JP7152209B2 - X-ray CT device - Google Patents

Description

An embodiment of the present invention relates to an X-ray CT apparatus.

When the photon counting detector is configured as a surface detector, an ASIC (Application Specific Integrated Circuit) is installed in the immediate vicinity of the photon counting detector in order to measure the minute output current from the photon counting detector. Arranged densely. The ASIC generates heat depending on the count rate as it collects count results. Since this ASIC is arranged in the vicinity of the photon-counting detector, the heat generated by the ASIC is easily transferred to the photon-counting detector.

For this reason, a method has been proposed in which a heater is placed near the photon-counting detector and the output from the temperature sensor is used as a control signal to control the photon-counting detector to a constant temperature. . Also proposed is a method of controlling the temperature of the photon-counting detector by estimating the temperature from the dark current value from the photon-counting detector before scanning without using a temperature sensor.

U.S. Patent Application Publication No. 2015/0076357 U.S. Pat. No. 9,229,115 JP-A-2003-130961 JP-A-10-234722 U.S. Patent Application Publication No. 2013/0248729

A problem to be solved by the present invention is to provide an X-ray CT apparatus that can cope with local temperature changes of the detector.

An X-ray CT (Computed Tomography) apparatus according to an embodiment includes a photon counting detector, a calculator, and a controller. A photon-counting detector has a plurality of detection areas composed of a plurality of detection elements in the channel direction and the row direction, and outputs a detection signal corresponding to the number of incident photons. The calculator calculates the amount of heat generated in each detection area based on the detection signal corresponding to the incident photons detected in the detection area. The control unit determines a control amount based on the amount of heat generated in each detection area, and controls the temperature in the detection area using the determined control amount.

FIG. 1 is a block diagram showing a configuration example of an X-ray CT apparatus according to the first embodiment. FIG. 2 is a front view of the pedestal according to the first embodiment. FIG. 3 is a diagram for explaining an example of a detector according to the first embodiment; FIG. 4A is a diagram for explaining the structure of the detector according to the first embodiment; FIG. 4B is a diagram for explaining the structure of the detector according to the first embodiment; FIG. 5 is a block diagram illustrating a configuration example of an ASIC according to the first embodiment; FIG. 6 is a diagram for explaining the number of incident photons depending on the position of the detector. FIG. 7 is a flow chart showing the procedure of processing for reconstructing an X-ray CT image by the X-ray CT apparatus according to the first embodiment. FIG. 8 is a flow chart showing the procedure of temperature control processing by the X-ray CT apparatus according to the first embodiment. FIG. 9 is a diagram showing an example of information stored in first correspondence information according to the first embodiment. FIG. 10 is a diagram showing an example of information stored in second correspondence information according to the first embodiment. FIG. 11 is a diagram for explaining the first embodiment. FIG. 12 is a block diagram showing a configuration example of an X-ray CT apparatus according to the second embodiment. FIG. 13 is a flow chart showing the procedure of temperature control processing by the X-ray CT apparatus according to the second embodiment. FIG. 14 is a diagram illustrating an example of information stored in second correspondence information according to the second embodiment. FIG. 15 is a block diagram showing a configuration example of an X-ray CT apparatus according to the third embodiment. FIG. 16 is a flow chart showing the procedure of processing for reconstructing an X-ray CT image by the X-ray CT apparatus according to the third embodiment. FIG. 17 is a flow chart showing the procedure of correction amount calculation processing by the X-ray CT apparatus according to the third embodiment. FIG. 18 is a diagram showing an example of information stored in third correspondence information according to the third embodiment. FIG. 19 is a block diagram showing a configuration example of an X-ray CT apparatus according to the fourth embodiment. FIG. 20 is a diagram showing an example of information stored in fourth correspondence information according to the fourth embodiment. FIG. 21 is a diagram for explaining an example of the size of the detection area.

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

The X-ray CT apparatus described in the following embodiments is an apparatus capable of performing photon counting CT. That is, the X-ray CT apparatus described in the following embodiments counts the X-rays transmitted through the subject using a photon counting type detector instead of a conventional integrating type (current mode measurement type) detector. Thus, the apparatus can reconstruct X-ray CT image data with a high SN ratio. In principle, the contents described in one embodiment are similarly applied to other embodiments.

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

The gantry 10 is a device that irradiates the subject P with X-rays and collects data on the X-rays that have passed through the subject P. , a data acquisition circuit 14 , a rotating frame 15 , a gantry controller 16 and a temperature controller 17 . Further, in the gantry 10, as shown in FIG. 1, an orthogonal coordinate system consisting of X, Y and Z axes is defined. That is, the X-axis indicates the horizontal direction, the Y-axis indicates the vertical direction, and the Z-axis indicates the rotation center axis direction of the rotating frame 15 when the gantry 10 is not tilted.

FIG. 2 is a front view of the gantry 10 according to the first embodiment. As shown in FIG. 2, the rotating frame 15 supports the X-ray generator 12 and the detector 13 so as to face each other with the subject P interposed therebetween. It is an annular frame that rotates in a circular orbit at high speed.

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

Returning to FIG. 1, the X-ray tube 12a is a vacuum tube that receives a high voltage supply from the X-ray high voltage device 11 and irradiates thermal electrons from a cathode (sometimes called a filament) toward an anode (target). , and the subject P is irradiated with the X-ray beam as the rotating frame 15 rotates. That is, the X-ray tube 12a uses the high voltage supplied from the X-ray high voltage device 11 to generate X-rays.

Also, the X-ray tube 12a generates an X-ray beam that spreads with a fan angle and a cone angle. For example, under the control of the X-ray high-voltage device 11, the X-ray tube 12a continuously emits X-rays all around the subject P for full reconstruction, or half-reconfigurable exposure for half-reconstruction. It is possible to continuously irradiate X-rays in an 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 device 11 . The X-ray high-voltage device 11 can also modulate the intensity of X-rays emitted from the X-ray tube 12a. For example, the X-ray high-voltage device 11 increases the intensity of the X-rays emitted from the X-ray tube 12a at a specific tube position, and increases the intensity of the X-rays emitted from the X-ray tube 12a at ranges other than the specific tube position. Decrease the intensity of the emitted X-rays.

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

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

Note that the X-ray source of the X-ray generator 12 is not limited to the X-ray tube 12a. For example, instead of the X-ray tube 12a, the X-ray generator 12 includes a focus coil for focusing the electron beam generated from the electron gun, a deflection coil for electromagnetically deflecting the electron beam, and a deflected electron beam that surrounds the half circumference of the subject P and collides with it. and a target ring for generating X-rays.

The X-ray high-voltage device 11 is composed of electric circuits such as a transformer and a rectifier. It is composed of an X-ray control device for controlling the output voltage according to the X-rays to be emitted. The high voltage generator may be of a transformer type or an inverter type. For example, the X-ray high-voltage device 11 adjusts the X-ray dosage with which the subject P is irradiated by adjusting the tube voltage and tube current supplied to the X-ray tube 12a. Also, the X-ray high voltage device 11 is controlled by the scan control circuit 33 of the console 30 .

The gantry control device 16 includes a processing circuit configured by a CPU (Central Processing Unit) and the like, and drive mechanisms such as motors and actuators. The gantry controller 16 has a function of receiving an input signal from an input interface 31 attached to the console 30 or an input interface attached to the gantry 10 and controlling the operation of the gantry 10 . For example, the gantry controller 16 receives an input signal and rotates the rotating frame 15 to control the rotation of the X-ray tube 12a and the detector 13 on a circular orbit centered on the subject P, and control the rotation of the gantry 10. and control to operate the bed 20 and the top board 22 . The gantry controller 16 is controlled by the scan control circuit 33 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), the data acquisition circuit 14 starts acquiring data. output a view trigger signal indicating For example, when the total number of views in rotational imaging is 2400, the gantry controller 16 outputs a view trigger signal each time the X-ray tube 12a moves 0.15 degrees (=360/2400) on the circular orbit. .

Returning to FIG. 1, temperature controller 17 controls the temperature of detector 13 . For example, the temperature controller 17 controls the temperature of the detector 13 based on the control amount determined by the control circuit 147, which will be described later. Here, the temperature controller 17 is, for example, a thermoelectric conversion device such as a Peltier element. In such a case, the temperature controller 17 receives from the control circuit 147, for example, the polarity of the current and the magnitude of the current as the control amount.

The temperature controller 17 is not limited to a thermoelectric conversion device such as a Peltier element, and may be an air-cooled or water-cooled device as long as the temperature of the detector 13 can be controlled. In the case of an air-cooled system, the temperature controller 17 is, for example, a fan, and receives the number of revolutions of the fan from the control circuit 147 as a controlled variable. In the case of a water-cooled type, the temperature controller 17 is composed of cooling water and a radiator, for example, and receives from the control circuit 147 the amount of cooling air for cooling the radiator as a control amount.

