JP2013173033A - X-ray computer tomography apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of image reconstruction processing, and to enlarge a practical use range of projection data, in an X-ray computer tomography apparatus which copes with helical scan.SOLUTION: An X-ray computer tomography apparatus includes: an X-ray tube 10; a multislice type X-ray detector 23; a bed 2; a rotation mechanism 12 supporting the X-ray tube and the X-ray detector rotatably around a subject; a controller 30 controlling the bed and the rotation mechanism so as to execute a helical scan; a data storage device 35 storing projection data collected by the helical scan; a scanogram generation unit 43 generating data on a plurality of scanograms having different projection directions based on the projection data read from the data storage device; a display part 38 displaying the plurality of scanograms; and a reconstruction unit 36 reconstructing data on a tomographic image corresponding to a position designated on the displayed scanogram based on the projection data stored in the data storage device.

Description

  The present invention relates to an X-ray computed tomography apparatus compatible with helical scanning.

  The helical scan is realized by continuously moving the couch top on which the subject is placed while continuously rotating the X-ray tube and the X-ray detector and repeating data collection. Further, the technical development related to the X-ray detector is remarkable, and the improvement of the spatial resolution inherent to the X-ray detector is particularly remarkable. For example, isotropic X-ray detection with a high resolution by arranging 40 rows in the slice direction at a pitch of 0.5 mm and arranging as many as 916 detector elements at a pitch of 0.5 mm. A vessel has appeared. When the spatial resolution unique to the X-ray detector is improved, the spatial resolution of the reconstructed image is improved accordingly, and the detection rate of finer abnormal parts can be improved.

  On the other hand, however, the improvement in spatial resolution increases the amount of data to be collected, thereby increasing the amount of processing for image reconstruction and increasing the processing time. The current situation is that the convenience is lowered due to the increase in time.

  Japanese Patent Application Laid-Open No. 5-192327 discloses a technique for generating and displaying a scanogram from projection data collected by a helical scan. This technique is very spatial resolution as an index of a slice position. However, the current situation is that the data collected with very high spatial resolution is not fully utilized.

JP-A-5-192327

  An object of the present invention is to improve the efficiency of image reconstruction processing and expand the application range of projection data in an X-ray computed tomography apparatus compatible with helical scanning.

  An X-ray computed tomography apparatus according to the present invention includes an X-ray tube, a multi-slice X-ray detector, a bed on which a subject is placed between the X-ray tube and the X-ray detector, A rotation mechanism that supports the X-ray tube and the X-ray detector so as to be rotatable around the subject, a controller that controls the bed and the rotation mechanism to perform a helical scan, and collection by the helical scan A data storage device for storing the projected data, a selection means for selecting an image display template, the projection direction based on the selected display template and the projection data read from the data storage device A scanogram generation unit for generating data of a plurality of scanograms having different sizes, and displaying the plurality of scanograms based on the display template And that the display unit, the data storage device based on the projection data stored in, comprising a reconstruction unit for reconstructing the data of the corresponding tomographic image on the position specified on the displayed scanogram.

  According to the present invention, the efficiency of image reconstruction processing can be improved, and the range of utilization of projection data can be expanded.

