JP2019005490A - X-ray CT apparatus - Google Patents

Abstract

To provide an X-ray CT apparatus having high image quality and high object discrimination performance.SOLUTION: An X-ray CT apparatus according to an embodiment includes a photon counting-type detector and a setting part. The photon counting-type detector includes a plurality of detecting elements comprising a scintillator and an optical sensor. At the time of imaging, the setting part sets a driving voltage according to the position of each of the scintillators in the photon counting-type detector in the optical sensor corresponding to each of the scintillators.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to an X-ray CT apparatus.

  Photon counting CT (Computed Tomography) may be configured with an indirect detector combining a scintillator and a photodetector (also referred to as an optical sensor). In an indirect detector, in order to detect individual X-ray pulses with high accuracy, a photomultiplier tube (PMT), avalanche photodiode (APD), or silicon with a plurality of pixels arranged with APDs is used. Photomultipliers (SiPM) are often used as photodetectors.

  In SiPM and the like, characteristics such as detection efficiency (PDE: Photon Detection Efficiency) and gain change depending on the driving voltage. For example, when the drive voltage is increased, the PDE increases and the gain increases, but the effective pulse width increases and the frequency characteristic decreases. On the other hand, when the drive voltage is lowered, the PDE is lowered and the gain is lowered, but the effective pulse width is narrowed and the frequency characteristics are improved. For this reason, it is necessary to appropriately select the driving voltage according to the dose of incident X-rays, the required image quality and the substance discrimination ability.

US Pat. No. 7,403,589

  The problem to be solved by the present invention is to provide an X-ray CT apparatus having high image quality and high substance discrimination ability.

  The X-ray CT apparatus according to the embodiment includes a photon counting detector and a setting unit. The photon counting detector has a plurality of detection elements including a scintillator and an optical sensor. The setting unit sets a driving voltage corresponding to the position of each scintillator in the photon counting detector to the optical sensor corresponding to each scintillator during imaging.

FIG. 1 is a diagram illustrating a configuration example of an X-ray CT apparatus according to the first embodiment. FIG. 2A is a diagram for explaining the X-ray detector according to the first embodiment. FIG. 2B is a diagram for explaining the photosensor according to the first embodiment. FIG. 3 is a diagram for explaining the data collection circuit according to the first embodiment. FIG. 4 is a diagram for explaining a comparative example. FIG. 5 is a flowchart illustrating a processing procedure performed by the X-ray CT apparatus according to the first embodiment. FIG. 6 is a diagram for explaining the first embodiment. FIG. 7 is a diagram for explaining the first embodiment. FIG. 8 is a diagram for explaining the first embodiment. FIG. 9 is a diagram for explaining a modification of the first embodiment. FIG. 10 is a diagram for explaining the second embodiment. FIG. 11 is a diagram for explaining the second embodiment. FIG. 12 is a flowchart illustrating a processing procedure performed by the FPGA according to the second embodiment. FIG. 13 is a diagram for explaining the third embodiment. FIG. 14 is a flowchart illustrating a processing procedure performed by the FPGA 14a according to the third embodiment. FIG. 15 is a diagram for explaining the third embodiment. FIG. 16 is a diagram for explaining a modification of the third embodiment.

  Hereinafter, an X-ray CT apparatus according to an embodiment will be described with reference to the drawings.

  An X-ray CT (Computed Tomography) apparatus described in the following embodiment is an apparatus capable of performing photon counting CT. That is, the X-ray CT apparatus described in the following embodiment counts X-rays that have passed through the subject using a photon counting type detector instead of a conventional integral type (current mode measurement type) detector. Thus, the apparatus can reconstruct X-ray CT image data having a high S / N ratio. In addition, the content described in one embodiment is similarly applied to other embodiments in principle.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration example of an X-ray CT apparatus 1 according to the first embodiment. As shown in FIG. 1, the X-ray CT apparatus 1 according to the first embodiment includes a gantry 10, a bed 20, and a console 30.

  The gantry 10 is an apparatus that irradiates the subject P with X-rays and collects data related to the X-rays transmitted through the subject P. The gantry 10 includes an X-ray high-voltage device 11, an X-ray generator 12, and an X-ray detector. 13, a data collection circuit 14, a rotating frame 15, and a gantry control device 16. Further, in the gantry 10, as shown in FIG. 1, an orthogonal coordinate system including an X axis, a Y axis, and a Z axis is defined. That is, the X axis indicates the horizontal direction, the Y axis indicates the vertical direction, and the Z axis indicates the direction of the rotation center axis of the rotating frame 15 when the gantry 10 is not tilted.

  The rotating frame 15 supports the X-ray generator 12 and the X-ray detector 13 so as to face each other with the subject P interposed therebetween, and is fast at a circular orbit centered on the subject P by a gantry control device 16 described later. It is an annular frame that rotates in a circle.

  The X-ray generator 12 is an apparatus that generates X-rays and irradiates the subject P with the generated X-rays. The X-ray generator 12 includes an X-ray tube 12a, a wedge 12b, and a collimator 12c.

  The X-ray tube 12a is a vacuum tube that receives a high voltage from the X-ray high voltage device 11 and irradiates thermoelectrons from a cathode (sometimes referred to as a filament) to an anode (target). The X-ray beam is irradiated to the subject P with the rotation of. That is, the X-ray tube 12 a generates X-rays using the high voltage supplied from the X-ray high voltage device 11.

  The X-ray tube 12a generates an X-ray beam that spreads with a fan angle and a cone angle. For example, the X-ray tube 12a controls the X-ray high-voltage apparatus 11 to continuously expose X-rays around the subject P for full reconstruction or exposure that can be reconfigured for half reconstruction. It is possible to continuously expose X-rays in the irradiation range (180 degrees + fan angle). Further, the X-ray tube 12a can intermittently emit X-rays (pulse X-rays) at a preset position (tube position) under the control of the X-ray high voltage apparatus 11. Further, the X-ray high voltage apparatus 11 can also modulate the intensity of X-rays exposed from the X-ray tube 12a. For example, the X-ray high voltage apparatus 11 increases the intensity of X-rays emitted from the X-ray tube 12a at a specific tube position, and exposes from the X-ray tube 12a in a range other than the specific tube position. Reduce the intensity of the emitted X-rays.

  The wedge 12b is an X-ray filter for adjusting the X-ray dose of X-rays emitted from the X-ray tube 12a. Specifically, the wedge 12b transmits the X-rays exposed from the X-ray tube 12a so that the X-rays irradiated from the X-ray tube 12a to the subject P have a predetermined distribution. Attenuating filter. For example, the wedge 12b is a filter obtained by processing aluminum so as to have a predetermined target angle or a predetermined thickness. The wedge is also called a wedge filter or a bow-tie filter.

  The collimator 12c is composed of a lead plate or the like and has a slit in part. For example, the collimator 12c narrows down the X-ray irradiation range in which the X-ray dose is adjusted by the wedge 12b with the slits under the control of the X-ray high voltage apparatus 11 described later.

  The X-ray source of the X-ray generator 12 is not limited to the X-ray tube 12a. For example, in place of the X-ray tube 12a, the X-ray generator 12 collides with a focus coil that focuses an electron beam generated from an electron gun, a deflection coil that electromagnetically deflects, and an electron beam that deflects around a half circumference of the subject P. And a target ring that generates X-rays.

  The X-ray high voltage device 11 is composed of an electric circuit such as a transformer and a rectifier, and has a function of generating a high voltage to be applied to the X-ray tube 12a, and the X-ray tube 12a emits light. An X-ray control device that controls the output voltage according to the X-ray to be performed. The high voltage generator may be a transformer system or an inverter system. For example, the X-ray high voltage apparatus 11 adjusts the X-ray dose irradiated to the subject P by adjusting the tube voltage and tube current supplied to the X-ray tube 12a. Further, the X-ray high voltage apparatus 11 receives control from the processing circuit 37 of the console 30.

  The gantry control device 16 includes a processing circuit configured by a CPU (Central Processing Unit) and the like and a driving mechanism such as a motor and an actuator. The gantry control device 16 has a function of controlling the operation of the gantry 10 by receiving an input signal from the input interface 31 attached to the console 30 or the input interface attached to the gantry 10. For example, the gantry control device 16 receives the input signal and rotates the rotary frame 15 to rotate the X-ray tube 12a and the X-ray detector 13 on a circular orbit around the subject P. Control for tilting the gantry 10 and control for operating the bed 20 and the top plate 22 are performed. The gantry control device 16 receives control from the processing circuit 37 of the console 30.

  Further, the gantry control device 16 monitors the position of the X-ray tube 12a, and when the X-ray tube 12a reaches a predetermined rotation angle (imaging angle), a timing at which data acquisition to the data acquisition circuit 14 is started. A view trigger signal indicating is output. For example, when the total number of views in rotational imaging is 2460 views, the gantry control device 16 outputs a view trigger signal every time the X-ray tube 12a moves about 0.15 degrees (= 360/2460) on a circular orbit. To do.

  The X-ray detector 13 is an example of a photon counting detector that includes a plurality of detection elements and outputs a signal corresponding to the counted number of photons. In the X-ray detector 13, for example, a plurality of X-ray detection elements (also referred to as “sensors” or simply “detection elements”) are arranged in the channel direction along one circular arc with the focal point of the X-ray tube 12a as the center. It is composed of a plurality of X-ray detection element arrays. The X-ray detector 13 has a structure in which a plurality of X-ray detection element arrays in which a plurality of X-ray detection elements are arranged in the channel direction are arranged in the slice direction. Each X-ray detection element of the X-ray detector 13 detects X-rays irradiated from the X-ray generator 12 and passed through the subject P, and outputs an electric signal (pulse) corresponding to the X-ray dose to the data collection circuit 14. To output. The electric signal output by each X-ray detection element is also referred to as a detection signal. FIG. 2A is a diagram for explaining the X-ray detector 13 according to the first embodiment.

