JP7098292B2 - X-ray CT device - Google Patents

Description

Embodiments of the present invention relate to an X-ray CT device.

X-ray CT (Computed Tomography) devices may recently perform monitoring scans, CT fluoroscopy, and the like. The monitoring scan is used to take various timings such as the start timing of the main scan while the contrast effect changes. CT fluoroscopy is also used, for example, for biopsy guidance.

In monitoring scans and CT fluoroscopy, although the tube current is lower than that in the main scan, imaging is often performed continuously in time, so the exposure dose of the subject may increase. As a method for reducing the exposure dose of a subject in X-ray CT imaging, for example, a method using pulsed X-rays has been developed. This method using pulsed X-rays is a method of performing discrete X-ray irradiation during one rotation of the X-ray tube, instead of continuously irradiating X-rays during the rotation of the X-ray tube (continuous X-ray irradiation). Is.

However, in this method using pulse X-rays, pulse X-rays are only uniformly irradiated at a preset X-ray irradiation timing. Therefore, it is difficult to adaptively reduce the exposure dose of the subject by simply applying this method using pulsed X-rays to monitoring scans and CT fluoroscopy.

Japanese Unexamined Patent Publication No. 2014-226410

An object to be solved by the present invention is to provide an X-ray CT apparatus capable of adjusting the X-ray irradiation timing in pulsed X-ray irradiation according to at least one of the imaging conditions and the image quality of the obtained reconstructed image. Is.

The X-ray CT apparatus according to the embodiment of the present invention controls an X-ray irradiator that generates X-rays to be irradiated to the subject and the X-ray irradiator in order to solve the above-mentioned problems. An X-ray control unit that controls the generation of X-rays, an X-ray detector that detects X-rays that have passed through the subject, and projection data about the subject are collected based on the output of the X-ray detector. A data collection unit and the X-ray control unit control the X-ray irradiator so as to generate pulsed X-rays, and X-rays in a part of a plurality of predetermined views in one rotation. The generation of the X-ray is controlled so as not to be exposed to the X-ray.

The block diagram which shows an example of the X-ray CT apparatus which concerns on one Embodiment of this invention. A schematic block diagram showing an example of a function realized by a processor of a processing circuit. An explanatory diagram showing an example of the relationship between the thinning pattern and the image quality. A flowchart showing an example of a procedure for adjusting the X-ray irradiation timing in pulse X-ray irradiation according to at least one of the imaging conditions and the image quality of the obtained reconstructed image by the processing circuit of the X-ray CT apparatus shown in FIG. .. Explanatory drawing which shows an example of the positional relationship between a region of interest ROI and a photographing region. The explanatory view which shows the 1st example of the method of repeating the thinning pattern different from each other. The explanatory view which shows the 2nd example of the method of repeating the thinning pattern different from each other. The explanatory view which shows the 3rd example of the method of repeating the thinning pattern different from each other. The explanatory view which shows the 4th example of the method of repeating the thinning pattern different from each other. (A) is an explanatory diagram showing an example of a thinning pattern when thinning out an unreliable view of collected data, and (b) is thinning out to avoid X-ray irradiation toward a place where the subject has high X-ray sensitivity. Explanatory drawing which shows an example of a pattern.

An embodiment of the X-ray CT apparatus according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an example of an X-ray CT device 10 according to an embodiment of the present invention.

The X-ray CT device is a rotation / rotation (ROTATE / ROTATE) type in which an X-ray tube and a detector are integrated to rotate around a subject, and a large number of detection elements are arranged in an annular shape to form an X-ray. There are various types such as a fixed / rotating type in which only the tube rotates around the subject, and a type in which the position of the X-ray source is electronically moved on the target by deflecting the electron beam. However, the configuration shown in this embodiment is applicable to any type. In the type using an electron beam, it can be applied by appropriately reading the X-ray tube as an X-ray source. In the present embodiment, an example is shown in which the X-ray CT apparatus 10 is a rotation / rotation (ROTATE / ROTATE) type in which an X-ray tube and an X-ray detector are integrated and rotate around the subject O.