1 is a configuration diagram of an X-ray computed tomography apparatus according to an embodiment of the present invention. The figure which shows the detection element arrangement | sequence of the multi-slice type | mold X-ray detector of FIG. The flowchart which shows operation | movement of this embodiment. The figure which shows the helical pitch of the helical scan of S1 of FIG. The figure which shows the 1st display template of a scanogram in this embodiment. The figure which shows the 2nd display template of a scanogram in this embodiment. The figure which shows the 3rd display template of a scanogram in this embodiment. The figure which shows the 4th display template of a scanogram in this embodiment. The figure which shows the example of the matrix size of the original scanogram of S6 of FIG. The figure which shows the group of the pixel bundling number (6 pixels) and the pixel bundling method (6 pixels) determined by the spatial resolution determination part of FIG. The figure which shows the group of the pixel bundling number (4 pixels) and the pixel bundling method (4 pixels) determined by the spatial resolution determination part of FIG. The figure which shows the group of the pixel bundling number (3 pixels) and the pixel bundling method (3 pixels) determined by the spatial resolution determination part of FIG. The figure which shows the group of the pixel bundling number (4 pixels) and the pixel bundling method (2 pixels) determined by the spatial resolution determination part of FIG. The figure which shows the example of a display when the see-through | perspective direction is rotated +10 degrees in S12 of FIG. The figure which shows the example of a display when a fluoroscopic direction is rotated -15 degrees in S12 of FIG. The figure which shows the slice mark by which slice thickness was expanded in S11 of FIG. The figure which shows the slice mark when a slice is added in S11 of FIG. The figure which shows the slice mark inclined in S11 of FIG. The figure which shows an example of the display screen at the time of 1 slice in S18 of FIG. The figure which shows an example of the display screen at the time of 2 slices in S18 of FIG. The figure which shows an example of the display screen at the time of 4 slices in S18 of FIG. The figure which shows an example of the display screen at the time of 4 slices inclined in S18 of FIG.

  Embodiments of an X-ray computed tomography apparatus (X-ray CT apparatus) according to the present invention will be described below with reference to the drawings. The X-ray CT apparatus has a rotation / rotation (ROTATE / ROTATE) type in which an X-ray tube and a radiation detector are rotated as one body, and a large number of detection elements are arrayed in a ring shape. There are various types such as a fixed / rotation (STATIONARY / ROTATE) type in which only the X-ray tube rotates around the subject, and the present invention can be applied to any type. Here, the rotation / rotation type that currently occupies the mainstream will be described. In addition, to reconstruct one slice of tomographic image data, projection data for about 360 ° around the periphery of the subject is required, and projection data for 180 ° + view angle is also required in the half scan method. . The present invention can be applied to any reconstruction method. Here, a case where a tomographic image is reconstructed from projection data of about 360 ° will be described. In addition, the mechanism for converting incident X-rays into electric charges is based on an indirect conversion type in which X-rays are converted into light by a phosphor such as a scintillator and the light is further converted into electric charges by a photoelectric conversion element such as a photodiode. The generation of electron-hole pairs in semiconductors 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 adopted as the X-ray detector. Here, the former indirect conversion form will be described. In recent years, the so-called multi-tube type X-ray CT apparatus in which a plurality of pairs of X-ray tubes and X-ray detectors are mounted on a rotating ring has been commercialized, and the development of peripheral technologies has been advanced. The present invention can be applied to both a conventional single-tube X-ray CT apparatus and a multi-tube X-ray CT apparatus. Here, a single tube type will be described.

  FIG. 1 shows the configuration of an X-ray computed tomography apparatus according to this embodiment. The X-ray computed tomography apparatus is largely composed of a gantry 1 and a computer unit 3. The gantry 1 accommodates an annular rotating frame 12 that is rotationally driven by a gantry driving device 25. An X-ray tube 10 and a multi-slice X-ray detector 23 are mounted on the rotating frame 12 so as to face each other with an imaging region interposed therebetween. A high voltage is applied to the X-ray tube 10 from the high voltage generator 21 via a slip ring. Thereby, X-rays are generated from the X-ray tube 10. A subject P placed on the top 2a of the bed 2 is inserted into the imaging region. The couch 2 has a top plate driving unit 2b for electrically moving the top plate 2a in the slice direction. Usually, the subject P is placed on the top 2a so that the slice direction is substantially parallel to the direction of the body axis of the subject P.

  As shown in FIG. 2, the multi-slice X-ray detector 23 has a two-dimensional array structure of a plurality of detection elements 26 having an isotropic property of 0.5 mm × 0.5 mm, for example. For example, 916 detection elements are arranged in the channel direction at a pitch of 0.5 mm, for example. For example, 40 rows (segments) of 916 detection elements are arranged in the slice direction at a pitch of 0.5 mm. The data collection device 24 collects X-rays that have passed through the subject P via each detection element. The data collection device 24 mainly has a function of amplifying the collected analog electric signal and converting it into a digital signal. The data amplified by the data collecting device 24 and converted into a digital signal is referred to as “raw data”. The raw data is supplied to the preprocessing unit 34 via a slip ring (contact type) or a non-contact type data transmission device using light or magnetism. The pre-processing unit 34 corrects non-uniform sensitivity between channels with respect to the raw data from the data acquisition device 24, and causes an extreme decrease in signal intensity or signal dropout due to an X-ray strong absorber, mainly a metal part. Pre-processing such as correcting is performed. Note that data that has undergone preprocessing is referred to as projection data, and is distinguished from raw data that is in the previous stage of being subjected to preprocessing.