  As shown in FIG. 2A, the X-ray detector 13 includes a detection element 130 that detects X-ray photons, and an ASIC (Application Specific Integrated) that is connected to the detection element 130 and counts X-ray photons detected by the detection element 130. Circuit) 133 is a photon counting detector having a plurality of detection units. In the example of FIG. 2A, only one ASIC 133 is illustrated among the four detection elements 130 and the ASIC 133 that each detection element 130 has.

  As illustrated in FIG. 2A, each detection element 130 is an indirect conversion type detector configured by a scintillator 131 and an optical sensor 132. That is, the X-ray detector 13 includes a plurality of detection elements 130 each including a scintillator 131 and an optical sensor 132. The scintillator 131 is composed of a scintillator crystal that outputs light having a photon amount corresponding to the incident X-ray dose. The optical sensor 132 has a function of converting into an electric signal corresponding to the amount of light from the scintillator 131, and is, for example, an APD (Avalanche Photo-Diode) or SiPM (Silicon photomultiplier). Note that the optical sensor 132 provided in each scintillator 131 constitutes one pixel. For this reason, the optical sensor 132 is also referred to as one pixel. Although not shown in FIG. 2A, a grid is arranged on the surface of the scintillator 131 on the X-ray incident side. The grid is composed of an X-ray shielding plate having a function of absorbing scattered X-rays.

  Below, the case where the optical sensor 132 is SiPM is demonstrated. The optical sensor 132 includes an APD cell 140 that includes a plurality of APDs 141 that operate individually. In general, hundreds to thousands of APDs are arranged in one pixel. FIG. 2B is a diagram for explaining the photosensor according to the first embodiment. In the example shown in FIG. 2B, among the APDs 141 included in the APD cell 140, 72 APDs 141 arranged in 9 horizontal rows and 8 vertical rows are illustrated.

  The APD 141 is a photodiode having an avalanche region 141a, and is a photodiode using an avalanche doubling action in which photocurrent is multiplied by applying a reverse voltage (also referred to as “reverse bias voltage” or “drive voltage”). is there. Avalanche doubling action means that when a reverse voltage is applied to the PN junction, the pair of electrons and holes generated in the depletion layer has electrons flowing to the N layer and holes flowing to the P layer. The electrons and holes collide with other atoms to form new electron-hole pairs. A chain reaction occurs such that these electrons and holes collide with atoms, and pairs of electrons and holes are newly formed. That is, in the APD 141, more pairs of electrons and holes are generated than pairs of electrons and holes generated by incident light. As described above, the APD 141 is a highly sensitive photodiode capable of obtaining a high output even with weak light.

  When the scintillator 131 absorbs X-rays, the scintillator 131 emits visible light whose number is approximately proportional to the energy of the absorbed X-rays. A part of the light enters the APD cell 140. The APD cell 141 that has absorbed one or more visible lights outputs a signal. Then, the APD cell 140 outputs the sum of the signals output from all the APDs 141 in the APD cell 140 as an output signal for one pixel.

  More specifically, each APD 141 of the APD cell 140 outputs the same pulse when one or more lights are detected. Therefore, the APD cell 140 outputs an output signal corresponding to the total number of APDs 141 that have detected light. For example, let A be the output signal when one light is detected. The APD cell 140 outputs an output signal A when one light is detected, and outputs an output signal n × A when n lights are detected. Thus, the APD cell 140 outputs an output signal corresponding to the total number of APDs 141 that have detected light per pixel. In other words, the APD cell 140 outputs an output signal corresponding to the X-ray energy.

  Returning to FIG. 2A. The ASIC 133 counts the number of X-ray photons incident on the detection element 130 by discriminating individual charges output from the detection element 130. The ASIC 133 measures the energy of the counted X-ray photons by performing arithmetic processing based on the magnitude of each charge. The ASIC 133 includes, for example, a capacitor 133a, an amplifier circuit 133b, a waveform shaping circuit 133c, a comparator circuit 133d, and a counter 133e.

  The capacitor 133a accumulates the individual charges output from the detection element 130. The amplifier circuit 133b is a circuit that integrates the charges collected by the capacitor 133a in response to the X-ray photons incident on the detection element 130 and outputs the result as an electric pulse signal. This pulse signal has a wave height and an area corresponding to the amount of energy of photons. That is, the peak value of this electric signal (pulse) has a correlation with the energy value of the X-ray photon.

  The waveform shaping circuit 133c is a circuit that adjusts the frequency characteristics of the pulse signal output from the amplifier circuit 133b and shapes the waveform of the pulse signal by giving a gain and an offset.

  The comparator circuit 133d compares the wave height or area of the response pulse signal to the incident photon with a threshold value set in advance corresponding to a plurality of energy bands to be distinguished, and the comparison result with the threshold value is sent to the counter 133e at the subsequent stage. It is a circuit to output.

  The counter 133e counts the discrimination result of the waveform of the response pulse signal for each corresponding energy band, and outputs the photon count result to the data collection circuit 14 as digital data.

  The data acquisition circuit 14 (DAS: Data Acquisition System) is a circuit that collects the result of the counting process from each detection element 130 of the X-ray detector 13 and generates detection data. In other words, the data collection circuit 14 collects the count results obtained by the X-ray detector 13. Here, the detection data is, for example, a sinogram. The sinogram is data in which the results of the counting process incident on each detection element 130 at each position of the X-ray tube 12a are arranged. The data acquisition circuit 14 collects the result of the counting process at each view angle from the X-ray detector 13 in synchronization with the view trigger signal, and generates a sinogram. The data collection circuit 14 outputs the data for one round of the view by repeating the process of outputting or storing the result of the counting process at regular intervals (views) or storing it in the storage circuit 35 and the process of resetting the result of the counting process. To get.

  The data acquisition circuit 14 transmits various control signals to the X-ray detector 13. FIG. 3 is a diagram for explaining the data collection circuit 14 according to the first embodiment. As shown in FIG. 3, the data collection circuit 14 includes an FPGA (Field-Programmable Gate Array) 14a. As shown in FIG. 3, the data collection circuit 14 is connected to the X-ray detector 13 by, for example, a rigid flexible board 17. The rigid flexible substrate 17 is a substrate in which a rigid wiring board portion having hardness and strength for mounting components and a flexible wiring board that can be bent are integrated. For example, the FPGA 14a receives a view trigger signal from the gantry control device 16, and controls the X-ray detector 13 based on the received view trigger signal. The data collection circuit 14 is an example of a collection unit, and the FPGA 14a is an example of a setting unit.

  The data output from the data collection circuit 14 is referred to as detection data, and logarithmic conversion processing, offset correction processing, sensitivity correction processing between channels, gain correction processing between channels, pile-up correction processing, response to the detection data. Data subjected to preprocessing such as function correction processing and beam hardening correction is referred to as raw data. Further, the detection data and the raw data are collectively referred to as projection data.

  The bed 20 is a device for placing and moving the subject P to be scanned, and includes a bed driving device 21, a top plate 22, a base 23, and a base (support frame) 24.

  The top plate 22 is a plate on which the subject P is placed. The base 24 supports the top plate 22. The base 23 is a housing that supports the base 24 so as to be movable in the vertical direction. The couch driving device 21 is a motor or an actuator that moves the subject P into the rotary frame 15 by moving the top 22 on which the subject P is placed in the major axis direction of the top 22. The couch driving device 21 can move the top plate 22 also in the X-axis direction.

  The top plate moving method may be a method of moving only the top plate 22 or a method of moving the base 24 of the bed 20 together. In the case of standing CT, a method of moving a patient moving mechanism corresponding to the top board 22 may be used.

  For example, the gantry 10 executes a helical scan that rotates the rotating frame 15 while moving the top plate 22 to scan the subject P in a spiral shape. Alternatively, the gantry 10 performs a conventional scan in which the subject P is scanned in a circular orbit by rotating the rotating frame 15 while the position of the subject P is fixed after the top plate 22 is moved. In the following embodiment, a change in the relative position between the gantry 10 and the top plate 22 will be described as being realized by controlling the top plate 22, but the embodiment is not limited to this. For example, when the gantry 10 is self-propelled, a change in the relative position between the gantry 10 and the top plate 22 may be realized by controlling the traveling of the gantry 10. Further, the relative position of the gantry 10 and the top plate 22 may be changed by controlling the traveling of the gantry 10 and the top plate 22.

  The console 30 is a device that accepts an operation of the X-ray CT apparatus 1 by an operator and reconstructs X-ray CT image data using the counting results collected by the gantry 10. As shown in FIG. 1, the console 30 includes an input interface 31, a display 32, a storage circuit 35, and a processing circuit 37.

  The input interface 31 receives various input operations from the operator, converts the received input operations into electrical signals, and outputs them to the processing circuit 37. For example, the input interface 31 receives from the operator collection conditions when collecting projection data, reconstruction conditions when reconstructing a CT image, image processing conditions when generating a post-processed image from a CT image, and the like. . For example, the input interface 31 is realized by a mouse, a keyboard, a trackball, a switch, a button, a joystick, or the like.

  The display 32 displays various information. For example, the display 32 outputs a medical image (CT image) generated by the processing circuit 37, a GUI (Graphical User Interface) for receiving various operations from the operator, and the like. For example, the display 32 is configured by a liquid crystal display, a CRT (Cathode Ray Tube) display, or the like.

  The storage circuit 35 is realized by, for example, a RAM (Random Access Memory), a semiconductor memory element such as a flash memory, a hard disk, an optical disk, or the like. The storage circuit 35 stores, for example, projection data and reconstructed image data.