The detector 13 is a photon-counting detector, and includes a plurality of X-ray detection elements (also referred to as "sensors" or simply "detection elements") for counting light derived from X-rays that have passed through the subject P. have For example, the X-ray detection element of the detector 13 according to the first embodiment is an indirect conversion type surface detector composed of a scintillator and a photosensor. Here, the optical sensor is, for example, SiPM (Silicon photomultiplier). The detector 13 may be a direct conversion type detector composed of a semiconductor device that converts incident X-rays into electrical signals. Also, the detector 13 is an example of a photon counting detector.

Each X-ray detection element of the detector 13 outputs an electrical signal (pulse) corresponding to the incident X-ray photon. An electric signal output by each X-ray detection element is also called a detection signal. That is, the detector 13 is composed of a plurality of detection elements and outputs a detection signal corresponding to the number of incident photons. The crest value of this electrical signal (pulse) has a correlation with the energy value of the X-ray photons. FIG. 3 is a diagram for explaining an example of the detector 13 according to the first embodiment.

In FIG. 3, the detector 13 shown in FIG. 2 is shown enlarged. FIG. 3 shows the detector 13 viewed from the Y-axis side. As shown in FIG. 3, the X-ray detection elements are two-dimensionally arranged on the surface of the detector 13 . For example, the X-ray detection element rows arranged in the channel direction (the X-axis direction in FIG. 3) are arranged in multiple rows along the body axis (row) direction of the subject P (the Z-axis direction shown in FIG. 3). there is In other words, the detector 13 comprises a plurality of detector elements in channel direction and column direction.

Further, the detector 13, which is a multi-row plane detector, has a plurality of detection areas composed of a plurality of detection elements. 4A and 4B are diagrams for explaining the structure of the detector 13 according to the first embodiment. In the example of FIG. 4A, the figure which looked at the detector 13 from the incident surface side is shown. Also, FIG. 4A shows an enlarged view of a region arranged on the upper left side of the detector 13 .

As shown in FIG. 4A, the detector 13 comprises multiple detection areas. In the example shown in FIG. 4A, four detection areas are illustrated with four columns and four channels as one unit. That is, in FIG. 4A, each sensing area includes 16 sensing elements. Further, in the detector 13 according to the first embodiment, a temperature controller 17 is provided for each detection area. That is, each temperature controller 17 controls the temperature of the corresponding detection area among the plurality of detection areas of the detector 13, which is a photon counting detector.

The example of FIG. 4B shows a view of the region enlarged in FIG. 4A viewed from the back side of the incident surface. An ASIC 140 , which will be described later, is arranged for each detection area on the back side of the incident surface of the detector 13 . In the example shown in FIG. 4A, the detection area has been described as a unit of 4 columns and 4 channels, but the number of detection elements included in the detection area is not limited to this, and can be arbitrarily changed. is. For example, the detection area may be a module with 16 rows and 6 channels as a unit.

Returning to FIG. 1, the data collection circuit 14 is an electric circuit having a function of collecting the counting result, which is the result of counting processing using the detection signal of the detector 13 . The data collection circuit 14 counts photons (X-ray photons) derived from X-rays emitted from the X-ray tube 12a and transmitted through the subject P, and collects the result of discriminating the energy of the counted photons as a count result. do. The data collection circuit 14 then transmits the counting result to the console 30 . The data acquisition circuit 14 is also called DAS (Data Acquisition System).

Further, for example, as shown in FIG. 1, the data collection circuit 14 includes an ASIC (Application Specific Integrated Circuit) 140, a calculation circuit 146, a control circuit 147, a first correspondence information storage circuit 148, and a second correspondence circuit. and an information storage circuit 149 . Here, when the detector 13 is configured as a surface detector, it is necessary to arrange the ASICs 140 in the very vicinity of the detector 13 at a high density in order to measure a minute output current from the detector 13 . FIG. 5 is a block diagram showing a configuration example of the ASIC 140 according to the first embodiment. Note that the ASIC 140 is an example of a computing unit.

As shown in FIG. 5, ASIC 140 couples to the sensing elements of detector 13 through a substrate. Here, the ASIC 140 is coupled via a substrate to multiple sensing elements included in, for example, the same sensing area. Each ASIC 140 also receives detection signals from a plurality of detection elements. Each ASIC 140 then collects the count results for each area. That is, the ASIC 140 calculates the count rate based on the detection signal corresponding to the incident photons detected in the detection area. In such a case, each ASIC 140 may receive detection signals from a plurality of detection elements in parallel, or may receive detection signals from a plurality of detection elements in a time division manner. Although only one ASIC 140 is shown in FIG. 5, a plurality of ASICs 140 may be mounted for each detection area. When multiple ASICs 140 are implemented in each detection area, each ASIC 140 in each area may receive detection signals from detection elements for each region in each area, or may detect signals from all detection elements in each area. A signal may be received. When receiving detection signals from the detection elements for each region in each area, the total value of the detection signals received by each ASIC 140 may be used as the counting result. The average value of the received detection signals may be used as the counting result.

Also, as shown in FIG. 5, the ASIC 140 has a charge amplifier 141, a waveform shaping circuit 143, a waveform discrimination circuit 144 and a counter 145. FIG. The charge amplifier 141 is an electric circuit having a function of integrating and amplifying charges collected in response to photons incident on the X-ray detection element and outputting the electric charge as a pulse signal. More specifically, charge amplifier 141 is an electronic circuit having an amplification function. The pulse signal output by the charge amplifier 141 has a wave height and area corresponding to the energy amount of photons. A waveform shaping circuit 143 is connected to the output side of the charge amplifier 141 .

The waveform shaping circuit 143 adjusts the frequency characteristics of the pulse signal output from the charge amplifier 141 and shapes the waveform of the pulse signal by applying gain and offset. A waveform discrimination circuit 144 is connected to the output side of the waveform shaping circuit 143 .

The waveform discriminating circuit 144 compares the wave height or area of the response pulse signal to the incident photon with preset thresholds corresponding to a plurality of energy bands to be discriminated, and outputs the result of the comparison with the thresholds to the subsequent counter 145 . It is an electric circuit that has the function of outputting to

The counter 145 is an electric circuit having a function of counting discrimination results of the response pulse signal waveform for each corresponding energy band and outputting the photon counting results to the preprocessing circuit 34 of the console 30 as digital data. More specifically, counter 145 is a digital circuit that processes numerical values, for example, by counting clock pulses.

Specifically, the counter 145 discriminates and counts each pulse output by the X-ray detection element, and counts the incident position (detection position) of the X-ray photon and the energy value of the X-ray photon as the count result. Collect for each phase of the tube 12a (tube phase). The counter 145 uses, for example, the position of the X-ray detection element that outputs the pulse used for counting as the incident position.

For example, the count results collected by the counter 145 are such that “at the tube phase “α1”, the count value of the photons in the energy discrimination region “E1<E≦E2” at the X-ray detection element at the incident position “P11” is “N1 and the count value of photons in the energy discrimination area "E2<E≦E3" is "N2". Alternatively, the counting result collected by the counter 145 is the total number of photons per unit time in the energy discrimination region “E1<E≦E2” at the X-ray detection element at the incident position “P11” at the tube phase “α1”. The numerical value is "n1", and the count value of photons per unit time in the energy discrimination region "E2<E≤E3" is "n2".

In this way, the X-ray detection element corresponding to one pixel of the detector 13 outputs the count results corresponding to a plurality of energy bands to the preprocessing circuit 34 as detection data. As a result, the image reconstruction circuit 36 generates an image using the calibrated detection signals of each detection element.

The data output from the data acquisition circuit 14 is referred to as detection data, and logarithmic conversion processing, offset correction processing, inter-channel sensitivity correction processing, inter-channel gain correction processing, pile-up correction processing, and response processing are performed on the detection data. Data that has undergone preprocessing such as function correction processing and beam hardening correction is referred to as raw data. Further, detection data and raw data are collectively referred to as projection data. Also, the calculation circuit 146, the control circuit 147, the first correspondence information storage circuit 148, and the second correspondence information storage circuit 149 will be described later.

Returning to FIG. 1 , the bed 20 is a device on which the subject P is placed, and has a top plate 22 and a bed driving device 21 . The tabletop 22 is a board on which the subject P is placed, and the bed driving device 21 moves the tabletop 22 in the Z-axis direction to move the subject P into the rotating frame 15 . The bed driving device 21 can also move the top plate 22 in the X-axis direction.

