JP5269386B2 - X-ray computed tomography apparatus and medical imaging apparatus - Google Patents

Description

  The present invention relates to an X-ray computed tomography apparatus, a medical image imaging apparatus, and a medical image display apparatus for reconstructing an image related to a cross section of a subject.

  Even if a subject that does not move at all is photographed, periodic subtle blurring occurs on the video. This is not due to image noise. For example, in the case of a 0.4 second scan, a subtle movement with a period of 0.4 second occurs in the subject. This is mainly due to mechanical fluctuations on the device side, such as shaking of the pedestal due to gravity and centrifugal force, displacement of the tube focal point, etc., and the position of the tube (focal point) -detector in a cycle of 360 °. When moving out of the ideal state, blurring occurs on the moving image. In the image diagnosis using a still image, the level difference is not recognized by the observer, but the motion is recognized when an object that does not move is observed with a moving image.

  In an actual clinical field, an examination using an X-ray computed tomography apparatus is effective for evaluating the risk of rupture of a cerebral aneurysm. Since the shape of a cerebral aneurysm with a high risk of rupture changes as the blood pressure changes, video observation is effective. The electrocardiogram information is electrical information generated by a change in the state of the myocardium. If the relationship between the shape change and the rupture risk can be clarified, the urgency of the operation can be appropriately determined.

  An object of the present invention is to reduce the position variation of a subject image on a moving image caused by mechanical shake or the like caused by rotation of a gantry.

  In one aspect, the present invention provides an X-ray tube, an X-ray detector, a rotation mechanism unit that continuously rotates the X-ray tube together with the X-ray detector around the subject, and an X-ray detector. A data storage unit that stores projection data corresponding to the output in association with the angle of the X-ray tube at the time of data collection, and a reconfiguration that reconstructs a plurality of images based on a plurality of projection data sets stored in the data storage unit. An X-ray computer comprising: a configuration processing unit; and a display unit that displays a plurality of reconstructed images corresponding to the same range from the first view angle to the second view angle in the plurality of projection data sets. A tomography apparatus is provided.

  According to the present invention, it is possible to reduce fluctuations in the position of the subject image on the moving image due to mechanical shake or the like caused by the rotation of the gantry.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of an X-ray computed tomography apparatus according to this embodiment. The gantry 100 includes an X-ray tube 101 and an X-ray detector 103. A tube voltage is applied from the high voltage generator 109 to the X-ray tube 101 via the slip ring 111, and a filament current is supplied. Thereby, X-rays are generated from the X-ray tube 101. As the X-ray detector 103, for example, a 256-slice multi-slice type is adopted. However, the X-ray detector 103 may be a multi-slice type or single-slice type detector having another number of columns. The mechanism for converting incident X-rays into electric charge is an indirect conversion type in which X-rays are converted into light by a phosphor such as a scintillator, and the light is converted into electric charge by a photoelectric conversion element such as a photodiode. The generation of electron hole pairs and their transfer to the electrode, that is, the direct conversion type utilizing a photoconductive phenomenon, is the mainstream. Any of these methods may be employed as the X-ray detection element of the X-ray detector 103.

  An electrocardiograph (ECG) 117 detects an electrocardiogram representing a temporal change in action potential reflecting a heart beat (heart beat motion) as a repeated biological phenomenon of the subject, and outputs it as a digital signal (electrocardiogram data). To do. The electrocardiogram data, that is, the action potential value data at each time is stored in the data storage unit 112 in association with the time code representing the time. Although the heartbeat is taken as an example of the biological phenomenon of the subject, respiratory movement may be used as another biological phenomenon.

  The X-ray tube 101 and the X-ray detector 103 are mounted on an annular rotating frame 102 that is supported so as to be rotatable about a rotation axis RA. The X-ray detector 103 is disposed at a position and an orientation facing the X-ray tube 101 with the opening 122 interposed therebetween. A subject placed on a couch top (not shown) is inserted into the opening 122. The X-ray detector 103 detects X-rays generated from the X-ray tube 101 and transmitted through the subject.

  The rotating frame 102 is continuously rotated at a high speed of, for example, 0.4 seconds / rotation by driving of the rotation driving unit 107. The tube position detection unit 118 is provided for detecting the angle of the X-ray tube 101 and typically includes a rotary encoder. The angle of the X-ray tube 101 is typically detected as a displacement angle from the reference angle (0 °) when the X-ray tube 101 is at the uppermost position. The angle (180 °) corresponds to the lowest position.