Further, in recent years, the commercialization of a so-called multi-tube type X-ray CT device in which a plurality of pairs of an X-ray tube and an X-ray detector are mounted on a rotating ring has progressed, and the development of peripheral techniques thereof has progressed. The X-ray CT apparatus 10 according to the present embodiment can be applied to either a single tube type or a multi-tube type. Here, an example in the case where the X-ray CT device 10 is a single tube type will be described.

As shown in FIG. 1, the X-ray CT device 10 has a pedestal 11, a bed device 12, and a console 13.

The gantry 11 has a fixed pedestal 21 and a rotary pedestal 22. The fixed pedestal 21 is fixed to an installation surface such as a floor surface, and has a pedestal control circuit 26 and a data transmission device 27. The rotary pedestal 22 integrally holds an X-ray irradiator 30, an X-ray detector 33, and a DAS (Data Acquisition System) 34, including an X-ray tube 31 and a throttle 32, and rotates around an opening in a central portion. .. In this embodiment, the direction parallel to the rotation center axis of the rotary base 22 is defined as the z-axis direction, the normal direction of the installation surface is defined as the y-axis direction, and the direction parallel to the installation surface is defined as the x-axis direction (FIG. 1). reference).

The X-ray tube 31 of the X-ray irradiator 30 is controlled by the gantry control circuit 26, and a high voltage generated by a high-voltage power supply (not shown) of the fixed gantry 21 is supplied via, for example, a slip ring. The high voltage power supply may be provided on the rotary stand 22.

The X-rays generated by the X-ray tube 31 are irradiated toward the subject O as fan beam X-rays or cone beam X-rays.

The aperture 32 of the X-ray irradiator 30 is configured by, for example, a wedge filter, and is controlled by the gantry control circuit 26 in the slice direction (z direction, column direction) and channel direction of the X-rays emitted from the X-ray tube 31. Adjust at least one irradiation range.

The X-ray irradiator 30 is controlled by the console 13 via the gantry control circuit 26 to control the X-ray irradiation timing. Specifically, the X-ray irradiator 30 is a view that irradiates pulsed X-rays for each of the plurality of views constituting one rotation (hereinafter referred to as an irradiation view), or a non-irradiation view (hereinafter, non-irradiation view). The view) is controlled by the console 13.

The pulse X-ray irradiation control may be performed, for example, by controlling the grid voltage of the X-ray tube 31, or by controlling the opening / closing of the diaphragm 32 or the rotation control of the chopper provided in the vicinity of the diaphragm 32, for example. You may.

The X-ray detector 33 is composed of a plurality of X-ray detection elements (charge storage elements). This X-ray detection element (radiation detection element) detects X-rays irradiated from the X-ray tube 31 and transmitted through the subject O. The X-ray tube 31 and the X-ray detector 33 are supported by the rotary pedestal 22 so as to be opposite to each other with the subject O placed on the bed device 12 interposed therebetween.

The X-ray detector 33 is, for example, a so-called one-dimensional array type (single slice type) having one row in the slice direction (z direction) and a plurality of X-ray detection elements in the channel direction orthogonal to the slice direction. Can be used. Further, a so-called two-dimensional array type (multi-slice type) having a plurality of rows such as 320 rows in the slice direction and a plurality of X-ray detection elements in the channel direction may be used. In the case of the multi-slice type, a plurality of rows of X-ray detection elements having a plurality of channels in the channel direction can be arranged in the slice direction (z direction). Further, in the case of the two-dimensional array type, the X-ray detector 33 can be configured by a plurality of X-ray detection elements densely distributed and arranged in both the slice direction (z direction) and the channel direction.

In the following description, when the X-ray detector 33 is composed of a plurality of X-ray detection elements densely arranged in two dimensions of the slice direction axis (first axis) and the channel direction axis (second axis). An example is shown. Further, the X-ray CT apparatus 10 according to the present embodiment uses data of a part (for example, about 4 rows) of elements in, for example, 320 rows in the channel direction in monitoring scan and CT fluoroscopy.

The DAS 34 receives an analog signal output by a plurality of X-ray detection elements constituting the X-ray detector 33, and performs processing such as current-voltage conversion, amplification, and analog-digital conversion (AD conversion) on the signal. Then, the DAS 34 generates transmission data using these processed signals and transmits the transmission data to the console 13 via the data transmission device 27. The console 13 performs a reconstruction process based on the projection data included in the transmission data, and generates a reconstruction image.