  The computer unit 3 including the preprocessing unit 34 includes a system controller 29, a display 38, a scan controller 30, an input device 39 including a keyboard and a mouse, a computer system such as projection data, scanogram data, and tomographic image data. A data storage device 35 for storing data handled in the data storage unit 35, a reconstruction unit 36 for reconstructing tomographic image data based on the projection data stored in the data storage device 35, and a projection data stored in the data storage device 117. The scanogram generation unit 43 for generating scanogram data, the spatial resolution determination unit 42 for determining the spatial resolution of the scanogram data generated by the scanogram generation unit 43, and the GUI generation unit 41 for generating a GUI (graphical interface) screen , Generate And a display processor 37 which constitute the display screen scanogram data fitted to a scanogram display area of the GUI screen.

  Next, the operation of this embodiment will be described. As the operation of the present embodiment, first, second, and third operation modes are prepared. The first, second, and third operation modes can be arbitrarily selected by the user via the input device 115.

  FIG. 3 shows an operation flow of the present embodiment. First, collection of projection data is started by helical scanning (S1). In the helical scan, as is well known, generation of X-rays and data collection are repeated under the control of the scan controller 30 while the rotating frame 12 is rotated at a constant speed. Move with P at a constant speed. As shown in FIG. 4, the X-ray tube 10 draws a trajectory in a spiral relative to the subject P by the combined movement of rotation and movement as described above. The projection data collected by this helical scan is stored in the data storage device 35 (S2). The data storage device 35 stores the raw data that has not undergone preprocessing along with the projection data. The distance that the top plate 2a moves during one rotation of the X-ray tube 10, that is, the helical pitch, is set to 20 mm (= 0.5 mm × 40 rows). As a result, data is collected with the highest spatial resolution inherent in the X-ray detector 23, that is, with an isotropic spatial resolution of 0.5 mm vertically and horizontally. The helical scan ends when data collection for the scheduled scan range is completed (S3).

  After the helical scan is completed, a display template selection screen is generated by the GUI generator 41 and the display processor 37 under the control of the system controller 29 and displayed on the display 38 (S4).

  The display template is a template for displaying a scanogram. For example, four types shown in FIGS. 5 to 8 are prepared. The template shown in FIG. 5 is initially represented by a single scanogram display area for displaying a scanogram from the top view (the rotation angle (projection angle) of the X-ray tube 10 is 0 °) and an icon. It consists of multiple operation buttons.

  The single scanogram display area can be moved freely by the operation of the mouse, etc. The line-shaped "high-resolution display range center setting cross mark" that can be moved arbitrarily by the operation of the mouse, etc. In addition, a rectangular “slice position / slice thickness setting slice mark” that can be arbitrarily tilted is superimposed. The plurality of operation buttons have a button 101 for instructing to rotate the projection angle in the forward direction by a predetermined angle (for example, 5 °), and rotate the projection angle in the reverse direction by a predetermined angle (for example, 5 °). A button 102 for instructing to switch, and a button 103 for instructing to switch display from a currently displayed scanogram to a scanogram having a higher (shorter) spatial resolution (scale distance between two adjacent pixels) than the currently displayed scanogram. A button 104 for instructing display switching from a scanogram to a scanogram having a lower (longer) spatial resolution, a button 105 for instructing addition of one of the slice marks, and a re-display of the scanogram without changing the spatial resolution The tomographic image is displayed with the button 106, the slice position, slice thickness, and inclination (oblique) corresponding to the slice mark. A button 107 for instructing the reconfiguration of the data is included.

