JP6933471B2 - Photon counting type detector and X-ray CT device - Google Patents

Description

Embodiments of the present invention relate to a photon counting type detector and an X-ray CT apparatus.

A photon counting type X-ray detector is known as an X-ray detector used in an X-ray CT apparatus. The photon counting type X-ray detector captures each incident X-ray as a photon and measures the intensity of the X-ray by counting the number of photons. Further, the photon counting type X-ray detector measures the energy of each X-ray photon because when the X-ray photon is converted into a charge, the amount of charge corresponding to the energy of the X-ray photon is generated. .. Therefore, the photon counting type X-ray detector can also measure the energy spectrum of X-rays.

International Publication No. 10/035671 Japanese Unexamined Patent Publication No. 2013-090233

An object to be solved by the present invention is to provide a photon counting type detector and an X-ray CT apparatus capable of improving the accuracy of photon counting processing.

The photon counting type detector of the embodiment includes a plurality of X-ray detection elements, a capacitor, and a generation unit. The plurality of X-ray detection elements detect X-rays and generate an electric signal. A capacitor is provided for each X-ray detection element and stores an electric signal generated in each X-ray detection element. The generation unit has low radiosensitivity and generates a digital signal by using the accumulation result of the electric signal in the plurality of capacitors and the reference information stored in advance.

FIG. 1 is a diagram showing a configuration example of an X-ray CT apparatus according to the first embodiment. FIG. 2A is a diagram for explaining the detector according to the first embodiment. FIG. 2B is a diagram for explaining the detector according to the first embodiment. FIG. 2C is a diagram for explaining the detector according to the first embodiment. FIG. 2D is a diagram for explaining the detector according to the first embodiment. FIG. 2E is a diagram for explaining the detector according to the first embodiment. FIG. 3 is a diagram showing a configuration example of SiPM according to the first embodiment. FIG. 4 is a diagram for explaining the processing operation of the capacitor group according to the first embodiment. FIG. 5 is a diagram for explaining the processing operation of the LUT according to the first embodiment. FIG. 6 is a diagram for explaining the processing operation of the LUT according to the first embodiment. FIG. 7A is a diagram for explaining a modified example of the first embodiment. FIG. 7B is a diagram for explaining a modified example of the first embodiment. FIG. 7C is a diagram for explaining a modified example of the first embodiment. FIG. 8 is a diagram showing a configuration example of the detector according to the second embodiment. FIG. 9 is a diagram showing a configuration example of SiPM according to the third embodiment. FIG. 10A is a diagram for explaining a capacitor group according to another embodiment. FIG. 10B is a diagram for explaining a capacitor group according to another embodiment. FIG. 10C is a diagram for explaining a capacitor group according to another embodiment. FIG. 10D is a diagram for explaining a capacitor group according to another embodiment. FIG. 11 is a diagram showing a configuration example of SiPM according to another embodiment.

Hereinafter, the photon counting type detector and the X-ray CT apparatus according to the embodiment will be described with reference to the drawings. The embodiment is not limited to the following embodiments. In principle, the contents described in one embodiment are similarly applied to other embodiments.

The X-ray CT apparatus described in the following embodiment is an apparatus capable of performing photon counting CT. That is, the X-ray CT apparatus described in the following embodiment counts the X-rays that have passed through the subject using a photon counting type detector instead of the conventional integral type (current mode measurement method) detector. Therefore, it is a device capable of reconstructing X-ray CT image data having a high SN ratio.

(First Embodiment)
FIG. 1 is a 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 includes a pedestal 10, a sleeper 20, and a console 30.

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. The high voltage generator 11, the X-ray tube 12, the detector 13, and the data. It has a collection circuit 14, a rotating frame 15, and a gantry drive circuit 16.

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

The X-ray tube 12 is a vacuum tube that irradiates the subject P with an X-ray beam by a high voltage supplied by a high voltage generator 11 described later, and causes the X-ray beam to be applied to the subject P as the rotating frame 15 rotates. Irradiate to. The X-ray tube 12 is an X-ray source that emits X-rays.