The method of moving the tabletop may be to move only the tabletop 22 or to move the entire base of the bed 20 . Also, in the case of standing CT, a method of moving a patient moving mechanism corresponding to the top board 22 may be used.

Note that the gantry 10 performs helical scanning in which the subject P is spirally scanned by, for example, rotating the rotating frame 15 while moving the top plate 22 . Alternatively, after moving the tabletop 22, the gantry 10 rotates the rotation frame 15 while fixing the position of the subject P to perform conventional scanning in which the subject P is scanned in a circular orbit. In the following embodiment, it is assumed that the change in the relative position between the pedestal 10 and the top plate 22 is realized by controlling the top plate 22, but the embodiment is not limited to this. For example, if the gantry 10 is self-propelled, the relative position between the gantry 10 and the top plate 22 may be changed by controlling the movement of the gantry 10 . Further, by controlling the traveling of the gantry 10 and the top plate 22, the change in the relative position between the gantry 10 and the top plate 22 may be realized.

The console 30 is a device that receives an operator's operation of the X-ray CT apparatus and reconstructs X-ray CT image data using the counting results collected by the gantry 10 . The console 30 includes, as shown in FIG. and a system control circuit 38 .

The input interface 31 has a mouse, a keyboard, etc., which are used by the operator of the X-ray CT apparatus to input various instructions and various settings, and transfers instructions and setting information received from the operator to the system control circuit 38 . For example, the input interface 31 receives, from the operator, reconstruction conditions for reconstructing X-ray CT image data, image processing conditions for X-ray CT image data, and the like. Further, for example, the input interface 31 receives an instruction from the operator to perform temperature control processing of the X-ray detection element. The input interface 31 instructs the scan control circuit 33 via the system control circuit 38 to reconstruct X-ray CT image data and perform temperature control processing.

The display 32 is a monitor referred to by the operator, and under the control of the system control circuit 38, displays the X-ray CT image data to the operator, and receives various instructions from the operator via the input interface 31. It displays a GUI (Graphical User Interface) for accepting settings and the like.

The scan control circuit 33 controls the operations of the X-ray high voltage device 11, the detector 13, the gantry control device 16, the data acquisition circuit 14, and the bed drive device 21 under the control of a system control circuit 38, which will be described later. , is an electric circuit having a function of controlling collection processing of counting results in the gantry 10 .

The preprocessing circuit 34 performs logarithmic conversion processing, offset correction processing, inter-channel sensitivity correction processing, inter-channel gain correction processing, pile-up correction processing, and response function correction processing on the count results transmitted from the data acquisition circuit 14. , beam hardening correction and other preprocessing to generate raw data.

The projection data storage circuit 35 is, for example, a NAND (Not AND) type flash memory or HDD (Hard Disk Drive), and stores the projection data generated by the preprocessing circuit 34 . That is, the projection data storage circuit 35 stores projection data for reconstructing X-ray CT image data.

The image reconstruction circuit 36 performs reconstruction processing using the filtered back projection method, the iterative reconstruction method, etc. on the projection data generated by the preprocessing circuit 34 to generate X-ray CT image data. do. Note that the image reconstruction circuit 36 is an example of a reconstruction unit.

The image reconstruction circuit 36 stores the reconstructed X-ray CT image data in the image storage circuit 37 . X-ray CT image data reconstructed from data containing all energy information by adding information of all bins pixel by pixel is also called a "base image".

Here, the projection data generated from the counting results obtained by the photon counting CT contains information on the energy of X-rays attenuated by passing through the subject P. FIG. Therefore, the image reconstruction circuit 36 can reconstruct, for example, X-ray CT image data of specific energy components. Also, the image reconstruction circuit 36 can reconstruct, for example, X-ray CT image data of each of a plurality of energy components.

Further, the image reconstruction circuit 36 assigns, for example, a color tone according 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. generated image data. In addition, the image reconstruction circuit 36 can generate image data that enables identification of the substance, for example, using the substance-specific K absorption edge. Other image data generated by the image reconstruction circuit 36 include monochromatic X-ray image data, density image data, effective atomic number image data, and the like.

Further, as an application of X-ray CT, there is a technique of discriminating the type, abundance, density, etc. of substances contained in the subject P by utilizing the fact that X-ray absorption characteristics differ for each substance. This is called material discrimination. For example, image reconstruction circuitry 36 performs material discrimination on the projection data to obtain material discrimination information. Then, the image reconstruction circuit 36 reconstructs a material discrimination image using the material discrimination information that is the result of the material discrimination.

The image reconstruction circuit 36 can apply a full-scan reconstruction method and a half-scan reconstruction method to reconstruct a CT image. For example, the image reconstruction circuit 36 requires projection data for 360 degrees around the object P in the full scan reconstruction method. Further, the image reconstruction circuit 36 requires projection data for 180 degrees plus the fan angle in the half-scan reconstruction method. To simplify the explanation, the image reconstruction circuit 36 uses a full-scan reconstruction method for reconstruction using projection data for 360 degrees around the subject P. FIG.

The system control circuit 38 is an electric circuit having a function of controlling the entire X-ray CT apparatus by controlling the operations of the gantry 10, the bed 20 and the console 30. FIG. Specifically, the system control circuit 38 controls the CT scan performed on the gantry 10 by controlling the scan control circuit 33 . Further, the system control circuit 38 controls image reconstruction processing and image generation processing in the console 30 by controlling the preprocessing circuit 34 and the image reconstruction circuit 36 . The system control circuit 38 also controls the display 32 to display various image data stored in the image storage circuit 37 . The image storage circuit 37 is, for example, a NAND flash memory or HDD, and stores various image data.

The overall configuration of the X-ray CT apparatus according to the first embodiment has been described above. With this configuration, the X-ray CT apparatus according to the first embodiment reconstructs X-ray CT image data using a photon counting type detector.

By the way, the ASIC 140 generates heat according to the counting rate when collecting counting results. Since the ASIC 140 is arranged in the vicinity of the detector 13 , the heat generated by the ASIC 140 is easily transmitted to the detector 13 . Here, when a large number of detectors 13 are configured as surface detectors, the number of incident photons differs depending on the position of the detectors 13 . FIG. 6 is a diagram for explaining the number of incident photons depending on the position of the detector 13. In FIG. FIG. 6 shows a subject P, and an X-ray tube 12a and a detector 13 rotating on a circular orbit centered on the subject P. FIG.

The cross section of the subject P is not circular but elliptical. Therefore, as shown in FIG. 6, a large amount of photons enter the periphery H of the detector 13 because the amount of light transmitted through the subject P is small. On the other hand, at the central portion L of the detector 13, a small amount of photons enter because the amount of transmission through the object P is large. Therefore, the ASIC 140 coupled to the peripheral portion H of the detector 13 has a high counting rate and tends to become hot. On the other hand, the ASIC 140 coupled to the central portion L of the detector 13 has a low count rate and does not easily heat up. That is, the counting rate differs among the ASICs 140 according to the position of the detection area arranged in the detector 13 . For this reason, the amount of heat transmitted from the ASIC 140 differs between local portions of the detector 13 .

Also, the characteristics of the detector 13 are highly dependent on temperature. The correspondence between the ambient temperature and the dark count rate value is such that the dark count rate increases as the ambient temperature increases. Further, regarding the correspondence relationship between the ambient temperature and the multiplication factor, the multiplication factor decreases as the ambient temperature rises. Therefore, the heat generated by the ASIC 140 affects the characteristics of the detector 13 . For this reason, local temperature control of the detector 13 is desired.

Therefore, the X-ray CT apparatus according to the first embodiment responds to local temperature changes of the detector 13 by executing temperature control processing. For example, the X-ray CT apparatus according to the first embodiment calculates the calorific value for each detection area on the detector 13 . Then, the X-ray CT apparatus according to the first embodiment determines the control amount based on the amount of heat generated, and uses the determined control amount to control the temperature of each detection area of the photon counting detector. Such temperature control processing by the X-ray CT apparatus is realized by the calculation circuit 146 and the control circuit 147 using the first correspondence information storage circuit 148 and the second correspondence information storage circuit 149 . The calculation circuit 146 and the control circuit 147 according to the first embodiment will be described in detail below with reference to FIGS. 7 to 10. FIG.

The first correspondence information storage circuit 148 is, for example, a NAND flash memory or HDD, and stores the first correspondence information. FIG. 9 is a diagram showing an example of information stored in first correspondence information according to the first embodiment. As shown in FIG. 9, the first correspondence information stores information in which "count rate" and "calorific value" are associated with each other. Note that the first correspondence information is generated by estimating in advance the count rate for each view from each detection area of the detector 13 output from the ASIC 140 and the amount of heat generated by the ASIC 140 by measurement or simulation.