The rotary pedestal 22 integrally holds the X-ray tube 31, the diaphragm 32, the X-ray detector 33, and the DAS 34, and is supported by the fixed pedestal 21. As the rotary gantry 22 is controlled and rotated by the gantry control circuit 26, the X-ray tube 31, the diaphragm 32, the X-ray detector 33, and the DAS 34 are integrally rotated around the opening of the central portion of the rotary gantry 22. , Rotate around the subject O. Further, the rotary pedestal 22 may be configured to be tiltable with respect to the fixed pedestal 21. Information on the current rotation speed of the rotary gantry 22, tilt operation, and information on the current tilt angle are given to the console 13 via the gantry control circuit 26.

The bed device 12 includes a base 36 installed on an installation surface such as a floor surface, a top plate 37 supported by the base 36, and a top plate drive device 38.

The top plate 37 is configured so that the subject O can be placed on it. The top plate drive device 38 is controlled by the gantry control circuit 26 to move the top plate 37 up and down in the y-axis direction (vertical direction). Further, the top plate drive device 38 is controlled by the gantry control circuit 26 to move the top plate 37 to the X-ray irradiation field at the opening of the central portion of the rotary gantry 22 along the z-axis direction (longitudinal direction of the top plate 37). And transfer. Further, the top plate drive device 38 is controlled by the gantry control circuit 26 to transfer the top plate 37 in the x-axis direction (horizontal direction of the top plate 37). Further, the top plate drive device 38 is controlled by the gantry control circuit 26, and the top plate 37 can be rotated (thrued) about each axis of the xyz axis. Information regarding the movement of the top plate 37 (movement speed and movement direction) and information on the current position are given to the console 13 via the top plate drive device 38 and the gantry control circuit 26.

The gantry control circuit 26 has at least a processor and a storage circuit. The gantry control circuit 26 is controlled by the console 13 and controls the gantry 11 according to a program stored in the storage circuit to execute X-ray CT imaging of the subject O.

Although FIG. 1 shows an example in which the gantry control circuit 26 and the console 13 are connected by wire, the gantry control circuit 26 and the console 13 may be connected so as to be able to transmit and receive data via a network.

The data transmission device 27 performs parallel / serial conversion, electrical / optical / electrical conversion, and serial / parallel conversion on the transmission data output from the DAS 34. The data transmission device 27 includes, for example, a parallel / serial converter (not shown), an electric / optical / electric converter, and a serial / parallel converter (not shown). The transmission data of a plurality of channels output from the DAS 34 is converted into time-series one-channel data by the parallel / serial converter provided on the rotary stand 22, and optical communication using the electric / optical / electric converter, etc. Is supplied to the serial / parallel converter provided on the fixed frame 21.

Subsequently, the transmission data of one channel is returned to the transmission data of a plurality of channels by the above-mentioned serial / parallel converter. The projection data of the plurality of channels obtained in time series is stored in the console 13 with the arrangement position information and rotation angle information of the radiation detection elements in the channel direction and the position information (shooting position) of the projection data in the slice direction as incidental information. ..

The data transmission method by the data transmission device 27 may be another method as long as data transmission between the DAS 34 provided on the rotary gantry 22 and the gantry control circuit 26 provided on the fixed gantry 21 is possible. For example, a device such as a slip ring may be used for data transmission by the data transmission device 27, or a non-contact transmission method may be used.

On the other hand, the console 13 of the X-ray CT device 10 is composed of, for example, a general personal computer or a workstation, and has an input circuit 41, a display 42, a storage circuit 43, and a processing circuit 44. The console 13 does not have to be provided independently, and a part of the configurations 41-44 of the console 13 may be provided dispersedly on the gantry 11.

The input circuit 41 is composed of a general input device such as a trackball, a switch button, a mouse, a keyboard, and a numeric keypad, and outputs an operation input signal corresponding to the user's operation to the processing circuit 44. For example, the user can set the imaging conditions for monitoring scan and CT fluoroscopy via the input circuit 41. In the present embodiment, the imaging condition includes at least one of the inspection purpose, the imaging target site, and the position of the region of interest in the scan effective field of view (Scan Field Of View). Some or all of the shooting conditions may be set via the input circuit 41 or may be acquired via the network.