  The processing circuit 37 executes, for example, a system control function 371, a preprocessing function 372, a reconstruction processing function 373, an image processing function 374, a scan control function 375, a display control function 376, and a determination function 377. Here, for example, the system control function 371, the pre-processing function 372, the reconstruction processing function 373, the image processing function 374, the scan control function 375, the display control function 376, and the determination, which are components of the processing circuit 37 shown in FIG. Each processing function executed by the function 377 is recorded in the storage circuit 35 in the form of a program executable by a computer. The processing circuit 37 is, for example, a processor, and realizes a function corresponding to each read program by reading and executing each program from the storage circuit 35. In other words, the processing circuit 37 in a state where each program is read has each function shown in the processing circuit 37 of FIG.

  The system control function 371 controls various functions of the processing circuit 37 based on the input operation received from the operator via the input interface 31.

  The pre-processing function 372 performs logarithmic conversion processing, offset correction processing, sensitivity correction processing between channels, gain correction processing between channels, pile-up correction processing, response function correction processing on the detection data output from the data acquisition circuit 14. The raw data is generated by performing pre-processing such as beam hardening correction. The preprocessing function 372 is an example of a correction unit.

  The reconstruction processing function 373 generates X-ray CT image data by performing reconstruction processing using a filter-corrected back projection method, successive approximation reconstruction method, or the like on the projection data generated by the preprocessing function 372. To do. The reconstruction processing function 373 stores the reconstructed X-ray CT image data in the storage circuit 35. Note that X-ray CT image data reconstructed from data including all energy information by adding all bin information for each pixel is also referred to as a “base image”.

  Here, the projection data generated from the counting result obtained by the photon counting CT includes information on the energy of X-rays attenuated by passing through the subject P. For this reason, the reconstruction processing function 373 can reconstruct X-ray CT image data of a specific energy component, for example. The reconstruction processing function 373 can reconstruct X-ray CT image data of each of a plurality of energy components, for example.

  Further, the reconstruction processing function 373 assigns a color tone corresponding to the energy component to each pixel of the X-ray CT image data of each energy component, and superimposes a plurality of X-ray CT image data color-coded according to the energy component, for example. Generated image data is generated. In addition, the reconstruction processing function 373 can generate image data that enables identification of the substance by using, for example, the K absorption edge unique to the substance. Other image data generated by the reconstruction processing function 373 includes monochromatic X-ray image data, density image data, effective atomic number image data, and the like.

  In addition, as an application of X-ray CT, there is a technique for discriminating the type, abundance, density, and the like of a substance contained in the subject P using the fact that the X-ray absorption characteristics differ for each substance. This is called substance discrimination. For example, the reconstruction processing function 373 performs substance discrimination on the projection data and obtains substance discrimination information. Then, the reconstruction processing function 373 reconstructs a substance discrimination image using the substance discrimination information that is a result of substance discrimination.

  The reconstruction processing function 373 can apply a full scan reconstruction method and a half scan reconstruction method to reconstruct a CT image. For example, the reconstruction processing function 373 requires 360 degrees of projection data around the subject in the full scan reconstruction method. Also, the reconstruction processing function 373 requires projection data for 180 degrees + fan angle in the half-scan reconstruction method. Hereinafter, in order to simplify the description, it is assumed that the reconstruction processing function 373 uses a full-scan reconstruction method in which reconstruction is performed using projection data for 360 degrees around the subject. The reconstruction processing function 373 is an example of a reconstruction processing unit.

  The image processing function 374 is based on the input operation received from the operator via the input interface 31, and the X-ray CT image data generated by the reconstruction processing function 373 is generated by a known method, such as a tomographic image of any section or rendering. It is converted into image data such as a three-dimensional image by processing. The image processing function 374 stores the converted image data in the storage circuit 35.

  The scan control function 375 controls the CT scan performed on the gantry 10. For example, the scan control function 375 controls the operations of the X-ray high voltage device 11, the X-ray detector 13, the gantry control device 16, the data collection circuit 14, and the couch driving device 21, thereby starting scanning on the gantry 10, Control execution of scan and end of scan. Specifically, the scan control function 375 controls the collection processing of projection data in photographing for collecting positioning images (scanograms, scanograms) and main photographing (scanning) for collecting images used for diagnosis.

  Here, the scan control function 375 can capture a two-dimensional scano image and a three-dimensional scano image. For example, the scan control function 375 performs continuous imaging while fixing the X-ray tube 12a at a position of 0 degree (a position in the front direction with respect to the subject P) and moving the top plate 22 at a constant speed. Take a two-dimensional scano image with. Alternatively, the scan control function 375 may repeat the imaging intermittently in synchronization with the movement of the top plate 22 while the X-ray tube 12a is fixed at the 0 degree position and the top plate 22 is moved intermittently. Take a two-dimensional scano image. The scan control function 375 can capture a positioning image not only from the front direction but also from any direction (for example, the side surface direction) with respect to the subject. For example, when the X-ray tube 12a is imaged at a position of 90 degrees (position in the lateral direction with respect to the subject P), imaging from the side surface of the subject P is performed and a two-dimensional scan image is obtained. Note that the position of the X-ray tube 12a can be taken from a plurality of arbitrary positions if necessary.

  The scan control function 375 captures a three-dimensional scanogram by collecting projection data for the entire circumference of the subject in scanogram capture. For example, the scan control function 375 collects projection data for the entire circumference of the subject by helical scanning or non-helical scanning. Here, the scan control function 375 executes a helical scan or a non-helical scan with a lower dose than the main imaging over a wide range such as the entire chest, abdomen, the entire upper body, and the whole body of the subject. As the non-helical scan, for example, a step-and-shoot scan is executed.

  The display control function 376 controls the display 32 to display various image data stored in the storage circuit 35.

  The determination function 377 determines a driving voltage corresponding to the position of each scintillator 131 in the X-ray detector 13 in the optical sensor 132 corresponding to each scintillator 131 at the time of imaging. Details of the determination function 377 will be described later.

  The configuration of the X-ray CT apparatus 1 according to the first embodiment has been described above. With this configuration, the X-ray CT apparatus 1 according to the first embodiment integrates the output signal (charge) of the X-ray detector 13 and shapes the waveform, and then divides the signal into a plurality of windows according to the signal level. Then, the number of incident X-rays in each window is counted with a counter. The X-ray CT apparatus 1 acquires data for a necessary circumference and acquires CT images with a plurality of energy windows. Here, in the optical sensor 132 such as SiPM, characteristics such as detection efficiency (PDE: Photon Detection Efficiency) and gain change depending on the driving voltage set in the APD 141.

  For example, when the drive voltage of the APD 141 is increased, the PDE increases and the gain increases, but the effective pulse width increases and the frequency characteristic decreases. On the other hand, when the drive voltage of the APD 141 is lowered, the PDE is lowered and the gain is lowered, but the effective pulse width is narrowed and the frequency characteristics are improved. For this reason, it is necessary to appropriately select the driving voltage of the APD 141 according to the dose of incident X-rays, the required image quality and the substance discrimination ability. In the following, “driving voltage of APD 141” is appropriately described as “driving voltage of optical sensor 132”.

  Here, as a comparative example, the case where the driving voltage of each optical sensor 132 is set to a constant value in the X-ray detector 13 will be described. That is, in the comparative example, it is assumed that the drive voltage having the same value is set in all the optical sensors 132. The problem in the comparative example will be described with reference to FIG. FIG. 4 is a diagram for explaining a comparative example.

  In the X-ray detector 13, the X-ray dose incident on the scintillator 131 of each detection element 130 varies depending on the position in the X-ray detector 13. For example, as shown in FIG. 4, since the amount of absorption by the subject P is large in the central portion of the X-ray detector 13, the X-ray dose incident on the scintillator 131 is low. Here, for convenience of explanation, the X-ray dose is assumed to be n1 (c / s). On the other hand, the peripheral portion of the X-ray detector 13 has little or no absorption by the subject P, and therefore the X-ray dose incident on the scintillator 131 is high. Here, for convenience of explanation, the X-ray dose is n2 (c / s). The central portion of the X-ray detector 13 indicates a region near the center in the channel direction of the X-ray detector 13, and the peripheral portion of the X-ray detector 13 is the center in the channel direction of the X-ray detector 13. The peripheral area away from.

  In the X-ray CT apparatus 1, when the number of X-ray photons incident on the X-ray detector 13 is large, a pile in which another X-ray photon is incident during the processing time of a signal generated by one X-ray photon. A phenomenon called up may occur continuously. When pile-up occurs, the number of X-ray photons to be detected and the energy value of the detected X-ray photons are not correct values, and the finally obtained image quality deteriorates.

  In order to prevent such image quality deterioration due to pile-up, high frequency characteristics are required, and the drive voltage of the optical sensor 132 needs to be lowered. If the drive voltage of the optical sensor 132 is lowered, the image quality is improved at the periphery where the X-ray dose incident on the scintillator 131 is high, and the image quality is improved. However, the PDE and gain are lowered, and the S / N ratio is lowered. In the central part where the X-ray dose incident on the scintillator 131 is low, the substance discrimination ability decreases. On the other hand, when the drive voltage of the optical sensor 132 is increased, the PDE and gain are increased, and the S / N ratio is improved. Therefore, the substance discrimination ability is improved in the central portion where the X-ray dose incident on the scintillator 131 is low. In the peripheral portion where the incident X-ray dose is high, the image quality is deteriorated because it is easily affected by pile-up.

  For this reason, the X-ray CT apparatus 1 according to the first embodiment applies a driving voltage corresponding to the position of each scintillator 131 in the photon counting detector to the optical sensor 132 corresponding to each scintillator 131 during imaging. Set. Hereinafter, the first embodiment will be described with reference to FIGS. 5 to 8. FIG. 5 is a flowchart showing a processing procedure performed by the X-ray CT apparatus 1 according to the first embodiment, and FIGS. 6 to 8 are diagrams for explaining the first embodiment.