Here, the count rate for each view is described as being the average value of detection signals from a plurality of detection elements included in each detection area. Note that the count rate is not limited to the average value, and may be, for example, the maximum value or minimum value of detection signals from a plurality of detection elements.

"Count rate" in the first correspondence information indicates the count result in the view. For example, "count rate" stores information such as "C<C1" indicating that it is less than C1, and "C1≤C<C2" indicating that it is greater than or equal to C1 and less than C2. Also, the "calorific value" in the first correspondence information indicates the calorific value of the ASIC 140 based on the count rate. For example, information such as "Q1" and "Q2" is stored in the "calorific value".

For example, the first correspondence information shown in FIG. 9 indicates that the heat generation amount of the ASIC 140 is Q1 when the count rate is less than C1, It indicates that the calorific value is Q2.

The second correspondence information storage circuit 149 is, for example, a NAND flash memory or HDD, and stores the second correspondence information. FIG. 10 is a diagram showing an example of information stored in second correspondence information according to the first embodiment. As shown in FIG. 10, the second correspondence information stores information in which "detection area ID", "calorific value" and "control amount" are associated with each other. The second correspondence information is generated by estimating or measuring in advance the temperature change that the amount of heat generated by the ASIC 140 gives to the detector 13 .

“Detection area ID” in the second correspondence information indicates an identifier for specifying the position of the detection area in the photon counting detector 13 . For example, "detection area ID" stores information such as "A1" and "A2".

The "calorific value" in the second correspondence information is the same as the "calorific value" in the first correspondence information. Also, the "controlled amount" in the second correspondence information indicates the controlled amount of the temperature controller 17 based on the amount of heat generated. For example, "control amount" stores information such as "R1" and "R2".

For example, the second correspondence information shown in FIG. 10 indicates that the control amount of the temperature controller 17 is R1 when the heat generation amount of the detection area whose identifier is "A1" is Q1. indicates that the control amount of the temperature controller 17 is R2 when the calorific value of the detection area whose identifier is "A1" is Q2.

FIG. 7 is a flow chart showing the procedure of processing for reconstructing an X-ray CT image by the X-ray CT apparatus according to the first embodiment. For example, the processing shown in FIG. 7 is executed when the input interface 31 receives an instruction to perform actual imaging from the operator and the received instruction is transferred to the system control circuit 38 . Step S<b>1 in FIG. 7 is a step implemented by the scan control circuit 33 . In step S1, the scan control circuit 33 controls the X-ray tube 12a to emit X-rays, thereby causing the data acquisition circuit 14 to start collecting count results. Step S<b>2 is implemented by the calculation circuit 146 and the control circuit 147 . In step S2, the calculation circuit 146 and the control circuit 147 execute temperature control processing. Details of step S2 will be described later with reference to FIG.

Step S<b>3 is a step implemented by the image reconstruction circuit 36 . In step S3, the image reconstruction circuit 36 reconstructs X-ray CT image data based on the collected counting results. In other words, image reconstruction circuit 36 reconstructs an image using projection data based on the collected detection signals. Step S<b>4 is a step implemented by the system control circuit 38 . At step S4, the system control circuit 38 causes the display 32 to display the reconstructed X-ray CT image.

FIG. 8 is a flow chart showing the procedure of temperature control processing by the X-ray CT apparatus according to the first embodiment. The processing procedure shown in FIG. 8 corresponds to the processing of step S2 shown in FIG. Steps S101 to S103 are steps implemented by the calculation circuit 146 . In step S101, the calculation circuit 146 determines whether or not a view trigger signal has been received. Here, when the calculation circuit 146 determines that the view trigger signal has been received (step S101, Yes), the process proceeds to step S102. On the other hand, if the calculation circuit 146 does not determine that the view trigger signal has been received (step S101, No), it repeats the determination process of step S101.

At step S102, the calculation circuit 146 acquires the count rate for each detection area. For example, the calculation circuit 146 acquires the count result of the ASIC 140 for each view in units of detection areas. The calculation circuit 146 acquires, for example, the average value of detection signals from a plurality of detection elements within the detection area as the count rate for each view. Note that the calculation circuit 146 may acquire, for example, the maximum value or the minimum value of the detection signals from a plurality of detection elements within the detection area as the count rate for each view.

Then, in step S<b>103 , the calculation circuit 146 calculates the calorific value for each detection area in the detector 13 . For example, the calculation circuit 146 uses the first correspondence information shown in FIG. 9 to specify the amount of heat generated corresponding to the count rate acquired in step S102 for each view in units of detection areas.

For example, the calculation circuit 146 uses the first correspondence information shown in FIG. If less, identify the heat output of the ASIC 140 as Q2. That is, the calculation circuit 146 calculates the amount of heat generated for each detection area using the counting result based on the detection signal from each detection element in each detection area. Thus, the calculation circuit 146 calculates the amount of heat generated for each detection area based on the count rate based on the detection signal. That is, the calculation circuit 146 calculates the amount of heat generated for each detection area based on the detection signal corresponding to the incident photons detected in each detection area. Note that the calculation circuit 146 is an example of a calculation unit.

Steps S104 to S106 are steps implemented by the control circuit 147 . In step S104, the control circuit 147 determines the control amount from the amount of heat generated. For example, the control circuit 147 uses the second correspondence information shown in FIG. 10 to identify the control amount corresponding to the amount of heat generation identified in step S103 for each detection area and for each view. In other words, the control circuit 147 determines the control amount based on the amount of heat generated for each detection area, and controls the temperature in the detection area using the determined control amount. Note that the control circuit 147 is an example of a control unit.

Here, an air-cooling fan is provided near the DAS for controlling the temperature of the entire DAS by exhausting the heat of the DAS. Here, when only one air cooling fan is provided, the efficiency of exhaust heat may differ between near and far from the air cooling fan. In this way, when the efficiency of exhaust heat differs between the ASIC 140 in the central part of the detector 13 and the ASIC 140 in the peripheral part due to the number of air cooling fans provided near the DAS, the ASIC 140 in the central part and the peripheral part of the detector 13 is different. Even if the calorific value is the same, a different amount of control is required. Therefore, a case will be described below in which the number of air cooling fans provided near the DAS is one and the ASICs 140 have different heat exhaust efficiencies.

In such a case, the control circuit 147 determines the control amount according to the position of the detection area in the photon counting detector 13 . For example, the control circuit 147 controls the temperature controller 17 using the second correspondence information shown in FIG. If the amount is specified as R1 and the amount of heat generated in the detection area with the identifier of the detection area "A1" is Q2, the control amount of the temperature controller 17 is specified as R2. Further, the control circuit 147 uses the second correspondence information shown in FIG. to be specified. That is, the control circuit 147 determines the control amount based on the amount of heat generated.

At step S<b>105 , the control circuit 147 controls the temperature controller 17 . For example, the control circuit 147 instructs the temperature controller 17 to set the control amount specified in step S104. In other words, the control circuit 147 controls the temperature of each detection area of the detector 13 using the determined control amount. Here, the control circuit 147 instructs each temperature controller 17 to control the amount of each view.

In step S106, the control circuit 147 determines whether or not the end of photographing has been accepted. Here, when the control circuit 147 determines that the end of photographing has been accepted (step S106, Yes), it ends the temperature control process. On the other hand, when the control circuit 147 does not determine that the end of photographing has been accepted (step S106, No), the process proceeds to step S101.

As described above, in the first embodiment, the control amount for compensating the temperature rise in each detection area of the detector 13 is determined from the output value (count rate) of the ASIC 140 during scanning, and the temperature controller 17 is operated. . In other words, in the first embodiment, the calorific value is calculated for each detection area in the photon counting detector, and the temperature of each detection area of the photon counting detector is adjusted using the control amount determined based on the calorific value. Control. For example, in the first embodiment, a temperature controller 17 is arranged for each detection area. This makes it possible to reduce the scale of the area to be controlled, rather than coping with temperature changes with the entire detector 13 . By reducing the scale of the region to be controlled in this way, it becomes easier to predict temperature changes. As a result, according to the first embodiment, local temperature changes of the detector 13 can be dealt with.

By the way, as an alternative method for coping with temperature changes, it is conceivable to combine temperature measurement by a temperature sensor and a temperature controller (cooler/heater), and control the temperature controller by feedback from the temperature sensor. In such a case, a temperature sensor is arranged near the detector 13 and the temperature of the detector 13 is controlled from the output value of the temperature sensor. However, this alternative method results in placing a large number of temperature sensors on the detector 13, thus increasing the mounting and signal lines of the temperature sensors. Therefore, the alternative method has implementation difficulties.