The display 42 is composed of a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display, and displays a real-time reconstructed image or the like under the control of the processing circuit 44.

The storage circuit 43 has a configuration including a recording medium readable by a processor, such as a magnetic or optical recording medium or a semiconductor memory. Some or all of the programs and data in these recording media may be configured to be downloaded by communication via an electronic network. The storage circuit 43 stores, for example, projection data transmitted from the DAS 34, a reconstructed image generated by the processing circuit 44, and the like.

Further, the storage circuit 43 may store in advance the association information in which the threshold value of the numerical value related to the image quality and the thinning pattern are associated with each other. As the numerical value related to the image quality, a value evaluated by evaluating the noise of the image as a standard deviation value, a value evaluated by spatial frequency analysis of the image resolution by Fourier transform, and the like can be used. Further, the thinning pattern refers to an exposure pattern of each view during one rotation, and includes at least information on whether to irradiate pulse X-rays or not to irradiate each of a plurality of views constituting one rotation.

The processing circuit 44 reads and executes the program stored in the storage circuit 43 to adjust the X-ray irradiation timing in the pulsed X-ray irradiation according to at least one of the shooting conditions and the image quality of the obtained reconstructed image. A processor that executes processing.

FIG. 2 is a schematic block diagram showing an example of a function realized by the processor of the processing circuit 44. As shown in FIG. 2, the processor of the processing circuit 44 realizes at least a condition acquisition function 51, a thinning setting function 52, an imaging control function 53, an X-ray control function 54, and a reconstruction function 55. Each of these functions is stored in the storage circuit 43 in the form of a program.

When the user instructs the start of monitoring scan or CT fluoroscopy via the input circuit 41, the condition acquisition function 51 acquires the imaging conditions if the imaging conditions are set.

The thinning setting function 52 emits pulsed X-rays for each of the plurality of views constituting one rotation based on at least one of the information of the imaging condition of the subject O and the image quality of the real-time reconstructed image of the subject O. Set a thinning pattern that includes at least information on whether to irradiate or not.

FIG. 3 is an explanatory diagram showing an example of the relationship between the thinning pattern and the image quality. One rotation can be divided into a large number of views such as 900 views, but FIG. 3 shows an example in which one rotation is divided into 24 views for convenience of explanation.

The thinning setting function 52 evaluates, for example, the image quality of the reconstructed image obtained by reconstructing in real time, and sets the lower pattern of FIG. 3 so as to increase the ratio of thinning when sufficient image quality is obtained. On the other hand, if there is no margin in image quality, the pattern on the upper side of FIG. 3 is set so as to reduce the ratio of thinning out. For example, when the resolution of the real-time reconstructed image is higher than a predetermined threshold value, the thinning setting function 52 sets a thinning pattern having a high thinning ratio.

Therefore, when there is a margin in image quality, the thinning ratio can be adaptively increased, and the exposure dose of the subject O can be reduced. If there is no margin in image quality, the ratio of thinning out can be reduced to ensure image quality. Whether or not there is a margin in the image quality may be determined, for example, by comparing the threshold value indicating the allowable image quality stored in the storage circuit 43 in advance with the image quality of the reconstructed image. By setting the permissible image quality, the exposure can be reduced within the permissible image quality range.

The imaging control function 53 photographs the subject O by controlling the X-ray control function 54 according to the thinning pattern.

The X-ray control function 54 controls the X-ray irradiation timing of the X-ray irradiator 30 according to the control of the imaging control function 53.

The reconstruction function 55 performs a reconstruction process in real time based on the projection data included in the data transmitted from the DAS 34 via the data transmission device 27, and generates a tomographic image as a reconstruction image.

Next, an example of the operation of the X-ray CT device 10 according to the present embodiment will be described.

FIG. 4 shows an X-ray irradiation timing in pulsed X-ray irradiation adjusted by the processing circuit 44 of the X-ray CT apparatus 10 shown in FIG. 1 according to at least one of the imaging conditions and the image quality of the obtained reconstructed image. It is a flowchart which shows an example of a procedure. In FIG. 4, reference numerals with numbers attached to S indicate each step in the flowchart.