The high voltage generator 11 is a device that supplies a high voltage to the X-ray tube 12, and the X-ray tube 12 generates X-rays using the high voltage supplied from the high voltage generator 11. That is, the high voltage generator 11 adjusts the X-ray dose radiated to the subject P by adjusting the tube voltage and the tube current supplied to the X-ray tube 12.

The gantry drive circuit 16 rotates the rotating frame 15 to rotate the X-ray tube 12 and the detector 13 on a circular orbit centered on the subject P.

The detector 13 has a plurality of detection elements that detect X-rays transmitted through the subject P and generate an electric signal. The detector 13 will be described with reference to FIGS. 2A to 2E. 2A to 2E are diagrams for explaining the detector 13 according to the first embodiment.

The detection element included in the detector 13 will be described with reference to FIG. 2A. FIG. 2A illustrates 16 detection elements arranged in 4 vertical rows and 4 horizontal rows among the plurality of detection elements included in the detector 13. As shown in FIG. 2A, the detection element included in the detector 13 according to the first embodiment is an indirect conversion type detector composed of a scintillator and an optical sensor.

The scintillator converts the incident X-rays emitted from the X-ray source into scintillator light. This scintillator light is composed of a number of photons corresponding to the energy of incident X-rays. Then, in the scintillator, a SiPM (Silicon photomultiplier) 130 as an optical sensor is arranged at an end portion on the side facing the X-ray incident direction side. The SiPM provided in each scintillator constitutes one pixel. Therefore, the SiPM 130 is also referred to as one pixel.

The SiPM 130 according to the first embodiment has an APD cell 140 including a plurality of APDs (Avalanche Photo-Diode) 141, each of which operates individually. Generally, hundreds to thousands of APDs are arranged in one pixel. In the example shown in FIG. 2B, of the APD 141 included in the APD cell 140, 72 APD 141s arranged in 9 horizontal rows and 8 vertical rows are shown. The APD 141 is also referred to as a photoelectric conversion unit.

As shown in FIG. 2C, the APD 141 is a photodiode having an avalanche region 141a, and is a photodiode utilizing an avalanche doubling action in which the photocurrent is multiplied by applying a reverse bias. The avalanche doubling action is that when a reverse voltage is applied to the PN junction, the pair of electrons and holes generated in the depletion layer flows to the N layer for electrons and to the P layer for holes, but part of it. The electrons and holes collide with other atoms to form a new pair of electrons and holes. A chain reaction occurs in which these electrons and holes collide with further atoms and a new pair of electrons and holes is formed. That is, in APD 141, more electron-hole pairs are generated than the electron-hole pairs generated by the incident light. As described above, the APD 141 is a high-sensitivity photodiode that can obtain a high output even with weak light.

Return to FIG. 2B. In the APD cell 140, the number of cells APD 141 proportional to the energy of the incident X-ray is ignited. In other words, in the APD cell 140, the number of cells APD 141 proportional to the energy of the incident X-rays produces a signal current. For example, in the APD cell 140, each ignited APD 141 detects one photon and outputs a signal. Then, the APD cell 140 outputs the sum of the signals output from all the APD 141 in the APD cell 140 as an output signal of one pixel.

More specifically, each APD 141 of the APD cell 140 outputs the same pulse when one photon is detected. Therefore, the APD cell 140 outputs an output signal corresponding to the total number of APD 141s that have detected photons. For example, let A be the output signal when one photon is detected. As shown in FIG. 2D, the APD cell 140 outputs an output signal A when one photon is detected, and outputs an output signal n × A when n photons are detected. In this way, the APD cell 140 outputs an output signal corresponding to the total number of APD 141s that have detected photons per pixel. In other words, the APD cell 140 outputs an output signal according to the energy of the X-ray.