On the other hand, the first embodiment responds to local temperature changes of the detector 13 without using a temperature sensor. That is, according to the first embodiment, it is not necessary to arrange a large number of temperature sensors. Therefore, according to the first embodiment, it is possible to deal with local temperature changes of the detector 13 while avoiding mounting difficulties.

Also, in the alternative method, the control can only be started after the temperature sensor detects the temperature rise. In this case, the control amount tends to overshoot (undershoot). On the other hand, in the first embodiment, the amount of heat generated for each detection area is calculated using the counting result based on the detection signal from each detection element in each detection area. As a result, according to the first embodiment, it is possible to improve the ability of the detector 13 to follow temperature changes. FIG. 11 is a diagram for explaining the first embodiment.

In FIG. 11, the horizontal axis indicates time, and the vertical axis indicates the count rate and the temperature of the detector 13, respectively. Here, for example, in an alternative method, temperature is measured by a temperature sensor, and control of the temperature controller 17 is started at time T2 when the temperature of the detector 13 begins to rise. That is, in the alternative method, control of the temperature controller 17 is started after the temperature sensor detects a temperature rise. On the other hand, according to the first embodiment, control of the temperature controller 17 is started at time T1 when the count rate begins to rise. That is, in the first embodiment, the control of the temperature controller 17 is started before the temperature sensor detects the temperature rise. As a result, in the temperature control method according to the first embodiment, it is possible to start controlling the temperature controller 17 earlier by time ΔT (T2-T1) than in the alternative method. become. As a result, according to the first embodiment, it is possible to prevent the temperature rise of the detector 13 more efficiently before the temperature of the detector 13 starts to rise. In other words, according to the first embodiment, overshoot (undershoot) of the control amount can be suppressed.

Further, the detector 13 may have a heat insulating structure between detection areas. For example, a layer of high thermal conductivity is sandwiched between the ASIC 140 and the detector 13 to prevent heat from concentrating at a specific point within the detection area. In such a case, the ground layer or power supply layer of the circuit is used as the layer with high thermal conductivity. It should be noted that having such a heat insulating structure is effective when the detection area is a module.

(Second embodiment)
In the second embodiment, a case will be described in which the temperature in the vicinity of the detector 13 is further taken into consideration when the temperature control process is performed. FIG. 12 is a block diagram showing a configuration example of an X-ray CT apparatus according to the second embodiment. In addition, in FIG. 12, the same reference numerals are assigned to the components having the same functions as those shown in FIG. 1, and detailed description thereof will be omitted. As shown in FIG. 12, the X-ray CT apparatus according to the second embodiment has a pedestal 10a, a bed 20, and a console 30. As shown in FIG.

The pedestal 10a has the same configuration as the pedestal 10 shown in FIG. 1 except that it further has a temperature sensor 18 and the configuration of the data collection circuit 14a is partially different from the configuration of the data collection circuit 14 according to the first embodiment. It is the same. Therefore, only the configuration of the temperature sensor 18 according to the second embodiment and the configuration of the data collection circuit 14a according to the second embodiment will be described below.

A temperature sensor 18 is arranged near the detector 13 and detects the temperature near the detector 13 . The data collection circuit 14a has an ASIC 140, a calculation circuit 146, a control circuit 147a, a first correspondence information storage circuit 148 and a second correspondence information storage circuit 149a. The configuration of the ASIC 140, the calculation circuit 146, and the first correspondence information storage circuit 148 included in the data collection circuit 14a is similar to that of the ASIC 140, the calculation circuit 146, and the first correspondence information storage circuit 148 included in the data collection circuit 14. is the same as the configuration of

The second correspondence information storage circuit 149a is, for example, a NAND flash memory or HDD, and stores the second correspondence information. FIG. 14 is a diagram illustrating an example of information stored in second correspondence information according to the second embodiment. As shown in FIG. 14, the second correspondence information stores information in which "detection area ID", "calorific value", "external temperature" and "control amount" are associated with each other. The "detection area ID" in the second correspondence information is the same as the "detection area ID" in the second correspondence information shown in FIG. The "calorific value" in the second correspondence information is the same as the "calorific value" in the first correspondence information shown in FIG. The second correspondence information is generated by estimating or measuring in advance the temperature change that the amount of heat generated by the ASIC 140 gives to the detector 13, taking into consideration the influence of the difference in the external temperature.

Also, the “external temperature” in the second correspondence information indicates the temperature near the detector 13 acquired from the temperature sensor 18 . For example, the "external temperature" includes "T<T1" indicating that the temperature near the detector 13 is less than T1, or "T1≤T <T2” and other information is stored.

"Controlled amount" in the second correspondence information indicates the controlled amount of the temperature controller 17 based on the amount of heat generated and the temperature near the detector 13. FIG. For example, "control amount" stores information such as "R11" and "R12".

As an example, the second correspondence information shown in FIG. 14 indicates that the amount of heat generated in the detection area having the detection area identifier "A1" is Q1, and the temperature near the detector 13 is T1 or more and less than T2. , indicates that the control amount of the temperature controller 17 is R12, the amount of heat generated in the detection area whose identifier is "A1" is Q2, and the temperature in the vicinity of the detector 13 is T2 or higher, the temperature This indicates that the controlled variable of the controller 17 is R23.

The control circuit 147a uses the amount of heat generated and the temperature in the vicinity of the photon-counting detector 13 obtained from the temperature sensor 18 to determine the control amount. Then, the control circuit 147a controls the temperature of each detection area of the detector 13 using the determined control amount.

Next, a procedure of processing by the X-ray CT apparatus according to the second embodiment will be described. The procedure for reconstructing an X-ray CT image by the X-ray CT apparatus according to the second embodiment is similar to that of the first embodiment shown in FIG. 7, except for the details of the process in step S2. This is the same as the procedure for reconstructing an X-ray CT image by such an X-ray CT apparatus. Therefore, in the second embodiment, only the procedure of temperature control processing will be described. FIG. 13 is a flow chart showing the procedure of temperature control processing by the X-ray CT apparatus according to the second embodiment.

The processing procedure shown in FIG. 13 corresponds to the processing of step S2 shown in FIG. Steps S201 to S203 are steps implemented by the calculation circuit 146 . The processing from step S201 to step S203 corresponds to the processing from step S101 to step S103 shown in FIG.

Steps S204 to S207 are steps implemented by the control circuit 147a. In step S<b>204 , the control circuit 147 a obtains the temperature from the temperature sensor 18 . At step S205, the control circuit 147a calculates the control amount from the amount of heat generated and the temperature. For example, the control circuit 147a uses the second correspondence information shown in FIG. 14 to specify the control amount corresponding to the heat generation amount specified in step S203 and the temperature acquired in step S204 for each detection area and for each view. do. In other words, the control circuit 147a uses the amount of heat generated for each detection area and the temperature near the photon counting detector 13 obtained from the temperature sensor 18 to determine the control amount.

For example, the control circuit 147a uses the second correspondence information shown in FIG. When T1 or more and less than T2, the control amount of the temperature controller 17 is identified as R12, the heat generation amount of the detection area with the detection area identifier "A1" is Q2, and the temperature near the detector 13 is If it is equal to or greater than T2, the control amount of the temperature controller 17 is identified as R23. That is, the control circuit 147a uses the amount of heat generated and the temperature near the detector 13 obtained from the temperature sensor 18 to determine the control amount.

At step S<b>206 , the control circuit 147 a controls the temperature controller 17 . For example, the control circuit 147a instructs the temperature controller 17 to set the control amount specified in step S205. Here, the control circuit 147a instructs each temperature controller 17 to control the amount of each view.

In step S207, the control circuit 147a determines whether or not the end of imaging has been accepted. Here, when the control circuit 147a determines that the end of photographing has been accepted (step S207, Yes), it ends the temperature control process. On the other hand, when the control circuit 147a does not determine that the end of imaging has been received (step S207, No), the process proceeds to step S201.

As described above, in the second embodiment, the X-ray CT apparatus detects the temperature rise in each detection area of the detector 13 from the output value (count rate) of the ASIC 140 during scanning and the temperature near the detector 13. is determined, and the temperature controller 17 is operated. That is, in the second embodiment, temperature control processing is performed by further considering the temperature in the vicinity of the detector 13 . Thus, according to the second embodiment, it becomes possible to more accurately respond to local temperature changes of the detector 13 .