This procedure starts when the start of a monitoring scan or CT fluoroscopy is instructed.

First, in step S1, the condition acquisition function 51 acquires shooting conditions. The imaging condition includes at least one of the inspection purpose, the imaging target portion, and the position of the region of interest in the scan effective field of view (Scan Field Of View). If the shooting conditions are not set, this step S1 is omitted.

Next, in step S2, the thinning setting function 52 determines whether or not thinning is performed from the start of imaging of the subject O to a predetermined rotation. The setting information of whether or not to perform thinning immediately after the start of shooting may be stored in the storage circuit 43 in advance, or may be given by the user via the input circuit 41 each time shooting is performed.

If thinning is performed immediately after the start of shooting, the process proceeds to step S5. On the other hand, if thinning is not performed immediately after the start of imaging, the imaging control function 53 controls the X-ray control function 54 so as to perform continuous X-ray imaging only for a predetermined rotation (step S3), and the reconstruction function 55 controls this continuous X-ray. A reconstructed image is generated in real time based on the projection data collected by radiography. The images generated by the reconstruction function 55 are sequentially displayed on the display 42.

Next, in step S5, the thinning setting function 52 sets the thinning pattern according to the shooting conditions.

For example, if the object to be monitored is the aorta of the chest, a site having a size of, for example, about 15-20 mm will be monitored. On the other hand, when the head is to be photographed by the main scan, the carotid artery in the cervix will be monitored, and in this case, the part with a size of about 3-5 mm, which is smaller than the aorta, will be focused on.

When the monitoring target is large, it is considered that the monitoring can be maintained even if the image quality is poor. Therefore, it is advisable to increase the thinning ratio to reduce the exposure of the subject O (for example, irradiation view: non-irradiation view =). 1: 4, etc.). On the other hand, when the monitoring target is small, it is considered difficult to monitor if the image quality is poor, so it is advisable to prohibit thinning or reduce the ratio of thinning (for example, irradiation view: non-irradiation view = 1: 2). ..

FIG. 5 is an explanatory diagram showing an example of the positional relationship between the ROI of interest and the imaging region. Here, the imaging region refers to a scan FOV centered on the center of rotation of the X-ray tube 31.

For example, the thinning setting function 52 may adjust the thinning ratio according to the position of the region of interest (monitoring target) in the scan effective field of view in step S5. For example, in the example shown in FIG. 5, the region of interest ROI1 is in the central region of the scan FOV (photographed area), and the region of interest ROI2 is in the peripheral region of the scan FOV (photographed area).

It is known that even when shooting with the same number of views, the resolution is good near the center of the shooting area and bad in the peripheral area. Therefore, in the thinning setting function 52, it is preferable that the ratio of thinning is increased as the area of interest is closer to the center of the photographing area, and the ratio of thinning is decreased as the peripheral day floor is closer. For example, if the aorta is a ROI (monitoring target) and is in the central region of the imaging region, the irradiated view: non-irradiated view can be made larger, for example 1: 8.

If the condition acquisition function 51 has not acquired the imaging conditions, such as when the imaging conditions have not been set, step S5 is omitted.

Next, in step S6, the imaging control function 53 controls the X-ray control function 54 according to the thinning pattern set by the thinning setting function 52, and performs pulse X-ray imaging of the subject O. The same applies when returning from step S10 to step S6.

Next, in step S7, the reconstruction function 55 generates a reconstruction image in real time based on the projection data collected by the pulse X-ray photography according to the thinning pattern set by the thinning setting function 52. The images generated by the reconstruction function 55 are sequentially displayed on the display 42.

When the monitoring scan using pulse X-rays or CT fluoroscopy should be terminated (YES in step S8), such as when the user gives an instruction to end imaging via the input circuit 41, the series of procedures is terminated.

On the other hand, when monitoring scan or CT fluoroscopy should be continued (NO in step S8), the thinning setting function 52 in step S9 evaluates the image quality of the reconstructed image generated in step S7 in real time.