Further, as shown in FIG. 2E, the detector 13 is a surface detector in which SiPMs are arranged in multiple rows in the channel direction and the slice direction. The more rows in the slice direction, the wider the range of images that can be collected in one rotation. Further, although the number of pixels of the detector 13 is arbitrary, it will be described as an example assuming that the number of pixels is about 8000 pixels. For example, the detector 13 shoots at 3000 (views / sec). Here, when the detector 13 rotates three times per second, the number of views captured in one rotation is 1000 views.

Returning to FIG. 1, the data acquisition circuit 14 collects the counting result which is the result of the counting process using the output signal of the detector 13. The data collection circuit 14 counts photons (X-ray photons) derived from X-rays irradiated from the X-ray tube 12 and transmitted through the subject P, and collects the result of discriminating the energy of the counted photons as the counting result. do. Then, the data acquisition circuit 14 transmits the counting result to the console 30.

Specifically, the data acquisition circuit 14 discriminates and counts each pulse output by the 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 counting result of the X-ray. Collect for each phase of the tube 12 (tube phase). In the data acquisition circuit 14, for example, the position of the detection element that outputs the pulse used for counting is set as the incident position. Further, the data acquisition circuit 14 calculates the energy value from, for example, the peak value of the pulse and the response function peculiar to the system. Alternatively, the data acquisition circuit 14 calculates the energy value, for example, by integrating the intensity of the pulse. The data collection circuit 14 distributes the calculated energy value (E) to a plurality of energy discrimination regions.

The data collection circuit 14 according to the present embodiment distributes the calculated energy value to a plurality of energy discrimination regions by using, for example, a comparator. The plurality of energy discrimination regions are energy division sets set by using a threshold value so that the data acquisition circuit 14 discriminates and distributes the energy value into the energy range of a predetermined particle size.

For example, the counting result collected by the data acquisition circuit 14 is "In the tube phase" α1 ", the counting value of the photons in the energy discrimination region" E1 <E≤E2 "in the detection element at the incident position" P11 "is" N1 ". , And the count value of photons in the energy discrimination region “E2 <E ≦ E3” is “N2” ”. Alternatively, the counting result collected by the data acquisition circuit 14 is "in the tube phase" α1 ", the total per unit time of the photons in the energy discrimination region" E1 <E≤E2 "in the detection element at the incident position" P11 ". The numerical value is "n1", and the count value of photons in the energy discrimination region "E2 <E≤E3" per unit time is "n2". "

The sleeper 20 is a device on which the subject P is placed, and has a top plate 22 and a sleeper drive device 21. The top plate 22 is a plate on which the subject P is placed, and the sleeper driving device 21 moves the top plate 22 in the Z-axis direction to move the subject P into the rotating frame 15.

The gantry 10 executes, for example, a helical scan in which the rotating frame 15 is rotated while the top plate 22 is moved to scan the subject P in a spiral shape. Alternatively, the gantry 10 executes a conventional scan in which the rotating frame 15 is rotated while the position of the subject P is fixed after the top plate 22 is moved to scan the subject P in a circular orbit.

The console 30 is a device that accepts the operation of the X-ray CT device by the operator and reconstructs the X-ray CT image data using the counting information collected by the gantry 10. As shown in FIG. 1, the console 30 includes an input interface 31, a display 32, a scan control circuit 33, a preprocessing circuit 34, a projection data storage circuit 35, an image reconstruction circuit 36, and an image storage circuit 37. And the system control circuit 38.

The input interface 31 has a mouse, a keyboard, and the like used by the operator of the X-ray CT apparatus to input various instructions and various settings, and transfers the information of the instructions and settings received from the operator to the system control circuit 38. For example, the input interface 31 receives a reconstruction condition for reconstructing the X-ray CT image data, an image processing condition for the X-ray CT image data, and the like from the operator.

The display 32 is a monitor referred to by the operator, and under the control of the system control circuit 38, displays X-ray CT image data to the operator, and gives various instructions and 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 high voltage generator 11, the gantry drive circuit 16, the data acquisition circuit 14, and the sleeper drive device 21 under the control of the system control circuit 38 described later, thereby counting on the gantry 10. Control the information collection process.

