  Furthermore, as shown in step S244, it is checked whether or not the processing in steps S241 to S243 has been completed for all the axial cross-sectional images. If not completed, the processes in steps S241 to S243 are repeated.

  Each axial sectional image 60 in which the streak artifact disappears in this way is displayed on the display device 80 via the image display means 120.

  In the cone beam X-ray CT apparatus configured as described above, the operation of the rotation adding unit 240 is performed by rotating the axial sectional image and adding the axial sectional image obtained by the rotating processing and the original axial sectional image. Therefore, it is possible to significantly reduce the arithmetic processing, thereby reducing the occurrence of radial artifacts without increasing the calculation time.

  In the above-described embodiment, the rotation center of the axial cross-sectional image 40 to be rotated is a portion corresponding to the rotation center axis 4, but is changed according to the distribution of the X-ray absorption coefficient of the axial cross-sectional image 40. It may be.

  This is because a superabsorbent such as a catheter, a contrasted blood vessel, or a metal in the subject 2 that causes the streak artifact 42 is not always on the rotation center axis 4.

  As in the embodiment shown in FIG. 5, even if the superabsorber or the center of gravity of the superabsorber distribution is approximated to be on the rotation center axis 4, a certain degree of artifact reduction effect can be obtained. However, as shown in FIG. 6, when the position of the superabsorber 41 varies according to the axial cross-sectional image, radial artifacts can be reduced more effectively by using the location of the superabsorber as the center of rotation. Can do. FIG. 6 shows a stack of a plurality of axial cross-sectional images 40, and among them, the axial cross-sectional image 70 shows a case where there is no superabsorbent body 41 exceeding a certain threshold.

  FIG. 7 is a flow chart showing the operation of another embodiment of the rotation adding means 240. The center of gravity of the CT value in each axial cross-sectional image is calculated, rotated around this center of gravity, and the original axial cross-sectional image. Is configured to be added.

  In FIG. 7, first, as shown in step S251, the axial sectional image 40 calculated by the back projection unit 230 is read.

  Next, as shown in step S <b> 252, it is checked whether or not the axial cross-sectional image 40 includes pixels that are equal to or larger than the threshold value. If "YES" is determined, the process proceeds to step S253, and the rotation addition process described below is performed. If “NO” is determined, the process proceeds to step S257 to skip the rotation addition process. As a method for determining the threshold value, a method for determining the absolute value of the pixel value of the axial cross-sectional image 40, or a differential filter image or an edge-enhanced image of the axial cross-sectional image 40, and the amount of change in the pixel value is greater than a certain threshold value. There is a method of determining “YES” for an axial cross-sectional image.

  Next, as shown in step S253, if “YES” is determined in step S252, the longitudinal sectional images before and after are read, and the barycentric coordinates of the respective X-ray absorption distributions are calculated. The number of axial cross-sectional images before and after reading and one axial cross-sectional image read in step S251 will be five as a standard. For calculation of the barycentric coordinates, as is well known, a first-order moment related to the X coordinate or Y coordinate of the pixel value is used. At this time, in order to suppress an error due to background, a first moment may be calculated by setting a threshold value and inputting the pixel value and the coordinate value thereof for pixels equal to or higher than the threshold value.

  Next, as shown in step S254, the barycentric coordinates of the X-ray absorption distribution of each axial cross-sectional image obtained in step S254 are averaged to obtain center coordinates for rotating the axial cross-sectional image. By taking the average of the barycentric coordinates, the center coordinates of the rotation can be smoothly changed in the axial direction.

  Next, as shown in step S255, the axial section rotated by the rotation angle (b / 3 to b / 2) set by the rotation addition angle input means 300 around the rotation center coordinate obtained in step S253. An image 50 is created. Here, b is the projection angle interval.

  Next, as shown in step S256, the axial cross-sectional image 50 created in step S255 is multiplied by the addition coefficient set by the rotation addition angle input means 300 and added to the original axial cross-sectional image 40.

  Furthermore, as shown in step S257, it is checked whether or not the processing in steps S241 to S243 has been completed for all the axial cross-sectional images. If not completed, the processes in steps S241 to S256 are repeated.

  In the above-described embodiment, the arithmetic operation for sequentially rotating and adding the axial sectional images input to the rotation adding means 240 is performed and displayed on the display device 80. However, the present invention is not limited to this. For example, an axial cross-sectional image that has not been subjected to rotation addition (corresponding to the axial cross-sectional image 40 shown in FIG. 5A) is stored, and rotation addition is performed in real time when the image is displayed. Processing may be performed to display an axial cross-sectional image (corresponding to the axial cross-sectional image 60 shown in FIG. 5C) with reduced radial artifacts.

  FIG. 8 is an explanatory view showing a part of the axial cross-sectional image 60 obtained in this way by the display device 80 in an enlarged manner. In FIG. 8, a dotted line indicated by reference numeral 44 in the drawing is a circle indicating the axial reconstruction field boundary, and a part of the reconstruction field is displayed on the screen (display area) of the display device 80. Reference numeral 71 denotes a superabsorber outside the display area.