  FIG. 5 shows a flowchart for explaining the operation of the X-ray CT apparatus 1 and describes which step in the flowchart corresponds to each component. Step S <b> 1 is a step corresponding to the scan control function 375. This is a step in which the scan control function 375 is realized by the processing circuit 37 calling and executing a predetermined program corresponding to the scan control function 375 from the storage circuit 35. In step S1, the scan control function 375 captures a scanogram. For example, the scan control function 375 captures a two-dimensional scan image while fixing the X-ray tube 12a at a position of 0 degree (a position in the front direction with respect to the subject P).

  Step S2 is a step corresponding to the determination function 377. This is a step in which the determination function 377 is realized by the processing circuit 37 calling and executing a predetermined program corresponding to the determination function 377 from the storage circuit 35. In step S2, the determination function 377 determines the drive voltage.

  Here, the determination function 377 determines a drive voltage based on the X-ray dose incident on each scintillator 131 and generates correspondence information. For example, the determination function 377 estimates the X-ray dose incident on each scintillator 131 from the count result of each detection element 130, and determines a drive voltage based on the estimated X-ray dose. For example, the determination function 377 determines the driving voltage by estimating the X-ray dose incident on the scintillator 131 from the scanogram count result obtained in step S1.

  The determination function 377 performs a threshold determination process described below on the scanogram count result to determine the drive voltage. For example, in the channel direction, the determination function 377 estimates an area where the scanogram count result is equal to or greater than a threshold value, estimates that the X-ray dose incident on the scintillator 131 is a high dose, and selects the high dose area. Then, the determination function 377 reduces the drive voltage of the optical sensor 132 corresponding to the scintillator 131 corresponding to the high dose region. On the other hand, the determination function 377 estimates that the X-ray dose incident on the scintillator 131 is a low dose area in the channel direction where the scanogram count result is less than the threshold, and selects the low dose area. Then, the determination function 377 increases the drive voltage of the optical sensor 132 corresponding to the scintillator 131 corresponding to the low dose region.

  More specifically, since the absorption by the subject P is large in the central part in the channel direction, the dose of incident X-rays is low. For this reason, the determination function 377 selects the central portion in the channel direction as the low-dose region, and increases the driving voltage in the central portion in the channel direction as shown in FIG. Further, since the absorption by the subject P is small or absent at the peripheral edge in the channel direction, the dose of incident X-rays becomes high. For this reason, the determination function 377 selects the peripheral portion in the channel direction as the high-dose region, and lowers the drive voltage of the peripheral portion in the channel direction as shown in FIG.

  Note that the determination function 377 may perform threshold determination processing in a representative slice to determine a drive voltage, and apply the determined drive voltage to other slices in the same manner. The driving voltage may be determined by performing each process. The representative slice is, for example, a central slice in the slice direction.

  Then, the determination function 377 generates correspondence information in which each scintillator 131 is associated with the driving voltage of the optical sensor 132 corresponding to the scintillator 131. More specifically, the determination function 377 generates correspondence information in which an ID is associated with a drive voltage as illustrated in FIG.

  Here, “ID” in the correspondence information indicates an identifier for uniquely identifying the scintillator 131, and “drive voltage” indicates the drive voltage of the optical sensor 132 corresponding to the scintillator 131 identified by the ID. In the example shown in FIG. 7, the scintillator 131 whose drive voltage V1 <drive voltage V2 and whose “ID” is “yyyy” and “zzz” is the high-dose region at the peripheral portion in the channel direction in the X-ray detector 13. The scintillator 131 whose “ID” is “xxxx” is arranged in the low-dose region at the center in the channel direction in the X-ray detector 13.

  For example, the determination function 377 determines that the drive voltage of each APD 141 included in the APD cell 140 of the optical sensor 132 corresponding to the scintillator 131 whose “ID” is “yyyy” and “zzz” is “V1”. Then, the driving voltage of each APD 141 included in the APD cell 140 of the optical sensor 132 corresponding to the scintillator 131 whose “ID” is “xxxx” is determined to be “V2”.

  Step S3 is a step realized by the FPGA 14a. In step S3, the FPGA 14a sets a drive voltage. Here, the FPGA 14a sets a driving voltage corresponding to the position of the scintillator 131 in the photon counting detector to the optical sensor 132 corresponding to each scintillator 131 at the time of photographing. For example, the FPGA 14 a sets a driving voltage based on the X-ray dose incident on each scintillator 131 to the optical sensor 132 corresponding to each scintillator 131.

  As an example, the FPGA 14a refers to the correspondence information shown in FIG. In other words, the FPGA 14 a sets the drive voltage based on the X-ray dose incident on each scintillator 131 estimated from the count result of each detection element 130 in each optical sensor 132. More specifically, the FPGA 14a sets the drive voltage “V1” to each APD 141 included in the APD cell 140 of the optical sensor 132 corresponding to the scintillator 131 whose IDs are “yyyy” and “zzz”. Further, the FPGA 14 a sets the drive voltage “V2” to each APD 141 included in the APD cell 140 of the optical sensor 132 corresponding to the scintillator 131 whose ID is “xxxx”. In this manner, the FPGA 14a applies a larger driving voltage to the optical sensor 132 corresponding to the scintillator 131 whose incident X-ray dose is less than the threshold value than the optical sensor 132 corresponding to the scintillator 131 whose incident X-ray dose is equal to or higher than the threshold value. Set. Note that in the first embodiment, the drive voltage set for each optical sensor 132 at the start of shooting remains fixed during shooting.

  Step S4 is a step corresponding to the scan control function 375. This is a step in which the scan control function 375 is realized by the processing circuit 37 calling and executing a predetermined program corresponding to the scan control function 375 from the storage circuit 35. In step S4, the scan control function 375 executes a main scan.

  Step S <b> 5 is a step corresponding to the preprocessing function 372. This is a step in which the preprocessing function 372 is realized by the processing circuit 37 calling and executing a predetermined program corresponding to the preprocessing function 372 from the storage circuit 35. By the way, the detection data obtained in the main scan in step S4 is a signal obtained as a result of processing with different driving voltages in each optical sensor 132. Here, as the drive voltage changes, the pile-up occurrence rate also changes. By changing the occurrence rate of pile-up, for example, the number of counts decreases, and the rate at which the spectrum shifts higher changes. That is, by setting different drive voltages, the detection data changes in the count number and spectrum. For this reason, in step S5, the preprocessing function 372 corrects the detection data. In other words, the preprocessing function 372 corrects the counting result by the data collection circuit 14.

  FIG. 8 illustrates a case where the count number of detected data is corrected. In FIG. 8, the horizontal axis indicates the tube current value (mA), and the vertical axis indicates the number of detected X-rays. Here, the number of detected X-rays should theoretically have a linear relationship with the dose of X-rays to be irradiated. For example, as indicated by V0 in FIG. 8, the number of detected X-rays increases linearly as the dose of X-rays to be irradiated increases. However, in actual measurement, the number of detected X-rays reaches a peak as the irradiation dose increases, resulting in a non-linear relationship. Here, the dose that reaches the peak is determined by the drive voltage. For example, as the drive voltage increases, the number of detected X-rays decreases. For this reason, the pre-processing function 372 identifies the drive voltage set for each optical sensor 132 and corrects the number of X-rays as the counting result in each ASIC 133. In the following, it is assumed that the driving voltage V1 <the driving voltage V2, and the number of X-rays detected with respect to the dose of X-rays to be irradiated is measured in advance at the driving voltage V1 and the driving voltage V2.

  For example, in the example shown in FIG. 8, when the number of detected X-rays is C1 and the drive voltage is V1, the preprocessing function 372 corrects the number of detected X-rays from C1 to C2. In the example shown in FIG. 8, when the number of detected X-rays is C1 and the drive voltage is V2, the preprocessing function 372 corrects the number of detected X-rays from C1 to C3.

  Step S 6 is a step corresponding to the reconstruction processing function 373. This is a step in which the reconfiguration processing function 373 is realized by the processing circuit 37 calling and executing a predetermined program corresponding to the reconfiguration processing function 373 from the storage circuit 35. In step S6, the reconstruction processing function 373 reconstructs an image. For example, the reconstruction processing function 373 generates a base image based on projection data obtained by performing preprocessing on the detection data corrected by the preprocessing function 372 in step S5. That is, the reconstruction processing function 373 reconstructs an image based on the corrected count result.

  Step S <b> 7 is a step corresponding to the display control function 376. This is a step in which the display control function 376 is realized by the processing circuit 37 calling and executing a predetermined program corresponding to the display control function 376 from the storage circuit 35. In step S <b> 7, the display control function 376 displays an image on the display 32.

  As described above, in the first embodiment, in the X-ray CT apparatus 1, the driving voltage corresponding to the position of each scintillator 131 in the X-ray detector 13 is set in the optical sensor 132 corresponding to each scintillator 131 at the time of imaging. To do. For example, the optical sensor 132 of the detection element 130 arranged in the low dose region that is the central portion in the channel direction of the X-ray detector 13 is connected to the detection element 130 arranged in the high dose region that is the peripheral portion in the channel direction. A driving voltage larger than that of the optical sensor 132 is set.

  Thereby, for example, since the driving voltage is high in the central portion of the X-ray detector 13 in the channel direction, the S / N ratio is improved and the substance discrimination ability is increased. On the other hand, since the driving voltage is low at the peripheral portion in the channel direction of the X-ray detector 13, it is difficult to be affected by pile-up even under a high dose, there is little deformation of the histogram, and an almost correct count rate can be obtained. Further, in the high-dose region at the peripheral portion in the channel direction of the X-ray detector 13, the necessity for material discrimination is low, and what is necessary for the material discrimination is the low-dose region in the center in the channel direction of the X-ray detector 13. . For this reason, according to the X-ray CT apparatus 1 according to the first embodiment, it is possible to obtain high image quality and high substance discrimination ability.