The preprocessing circuit 34 performs correction processing such as logarithmic conversion processing, offset correction, sensitivity correction, and beam hardening correction on the counting result transmitted from the data acquisition circuit 14, thereby projecting data for each energy discrimination region. To generate.

The projection data storage circuit 35 stores the projection data generated by the preprocessing circuit 34. That is, the projection data storage circuit 35 stores the projection data for reconstructing the X-ray CT image data.

The image reconstruction circuit 36 generates a CT image based on the signal output by the detector 13. The image reconstruction circuit 36 reconstructs the X-ray CT image data by, for example, back-projecting the projection data stored in the projection data storage circuit 35. Examples of the back projection process include back projection processing by the FBP (Filtered Back Projection) method. The image reconstruction circuit 36 may be subjected to reconstruction processing by, for example, the successive approximation method. Further, the image reconstruction circuit 36 generates image data by performing various image processing on the X-ray CT image data. The image reconstruction circuit 36 stores the reconstructed X-ray CT image data and image data generated by various image processes in the image storage circuit 37.

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

Further, the image reconstruction circuit 36 assigns, for example, a color tone corresponding to the energy component to each pixel of the X-ray CT image data of each energy component, and superimposes a plurality of color-coded X-ray CT image data according to the energy component. Image data can be generated. In addition, the image reconstruction circuit 36 can generate image data that enables identification of the substance by utilizing the K absorption edge peculiar to the substance. Examples of 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.

The system control circuit 38 controls the operation of the gantry 10, the sleeper 20, and the console 30 to control the entire X-ray CT apparatus. 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 the image reconstruction process and the image generation process in the console 30 by controlling the preprocessing circuit 34 and the image reconstruction circuit 36. Further, the system control circuit 38 controls the display 32 to display various image data stored in the image storage circuit 37.

The overall configuration of the X-ray CT apparatus according to the first embodiment has been described above. Under such a 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 SiPM 130 outputs an analog signal. This analog signal is weak, and it is desirable that the ADC (Analog to Digital Converter) be arranged in the vicinity of the SiPM 130 from the viewpoint of avoiding noise from being mixed into the analog signal. However, when the detector 13 is a surface detector, a sufficient space for arranging the ADC cannot be secured in the vicinity of the SiPM 130.

Further, the ADC is required to have processing performance satisfying 10 ^ 7 to 10 ^ 8 (cps) when receiving an analog signal and converting it into a digital signal. In order to satisfy such high-speed processing performance, current consumption and heat generation become problems in ADC. Further, the ADC cannot be miniaturized as much as the CMOS (Complementary MOS) process, which is disadvantageous for integration. As described above, there are many problems in realizing a large-scale surface detector in terms of circuit scale, power consumption, processing performance, and the like.

Therefore, there is a great merit that the signal output from the detector is output as a digital signal instead of an analog signal. For example, a combinational circuit is proposed on the premise of a CMOS circuit that directly counts the output value from the APD cell 140 as a digital value without using an ADC. In such a combinational circuit, the CMOS circuit has an FF (Flip-Flop), a counter, a SRAM (Static Random Access Memory), and the like as basic blocks. However, when the basic block is miniaturized, radiation may enter the semiconductor. In such a case, for example, in a basic block such as SRAM, there is a high possibility that a soft error in which the logic is inverted will occur. If a soft error occurs in the basic block, the reliability of the photon counting process in the detector 13 decreases.

Further, when the surface detector is configured by SiPM 130, several thousand pixels output data of several thousand views per second. These data require correction processing that depends on the detector element, and as the number of X-ray detection elements increases, the load of correction processing in the subsequent stage increases.