  When there are a plurality of superabsorbers in the axial reconstruction field of view, and some of them are outside the display area as shown in FIG. 8, the rotation is performed by rotating the axial cross-sectional image 40 by removing them. Find the center. In this case, an image with reduced radial artifacts can be displayed more effectively in the display area of the display device 80.

  FIG. 9 is a block diagram showing delivery of image data in such a configuration.

  In FIG. 9, after the back projection operation by the back projection unit 230, the axial section image 40 that has not been subjected to rotation addition is stored in the image database 70 by the image storage unit 231. When the image is displayed, the image reading means 232 reads the axial cross-sectional image 40 that has not been subjected to rotation addition from the image database 70. Next, the rotational addition means 240 generates an axial cross-sectional image with reduced radial artifacts in the display area. In this case, in step S253 shown in FIG. 7, the calculation of the center coordinates for rotating the axial cross-sectional image is performed only on the screen (display area) of the display device 80. Then, the axial sectional image generated by the rotation adding unit 240 is displayed on the display device 80 via the image display unit 120. In this case, it is also possible to store the axial sectional image after the rotation addition processing in the image database 70 using the image storage unit 231.

  As another embodiment, the rotation addition process is performed by changing the rotation angle of the axial sectional image and the addition coefficient of the rotation image set by the rotation addition angle input means 300 in several ways, and the most appropriate axial The cross-sectional image may be stored in the image database 70.

  Furthermore, in each of the above-described embodiments, the addition operation in the rotation addition unit 240 is performed only based on the rotation addition coefficient set in the rotation addition angle input unit 300 or the like. However, for example, an appropriate rotation addition processing parameter (rotation addition) is performed while observing a state in which an axial sectional image of one slice displayed on the display device 80 is rotated by a predetermined angle and added to the original axial sectional image. Coefficient, rotation image addition coefficient, etc.) may be set, and back projection calculation and rotation addition processing of the axial cross-sectional image composed of the remaining slices may be performed.

  FIG. 10 shows a block diagram of such a configuration. In FIG. 10, after the filtering process by the filtering unit 220, first, the back projection operation is performed on the axial slice image of one slice by the one slice back projection unit 230s. Here, the axial sectional image to be calculated may be any slice as long as the rotation addition process can be evaluated, and may be one middle slice or one fixed slice with a dentition.

  The back-projected axial cross-sectional image is rotated by, for example, an initially set rotation addition processing parameter, added to the original axial cross-sectional image, and displayed on the display device 80.

Then, the rotation addition angle input means 300 generates three rotation addition processing parameters for generating both the rotation angle coefficient, the rotation image addition coefficient, and the rotation addition image clockwise and counterclockwise, or using only one side. In this case, the setting is performed through a soft switch displayed on the screen (display area) of the display device 80.

  FIG. 11 shows a screen (display area) 81 of the display device 80. On the screen 81, for example, a rotation addition processing parameter setting means 81a and an image 81b after the rotation addition processing are displayed.

  In the display of the rotation addition processing parameter setting means 81a, a software switch for setting a rotation angle coefficient, a rotation image addition coefficient, and a rotation state of a rotation image to be added is provided. A value can be entered. The setting in this case can be made through several trials (tests) while observing the image 81b after the rotation addition processing.

  Then, when it is determined that the rotation addition processing parameter set in this way is appropriate, by clicking the soft switch on which “decision” is displayed, all the slices are set with the rotation addition processing parameter. The rotation addition means 240 is executed for the axial sectional image, and the result can be displayed by the display device 80.

  Each of the embodiments described above may be used alone or in combination. This is because the effects of the respective embodiments can be achieved independently or synergistically.