  The template shown in FIG. 6 includes two scanogram display areas that partially overlap each other and a plurality of operation buttons similar to those in FIG. One of the two scanogram display areas is provided to display a low resolution scanogram. A “high-resolution display range center setting cross mark” is superimposed on the display area of the low-resolution scanogram. The other scanogram display area is provided to display a high-resolution scanogram centered on the cross mark, and a “slice mark for setting the slice position / slice thickness” is superimposed on this area.

  The template shown in FIG. 7 includes four scanogram display areas and a plurality of operation buttons similar to those in FIG. Two of the four scanogram display areas are prepared as an area for displaying a top view low resolution scanogram and an area for displaying a top view high resolution scanogram. The remaining two of the four scanogram display areas are an area for displaying a low-resolution scanogram of the side view (rotation angle (projection angle) of the X-ray tube 10 is 90 °) and a high-resolution scanogram of the side view. This is the area to display. In the display area of the low-resolution scanogram of the top view and the side view, a “cross mark for setting the center of the high-resolution display range” that is linked to each other is superimposed. “Slice marks for setting slice position / slice thickness” that are linked to each other are superimposed on the display areas of the high-resolution scanograms of the top view and the side view.

  The template shown in FIG. 8 includes an 8-scanogram display area and a plurality of operation buttons similar to those in FIG. The 8-scanogram display area has a top view, a 30 ° oblique view (the rotation angle (projection angle) of the X-ray tube 10 is 30 °), and a 45 ° oblique view (the rotation angle (projection angle) of the X-ray tube 10) is 45. °), prepared for individually displaying two types of scanograms, low resolution and high resolution, for each side view perspective direction.

  In S4, a GUI screen configured to select one of the four types of display templates shown in FIGS. 5 to 8 is displayed, and one of the templates is selected according to the operation of the input device 39 (S5). ). Here, for convenience of explanation, it is assumed that the template of FIG. 5 is selected.

  After the template is selected, a set of projection data (or raw data) corresponding to the perspective direction, initially zero ° of the top view, is read from the data storage device 35, and a spatial resolution determination unit 42 and a scanogram generation unit 43 are read out. Are supplied as original scanogram data (S6). For example, as shown in FIG. 9, the original scanogram data has a matrix size of 916 × 1200 with a spatial resolution (distance between adjacent pixels) of 0.5 mm vertically and horizontally. In this case, the original scanogram corresponds to a range of 408 mm × 600 mm in terms of actual size.

  First, the spatial resolution determination unit 42 recognizes a matrix size of 916 × 1200 of the original scanogram data (S7). Compared to the recognized original scanogram data matrix size (916 × 1200), the scanogram display area matrix size (for example, 256 × 384) is compared separately in the vertical (slice direction) and horizontal (channel direction). Thus, the pixel bundling number and the pixel bundling method in the slice direction and the channel direction are determined so that the entire scan range is within the scanogram display area of the selected display template (S8).

  As the pixel bundling process, any one of the neighboring pixel simple addition process, simple addition averaging process, weighted addition process, and weighted addition averaging process is adopted, and the pixel bundling number is defined as the number of neighboring pixels to be added. Is defined as, for example, the moving distance of the target pixel at the center of the neighboring pixel. The number of pixel bundles is prepared stepwise in advance, for example, 6 pixels in each of the two directions as shown in FIG. 10, 36 pixels in the number of neighboring pixels, and 4 pixels in each of the two directions as shown in FIG. The number of pixels is 16 pixels, as shown in FIG. 12, 3 pixels in each of the two directions, 9 pixels in the number of neighboring pixels, 2 pixels in each of the two directions, 4 pixels in the number of neighboring pixels, and the number of bundles maintaining the original resolution. Five types of one pixel are prepared. There are five types of pixel bundling methods, that is, six pixels, four pixels, three pixels, two pixels (see FIG. 13), and one pixel as the moving distance of the center of neighboring pixels.

  The spatial resolution determination unit 42 first sets a combination of the pixel bundling number and the pixel bundling method on the condition that the entire scan range is within the scanogram display area of the selected display template and the maximum spatial resolution is ensured. Determine the initial value of. In order to fit the entire scan range within the matrix size 256 × 384 of the display area, for example, the pixel bundling number shown in FIG. It is determined.