Next, in step S10, the thinning setting function 52 sets the thinning pattern after the next rotation according to the image quality of the reconstructed tomographic image (see FIG. 3), and returns to step S6. The thinning pattern set here may not be used for the rotation immediately after the rotation in which the projection data corresponding to the tomographic image is collected. For example, the thinning pattern from the rotation in which the projection data is collected to the predetermined rotation. May be used after a predetermined rotation without changing.

By the above procedure, the X-ray irradiation timing in the pulse X-ray irradiation can be adjusted according to at least one of the shooting conditions and the image quality of the obtained reconstructed image.

Subsequently, a method of setting the thinning pattern according to the image quality of the reconstructed image in step S10 will be described in more detail.

FIG. 6 is an explanatory diagram showing a first example of a method of repeating different thinning patterns, FIG. 7 is an explanatory diagram showing the second example, and FIG. 8 is an explanatory diagram showing the third example.

The thinning setting function 52 may be set by combining a plurality of different thinning patterns. For example, the thinning setting function 52 may set the thinning pattern so as to repeat thinning patterns having the same thinning ratio but different from each other. At this time, the two patterns may be repeated as shown in FIG. 6 as the first example, or the four patterns may be repeated as shown in FIGS. 7-8 as the second and third examples. FIG. 7 is an example in which the amount of shift between thinning patterns is discrete, and FIG. 8 is an example in which each thinning pattern is continuously shifted by one view in the rotation direction.

For example, when repeating four patterns, the thinning setting function 52 may set the thinning patterns for four consecutive rotations in the order shown in FIGS. 7 and 8.

When a plurality of different thinning patterns are combined and set, each thinning pattern may not be switched in one rotation, and may be switched every predetermined rotation such as, for example, three rotations. Further, as a modification of the example shown in FIG. 8, the thinning setting function 52 may set the predetermined thinning pattern by shifting the predetermined thinning pattern by two or more predetermined views in the rotation direction for each predetermined rotation including one rotation.

Further, when the reconstruction function 55 is set by combining a plurality of different thinning patterns, the image may be generated so as to interpolate the thinning of each other. Specifically, the reconstruction function 55 continues to maintain the image data corresponding to the same pattern in the reconstructed image until the same thinning pattern is photographed, and the same as when the same thinning pattern is photographed. Update the image data corresponding to the pattern.

In any of the examples of FIGS. 6-8, the thinning data can be interpolated by maintaining the image data until the same thinning pattern is taken. By performing the interpolation processing, it is possible to secure the resolution while reducing the exposure dose of the subject O by thinning out. In particular, in the example shown in FIG. 7-8, since it is possible to shoot from the entire view in one rotation by repeating all the thinning patterns, it is possible to maintain the same resolution as continuous X-ray shooting.

On the other hand, when performing interpolation processing, for example, in the example shown in FIG. 7-8, the image data of the portion shot with one thinning pattern is not updated until four rotations, and the old information is maintained. It will be. Therefore, the interpolation process is effective when an organ that does not move much is the monitoring target, that is, when the required time resolution of the monitoring target portion of the image of the subject O is lower than a predetermined threshold value.

Further, as is clear from FIG. 6-8, when the interpolation process is performed, the example shown in FIG. 6 has a lower real-time property when the interpolation is performed than the example shown in FIG. 7-8. Is excellent. Therefore, when a moving organ is a monitoring target, it is advisable to advance the update timing by performing interpolation processing with a small number of repetitions of thinning patterns as shown in FIG.

FIG. 9 is an explanatory diagram showing a fourth example of a method of repeating thinning patterns different from each other.

FIG. 6-8 is an example in the case where the total number of views in one rotation is 24, and the irradiation view: non-irradiation view = 1: 3. In this case, the same pattern is repeated every 4 views in the rotation direction, that is, about the total number of views 24 in one rotation. The thinning pattern shown in FIGS. 3 and 6-8 is a thinning pattern in which the irradiated view or the non-irradiated view is set to be located at equal intervals.

On the other hand, FIG. 9 is an example in which the irradiation view: the non-irradiation view = 1: 4, that is, the same pattern is repeated every 5 views, which is not a divisor of the total number of views 24 in one rotation.