Therefore, in the first embodiment, the accuracy of the photon counting process is improved by configuring the detector 13 so as not to be affected by radiation. For example, SiPM 130 is provided for each X-ray detection element and has a capacitor for accumulating electric signals generated in each X-ray detection element and a result of accumulating electric signals in a plurality of capacitors having low radiation sensitivity. And a generation unit that generates a digital signal by using the reference information stored in advance. Hereinafter, the SiPM 130 according to the first embodiment will be described with reference to FIGS. 3 to 6.

FIG. 3 is a diagram showing a configuration example of SiPM 130 according to the first embodiment. Note that FIG. 3 shows only the SiPM 130 corresponding to one pixel. As shown in FIG. 3, the SiPM 130 has an APD cell 140, a LUT (Look Up Table) 150, and a capacitor group 160. In addition, Vh in FIG. 3 indicates an applied voltage, and is, for example, 80V. Further, the value of the applied voltage can be changed arbitrarily.

The APD cell 140 has a plurality of APDs as described above. Each APD detects one photon and outputs a signal as described above. Note that FIG. 3 illustrates an APD cell 140 having n APDs. Further, in FIG. 3, each APD is shown as D1, D2, ..., Dn. In the following, for example, APD which is D1 will be referred to as APD (D1).

The capacitor group 160 has a plurality of capacitors and a plurality of comparators, is provided for each X-ray detection element, and stores an electric signal generated by each X-ray detection element.

For example, the capacitor group 160 has a plurality of capacitors that store the electrical signals generated by each APD 141. Note that FIG. 3 illustrates a capacitor group 160 having n capacitors. Further, in FIG. 3, each capacitor is shown as C1, C2, ..., Cn. Here, the capacitor C1 is connected to the APD (D1) and stores the electric signal output from the APD (D1). Further, the capacitor C2 is connected to the APD (D2) and stores the electric signal output from the APD (D2). Similarly, the capacitor Cn is connected to the APD (Dn) and stores the electric signal output from the APD (Dn). That is, each capacitor stores the electrical signal output from the corresponding APD.

Further, a comparator is connected to each capacitor in the capacitor group 160. Note that FIG. 3 illustrates a capacitor group 160 having n comparators. Further, in FIG. 3, each comparator is shown as A1, A2, ..., An. Here, the comparator A1 is connected to the capacitor C1 and compares the electric signal stored in the capacitor C1 with the comparative potential Vth. Further, the comparator A2 is connected to the capacitor C2 and compares the electric signal stored in the capacitor C2 with the comparative potential Vth. Similarly, the comparator An is connected to the capacitor Cn and compares the electrical signal stored in the capacitor Cn with the comparative potential Vth. That is, each comparator compares the electrical signal stored in the corresponding capacitor with the comparative potential Vth.

FIG. 4 is a diagram for explaining the processing operation of the capacitor group 160 according to the first embodiment. FIG. 4 describes a processing operation at the time of accumulating an electric signal by using the capacitor C1 among a plurality of capacitors included in the capacitor group 160, but the processing operation at the time of accumulating an electric signal is the same for other capacitors. As shown in the middle right figure of FIG. 4, the capacitor C1 resets the accumulated electric signal by receiving the input of the reset signal and closing the switch. Then, as shown in the rightmost view of FIG. 4, the switch of the capacitor C1 is released, and the capacitor C1 is in a photon incident waiting state.

Subsequently, photons are randomly incident on the pixels during the period when the scintillator emits light. When a photon is incident on each cell in each pixel, the APD performs an avalanche operation, a current flows, and an electric charge is accumulated in a capacitor corresponding to each APD. For example, as shown in the leftmost diagram of FIG. 4, the capacitor C1 starts accumulating the electric signal output from the APD (D1) when the APD (D1) detects a photon.

Then, as shown in the middle left figure of FIG. 4, the comparator A1 detects the accumulated electric signal by sense-up and compares it with the comparative potential Vth. Then, when the comparator A1 determines that the accumulated electric signal is Vth or more, it outputs 1 as an output value to the LUT 150 as the accumulation result. On the other hand, when the comparator A1 determines that the accumulated electric signal is less than Vth, it outputs 0 as an output value to the LUT 150 as the accumulation result. Each comparator detects the electric signal stored in the corresponding capacitor by sense-up until the reset signal is input, and continuously executes the process of comparing the stored electric signal with the comparison potential Vth. ..