  The X-ray detector 103 detects X-rays that have passed through the subject. The data acquisition circuit 104 is generally called a DAS (data acquisition system). The data acquisition circuit 104 amplifies the signal read for each channel from the X-ray detector 103 and further converts it into a digital signal. Data output from the data acquisition circuit 104 reflects the intensity of incident X-rays and is generally referred to as pure raw data. The pre-processing unit 106 performs pre-processing such as logarithmic conversion and sensitivity correction on the pure raw data received from the data collection circuit 104 via the non-contact data transmission unit 105, and is immediately before the reconstruction processing. So-called projection data (also called raw data) is generated. The projection data is stored in the data storage unit 112 in association with a time code representing the time when the projection data is collected and data regarding the angle of the X-ray tube 101 at the time of the collection. The projection data can be associated with the electrocardiogram by the time code.

  The reconstruction processing unit 114 employs a so-called half reconstruction method, and reconstructs image (single slice, multi slice, or volume) data based on projection data for (180 ° + fan angle) around the subject. Can be configured. For convenience of explanation, the projection data for (180 ° + fan angle) is referred to as a projection data set as one unit. In addition, the angular position corresponding to the projection data set indicates one of the start position, end position, and center position for (180 ° + fan angle) required for half reconstruction, but here (180 The following description will be made on the assumption that the center position of (° + fan angle) is shown.

  The data set read control unit 119 accesses the data storage unit 112, reads a plurality of projection data sets from the stored projection data, and supplies them to the reconstruction processing unit 114. Note that the projection data set readout process by the readout control unit 119 may be a process that is substantially equivalent to the process of selectively reading out only the projection data corresponding to the angle range used for the reconstruction. Data is read and projection data corresponding to the angle range used for the reconstruction is assigned a weight of 1 and projection data not used for reconstruction outside the angle range is assigned a weight of 0 to contribute to the reconstructed image It also includes processing to prevent it. Here, for convenience of explanation, the reading process of the projection data set by the reading control unit 119 will be described as a process of selectively reading out only projection data corresponding to the angle range used for the reconstruction.

  The plurality of projection data sets to be read have the same angular width to cover (180 ° + α) required for half reconstruction, and the corresponding angular positions are the same. For example, when the projection data set covers the angle range of the X-ray tube 101 from the angle 0 ° to the angle (180 ° + α), the angular position corresponding to the projection data set is (90 ° + α / 2), This angular position is unified in all projection data sets.

  The reconstruction processing unit 114 reconstructs data of a plurality of images based on a plurality of projection data sets. The data of the reconstructed images is stored in the data storage unit 112. Although the angle position corresponding to the projection data set is initially set to (90 ° + α / 2), the operator can change the angle position to an arbitrary angle position via the operation unit 115.

  The image ordering processing unit 120 can associate the electrocardiogram with the electrocardiogram by the time code of the reconstructed images regardless of the collection time (collection order) of each of the reconstructed images. Order according to phase. The heartbeat phase is typically defined as a position within the interval expressed in units of% by normalizing the interval from one R wave to the next R wave by 100%.

  The image interpolation unit 121 generates a series of image sequences in which images are arranged at a constant interval of 1% or several% from a plurality of images ordered according to the heartbeat phase by interpolation processing. A series of image sequences generated by the interpolation is displayed on the display unit 116 as a moving image. Note that the image arrangement is initially 1% intervals, but the operator can change it to any interval via the operation unit 115.

  Next, the operation according to the present embodiment will be described. Under the control of the scan controller 110, the rotating frame 101 is continuously rotated at a constant speed, X-rays are continuously generated during the rotation period, and the X-ray detector 103 repeatedly reads data at a constant period. . The read data is the DAS 104 and the data transmission unit 105. It is stored in the data storage unit 112 as projection data via the preprocessing unit 106. Note that exposure may be reduced by irradiating the subject with X-rays limited to an angle range corresponding to the projection data set, and not irradiating the subject with X-rays in a range other than the angular range. . In addition, during multiple rotations, when it is predicted that the already collected projection data set will collect a projection data set corresponding to the same heartbeat phase as the corresponding heartbeat phase, during the collection period of the projection data set, X-ray irradiation may be stopped to reduce exposure. The X-rays may be continuous X-rays or pulsed X-rays. When the scheduled time or the planned number of rotations has elapsed, scanning is completed and signal processing described below is started.