  In the low dose region, the drive voltage is high, but since the dose is low, the influence of the pileup on the deformation of the histogram and the counting rate can be ignored. In the high-dose region, since the drive voltage is low, the S / N ratio is small, but the count rate is not affected and the influence on the image quality may be eliminated. For this reason, in the X-ray CT apparatus 1 according to the first embodiment, the correction process by the preprocessing function 372 described above may be omitted.

  In addition, the reconstruction processing function 373 may perform substance discrimination on the projection data and reconstruct a substance discrimination image using substance discrimination information that is a result of substance discrimination. Here, when reconstructing a substance discrimination image, in addition to the process of correcting the count number of detection data, a process of correcting the spectrum of detection data is required. Below, the process which correct | amends the spectrum of the detection data by the reconstruction process function 373 is demonstrated.

The relationship between the X-ray spectrum S (E) detected by the X-ray detector 13 and the X-ray spectrum S ₀ (E) incident on the X-ray detector 13 uses a response function R (E, nτ). Is represented by the following formula 1.

Here, S ₀ (E) is an X-ray spectrum irradiated to the subject P, μ is an average attenuation coefficient of the path, and L is a projection length of the path. Further, the response function R (E, nτ) includes an X-ray dose n and a time constant τ. Here, the time constant τ includes the time constant of the scintillator 131, the time constant of the X-ray detector 13, and the time constant of the circuit system such as the ASIC 133. A plurality of response functions R are set by the X-ray dose n and the drive voltage. Here, the raw data S (E), the spectrum S ₀ (E) of X-rays emitted from the X-ray tube 12a, and the response function R (E, nτ) are known. For this reason, the reconstruction processing function 373 can calculate the absorption amount (−μL) from Equation 1. That is, the reconstruction processing function 373 can perform substance discrimination in consideration of a change in the spectrum of detection data due to a difference in driving voltage. When generating the base image, it is only necessary to correct the count number of the detection data, and it is not necessary to correct the spectrum difference generated in the detection data.

(Modification of the first embodiment)
In the above-described embodiment, the case where the material discrimination is performed using the response function in consideration of the drive voltage has been described, but the embodiment is not limited to this. For example, substance discrimination may be performed using a lookup table. In such a case, the look-up table stores a detection spectrum that is determined in advance according to the projection length of each substance to be distinguished. Also, a plurality of lookup tables are created in advance under imaging conditions in which the tube current and tube voltage are variously changed. Then, the reconstruction processing function 373 discriminates materials by searching a detection spectrum corresponding to the detection data from a lookup table. FIG. 9 is a diagram for explaining a modification of the first embodiment.

FIG. 9 shows a case where water and calcium are distinguished from each other. As shown in FIG. 9, the look-up table shows the case where the thickness of calcium is changed to 1, 2, 3, 4 (mm) with respect to the thickness of water 5, 10, 15, 20 (cm). The histogram is stored. As an example, S (E) ₁₁ shows a histogram when water is 5 cm and calcium is 1 mm, and S (E) ₂₁ shows a histogram when water is 5 cm and calcium is 2 mm. Here, the reconstruction processing function 373 performs material discrimination by specifying a histogram similar to the detection data using a lookup table created under imaging conditions that are likely to cause pileup, for example.

(Second Embodiment)
In the first embodiment described above, the case where the drive voltage corresponding to the position of each scintillator 131 is set in the optical sensor 132 corresponding to each scintillator 131 at the time of shooting has been described. Here, in the first embodiment, the drive voltage set for each optical sensor 132 at the start of shooting remains fixed during shooting.

  By the way, the cross section of the subject P is not circular but elliptical. For this reason, as shown in FIG. 6, when the low drive voltage region and the high drive voltage region are fixed, the X-ray tube 12a makes one rotation around the subject P, and depending on the imaging angle, the high drive voltage is high. There is a case where a high dose of X-rays enters a region where a voltage is set. In such a case, the image quality deteriorates as a result of the count number being reduced or the spectrum being shifted to a higher one due to pileup.

  For this reason, the driving voltage set according to the position of each scintillator 131 may be dynamically changed according to the imaging angle of the X-ray tube 12a without being fixed during imaging. Therefore, in the second embodiment, a case where a driving voltage corresponding to the shooting angle is set in each optical sensor 132 will be described.

  The configuration of the X-ray CT apparatus 1 according to the second embodiment is the same as the configuration of the X-ray CT apparatus 1 shown in FIG. 1 except that the determination function 377 and a part of the FPGA 14a are different. For this reason, in the second embodiment, only the function executed by the determination function 377 and the FPGA 14a will be described.

  The determination function 377 determines the drive voltage corresponding to the imaging angle based on the X-ray dose incident on each detection element 130, and generates correspondence information. For example, the determination function 377 estimates the X-ray dose incident on each scintillator 131 from the count result of each detection element 130, and determines a drive voltage based on the estimated X-ray dose. For example, the determination function 377 estimates the X-ray dose incident on the scintillator 131 from the scanogram count result and determines the drive voltage. In the second embodiment, the scan control function 375 captures a two-dimensional scano image from two directions. For example, the scan control function 375 fixes the X-ray tube 12a at a position of 0 degree (a position in the front direction with respect to the subject P) and captures a two-dimensional scan image (0 degree scanogram). The X-ray tube 12a is fixed at a position of 90 degrees (position in the lateral direction with respect to the subject P) and a two-dimensional scan image (90 degrees scanogram) is taken.

  The determination function 377 performs a threshold determination process described below on the count result of the two-dimensional scano image from two directions to determine the drive voltage. In other words, the determination function 377 estimates the X-ray dose incident on each scintillator 131 using the two-dimensional scano image from two directions, and determines the drive voltage. FIG. 10 is a diagram for explaining the second embodiment.

  For example, in the channel direction, the determination function 377 estimates that the X-ray dose incident on the scintillator 131 is a high dose in an area where the 0-degree scanogram count result is equal to or greater than the threshold, and as shown in FIG. Select the area H1. Then, as shown in FIG. 10, the determination function 377 reduces the drive voltage of the optical sensor 132 corresponding to the scintillator 131 corresponding to the high dose region H1. On the other hand, the determination function 377 estimates that the X-ray dose incident on the scintillator 131 is a low dose in an area where the count result of the 0-degree scanogram is less than the threshold in the channel direction. Select the region L1. Then, as shown in FIG. 10, the determination function 377 increases the drive voltage of the optical sensor 132 corresponding to the scintillator 131 corresponding to the low-dose region L1.

  Further, for example, the determination function 377 estimates an area where the 90-degree scanogram count result is equal to or greater than a threshold in the channel direction, and the X-ray dose incident on the scintillator 131 is a high dose, as shown in FIG. The high dose region H2 is selected. Then, as shown in FIG. 10, the determination function 377 reduces the drive voltage of the optical sensor 132 corresponding to the scintillator 131 corresponding to the high dose region H2. On the other hand, the determination function 377 estimates that the X-ray dose incident on the scintillator 131 is a low dose in an area where the 90-degree scanogram count result is less than the threshold value in the channel direction. Select the region L2. Then, as shown in FIG. 10, the determination function 377 increases the drive voltage of the optical sensor 132 corresponding to the scintillator 131 corresponding to the low dose region L2.

  As described above, when the imaging angle is 90 degrees, the determination function 377 selects a range narrower than the low-dose area L1 when the imaging angle is 0 degrees as the low-dose area L2. Further, when the imaging angle is 90 degrees, the determination function 377 selects a range wider than the high dose area H1 when the imaging angle is 0 degrees as the high dose area H2.

  Note that the determination function 377 may perform threshold determination processing in a representative slice to determine a drive voltage, and apply the determined drive voltage to other slices in the same manner. The driving voltage may be determined by performing each process. The representative slice is, for example, a central slice in the slice direction.

  Then, the determination function 377 generates correspondence information in which each scintillator 131, the imaging angle, and the driving voltage of the optical sensor 132 corresponding to the scintillator 131 are associated with each other. FIG. 11 is a diagram for explaining the second embodiment. For example, as illustrated in FIG. 11, the determination function 377 generates correspondence information that associates an ID, the number of views, and a drive voltage.

  Here, “ID” in the correspondence information indicates an identifier for uniquely identifying the scintillator 131. “Number of views” indicates the integrated value of the view trigger signal received from the gantry control device 16. For example, the number of views includes “N1 << N <N2” indicating that the range of the view number is N1 or more and less than N2, and “N2 << N <N3” indicating that the range of the view number is N2 or more and less than N3. Etc. are stored. The number of views is information corresponding to the imaging angle of the X-ray tube 12a, and is reset every time the X-ray tube 12a rotates once. Further, here, the position where the X-ray tube 12a is 0 degrees (the position in the front direction with respect to the subject P) is set to the view number 0, and the X-ray tube 12a starts imaging from the position of 0 degrees when imaging starts. Assume that the number of views is accumulated each time the X-ray tube 12a moves on a circular orbit. “Drive voltage” indicates the drive voltage of the optical sensor 132 corresponding to the scintillator 131 identified by the ID in the corresponding number of views. In the example shown in FIG. 11, the scintillator 131 in which the driving voltage V1 <the driving voltage V2 and “ID” is “yyyy” is arranged in the high-dose region in the peripheral portion in the channel direction in the X-ray detector 13. It is assumed that the scintillator 131 whose “ID” is “xxxx” is arranged in the low-dose region at the center in the channel direction in the X-ray detector 13. In addition, the scintillator 131 whose “ID” is “yyyyx” is arranged in a region between the central portion and the peripheral portion in the channel direction in the X-ray detector 13, and a low dose is also applied to a high dose region according to an imaging angle. It can also be an area.