Return to FIG. The LUT 150 is provided for each X-ray detection element. For example, as shown in FIG. 3, the LUT 150 is connected to each comparator in one pixel. In the example shown in FIG. 3, the LUT 150 is connected to the comparator A1, the comparator A2, ..., The comparator An in the SiPM 130.

In addition, LUT150 is resistant to radiation. In other words, LUT150 has low radiosensitivity. In the first embodiment, the LUT 150 will be described as being composed of, for example, a mask ROM (Read Only Memory) or a magnetic memory.

In addition, the LUT 150 stores reference information in advance. The reference information referred to here is information in which the output values from each comparator are related to the binary representation values corresponding to the output values from all the comparators.

Then, the LUT 150 generates an output signal according to the accumulation result of the electric signal generated in each X-ray detection element at predetermined intervals using the reference information. For example, the LUT 150 generates a digital signal by using the accumulation result of the electric signal in a plurality of capacitors and the reference information stored in advance. The LUT 150 is also referred to as a generation unit. Subsequently, the processing operation of the LUT 150 will be described with reference to FIGS. 5 and 6. 5 and 6 are diagrams for explaining the processing operation of the LUT 150 according to the first embodiment.

As shown in the right figure of FIG. 5, the gate time (Tg) is set according to the period during which the scintillator does not emit light even if the next X-ray is incident (the insensitivity period of the scintillator) during the light emission period of the scintillator. This gate time corresponds to the time from the input of the reset signal to the input of the next reset signal. The LUT 150 generates an output signal according to the accumulation result of the electric signal for the photon detected by the APD at this gate time at predetermined intervals using the reference information. Here, the LUT 150 outputs a linear digital signal with respect to the accumulation result by using the reference information.

For example, the left figure of FIG. 5 shows a case where photons are detected in 6 APDs at the gate time in the APD cell 140. In the case of the example shown on the left side of FIG. 5, the LUT 150 receives an input of an output value 1 from six comparators and an input of an output value 0 from another comparator as a storage result. Here, when the reference information is information in which the value of the binary representation indicating the number of the output value 1 is related, the LUT 150 generates an output signal indicating the number whose output value is 1. More specifically, the LUT 150 generates an output signal "110" indicating 6 in binary. In this way, the LUT 150 accepts inputs of output values from a plurality of APDs and generates a digital signal corresponding to the total value of the input values based on the reference information.

FIG. 6 shows the timing of processing by the LUT 150. As shown in FIG. 6, the reset signal is input at time t1, time t3, time t5, and time t7. These reset signals are input at regular intervals. Further, the time from the input of the reset signal to the input of the next reset signal is the gate time Tg. In other words, the input timing of the reset signal is synchronized with Tg.

Further, in the example shown in FIG. 6, during the time from time t1 to time t3, the LUT 150 receives the input of the output value 1 output from the three comparators of the comparator A1, the comparator An, and the comparator A2. Then, the LUT 150 receives the input of the read signal immediately before the reset, generates an output signal, and outputs the generated output signal to the FIFA 170. For example, the LUT 150 receives an input of a read signal at time t2 and generates an output signal “11” indicating 3 in binary.

Further, in the example shown in FIG. 6, during the period from time t3 to time t5, the LUT 150 has an output value 1 output from three comparators A2, A3, and A1 and one comparator (not shown). Accept input. Then, the LUT 150 accepts the input of the read signal at the time t4 and generates the output signal “100” indicating 4 in the binary number.

Similarly, in the example shown in FIG. 6, during the time t5 to the time t7, the LUT 150 receives the input of the output value 1 output from the three comparators of the comparator An, the comparator A1, and the comparator A2. Then, the LUT 150 receives the input of the read signal at the time t6 and generates the output signal “11” indicating 3 in the binary number.