  In the scanogram generation unit 43, according to the pixel bundling number (4 × 4 16 pixels) determined as the initial value and the pixel bundling method (4 pixels), the spatial resolution is 0.5 mm vertically and horizontally, and the matrix size is A scanogram having a spatial resolution of 2 mm vertically and horizontally and a matrix size of approximately 229 × 300 is generated from the original 916 × 1200 scanogram data (S9).

  The initially generated scanogram data is inserted, for example, in the scanogram display area of the display template of FIG. 6 in the display processor 37 (S10) and displayed on the display 38 (S11). The entire scan range is displayed in the scanogram display area by the initially determined number of pixel bundling and pixel bundling method, and the observer can check the entire scan range.

  At this time or any time after enlargement, when the button 101 for rotating the fluoroscopic direction in the forward direction is clicked twice continuously in S12, for example, the process returns to S6 and the control of the system controller 29 is performed. Originally, a set of projection data collected when the X-ray tube 10 corresponding to the operation is at a rotation position of + 10 ° is read out, and after processing of S7 to S10, as shown in FIG. Scanogram data viewed from a fluoroscopic direction of ° is generated and displayed. In S12, when the button 102 for rotating the fluoroscopic direction in the reverse direction is clicked, for example, three times, the process returns to S6, and the X-ray tube 10 corresponding to the operation is at the -15 ° rotation position. The collected projection data set is read out, and through the processes of S7 to S10, as shown in FIG. 15, scanogram data viewed from the -15 ° perspective direction is generated and displayed. By repeating this operation, it is possible to search for a fluoroscopic direction in which a region of interest such as a tumor can be observed well.

  When the “ZOOM IN” button 103 is clicked in S13 after the perspective direction is changed or before and after, the spatial resolution is higher than the set of the pixel bundle number and the pixel bundle method of the currently displayed scanogram. A set of the pixel bundling number and the pixel bundling method so that becomes higher by one level is determined by the spatial resolution determination unit 42 (S14). For example, the pixel bundling number (3 × 3 9 pixels) and the pixel bundling method with higher spatial resolution than the set of the pixel bundling number (4 × 4 16 pixels) determined as the initial value and the pixel bundling method (4 pixels). A set of (3 pixels) or a set of pixel bundling number (4 × 4 16 pixels) and a pixel bundling method (2 pixels) is determined. The number of stages of spatial resolution and the set of pixel bundling and pixel bundling methods at each stage are preset on the manufacturer side or user side. The highest spatial resolution is that the number of pixel bundling is 1 pixel and the pixel bundling method is a set of 1 pixel. Under these conditions, the original scanogram data maintains its spatial resolution (0.5 mm). Is displayed.

  In S9, scanogram data is generated according to the set of pixel bundling number and pixel bundling method corresponding to the spatial resolution of the next stage determined in S14. The generated scanogram data is inserted into the scanogram display area of the display template in the display processor 37 with the position of the cross mark coinciding with the center of the scanogram display area (S10) and displayed on the display 38. (S11). When the cross mark is moved and the redisplay button 106 is clicked, the position of the scanogram is displaced in the scanogram display area and redisplayed. With high spatial resolution, the entire scanogram cannot be displayed in the scanogram display area, but any part can be viewed with high spatial resolution by moving the cross mark.

  After enlarging, the spatial resolution can be enlarged step by step to the original spatial resolution (0.5 mm) by changing the perspective direction to a desired direction as necessary and repeating the enlarged display.

  In this way, by displaying the scanogram by switching to the spatial resolution step by step up to the original spatial resolution (0.5 mm), not just as a guide image for determining the slice position but also as an interpretation image. Can do. That is, the scanogram can be interpreted as an X-ray simple photographed image.

  Of course, it is used as a guide image for deciding the slice position etc., for example, at the maximum or arbitrary stage where the site of interest where the tumor etc. is generated can be sufficiently confirmed, by operating the slice mark, The slice position is adjusted, the slice thickness is adjusted (see FIG. 16), the slice is added (see FIG. 17), and the slice of leak is adjusted (see FIG. 18).