In this case, for example, one thinning pattern is formed by combining four patterns for every five views and one pattern for every four views (see the upper left of FIG. 9). In this case, for example, a total of 24 types of thinning patterns in which the thinning pattern shown in the upper left of FIG. 9 is continuously shifted by one view in the rotation direction for each rotation are used, and the first thinning pattern at the 25th rotation (FIG. 9). It is good to repeat returning to (see the upper left of).

In this way, even when the interpolation processing is performed when the same pattern is repeated for each view that is not a divisor of the total number of views, for example, in combination with the third example shown in FIG. 8, that is, in the upper left of FIG. If the indicated thinning pattern is continuously shifted one view at a time in the rotation direction, it is possible to secure the resolution while reducing the exposure dose of the subject O. In particular, when reconstructing by the successive approximation method (Interactive Reconstruction), the degree of freedom is high, and in addition to the equally spaced thinning shown in FIGS. 3 and 6-8, the unevenly spaced thinning pattern as shown in FIG. 9 is used. It is possible.

FIG. 10A is an explanatory diagram showing an example of a thinning pattern in the case of thinning out an unreliable view of collected data, and FIG. 10B is an X-ray irradiation directed to a place where the subject O has high X-ray sensitivity. It is explanatory drawing which shows an example of the thinning pattern for avoiding.

For views that include areas with low detected doses and low reliability of collected data, such as the left and right sides of the patient's shoulder, a thinning pattern may be set to avoid X-ray irradiation (FIG. 10 (a)). reference). In this case, the thinning setting function 52 obtains an index value indicating the reliability of the collected data for each view, and the view whose index value is lower than the threshold value becomes a non-illuminated view after the next rotation and is excluded from shooting. As described above, it is advisable to set the thinning pattern after the next rotation. In this case, the exposure dose of the subject O can be further reduced by omitting the unnecessary shooting of the view.

The index value indicating the reliability of the collected data is obtained, for example, based on the count number of the collected data and the value of the standard deviation. This is because a view with a small count of collected data or a large standard deviation of the collected data is considered to be a view with low reliability of the collected data. In this case, the thinning setting function 52 may use an index value whose value becomes smaller as the count number of the collected data is smaller, or an index value whose value becomes smaller as the standard deviation value of the collected data is larger.

Further, when the subject O has a place with high X-ray sensitivity, it is advisable to set a thinning pattern so as to avoid X-ray irradiation toward this place. FIG. 10B shows an example in which there is a place with high X-ray sensitivity above the subject O. Further, when the operator is located in the vicinity of the subject O to perform a procedure or the like during a monitoring scan or CT fluoroscopy, a thinning pattern may be set so as to reduce the exposure dose of the operator.

According to at least one embodiment described above, the X-ray irradiation timing in pulse X-ray irradiation can be adjusted according to at least one of the imaging conditions and the image quality of the obtained reconstructed image.

The condition acquisition function 51, the thinning setting function 52, the imaging control function 53, the X-ray control function 54, and the reconstruction function 55 of the processing circuit 44 in the present embodiment are the thinning setting unit and the imaging control unit, respectively, within the scope of the claims. , An example of an X-ray control unit and a reconstruction unit.

In the above embodiment, the word "processor" refers to, for example, a dedicated or general-purpose CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an integrated circuit for a specific application (Application Specific Integrated Circuit: ASIC). It is intended to mean a circuit such as a programmable logic device (for example, Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (CPLD), and FPGA). The processor realizes various functions by reading and executing a program stored in a storage medium.

Further, in the above embodiment, an example in which a single processor of the processing circuit realizes each function has been shown, but a processing circuit is configured by combining a plurality of independent processors, and each processor realizes each function. May be good. When a plurality of processors are provided, the storage medium for storing the program may be provided individually for each processor, or one storage medium collectively stores the programs corresponding to the functions of all the processors. May be good.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

10 ... X-ray CT device 30 ... X-ray irradiator 33 ... X-ray detector 34 ... DAS
52 ... Thinning setting function 53 ... Shooting control function 54 ... X-ray control function 55 ... Reconstruction function

Claims (5)