(Third embodiment)
In the third embodiment, a case will be described in which an image is reconstructed by correcting the effect of the temperature change of the detector 13 on the detector characteristics. FIG. 15 is a block diagram showing a configuration example of an X-ray CT apparatus according to the third embodiment. In addition, in FIG. 15, the same reference numerals are assigned to components having the same functions as those shown in FIG. 1, and detailed description thereof will be omitted. As shown in FIG. 15, the X-ray CT apparatus according to the third embodiment has a pedestal 10b, a bed 20, and a console 30. As shown in FIG.

The pedestal 10b has the same configuration as the pedestal 10 shown in FIG. 1, except that the configuration of the data acquisition circuit 14b is partially different from the configuration of the data acquisition circuit 14 according to the first embodiment. Therefore, only the configuration of the data collection circuit 14b according to the third embodiment will be described below.

The data collection circuit 14b includes an ASIC 140, a calculation circuit 146, a control circuit 147, a first correspondence information storage circuit 148, a second correspondence information storage circuit 149, a correction amount calculation circuit 150, a correction circuit 151, and a third correspondence information storage circuit 152 . The configuration of the ASIC 140, the calculation circuit 146, the control circuit 147, the first correspondence information storage circuit 148, and the second correspondence information storage circuit 149, which the data collection circuit 14b has, is similar to that of the ASIC 140, the calculation circuit 149, and the data collection circuit 14. The configuration is the same as that of the circuit 146 , the control circuit 147 , the first correspondence information storage circuit 148 and the second correspondence information storage circuit 149 .

The third correspondence information storage circuit 152 is, for example, a NAND flash memory or HDD, and stores the third correspondence information. FIG. 18 is a diagram showing an example of information stored in third correspondence information according to the third embodiment. As shown in FIG. 18, the third correspondence information stores information in which the "variation amount of count rate", the "control amount", and the "correction amount" are associated with each other. It should be noted that the third correspondence information is generated by estimating or measuring in advance the temperature change given to the detector 13 by the amount of heat generated by the ASIC 140 and the characteristic change of the detector 13 due to the temperature change.

"Amount of change in count rate" in the third correspondence information indicates the difference between the count result in the current view and the count result in the previous view. For example, the "variation amount of count rate" stores information such as "ΔC<C11" indicating that the difference is less than C11, and "C11≦ΔC<C12" indicating that the difference is greater than or equal to C11 and less than C12. be done.

Also, the "control amount" in the third correspondence information indicates the control amount of the temperature controller 17 specified from the count rate of the previous view. For example, "control amount" stores information such as "R111" and "R112".

Also, the "correction amount" in the third correspondence information indicates the correction amount of the counting result based on the amount of change in the count rate. For example, "correction amount" stores information such as "α1" and "α2".

As an example, the third correspondence information shown in FIG. 18 indicates that when the amount of change in the count rate is less than C11 and the control amount of the temperature controller 17 is R111, the correction amount is α1, When the change amount of the count rate is less than C11 and the control amount of the temperature controller 17 is R113, it indicates that the correction amount is α3.

A correction amount calculation circuit 150 calculates a correction amount according to the temperature change of the detector 13 . Note that the correction amount calculation circuit 150 is an example of a correction amount calculation unit. The correction circuit 151 corrects the detection signal output from the detector 13 using the correction amount. Note that the correction circuit 151 is an example of a correction unit.

Next, a procedure of processing for reconstructing an X-ray CT image by the X-ray CT apparatus according to the third embodiment will be described. FIG. 16 is a flow chart showing the procedure of processing for reconstructing an X-ray CT image by the X-ray CT apparatus according to the third embodiment. Step S<b>301 in FIG. 16 is a step implemented by the scan control circuit 33 . In step S301, the scan control circuit 33 controls the X-ray tube 12a to emit X-rays, thereby causing the data acquisition circuit 14b to start collecting the count results.

Steps S302 and S303 are executed in parallel following step S301. Step S<b>302 is a step implemented by the calculation circuit 146 and the control circuit 147 . In step S302, the calculation circuit 146 and the control circuit 147 execute temperature control processing. Note that the processing procedure of step S302 is the same as the processing procedure described with reference to FIG. 8, for example.

Step S<b>303 is a step implemented by the correction amount calculation circuit 150 . In step S303, the correction amount calculation circuit 150 executes correction amount calculation processing. Details of step S303 will be described with reference to FIG.

FIG. 17 is a flow chart showing the procedure of correction amount calculation processing by the X-ray CT apparatus according to the third embodiment. The processing procedure shown in FIG. 17 corresponds to the processing of step S303 shown in FIG. Steps S401 to S407 are steps realized by the correction amount calculation circuit 150 .

In step S401, the correction amount calculation circuit 150 determines whether or not a view trigger signal has been received. Here, when the correction amount calculation circuit 150 determines that the view trigger signal has been received (step S401, Yes), the process proceeds to step S402. On the other hand, if the correction amount calculation circuit 150 does not determine that the view trigger signal has been received (step S401, No), it repeats the determination process of step S401.

In step S402, the correction amount calculation circuit 150 acquires the count rate for each detection area. For example, the correction amount calculation circuit 150 acquires the count result of the ASIC 140 for each view in units of detection areas. In step S403, the correction amount calculation circuit 150 calculates the amount of change in the count rate. For example, the correction amount calculation circuit 150 calculates the difference between the count rate obtained in the current view and the count rate obtained in the previous view.

In step S404, the correction amount calculation circuit 150 acquires the control amount. For example, the correction amount calculation circuit 150 refers to the first correspondence information and the second correspondence information and acquires the control amount in the previous view from the count rate of the previous view.

In step S405, the correction amount calculation circuit 150 calculates the correction amount from the change amount of the count rate and the control amount. For example, the correction amount calculation circuit 150 calculates the correction amount using the count rate change amount calculated in step S403, the control amount acquired in step S404, and the third correspondence information shown in FIG. That is, the correction amount calculation circuit 150 estimates the temperature change of the detector 13 and calculates the correction amount based on the history of count results for each view based on the detection signal from each detection element in each detection area and the control amount. calculate.

For example, the correction amount calculation circuit 150 uses the third correspondence information shown in FIG. If the amount is specified as α1, the amount of change in the count rate is less than C11, and the control amount of the temperature controller 17 is R113, the correction amount is specified as α3. For example, the correction amount calculation circuit 150 estimates the dark current value as the correction value from the count rate for each view. Alternatively, the correction amount calculation circuit 150 estimates the gain value of each pixel as the correction value from the count rate for each view.

Return to FIG. In step S406, the correction amount calculation circuit 150 associates and stores the current view number, the count result in the current view, and the correction amount calculated in step S405.

In step S407, the correction amount calculation circuit 150 determines whether or not the end of shooting has been received. Here, if the correction amount calculation circuit 150 determines that the end of shooting has been accepted (step S407, Yes), it ends the correction amount calculation process. On the other hand, when the correction amount calculation circuit 150 does not determine that the end of shooting has been received (step S407, No), the process proceeds to step S401.

Return to FIG. Step S<b>304 is a step implemented by the correction circuit 151 . In step S304, the correction circuit 151 corrects the counting result using the correction amount calculated in step S303. For example, the correction circuit 151 corrects the counting result using the correction amount stored in association with the counting result. For example, the correction circuit 151 corrects the counting result using the dark current value estimated from the count rate for each view. Alternatively, the correction circuit 151 corrects the counting result using the gain value of each pixel estimated from the count rate for each view.

Step S<b>305 is a step implemented by the image reconstruction circuit 36 . In step S305, the image reconstruction circuit 36 reconstructs the X-ray CT image data based on the counting result corrected in step S304. In other words, the image reconstruction circuit 36 reconstructs an image using projection data based on the corrected detection signals. Step S<b>306 is a step implemented by the system control circuit 38 . At step S306, the system control circuit 38 causes the display 32 to display the reconstructed X-ray CT image.

In the third embodiment, the temperature change of the detector 13 is estimated from the count rate history for each view, and the characteristic change corresponding to the estimated temperature change is calculated as the correction amount. That is, in the third embodiment, the counting result is further corrected while coping with local temperature changes of the detector 13 . As a result, according to the third embodiment, it becomes possible to reconstruct a more accurate image. In the third embodiment, the case of estimating the temperature change from the history of the current view and the previous view has been described, but the embodiment is not limited to this. For example, the temperature change may be estimated from the history of the current view, the previous view, two views before, and three views before.

(Modification of the third embodiment)
In the above-described third embodiment, the correction amount calculation circuit 150 calculates the temperature change of the detector 13 based on the history of count results for each view based on the signal from each detection element in each detection area and the control amount. The description has been given assuming that the correction amount is calculated by estimating. However, embodiments are not so limited. For example, if the X-ray CT apparatus has a temperature sensor, the temperature sensor may be used to detect temperature changes, the detector characteristic changes may be estimated from the detected temperature changes, and the correction values may be calculated.