  When the reconstruction button 107 is clicked when slice alignment is completed (S15), according to a known helical scan reconstruction process according to the position, width (slice thickness), and number (slice number) of the slice mark. Image data is reconstructed (S16). Using the image data together with the scanogram when the reconstruction button 107 is clicked, a GUI screen is constructed (S17) and displayed as shown in FIGS. 19 to 22 (S18).

  When the reconstruction button 107 is clicked, the scanogram is reduced and displayed as a guide image for guiding the position, thickness, and oblique (inclination angle) of each slice in the same screen as the image data. Also on this screen, a ZOOM IN (enlargement) button 103, a ZOOM OUT (reduction) button 104, a slice addition button 105, and a reconfiguration button 107 are displayed. These commands are effective, and the spatial resolution of the scanogram of the guide image is enlarged / reduced according to the command of each button, and a slice mark is added. In addition, the position, width and oblique of the slice mark can be arbitrarily readjusted on the guide image. After the readjustment, by clicking the reconstruct button 107, the image data is reconstructed and displayed under the readjusted conditions. When the return button 108 is clicked, it is possible to return to the previous screen, for example, a scanogram display screen with high spatial resolution.

  In this way, after appropriately setting the position, thickness, number, and oblique of the slice for the region of interest, the reconstruction process is limited to that slice, thereby shortening the time until image display. . In addition, since the scanogram can be displayed by gradually switching to the spatial resolution up to the original spatial resolution, the scanogram can be displayed as an interpretation image, not as a guide image for simply determining the slice position. That is, the scanogram can be interpreted as an X-ray simple photographed image.

(Modification)
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Furthermore, the above embodiment includes various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, some constituent requirements may be deleted from all the constituent requirements shown in the embodiment.

DESCRIPTION OF SYMBOLS 1 ... Gantry, 2 ... Bed, 3 ... Computer unit, 10 ... X-ray tube, 12 ... Rotating frame, 21 ... High voltage generator, 22 ... Slit, 23 ... Multi-slice type X-ray detector, 24 ... Data acquisition device (DAS), 25 ... gantry drive unit, 34 ... pre-processing unit, 29 ... system controller, 30 ... scan controller, 35 ... data storage device, 36 ... reconstruction unit, 37 ... display processor, 38 ... display, 39 ... input 41, GUI generation unit, 42 ... Spatial resolution determination unit, 43 ... Scanogram generation unit.

Claims (6)

An X-ray tube;
A multi-slice X-ray detector;
A bed for placing a subject between the X-ray tube and the X-ray detector;
A rotation mechanism that supports the X-ray tube and the X-ray detector so as to be rotatable around the subject;
A controller that controls the bed and the rotation mechanism to perform a helical scan;
A data storage device for storing projection data collected by the helical scan;
A selection means for selecting an image display template;
A scanogram generating unit that generates data of a plurality of scanograms having different projection directions based on the selected display template and projection data read from the data storage device;
A display unit for displaying the plurality of scanograms based on the display template;
A reconstruction unit for reconstructing tomographic image data corresponding to a position designated on the displayed scanogram based on projection data stored in the data storage device. Line computed tomography equipment. It further includes an operation unit having a function of inputting a display switching command to a scanogram having a high spatial resolution.
The scanogram generating unit generates data of another scanogram having a higher resolution than the scanogram based on projection data read from the data storage device according to the input of the command. X-ray computed tomography apparatus.   The X-ray computed tomography according to claim 1, wherein the scanogram generation unit generates the scanogram data from the projection data by simple addition, simple addition average, weighted addition, or weighted addition average of neighboring pixels. apparatus.   2. The X-ray computed tomography according to claim 1, wherein the scanogram generation unit generates the scanogram data with a spatial resolution that allows an entire scan range of the helical scan to be accommodated in a scanogram display area of the display template. apparatus.   2. The X-ray computed tomography according to claim 1, further comprising a spatial resolution determination unit that determines a spatial resolution of the scanogram so that an entire scan range by the helical scan falls within a scanogram display area of the display template. Shooting device.   2. The X-ray computed tomography apparatus according to claim 1, wherein the scanogram generation unit generates data of the other scanogram stepwise in response to repetition of an enlargement command by an operator.

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