  2 and 5, the range corresponding to a plurality of projection data sets used for half reconstruction read by the data reading control unit 119 according to the tube position with respect to the trajectory of the X-ray tube 101 is indicated by a bold line. ing. In FIG. 2, the projection data set covers the range in which the X-ray tube 101 rotates from the first view angle (A) 0 ° to the second view angle (B) (180 ° + α). The projection data set covers the range in which the X-ray tube 101 rotates from the view angle (90 ° −α / 2) to the view angle (270 ° + α / 2). Which of the view angles in FIGS. 2 and 5 is associated with the projection data set is arbitrary by the operator. Furthermore, the operator can arbitrarily associate other angular positions with the projection data set. In any case, the angular positions corresponding to the plurality of projection data sets may be the same. That is, the plurality of projection data sets only need to cover the same angle range.

  Since the rotation period and heartbeat period of the X-ray tube 101 are not synchronized, the heartbeat phase corresponding to each projection data set is indefinite. In FIG. 2, the projection data set PDS1 collected first corresponds to the heartbeat phase 40%, the projection data set PDS2 collected second corresponds to the heartbeat phase 60%, and the projection data set collected third. PDS3 corresponds to the heartbeat phase 85%, the fourth collected projection data set PDS4 corresponds to the heartbeat phase 10%, the fifth collected projection data set PDS5 corresponds to the heartbeat phase 30%, and the sixth. The projection data set PDS6 collected at 1 corresponds to a heartbeat phase of 50%. On the other hand, in FIG. 5, the projection data set PDS1 collected first corresponds to the heartbeat phase 60%, the projection data set PDS2 collected second corresponds to the heartbeat phase 90%, and the projection collected third. The data set PDS3 corresponds to the heart rate phase 5%, the fourth collected projection data set PDS4 corresponds to the heart rate phase 30%, the fifth collected projection data set PDS5 corresponds to the heart rate phase 50%, The sixth collected projection data set PDS6 corresponds to a heartbeat phase of 70%.

  Based on the plurality of projection data sets PDS1 to PDS6, the data of the plurality of images TI1 to TI6 are reconstructed by the reconstruction processing unit 114.

  The heartbeat phases corresponding to the reconstructed images TI1 to TI6 are specified by the image ordering processing unit 120. Inquiring of ECG data acquired together with scanning and stored in the data storage unit 112 by time codes corresponding to the respective angular positions of the plurality of projection data sets PDS1 to PDS6 from which the plurality of images TI1 to TI6 are based. Thus, the heartbeat phase is specified.

  The reconstructed images TI <b> 1 to TI <b> 6 are ordered according to the specified heartbeat phases by the image ordering processing unit 120. For example, in the case of FIG. 2, as shown in FIG. 3, an image TI4 having a heartbeat phase of 10%, an image TI5 having a heartbeat phase of 30%, an image TI1 having a heartbeat phase of 40%, an image TI6 having a heartbeat phase of 50%, and a heartbeat phase of 60%. The images TI2 and TI3 having a heart rate phase of 85% are rearranged in this order. Similarly, in the case of FIG. 5, as shown in FIG. 6, an image TI3 having a heartbeat phase of 5%, an image TI4 having a heartbeat phase of 30%, an image TI5 having a heartbeat phase of 50%, an image TI1 having a heartbeat phase of 60%, and a heartbeat phase. The images are rearranged in the order of 70% image TI6 and heart rate phase 90% image TI2.

  From a plurality of images TI1 to TI6 ordered according to the heartbeat phase, the image interpolation unit 121 generates a series of image sequences arranged at equal intervals at 1% or other pitches by interpolation processing. A series of image sequences generated by the interpolation is displayed on the display unit 116 as a moving image.

  As described above, in the half reconstruction, the angle positions corresponding to the plurality of projection data sets are made the same, that is, the plurality of projection data sets are cut out so as to cover the same angle range in 360 °. 4. As schematically shown in FIG. 7, the total amount of mechanical blur (shaded portion) mainly included in the plurality of projection data sets, such as the rotating frame 102, which fluctuates substantially periodically as the gantry rotates. Can be substantially aligned in a plurality of projection data sets (a plurality of images). Since the position of the subject image in the image varies due to the total amount of mechanical blur, aligning the total amount of the blur causes the positions of the subject images in a plurality of images to be substantially the same position. Can be fixed. In other words, the deviation of the subject image in the image mainly due to the total amount of blur can be unified with a plurality of images.

  Further, by displaying images in an order corresponding to the heartbeat phase, not in the order of acquisition, the motion of the heart can be smoothly reproduced as a moving image at a high frame rate.