It is a flowchart which shows one Example of operation | movement in the principal part of the X-ray CT apparatus by this invention. 1 is a block diagram showing a schematic configuration of a sitting-type cone beam X-ray CT apparatus to which the present invention is applied. 1 is a block diagram showing a schematic configuration of a C-arm type cone beam X-ray CT apparatus to which the present invention is applied. It is a block diagram which shows schematic structure of the other cone beam X-ray CT apparatus to which this invention is applied. It is explanatory drawing which shows one Example of the addition process of the axial cross section image made in the X-ray CT apparatus by this invention. It is a schematic diagram for demonstrating a mode that several axial cross-sectional images are laminated | stacked and the position of a high absorber is changing, and an axial cross-sectional image in which the high absorber more than a threshold value does not exist. It is a flowchart which shows the procedure which performs a rotation addition process and removes a streak artifact in the other Example of operation | movement of the X-ray CT apparatus by this invention. It is explanatory drawing which shows the other Example of the X-ray CT apparatus by this invention, and is a figure which shows displaying the image which expanded a part of axial sectional image in which a streak artifact exists. It is a block diagram which shows the other Example of the X-ray CT apparatus by this invention. It is a block diagram which shows the other Example of the X-ray CT apparatus by this invention. It is a block diagram which shows the other Example of the X-ray CT apparatus by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cone-beam X-ray CT apparatus, 1b ... Object rotation type cone beam X-ray CT apparatus, 1c ... C-arm type cone beam X-ray CT apparatus, 2 ... Subject, 3 ... Rotating orbit Plane (midplane), 4 ... Rotation center axis, 5 ... Swivel arm, 6 ... Post, 7 ... Chair, 8 ... Fixed mount, 10 ... Shooting unit, 10c ... C-arm type cone beam X-ray CT imaging unit, 11 ... X-ray source, 11t ... X-ray tube, 11c ... Collimator, 12 ... Two-dimensional X-ray detector, 13 ... C-type arm, 14 ... C-type arm holding Body, 15 ... ceiling support, 16 ... ceiling rail, 17 ... bed, 18 ... injector, 19 ... turntable, 20 ... control operation unit, 20c ... C-arm type cone beam X-ray CT Control imaging unit, 21 ... Projection of rotation center axis onto two-dimensional X-ray detector 40 …… Axial cross-sectional image, 41 …… Center point of occurrence of streak artifact, 42 …… Streak artifact, 44 …… Circle indicating axial reconstruction field boundary, 50 …… Rotated axial cross-sectional image, 52 …… Rotated streak Artifact, 60 ... Axial sectional image added, 70 ... Axial sectional image without superabsorber, 71 ... Superabsorber outside monitor display area, 80 ... Display device, 81a ... Rotation addition processing Parameter setting means, 81b... Image after rotation addition processing, 90... Information input device, 100, 100c .. photographing unit control means, 101... Photographing system rotation control means, 102. 103 ... X-ray irradiation control means, 104 ... Injector control means, 105 ... Chair position control means, 106 ... Sleeper control Stage 107... Detection system control means 110... Image collection means 120... Image display means 200 .. Reconstruction means 210... Pre-processing means 220. , 230S... 1 slice backprojection means, 240... Rotation addition means, 240S... 1 slice rotation addition means, 300.

Claims (11)

An X-ray source for irradiating the subject with X-rays, a two-dimensional X-ray detector for detecting transmitted X-rays of the subject opposed to each other with the subject interposed therebetween, and the X-ray source and two-dimensional X Rotating means for rotating the X-ray detector around the subject while facing the X-ray detector, and image reconstruction means for generating a first X-ray CT cross-sectional image from X-ray image data from the two-dimensional X-ray detector Adding means for adding the generated first X-ray CT cross-sectional image and a second X-ray CT cross-sectional image obtained by rotating the first X-ray CT cross-sectional image by a predetermined angle; An X-ray CT apparatus comprising: display means for displaying an X-ray CT cross-sectional image. 2. The X-ray CT according to claim 1 , wherein the rotation of the first X-ray CT cross-sectional image by a predetermined angle is performed around the center of gravity of the X-ray absorption distribution of the first X-ray CT cross-sectional image. apparatus. 3. A rotation angle coefficient input means for inputting a rotation angle coefficient when rotating the first X-ray CT cross-sectional image to obtain the second X-ray CT cross-sectional image. X-ray CT apparatus described in 1. The rotation image addition coefficient input means for inputting a rotation image addition coefficient, which is a weight when adding the first X-ray CT cross-sectional image and the second X-ray CT cross-sectional image. The X-ray CT apparatus according to 1 or 2. The second X-ray CT cross-sectional image is composed of two images obtained by rotating the first X-ray CT cross-sectional image clockwise and counterclockwise in both directions, or rotating in one direction. The X-ray CT apparatus according to claim 1, further comprising a selection unit that selects whether the image is composed of one image subjected to the processing. The rotation of the first X-ray CT cross-sectional image performed around the center of gravity of the X-ray absorption distribution is performed according to whether there is a pixel value that is equal to or greater than a first threshold value. The X-ray CT apparatus according to claim 2. The rotation of the first X-ray CT cross-sectional image performed at a predetermined angle centered on the center of gravity of the X-ray absorption amount distribution is whether there is a change amount of the pixel value of an adjacent pixel equal to or greater than a second threshold value. 3. The X-ray CT apparatus according to claim 2, wherein the X-ray CT apparatus is performed accordingly. The X-ray CT apparatus according to claim 2, wherein the center of gravity is obtained by calculating a first-order moment with respect to a pixel having a third threshold value or more. The X-ray CT apparatus according to claim 8, wherein a plurality of first X-ray CT cross-sectional images are used to obtain the center of gravity. The X-ray CT apparatus according to claim 1, wherein the first X-ray CT cross-sectional image is stored, and means for performing addition by the addition means at the time of image display is provided. The X-ray CT apparatus according to claim 2, further comprising means for performing addition by the adding means using only a part of the first X-ray CT tomogram.

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