  As an example, the decision function 377 indicates that the driving voltage of each APD 141 included in the APD cell 140 of the optical sensor 132 corresponding to the scintillator 131 whose “ID” is “yyyy” is “V1” regardless of the number of views. And decide. The determination function 377 determines that the drive voltage of each APD 141 included in the APD cell 140 of the optical sensor 132 corresponding to the scintillator 131 whose “ID” is “xxxx” is “V2” regardless of the number of views. . Further, the determination function 377 indicates that the driving voltage of each APD 141 included in the APD cell 140 of the optical sensor 132 corresponding to the scintillator 131 whose “ID” is “yyyyx” is “V2” when the view number “N1 << N <N2”. The view number “N2 << N <N3” is “V1”, the view number “N3 << N <N4” is “V2”, and the view number “N4 << N <N1” is “V1”. And decide.

  The FPGA 14a sets a driving voltage corresponding to the position of each scintillator 131 in the photon counting detector to the optical sensor 132 corresponding to each scintillator 131 at the time of photographing. For example, the FPGA 14 a sets a driving voltage based on the X-ray dose incident on each scintillator 131 to the optical sensor 132 corresponding to each scintillator 131.

  As an example, the FPGA 14a refers to the correspondence information shown in FIG. Here, the FPGA 14 a sets, for example, a driving voltage corresponding to the number of views at the start of shooting in each optical sensor 132. Here, it is assumed that the number of views at the start of shooting is N1. The FPGA 14a sets the drive voltage V1 to each APD 141 included in the APD cell 140 of the optical sensor 132 corresponding to the scintillator 131 whose ID is “yyyy”. Further, the FPGA 14 a sets the drive voltage V <b> 2 to each APD 141 included in the APD cell 140 of the optical sensor 132 corresponding to the scintillator 131 whose ID is “yyyyx” and “xxxx”. That is, the FPGA 14 a sets the drive voltage based on the X-ray dose incident on each scintillator 131 estimated from the counting result of each detection element 130 to the optical sensor 132 corresponding to each scintillator 131.

  Further, the FPGA 14a sets a driving voltage corresponding to the number of views to each optical sensor 132 during photographing. In other words, the FPGA 14a dynamically changes the drive voltage set before the start of shooting according to the shooting angle without being fixed during shooting. FIG. 12 is a flowchart illustrating a processing procedure performed by the FPGA 14a according to the second embodiment.

  Steps S101 to S106 are steps realized by the FPGA 14a. In step S <b> 101, the FPGA 14 a determines whether the start of imaging has been received from the gantry control device 16. Here, when the FPGA 14a determines that the start of imaging has been received from the gantry control device 16 (Yes in Step S101), the FPGA 14a proceeds to Step S102. On the other hand, if the FPGA 14a does not determine that the start of imaging has been received from the gantry control device 16 (No in step S101), the determination process in step S101 is repeated.

  In step S <b> 102, the FPGA 14 a determines whether a view trigger signal has been received from the gantry control device 16. If the FPGA 14a determines that a view trigger signal has been received from the gantry control device 16 (Yes in step S102), the process proceeds to step S103. On the other hand, if the FPGA 14a does not determine that the view trigger signal has been received from the gantry control device 16 (No in step S102), the determination process in step S102 is repeated.

  In step S103, the FPGA 14a reads the correspondence information. For example, the FPGA 14 a reads the correspondence information illustrated in FIG. 11 from the storage circuit 35. In step S104, the FPGA 14a determines whether to change the drive voltage. For example, the FPGA 14a updates the current view number every time a view trigger signal is received. Then, the FPGA 14a refers to the correspondence information and compares the drive voltage corresponding to the updated view number with the drive voltage corresponding to the updated view number for each scintillator 131. Here, the FPGA 14a determines to change the drive voltage when the compared drive voltages are different. On the other hand, the FPGA 14a determines that the drive voltage is not changed when the compared drive voltages are the same.

  If the FPGA 14a determines to change the drive voltage (step S104, Yes), the process proceeds to step S105. On the other hand, if the FPGA 14a does not determine to change the drive voltage (No at Step S104), the FPGA 14a proceeds to Step S106.

  In step S105, the FPGA 14a sets a drive voltage corresponding to the updated number of views. In step S <b> 106, the FPGA 14 a determines whether or not the end of photographing has been received from the gantry control device 16. Here, if the FPGA 14a determines that the end of shooting has been received from the gantry control device 16 (step S106, Yes), the shooting ends. On the other hand, if the FPGA 14a does not determine that the end of imaging has been received from the gantry control device 16 (No in step S106), the process proceeds to step S102 and executes the determination process.

  As described above, in the second embodiment, the FPGA 14a sets a driving voltage corresponding to the shooting angle to each optical sensor 132 during shooting. As a result, according to the second embodiment, it is possible to set an optimum driving voltage for all regions and angles to be imaged while the X-ray tube 12a and the X-ray detector 13 rotate once. For this reason, it becomes possible to obtain higher image quality and material discrimination ability.

  In the second embodiment described above, the case where the X-ray dose incident on each scintillator 131 is estimated and the drive voltage is determined using a two-dimensional scano image from two directions has been described. It is not limited to this. For example, for determining the driving voltage according to the imaging angle, the driving voltage may be determined by estimating the X-ray dose incident on each scintillator 131 based on a three-dimensional scano image. When the X-ray dose incident on each scintillator 131 is estimated based on a three-dimensional scanogram and the drive voltage is determined, the drive voltage can be set with a finer range of imaging angles.

  In the second embodiment described above, the FPGA 14a has been described as setting, for example, a driving voltage corresponding to the number of views at the start of shooting in each optical sensor 132. However, the embodiment is not limited thereto. is not. For example, the FPGA 14a sets the same drive voltage as an initial value to all the optical sensors 132 as an initial value at the first scan position (view number 1) at the start of shooting, and drives according to the shooting angle from the view number 2 onwards. The voltage may be set.

  Note that the reconstruction processing function 373 may perform substance discrimination on the projection data and reconstruct a substance discrimination image using substance discrimination information that is a result of substance discrimination. Here, the reconstruction processing function 373, in the case of reconstructing a substance discrimination image, in addition to the process of correcting the count number of detection data, in the first embodiment and the modification of the first embodiment The described processing for correcting the spectrum of the detection data is executed.

(Third embodiment)
In the third embodiment, a case where the incident X-ray dose is calculated in real time and the drive voltage is set based on the calculated X-ray dose will be described. The configuration of the X-ray CT apparatus 1 according to the third embodiment is the same as the configuration of the X-ray CT apparatus 1 shown in FIG. 1 except that the determination function 377 and a part of the FPGA 14a are different. For this reason, in the third embodiment, only the function executed by the determination function 377 and the FPGA 14a will be described.

  The determination function 377 determines a drive voltage based on the X-ray dose incident on each scintillator 131 and generates correspondence information. For example, the determination function 377 generates correspondence information in which each scintillator 131, the X-ray dose incident on each scintillator 131, and the driving voltage of the optical sensor 132 corresponding to the scintillator 131 are associated with each other. FIG. 13 is a diagram for explaining the third embodiment. For example, as illustrated in FIG. 13, the determination function 377 generates correspondence information in which an ID, a count number, and a drive voltage are associated with each other.

  Here, “ID” in the correspondence information indicates an identifier for uniquely identifying the scintillator 131. “Count” indicates the X-ray dose in view units incident on each scintillator 131. For example, “C <C11” indicating that the count value is less than C11 is stored in the “count number” corresponding to “yyy” in “ID” as the X-ray dose in view units corresponding to the low-dose region. The Further, for example, in “count value” corresponding to “yyy” in “ID”, “C11 << indicating that the count value is C11 or more and less than C12 as an X-ray dose in view units corresponding to a slightly low dose region. C <C12 ”is stored. Further, for example, “count value” corresponding to “yyy” in “ID” indicates “C12 << indicating that the count value is C12 or more and less than C13 as an X-ray dose in view units corresponding to a slightly high dose region. C <C13 ”is stored. Further, for example, “C13 << C” indicating that the count value is C13 or more as the X-ray dose in view units corresponding to the high-dose region is included in the “count value” corresponding to “yyy” in “ID”. Stored.

  Note that each optical sensor 132 has variations due to individual differences. For this reason, it is desirable to set different counts between IDs. For example, “C <C21” indicating that the count value is less than C21 is stored in the “count number” corresponding to “yyyx” as “X dose in view units corresponding to the low dose region”. The In addition, for example, in “count value” corresponding to “yyyx” in “ID”, “C21 << indicating that the count value is C21 or more and less than C22 as an X-ray dose in view units corresponding to a slightly low dose region. C <C22 ”is stored. Further, for example, in “count value” corresponding to “ID” of “yyyx”, “C22 << indicating that the count value is C22 or more and less than C23 as an X-ray dose in view units corresponding to a slightly high dose region. C <C23 ”is stored. Further, for example, “C23 << C” indicating that the count value is C23 or more as the X-ray dose in the view unit corresponding to the high-dose region is included in the “count value” corresponding to “yyyx” in “ID”. Stored.

  Similarly, for example, in “count number” corresponding to “xxxx” in “ID”, “C <C31” indicating that the count value is less than C31 as the X-ray dose in view units corresponding to the low-dose region. Is stored. Further, for example, “count value” corresponding to “xxxx” in “ID” indicates “C31 << indicating that the count value is C31 or more and less than C32 as an X-ray dose in view units corresponding to a slightly low dose region. C <C32 ”is stored. Further, for example, in “count value” corresponding to “xxxx” in “ID”, “C32 << indicating that the count value is C32 or more and less than C33 as an X-ray dose in view units corresponding to a slightly high dose region. C <C33 ”is stored. Further, for example, in “count value” corresponding to “xxxx” in “ID”, “C33 << C” indicating that the count value is equal to or greater than C33 as the X dose in view units corresponding to the high dose region. Stored.