  In the above description, a dynamic scan with a fixed scan position has been described as an example, but the present embodiment can also be applied to a helical scan. Alternatively, three-dimensional image data (volume data) may be generated from a plurality of images in the same angle range reconstructed under a helical scan, and a CT image representing a three-dimensional feature in the subject may be generated. good.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The figure which shows the structure of the X-ray computed tomography apparatus by embodiment of this invention. The figure which shows the some data set read for half reconstruction by the data set read control part of FIG. The figure which shows the ordering by the image ordering process part with respect to the some image corresponding to the some data set of FIG. The figure which shows the shake of the mount frame corresponding to each data set of FIG. The figure which shows the other some data set read for the half reconstruction by the data set read control part of FIG. The figure which shows the ordering by the image ordering process part with respect to the some image corresponding to the some data set of FIG. FIG. 6 is a diagram showing shaking of a gantry corresponding to each data set of FIG. 5.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Mount, 101 ... X-ray tube, 102 ... Rotating frame, 103 ... X-ray detector, 104 ... Data acquisition circuit, 105 ... Non-contact data transmission part, 106 ... Pre-processing part, 107 ... Rotation drive part, DESCRIPTION OF SYMBOLS 109 ... High voltage generation part, 110 ... Scan controller, 111 ... Slip ring, 112 ... Data storage part, 114 ... Reconstruction processing part, 115 ... Operation part, 116 ... Display part, 117 ... Electrocardiograph, 118 ... Tube Position detection unit, 119... Data set read control unit, 120... Image ordering processing unit, 121.

Claims (12)

An X-ray tube that generates X-rays;
An X-ray detector for detecting X-rays transmitted through the subject;
A rotation mechanism that continuously rotates the X-ray tube around the subject together with the X-ray detector;
A data storage unit for storing projection data based on the output of the X-ray detector;
A reconstruction processing unit that reconstructs a plurality of images based on a plurality of projection data sets stored in the data storage unit, and the plurality of projection data sets correspond to a plurality of rotations, respectively. Covering an angular range from the same first view angle to the same second view angle in one rotation;
A reordering processing unit for reordering the reconstructed images according to heartbeat phases at the time of collecting a plurality of corresponding projection data sets;
An X-ray computed tomography apparatus comprising: a display unit that sequentially displays the plurality of rearranged images.   The X-ray computed tomography apparatus according to claim 1, wherein the display unit sequentially displays the reconstructed images according to a heartbeat time phase of the subject.   The X-ray computed tomography apparatus according to claim 1, wherein the display unit sequentially displays the reconstructed images in accordance with a periodic biological phenomenon of the subject.   The X-ray computed tomography apparatus according to claim 1, wherein the reconstruction processing unit reconstructs the image under a half reconstruction method.   The first view angle is A ° (A ° is an arbitrary angle between 0 to 360 °), and the second view angle is (A + (180 ° + fan angle)). The X-ray computed tomography apparatus according to claim 1.   The X-ray computed tomography apparatus according to claim 1, further comprising a control unit that stops X-ray irradiation on the subject in a range other than an angular range corresponding to the plurality of projection data sets.   The X-ray computed tomography apparatus according to claim 1, further comprising a modulation unit that modulates the X-ray between an angle range corresponding to the plurality of projection data sets and a range other than the angle range. A data storage unit for storing projection data collected by continuously rotating an X-ray tube around the subject together with an X-ray detector;
A reconstruction processing unit for reconstructing a plurality of images based on a plurality of projection data sets stored in the data storage unit, the plurality of projection data sets are those corresponding to the plurality of rotation, its Resolution Covering a range of angles from the same first view angle to the same second view angle in one corresponding rotation;
A reordering processing unit for reordering the reconstructed images according to heartbeat phases at the time of collecting a plurality of corresponding projection data sets;
A medical image photographing apparatus comprising: a display unit that sequentially displays the plurality of rearranged images. The medical image photographing apparatus according to claim 8 , wherein the display unit displays the reconstructed images in order according to a heartbeat time phase of the subject. 9. The medical image photographing apparatus according to claim 8 , wherein the display unit sequentially displays the reconstructed images according to a periodic biological phenomenon of the subject. 9. The medical image photographing apparatus according to claim 8, wherein the reconstruction processing unit reconstructs the image under a half reconstruction method. The first view angle is A ° (A ° is an arbitrary angle between 0 to 360 °), and the second view angle is (A + (180 ° + fan angle)). The medical image photographing device according to claim 8 .

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