More specifically, in the modification of the third embodiment, information that associates "temperature change" with "correction amount" is stored as the third correspondence information. Note that the temperature change is, for example, the difference between the temperature detected by the temperature sensor in the current view and the temperature detected by the temperature sensor in the previous view. In such a case, the correction amount calculation circuit 150 calculates the correction amount corresponding to the temperature change. Then, the correction circuit 151 corrects the counting result using the correction amount.

Thus, the correction amount calculation circuit 150 estimates the temperature change of the detector 13 from the temperature near the detector 13 acquired from the temperature sensor, and calculates the correction amount. That is, in the modified example of the third embodiment, the counting result is further corrected while coping with local temperature changes of the detector 13 . As a result, according to the modified example of the third embodiment, it is possible to reconstruct a more accurate image.

In the third embodiment and the modified example of the third embodiment described above, the correction circuit 151 corrects the counting result, but the embodiment is not limited to this. For example, the preprocessing circuit 34 may use the correction amount calculated by the correction amount calculation circuit 150 to correct the counting result.

Further, in the third embodiment and the modified example of the third embodiment described above, the case where the counting result is further corrected while coping with the local temperature change of the detector 13 has been described. is not limited to For example, an image may be reconstructed by correcting the influence of the temperature change of the detector 13 on the detector characteristics without dealing with the local temperature change of the detector 13 . In this case, the data collection circuit 14b is configured to have an ASIC 140, a correction amount calculation circuit 150, a correction circuit 151, and a third correspondence information storage circuit 152. FIG.

(Fourth embodiment)
In the above-described first to third embodiments, in the actual imaging, the ASIC 140 calculates the count rate based on the detection signal corresponding to the incident photons detected in the corresponding detection area for each view. explained. In the first to third embodiments, the calculation circuit 146 calculates the amount of heat generated based on the count rate for each view and detection area, and the control circuits 147 and 147a calculate the heat generation amount for each view and detection area. In each case, the control amount is determined based on the amount of heat generated, and the temperature is controlled using the determined control amount.

However, in scanography (locating imaging) for collecting scanograms (locating images) performed prior to actual imaging, the ASIC generates detection signals corresponding to detected incident photons for each view and detection area. Then, in the actual imaging, the calculation circuit calculates the heat generation amount based on the count rate for each view and detection area, and the control circuit determines the control amount based on the heat generation amount Then, the determined control amount may be used to control the temperature. Therefore, such an embodiment will be described as a fourth embodiment.

FIG. 19 is a block diagram showing a configuration example of an X-ray CT apparatus according to the fourth embodiment. In addition, in FIG. 19, the same reference numerals are assigned to components having the same functions as those shown in FIG. 1, and detailed description thereof will be omitted. As shown in FIG. 19, the X-ray CT apparatus according to the fourth embodiment has a pedestal 10c, a bed 20, and a console 30. As shown in FIG.

The pedestal 10c has the same configuration as the pedestal 10 shown in FIG. 1, except that the configuration of the data acquisition circuit 14c is partially different from the configuration of the data acquisition circuit 14 according to the first embodiment. Therefore, only the configuration of the data collection circuit 14c according to the fourth embodiment will be described below.

The data collection circuit 14c has an ASIC 140a, a calculation circuit 146a, a control circuit 147, a first correspondence information storage circuit 148, a second correspondence information storage circuit 149, and a fourth correspondence information storage circuit 153. . The configuration of the control circuit 147, the first correspondence information storage circuit 148, and the second correspondence information storage circuit 149, which the data collection circuit 14c has, is similar to that of the control circuit 147, the first correspondence information, which the data collection circuit 14 has. The configuration is the same as that of the storage circuit 148 and the second correspondence information storage circuit 149 .

The fourth correspondence information storage circuit 153 is, for example, a NAND flash memory or HDD, and stores fourth correspondence information. FIG. 20 is a diagram showing an example of information stored in fourth correspondence information according to the fourth embodiment. As shown in FIG. 20, the fourth correspondence information stores information that associates the "count rate in scano imaging" with the "count rate in main imaging". The fourth correspondence information is the count rate per view from each detection area of the detector 13 output from the ASIC 140a in scanography, and the count rate from each detection area of the detector 13 output from the ASIC 140a in actual imaging. It is generated by estimating the count rate for each view in advance by measurement or simulation.

"Count rate in scanography" in the fourth correspondence information indicates the counting result in each view in scanography. For example, the "count rate in scanography" includes information such as "C<C5" indicating that the count rate is less than C5, and "C5≤C<C6" indicating that the count rate is greater than or equal to C5 and less than C6. is stored. Also, the "count rate in actual photography" in the fourth correspondence information indicates the counting result in each view in the actual photography. For example, the "count rate in the actual imaging" includes information such as "C<C1" indicating that the count rate is less than C1, and "C1≤C<C2" indicating that the count rate is greater than or equal to C1 and less than C2. is stored. Scanography is an example of first imaging. This photographing is an example of the second photographing.

For example, the fourth correspondence information shown in FIG. 20 indicates that when the count rate in scanography is less than C5, the count rate in main imaging is less than C1, and the count rate in scanography is C5 or higher. If it is less than C6, it indicates that the count rate in the actual imaging is greater than or equal to C1 and less than C2.

In the fourth embodiment, the X-ray CT apparatus performs scanography before performing main imaging. For example, in scanography, X-rays are emitted from the X-ray tube 12a in an X-ray dose smaller than the X-ray dose emitted from the X-ray tube 12a in actual radiography. Each ASIC 140a calculates the count rate based on the detection signal corresponding to the incident photons detected in each detection area in scanography, in the same manner as the count rate calculated by each ASIC 140 in the first embodiment. do.

In scanography, the X-ray tube 12a irradiates the subject P with X-rays, for example, in one view, two views separated by 90 degrees, or all views (2400 views, for example).

When X-rays are irradiated in one view in scanography, the ASIC 140a estimates the count rate in this view from the detection signal based on the X-rays irradiated in one view. In addition, the ASIC 140a estimates the thickness of the subject P based on the detection signal based on the X-rays irradiated in one view, and uses the estimated thickness to determine the thickness of the subject P when the X-rays are irradiated in another view. Calculate the count rate.

Also, when X-rays are emitted in two views in scanography, the ASIC 140a calculates count rates in each of the two views based on two detection signals based on the X-rays emitted in the two views. The ASIC 140a also estimates the thickness of the subject P based on the two detection signals, and estimates the shape of the subject P when the shape of the subject P is assumed to be an ellipse. Then, the ASIC 140a uses the estimated thickness and shape to calculate the count rate when X-rays are applied in another view.

Note that when X-rays are irradiated in all views in scanography, the count rate in each view is calculated based on each detection signal based on the X-rays irradiated in each view.

Then, each ASIC 140a generates information (scanography support information) in which a view corresponding to the calculated count rate, a detection area corresponding to the calculated count rate, and the calculated count rate are associated with each other (scanography support information). The information is stored in a memory (not shown) within the data collection circuit 14c. Thus, in the fourth embodiment, the count rate is calculated for each view and each detection area in scanography.

Then, the calculation circuit 146a refers to the scanography correspondence information in the actual photographing executed after the scanography photographing, and calculates the corresponding count rate from the scanography correspondence information for each detection area each time the view trigger signal is received. to get That is, the calculation circuit 146a acquires the corresponding count rate from the scanography correspondence information for each view and detection area. Here, the count rate acquired from the scanography support information is the count rate in scanography.

Then, the calculation circuit 146a refers to the fourth correspondence information, and obtains the count rate in the main imaging corresponding to the obtained count rate in the scanography from the fourth correspondence information. In this way, the calculation circuit 146a calculates the count rate in the actual photographing for each view and each detection area.

Then, the calculation circuit 146a according to the fourth embodiment uses the same method as the calculation circuit 146 in any one of the first to third embodiments to calculate the amount of heat generated based on the count rate. , the amount of heat generated is calculated based on the count rate in the actual imaging. That is, the calculation circuit 146a calculates the amount of heat generated based on the count rate in the main imaging for each view and each detection area. In this manner, the calculation circuit 146a according to the fourth embodiment calculates the amount of heat generated for each detection area in main imaging based on the detection signal corresponding to the incident photons detected in the detection area in scanography.

Then, the control circuit 147 according to the fourth embodiment determines the control amount based on the amount of heat generated by the control circuits 147 and 147a in any one of the first to third embodiments. The following processing is performed in the same manner as the method of controlling the temperature using the controlled variable. For example, the control circuit 147 according to the fourth embodiment determines the control amount based on the amount of heat generated for each view and detection area in the actual photographing, and controls the temperature using the determined control amount.