  “Drive voltage” indicates the drive voltage of the optical sensor 132 corresponding to the scintillator 131 identified by the ID in the corresponding count number of the view unit. In the example shown in FIG. 13, it is assumed that drive voltage V1 <drive voltage V2 <drive voltage V3 <drive voltage V4.

  As an example, the determination function 377 is configured so that the driving voltage of each APD 141 included in the APD cell 140 of the optical sensor 132 corresponding to the scintillator 131 whose “ID” is “yyyy” corresponds to the X-ray dose region corresponding to the low-dose region. X for the dose “C <C11” is “V4”, and the count number is “V3” for the X dose “C11 << C <C12”, and the count number is slightly corresponding to the high dose region. It is determined that the dose is “V2” for the dose “C12 << C <C13” and “V1” for the X dose “C13 << C” corresponding to the high dose region.

  The FPGA 14a sets a driving voltage corresponding to the position of each scintillator 131 in the photon counting detector to the optical sensor 132 corresponding to each scintillator 131 at the time of photographing. For example, the FPGA 14 a sets the drive voltage in the current view to the optical sensor 132 corresponding to each scintillator 131 based on the X-ray dose incident on each scintillator 131 in the view before the current view. In the third embodiment, the FPGA 14a sets the same drive voltage as an initial value for all the optical sensors 132 at the first scan position (view number 1) at the start of imaging. Then, the FPGA 14a executes processing for setting the driving voltage based on the X-ray dose incident on each scintillator 131 in each optical sensor 132 during each imaging. In the third embodiment, the case where the drive voltage is set using the count result of the immediately preceding view is described. However, the count result of the view before the current view is used, not limited to the count result of the immediately preceding view. Drive voltage may be set.

  FIG. 14 is a flowchart illustrating a processing procedure performed by the FPGA 14a according to the third embodiment. Note that the processing in step S201 and step S202 shown in FIG. 14 is the same as the processing in step S101 and step S102 shown in FIG.

  In step S203, the FPGA 14a acquires the count value from the counter 133e. For example, the FPGA 14a sets the drive voltage in the current view to the optical sensor 132 corresponding to each scintillator based on the X-ray dose incident on each scintillator 131 in the view immediately before the current view.

  Here, first, a process of acquiring the count result of the immediately preceding view will be described. The FPGA 14a acquires the count result of the previous view from the counter 133e. FIG. 15 is a diagram for explaining the third embodiment. FIG. 15 shows the output timing of the view trigger signal by the gantry control device 16. As shown in FIG. 15, one cycle of the view trigger signal is a period indicated by a double arrow 15a. This one-cycle view trigger signal consists of a positive pulse part in the first half and a negative pulse part in the second half. The FPGA 14a obtains the count result counted during the period of the one-cycle view trigger signal from the counter 133e.

  In step S204, the FPGA 14a reads the correspondence information. For example, the FPGA 14 a reads the correspondence information illustrated in FIG. 13 from the storage circuit 35. In step S205, the FPGA 14a determines whether to change the drive voltage. For example, each time the FPGA 14a acquires the count result of the immediately preceding view, the FPGA 14a specifies the drive voltage corresponding to the count result of the immediately preceding view for each scintillator 131 with reference to the correspondence information. Then, the FPGA 14a compares the identified drive voltage with the currently set drive voltage. Here, the FPGA 14a determines to change the drive voltage when the compared drive voltages are different. On the other hand, the FPGA 14a determines that the drive voltage is not changed when the compared drive voltages are the same.

  If the FPGA 14a determines to change the drive voltage (step S205, Yes), the process proceeds to step S206. On the other hand, if the FPGA 14a does not determine to change the drive voltage (No at Step S205), the FPGA 14a proceeds to Step S207.

  In step S206, the FPGA 14a sets a drive voltage corresponding to the count result of the immediately preceding view. For example, when the count result acquired from the counter 133e that counts the output result of the scintillator 131 identified by the ID “yyy” is a value that is greater than or equal to C11 and less than C12, the FPGA 14a is an optical sensor that corresponds to “yyy”. The drive voltage V3 is set to 132. Further, for example, when the count result acquired from the counter 133e that counts the output result of the scintillator 131 identified by the ID “yyyx” is a value less than C22 and less than C23, the FPGA 14a corresponds to “yyyyx”. A drive voltage V2 is set in the optical sensor 132.

  In step S207, the FPGA 14a determines whether or not the end of photographing has been received from the gantry control device 16. Here, if the FPGA 14a determines that the end of shooting has been received from the gantry control device 16 (Yes in step S207), the shooting ends. On the other hand, when the FPGA 14a does not determine that the end of imaging has been received from the gantry control device 16 (No in Step S207), the FPGA 14a proceeds to Step S202 and executes the determination process.

  As described above, in the third embodiment, the FPGA 14a sets the driving voltage based on the count result of the immediately preceding view for each view during the shooting. As a result, according to the third embodiment, it is possible to set an optimum driving voltage for all regions and angles to be imaged while the X-ray tube 12a and the X-ray detector 13 rotate once. For this reason, it becomes possible to obtain higher image quality and material discrimination ability.

  Note that the reconstruction processing function 373 may perform substance discrimination on the projection data and reconstruct a substance discrimination image using substance discrimination information that is a result of substance discrimination. Here, the reconstruction processing function 373, in the case of reconstructing a substance discrimination image, in addition to the process of correcting the count number of detection data, in the first embodiment and the modification of the first embodiment The described processing for correcting the spectrum of the detection data is executed. For example, the correspondence information shown in FIG. 13 is also stored in the storage circuit 35 of the console 30. The composition processing function 373 selects an appropriate response function with reference to the set value of the drive voltage when reconstructing the substance discrimination image.

(Modification of the third embodiment)
In the third embodiment described above, the case where the count value is calculated in the time of one cycle of the view trigger signal has been described, but the embodiment is not limited to this. For example, the count value may be calculated in the first half or the second half of the view trigger signal for one cycle. In other words, the FPGA 14 a sets the drive voltage in the current view to the photosensors 132 corresponding to each scintillator 131 based on the X-ray dose incident on each scintillator 131 during a predetermined period of the past view period. FIG. 16 is a diagram for explaining a modification of the third embodiment. The upper part of FIG. 16 describes the case where the count value is calculated in the first half of the view trigger signal for one cycle, and the lower part of FIG. 16 is the case where the count value is calculated in the second half of the view trigger signal for one cycle. Will be described.

  More specifically, as shown in the upper part of FIG. 16, the FPGA 14a calculates the count from only the first positive pulse part 16a of the view trigger signal and selects the drive voltage value in the second negative pulse part 16b. The drive voltage is set at the change point 16c of the next view trigger pulse. Alternatively, as shown in the lower part of FIG. 16, the FPGA 14a calculates the number of counts only from the negative pulse part 16d in the second half of the view trigger signal, selects the drive voltage value in the first positive pulse part 16e, and selects the next view trigger. The drive voltage is set at the pulse change point 16f. As described above, the FPGA 14a sets the drive voltage in the current view to the photosensor 132 corresponding to each scintillator 131 based on the X-ray dose incident on each scintillator in the first half or the second half of the past view period.

  Thereby, the FPGA 14a can eliminate the time lag of selection of the drive voltage and setting of the drive voltage. In such a case, the counter 133e outputs a count result for setting the drive voltage to the FPGA 14a separately from the count result for one cycle of the view trigger signal for reconstructing the X-ray CT image data. In addition, the period for calculating the count value is not limited to the first half or the second half of the view trigger signal for one cycle, and is the half of the first half or the second half of the view trigger signal for one cycle. It may be a period.

  In the third embodiment described above, the FPGA 14a is described as setting the same drive voltage as an initial value for all the optical sensors 132 at the first scan position (view number 1) at the start of imaging. However, the embodiment is not limited to this. For example, the FPGA 14a may set the drive voltage at the first scan position (view number 1) using the method described in the first embodiment. That is, at the first scan position (view number 1), the FPGA 14a refers to the correspondence information shown in FIG. 7 and applies the drive voltage based on the X-ray dose incident on each scintillator to the optical sensor 132 corresponding to each scintillator. Set.

  In the third embodiment described above, the case where the drive voltage is set for each view has been described. However, the embodiment is not limited to this. For example, the FPGA 14a may set the drive voltage for each predetermined view such as every five views.

(Other embodiments)
The embodiment is not limited to the above-described embodiment.

  In the above-described embodiment, the case where the driving voltage is determined using a two-dimensional scan image or a three-dimensional scan image obtained by photographing a scanogram before the main scan is described. The form is not limited to this. For example, the drive voltage may be determined using a past image of the same subject or an image captured by another medical image diagnostic apparatus.

  Further, the determination function 377 may determine the drive voltage by estimating the X-ray dose incident on each scintillator 131 from information related to the body shape of the subject. For example, the determination function 377 acquires the body thickness of the subject as information related to the body shape from the reconstructed image obtained by reconstructing a three-dimensional scanogram, and estimates the X-ray dose incident on each scintillator 131. More specifically, the determination function 377 acquires the vertical and horizontal lengths in the axial image obtained by reconstructing the three-dimensional scano image as the body thickness of the subject, and generates an X-ray according to the body thickness. The X-ray dose incident on each scintillator 131 is estimated from the attenuation amount. Then, the determination function 377 performs a threshold determination process on the estimated X-ray dose and determines a drive voltage. In such a case, the FPGA 14 a sets the drive voltage based on the X-ray dose incident on each scintillator 131 estimated from the information related to the body shape of the subject to the optical sensor 132 corresponding to each scintillator 131.