A rotating pedestal that rotates around the subject,
An X-ray irradiator provided on the rotary gantry and generating pulsed X-rays to be irradiated on the subject in each view of a plurality of views constituting one rotation of the rotary gantry.
An X-ray detector provided on the rotary pedestal at a position facing the X-ray irradiator and detecting X-rays transmitted through the subject, and an X-ray detector.
Based on the imaging conditions of the subject, a thinning pattern is set in which the pulse X-rays are irradiated in some of the views obtained by thinning out the plurality of views, while the pulsed X-rays are not irradiated in the remaining views. A thinning setting unit for setting a combination consisting of a plurality of thinning patterns such that the pulse X-rays are irradiated in the plurality of views in a plurality of rotations of the rotary pedestal.
An X-ray control unit that controls the X-ray irradiator so as to repeat a combination consisting of the plurality of thinning patterns.
A data acquisition unit that collects projection data of each view based on the output of the X-ray detector by repeating a combination consisting of the plurality of thinning patterns.
Of the projection data of each of the views, the subject is based on the projection data of the part of the view due to the latest rotation of the rotating pedestal and the projection data of the remaining views due to the past rotation of the rotating pedestal. Reconstruction part that reconstructs the tomographic image of
Equipped with
The thinning setting unit is based on the plurality of thinning patterns when the numerical value related to the noise of the tomographic image of the subject is lower than the predetermined threshold value or the numerical value related to the resolution of the tomographic image of the subject is higher than the predetermined threshold value. The combination consisting of the plurality of thinning patterns is reset so that the ratio of the remaining views contained in the plurality of views is higher than that of the combination.
X-ray CT device. A rotating pedestal that rotates around the subject,
An X-ray irradiator provided on the rotary gantry and generating pulsed X-rays to be irradiated on the subject in each view of a plurality of views constituting one rotation of the rotary gantry.
An X-ray detector provided on the rotary pedestal at a position facing the X-ray irradiator and detecting X-rays transmitted through the subject, and an X-ray detector.
Based on the imaging conditions of the subject, a thinning pattern is set in which the pulse X-rays are irradiated in some of the views obtained by thinning out the plurality of views, while the pulsed X-rays are not irradiated in the remaining views. A thinning setting unit for setting a combination consisting of a plurality of thinning patterns such that the pulse X-rays are irradiated in the plurality of views in a plurality of rotations of the rotary pedestal.
An X-ray control unit that controls the X-ray irradiator so as to repeat a combination consisting of the plurality of thinning patterns.
A data acquisition unit that collects projection data of each view based on the output of the X-ray detector by repeating a combination consisting of the plurality of thinning patterns.
Of the projection data of each of the views, the subject is based on the projection data of the part of the view due to the latest rotation of the rotating pedestal and the projection data of the remaining views due to the past rotation of the rotating pedestal. Reconstruction part that reconstructs the tomographic image of
Equipped with
The thinning setting unit is based on the plurality of thinning patterns when the numerical value related to the noise of the tomographic image of the subject is equal to or higher than a predetermined threshold value or the numerical value related to the resolution of the tomographic image of the subject is equal to or lower than a predetermined threshold value. The combination consisting of the plurality of thinning patterns is reset so that the ratio of the remaining views contained in the plurality of views is lower than that of the combination.
X-ray CT device. The thinning setting unit is
The plurality of thinning patterns are set as being shifted by a predetermined view in the rotation direction of the rotary pedestal.
The X-ray CT apparatus according to claim 1 or 2 . The thinning setting unit is
Each thinning pattern of the plurality of thinning patterns is set so that the partial view and the remaining views are located at equal intervals.
The X-ray CT apparatus according to any one of claims 1 to 3 . The X-ray control unit
The X-ray irradiator is controlled so as to continuously irradiate X-rays in the plurality of views from the start of imaging of the subject to the predetermined rotation of the rotary pedestal, while the X-ray irradiator is controlled after the predetermined rotation. The X-ray irradiator is controlled so as to irradiate the pulse X-rays in the plurality of views by combining a plurality of thinning patterns.
The reconstructed part is
From the start of imaging of the subject to the predetermined rotation, a tomographic image of the subject is further obtained based on the projection data of each view obtained by continuously irradiating the plurality of views with X-rays. Reconstruct,
The X-ray CT apparatus according to any one of claims 1 to 4 .

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