The X-ray CT apparatus according to the fourth embodiment has been described above. Also in the fourth embodiment, it is possible to cope with local temperature changes of the detector 13 as in the first embodiment.

(Other embodiments)
Embodiments are not limited to the embodiments described above.

In the above-described embodiment, the case where the temperature controller 17 is arranged for each detection area, that is, the case where the temperature controller 17 and the detection area are 1:1 has been described, but the embodiment is limited to this. not something. For example, temperature controllers 17 may be arranged for multiple detection areas. For example, if the detection areas are close to each other, one temperature controller 17 may control the temperatures of a plurality of detection areas. Further, for example, when the number of detection elements included in the detection area is large, one detection area may be temperature-controlled by a plurality of temperature controllers 17 .

Further, in the above-described embodiment, a case has been described where the sizes of the plurality of detection areas are the same, but the sizes of the detection areas may differ depending on the position in at least one of the channel direction and the column direction. FIG. 21 is a diagram for explaining an example of the size of the detection area.

For example, as shown in FIG. 21, at the central portion (central portion) of the detector 13 in the channel direction (Z-axis direction), the amount of X-rays transmitted through the subject P is large. It may be sized to contain 16 detector elements in a row of 4 channels.

On the other hand, in the peripheral portion of the detector 13 in the channel direction, since the amount of X-rays transmitted through the subject P is small, the size of the detection area may be set to include 64 detection elements in 8 rows and 8 channels. good.

That is, the size of the detection area may differ according to the amount of X-rays incident on the detection area transmitted through the subject P. FIG.

In the above-described embodiment, the ASIC 140 in the central portion of the detector 13 and the ASIC 140 in the peripheral portion have different exhaust heat efficiencies, but the embodiment is not limited to this. For example, if a plurality of cooling fans are provided near the DAS and the ASIC 140 in the central part of the detector 13 and the ASIC 140 in the peripheral part have the same exhaust heat efficiency, the control amount is set according to the detection area. It doesn't have to be. For example, in the second correspondence information shown in FIG. 10 and the second correspondence information shown in FIG. 14, the "detection area ID" may not be associated.

Further, in the above-described embodiment, the third correspondence information shown in FIG. 18 is not associated with the "detection area ID", but the embodiment is not limited to this. For example, "detection area ID" may be further associated with the third correspondence information.

Further, in the above-described embodiment, the ASICs 140 and 140a are arranged in the data acquisition circuit 14 (14a, 14b, 14c), but the embodiment is not limited to this. For example, ASICs 140 , 140 a may be located in detector 13 .

In the above-described embodiment, a Rotate/Rotate-Type (third generation CT) X-ray CT apparatus in which the X-ray tube 12a and the detector 13 are integrally rotated around the subject P has been described. It is not limited to this. For example, in the X-ray CT apparatus, in addition to the third-generation CT, an X-ray detector having a plurality of X-ray detection elements is dispersed and fixed in a ring shape, and only the X-ray tube rotates around the subject. There is Stationary/Rotate-Type (4th generation CT). The embodiments described above are also applicable to 4th generation CT. Also, the above-described embodiments are applicable to a hybrid X-ray CT apparatus combining third generation CT and fourth generation CT.

In addition, the above-described embodiments can also be applied to a conventional single-tube type X-ray CT apparatus, and a so-called multi-tube CT apparatus in which a plurality of pairs of X-ray tubes and detectors are mounted on a rotating ring. type X-ray CT apparatus.

Further, in the above-described embodiment, a plurality of functions are provided in the console 30 as independent circuits, and each circuit performs its own function, but the embodiment is not limited to this. For example, one processing circuit may perform multiple functions. For example, the processing circuitry performs scan control functions, preprocessing functions, image reconstruction functions, and system control functions. Here, each processing function executed by the scan control function, preprocessing function, image reconstruction function, and system control function, which are components of the processing circuit, is recorded in the storage circuit in the form of a computer-executable program. ing. The processing circuit is, for example, a processor, and reads each program from the storage circuit and executes it to realize the function corresponding to each read program.

Further, for example, one processing circuit may perform the functions of the ASICs 140 and 140a, the functions of the calculation circuits 146 and 146a, and the functions of the control circuits 147 and 147a.

Further, in the above-described embodiment, the preprocessing circuit 34 and the image reconstruction circuit 36 are executed within the console 30, but the embodiment is not limited to this. For example, preprocessing circuitry 34 and image reconstruction circuitry 36 may be executed on an external workstation.

Also, in the above-described embodiments, the X-ray CT apparatus has been described, but the embodiments are not limited to this. For example, the above-described embodiments are applicable to mammography apparatuses and X-ray diagnostic apparatuses having photon-counting X-ray detectors. That is, the above-described embodiments are also applicable to radiodiagnostic apparatuses.

The term "processor" used in the above description is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an application specific integrated circuit (ASIC), a programmable logic device (e.g., Circuits such as Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (CPLD), and Field Programmable Gate Array (FPGA)). A processor achieves its functions by reading and executing a program embedded in the circuitry of the processor. Note that the program may be stored in the image storage circuit 37 of the console 30 instead of incorporating the program into the circuit of the processor. In this case, the processor implements its function by reading and executing the program stored in the image storage circuit 37 . Note that each processor of the present embodiment is not limited to being configured as a single circuit for each processor, and may be configured as one processor by combining a plurality of independent circuits to realize its function. good. Furthermore, a plurality of components in FIGS. 1, 12, 15 and 19 may be integrated into one processor to realize its functions.

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

Moreover, the temperature control processing described in the above embodiments can also be realized by software. For example, the temperature control process is realized by causing a computer to execute a temperature control program that defines the procedure of the processes described as being performed by the calculation circuit 146 and the control circuit 147 in the above embodiment. The temperature control program is stored in, for example, a hard disk or a semiconductor memory device, and read and executed by a processor such as a CPU or MPU. This temperature control program can be distributed via a network such as the Internet. Also, this temperature control program can be recorded on a computer-readable recording medium such as a CD-ROM (Compact Disc-Read Only Memory), MO (Magnetic Optical disk), DVD (Digital Versatile Disc), or the like, and distributed.

According to at least one embodiment described above, it is possible to cope with local temperature changes of the detector.

While several embodiments of the invention have been described, these embodiments have been 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 modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

13 Detector 14 Data Acquisition Circuit 36 Image Reconstruction Circuit 146 Calculation Circuit 147 Control Circuit

Claims (9)

a photon-counting detector that includes a plurality of detection areas each formed of a plurality of detection elements in the channel direction and the column direction, and that outputs a detection signal corresponding to the number of incident photons;
a calculation unit that calculates an amount of heat generated in each detection area based on a detection signal corresponding to incident photons detected in the detection area;
a control unit that determines a control amount based on the amount of heat generated in each detection area and controls the temperature in the detection area using the determined control amount;
An X-ray CT apparatus comprising: 2. The X-ray CT apparatus according to claim 1, wherein said control unit determines said control amount using said amount of heat generated and a temperature near said photon counting detector obtained from a temperature sensor. 3. The X-ray CT apparatus according to claim 1, wherein said control unit determines said control amount according to the position of said detection area with respect to an air cooling fan that controls the temperature of said entire photon counting detector. 4. The X-ray CT apparatus according to any one of claims 1 to 3, further comprising a reconstruction unit that reconstructs an image using projection data based on said detection signal. a correction amount calculation unit that calculates a correction amount according to a temperature change of the photon counting detector;
a correction unit that corrects the detection signal output from the photon counting detector using the correction amount;
The X-ray CT apparatus according to any one of claims 1 to 3, further comprising: The correction amount calculator estimates the temperature change of the photon counting detector based on the control amount and the history of count results for each view based on the detection signal from each detection element in each detection area. 6. The X-ray CT apparatus according to claim 5, wherein said correction amount is calculated. 7. The X-ray CT apparatus according to claim 5, further comprising a reconstruction unit that reconstructs an image using projection data based on the corrected detection signals. The calculation unit calculates, based on a detection signal corresponding to the incident photon detected in the detection area in the first imaging, for each of the detection areas in a second imaging performed after the first imaging. Calculate the calorific value,
The control unit determines a control amount based on the amount of heat generated in each detection area, and controls the temperature in the detection area using the determined control amount.
The X-ray CT apparatus according to claim 1. The X-ray CT apparatus according to any one of claims 1 to 8, wherein the size of said detection area differs depending on the position in at least one of said channel direction and column direction.

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