  Further, the determination function 377 may determine the driving voltage by estimating the X-ray dose incident on each scintillator 131 from the information related to the body shape of the subject stored as patient information. For example, the determination function 377 acquires information such as the height, weight, chest circumference, and waist circumference of the subject P stored in the storage circuit 35 as patient information, and estimates the X-ray dose incident on each scintillator 131. Then, the determination function 377 performs a threshold determination process on the estimated X-ray dose and determines a drive voltage. Further, the determination function 377 receives input of information such as the height, weight, chest circumference, and girth of the subject P from the operator via the input interface 31, and estimates the X-ray dose incident on each scintillator 131 from the received information. Thus, the drive voltage may be determined. In such a case, the FPGA 14a sets the drive voltage based on the X-ray dose incident on each scintillator 131, which is estimated from the information related to the body shape of the subject stored as patient information, to the optical sensor 132 corresponding to each scintillator 131. To do.

  In the above-described embodiment, the case where one threshold value is set and two types of drive voltages are set has been described. However, the embodiment is not limited to this. For example, a plurality of threshold values may be set to determine three or more types of drive voltages. In such a case, the FPGA 14a sets the determined three or more types of driving voltages in each ASIC 133.

  In the above-described embodiment, the driving voltage is determined based on the X-ray dose incident on each scintillator 131. However, the embodiment is not limited to this. For example, the driving voltage may be set differently in the central portion and the peripheral portion in the channel direction without estimating the X-ray dose incident on each scintillator 131. For example, the FPGA 14a is disposed in the optical sensor 132 of the detection element 130 disposed in the first region that is the central portion in the channel direction of the X-ray detector 13 and in the second region that is the peripheral portion in the channel direction. A driving voltage larger than that of the optical sensor 132 of the detecting element 130 is set. In addition, the FPGA 14a may set a driving voltage that gradually decreases from the central portion to the peripheral portion in the channel direction of the X-ray detector 13.

  Further, the FPGA 14 a may set the driving voltage corresponding to the imaging angle to each optical sensor 132 without estimating the X-ray dose incident on each scintillator 131. For example, the FPGA 14a changes the range of the first area and the range of the second area according to the shooting angle, and the optical sensor 132 of the detection element 130 arranged in the first area after the change A driving voltage larger than that of the optical sensor 132 of the detection element 130 arranged in the second region after the change may be set.

  In the above-described embodiment, the ASIC 133 is described as being disposed in the X-ray detector 13, but the embodiment is not limited thereto. For example, the ASIC 133 may be disposed in the data collection circuit 14.

  In the above-described embodiment, the reconstruction processing function 373 has been described as performing material discrimination on projection data to obtain material discrimination information, but the embodiment is not limited thereto. For example, the reconstruction processing function 373 may perform substance discrimination on the image data to obtain substance discrimination information.

  In the above-described embodiment, the X-ray CT apparatus 1 of the Rotate / Rotate-Type (third generation CT) that rotates around the subject with the X-ray tube 12a and the X-ray detector 13 integrated is described. The form is not limited to this. For example, in the X-ray CT apparatus, in addition to the third generation CT, X-ray detectors having a plurality of X-ray detection elements are dispersed and fixed in a ring shape, and only the X-ray tube rotates around the subject. There is a Stationary / Rotate-Type (fourth generation CT). The embodiment described above can also be applied to the fourth generation CT. The above-described embodiment can also be applied to a hybrid X-ray CT apparatus that combines the third generation CT and the fourth generation CT.

  The above-described embodiment can also be applied to a conventional single-tube X-ray CT apparatus, and a plurality of pairs of X-ray tubes and X-ray detectors are mounted on a rotating ring. It can also be applied to a tube-type X-ray CT apparatus.

  In the above-described embodiment, the processing circuit 37 has been described as executing a plurality of functions. However, the embodiment is not limited to this. For example, a plurality of functions may be provided in the console 30 as independent circuits, and each circuit may execute each function. For example, a determination function 377 executed by the processing circuit 37 may be provided as a determination circuit, and the determination circuit may execute the determination function. Further, the preprocessing function 372 executed by the processing circuit 37 may be provided as a preprocessing circuit, and the preprocessing circuit may execute the preprocessing function. Further, the reconstruction processing function 373 executed by the processing circuit 37 may be provided as a reconstruction processing circuit, and the reconstruction processing circuit may execute the reconstruction processing function.

  In the above-described embodiment, the preprocessing function 372, the determination function 377, and the reconstruction processing function 373 are described as being executed in the console 30, but the embodiment is not limited to this. For example, the pre-processing function 372, the determination function 377, and the reconfiguration processing function 373 may be executed in an external workstation.

  Further, the drive voltage determination process and the substance discrimination process described in the above-described embodiment can be realized by software. For example, the drive voltage determination process is realized by causing a computer to execute a drive voltage determination program that defines the processing procedure described as being performed by the determination function 377 in the above embodiment. Further, for example, the substance discrimination processing is realized by causing a computer to execute a substance discrimination program that defines the processing procedure described as being performed by the preprocessing function 372 and the reconstruction processing function 373 in the above embodiment. The drive voltage determination program and the substance discrimination program are stored in, for example, a hard disk or a semiconductor memory element, and are read and executed by a processor such as a CPU or MPU. The substance discrimination program can be recorded and distributed on a computer-readable recording medium such as a CD-ROM (Compact Disc-Read Only Memory), an MO (Magnetic Optical disk), or a DVD (Digital Versatile Disc).

  The term “processor” used in the above description is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an application specific integrated circuit (ASIC), a programmable logic device (for example, It means circuits such as a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). The processor implements a function by reading and executing a program incorporated in the processor circuit. Instead of incorporating the program into the processor circuit, the program may be stored in the storage circuit 35 of the console 30. In this case, the processor implements the function by reading and executing the program stored in the storage circuit 35. Note that each processor of the present embodiment is not limited to being configured as a single circuit for each processor, but may be configured as a single processor by combining a plurality of independent circuits to realize the function. Good. Furthermore, a plurality of components in FIG. 1 may be integrated into one processor to realize the function.

  In the description of the above embodiment, each component of each illustrated apparatus is functionally conceptual and does not necessarily need to be physically configured as illustrated. In other words, the specific form of distribution / integration of each device is not limited to the one shown in the figure, and all or a part of the distribution / integration is functionally or physically distributed in arbitrary units according to various loads or usage conditions. Can be integrated and configured. Further, all or a part of each processing function performed in each device may be realized by a CPU and a program that is analyzed and executed by the CPU, or may be realized as hardware by wired logic.

  Moreover, the control method demonstrated by said embodiment is realizable by executing the control program prepared beforehand by computers, such as a personal computer and a workstation. This control program can be distributed via a network such as the Internet. The control program can also be executed by being recorded on a computer-readable recording medium such as a hard disk, a flexible disk (FD), a CD-ROM, an MO, and a DVD and being read from the recording medium by the computer.

  According to at least one embodiment described above, high image quality and high substance discrimination ability can be realized.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

10 frame 13 X-ray detector 14 data acquisition circuit 14a FPGA
30 Console 37 Processing circuit 372 Preprocessing function 373 Reconfiguration processing function 377 Determination function

Claims (14)

A photon counting detector having a plurality of detection elements each composed of a scintillator and an optical sensor;
A setting unit that sets a driving voltage corresponding to the position of each scintillator in the photon counting detector at the time of photographing in an optical sensor corresponding to each scintillator;
An X-ray CT apparatus comprising:   The X-ray CT apparatus according to claim 1, wherein the setting unit sets a drive voltage based on an X-ray dose incident on each scintillator to an optical sensor corresponding to each scintillator.   The X-ray CT apparatus according to claim 2, wherein the setting unit sets a driving voltage based on an X-ray dose incident on each scintillator, which is estimated from a counting result of each detection element, to each photosensor.   The X-ray CT apparatus according to claim 2, wherein the setting unit sets a driving voltage based on an X-ray dose incident on each scintillator, which is estimated from information related to a body shape of the subject, to each optical sensor.   The setting unit sets a drive voltage larger than that of a photosensor corresponding to a scintillator having an incident X-ray dose equal to or greater than the threshold value to a photosensor corresponding to a scintillator having an incident X-ray dose less than the threshold value. X-ray CT apparatus as described in any one of -4.   The X-ray CT apparatus according to claim 1, wherein the setting unit sets a driving voltage corresponding to an imaging angle to each optical sensor.   The setting unit is disposed in the optical sensor of the detection element disposed in the first region that is the central portion in the channel direction of the photon counting detector, and in the second region that is the peripheral portion in the channel direction. The X-ray CT apparatus according to claim 1, wherein a driving voltage larger than that of the optical sensor of the detecting element is set.   The setting unit changes the range of the first region and the range of the second region according to the shooting angle, and the photo sensor of the detection element arranged in the first region after the change, The X-ray CT apparatus according to claim 7, wherein a driving voltage larger than that of the optical sensor of the detection element arranged in the second region after the change is set.   2. The X according to claim 1, wherein the setting unit sets a driving voltage in the current view to an optical sensor corresponding to each scintillator based on an X-ray dose incident on each scintillator in a past view before the current view. Line CT device.   The setting unit sets a view immediately before the current view as the past view, and sets a driving voltage in the current view to an optical sensor corresponding to each scintillator based on an X-ray dose incident on each scintillator in the past view. An X-ray CT apparatus according to claim 9.   The setting unit sets a driving voltage in a current view to an optical sensor corresponding to each scintillator based on an X-ray dose incident on each scintillator in a predetermined period of the past view period. X-ray CT apparatus described in 1.   12. The setting unit sets a driving voltage in a current view to an optical sensor corresponding to each scintillator based on an X-ray dose incident on each scintillator in a first half part or a second half part of the past view period. X-ray CT apparatus described in 1. A collection unit for collecting the counting results by the photon counting detector;
A correction unit for correcting the counting result;
A reconstruction processing unit that reconstructs an image based on the corrected count result;
The X-ray CT apparatus according to claim 1, further comprising:   The X-ray CT apparatus according to claim 1, wherein the optical sensor is an avalanche photodiode or a silicon photomultiplier.

Images