Return to FIG. The LUT 150 outputs the generated output signal to, for example, a FIFO (First In First Out) 170 composed of a magnetic memory. The FIFA 170 receives the input of the output signal output from each LUT 150 included in the detector 13 in parallel and outputs the output signal to the data acquisition circuit 14 serially.

Then, the data acquisition circuit 14 collects an output signal from each X-ray detection element. For example, the data acquisition circuit 14 discriminates the output signal for each energy bin and adds the discriminated output signals to generate a histogram. As a result, the image reconstruction circuit 36 reconstructs the image using the output signal collected by the data acquisition circuit 14.

As described above, in the first embodiment, the radiation-resistant LUT150 uses reference information to generate an output signal according to the accumulation result of the electric signal generated by the APD that has detected the photon at predetermined intervals. Generate. That is, in the first embodiment, the output value from the APD cell 140 is output as a digital signal without using the ADC. This makes it possible to reduce the mixing of noise into the output value from the APD cell 140.

Further, in the first embodiment, the output value from the APD cell 140 is converted into a digital signal without using the ADC. This makes it possible to use the detector 13 as a surface detector without increasing the scale of the detector 13 in terms of circuit scale, power consumption, processing performance, and the like.

Further, since the LUT 150 is composed of a mask ROM that is not affected by radiation, it is possible to prevent the occurrence of soft errors even when radiation is incident on the semiconductor. As a result, it is possible to prevent the reliability of the photon counting process in the detector 13 from being lowered. As described above, according to the first embodiment, the accuracy of the photon counting process can be improved.

(Modified example of the first embodiment)
The first embodiment is not limited to the above-described embodiment. Hereinafter, a modified example of the first embodiment will be described with reference to FIGS. 7A to 7C. 7A to 7C are diagrams for explaining a modification of the first embodiment.

In the above-described embodiment, the number of APD 141s configured in one pixel is assumed to be several hundred to several thousand. For example, when the number of APD 141 configured in one pixel is n, the LUT 150 accepts the input of the output value output from the comparator corresponding to each APD 141, as shown in FIG. 7A. The comparator A1 shown in FIG. 7A is a comparator corresponding to APD (D1), and the comparator A2 is a comparator corresponding to APD (D2). Further, the comparator A3 shown in FIG. 7A is a comparator corresponding to APD (D3), the comparator A4 is a comparator corresponding to APD (D4), and the comparator An is a comparator corresponding to APD (Dn). be.

However, when the number of APD 141 configured in one pixel is large, the wiring between the capacitor group 160 and the LUT 150 becomes complicated. Therefore, as shown in FIG. 7B, for example, the APD 141 may be grouped in the row direction, and an output signal may be input to each LUT for each grouped unit. In other words, the LUT is provided for each of a predetermined number of capacitors, and a digital signal is generated by using the accumulation result of each of a predetermined number of capacitors and the reference information.

More specifically, in FIG. 7B, the comparator A1, the comparator A2, the comparator A3 and the comparator A4 corresponding to the APD141 on the first line are put together and the output signal is input to the LUT-A. Further, the comparator A5, the comparator A6, the comparator A7 and the comparator A8 corresponding to the APD 141 on the second line are put together, and the output signal is input to the LUT-B. Similarly, the comparator An-3, the comparator An-2, the comparator An-1 and the comparator An corresponding to the APD 141 on the nth line are put together, and the output signal is input to the LUT-J.

Then, each LUT generates a digital signal by using the accumulation result and the reference information for each of a predetermined number of capacitors. In such a case, each LUT outputs the generated digital signal to the FIFA 170.

Further, as shown in FIG. 7C, the LUT 150 may have a first LUT 151 and a second LUT 152. In the example shown in FIG. 7C, the LUT 150 has LUT-A, LUT-B, ..., LUT-J as the first LUT 151. Here, the first LUT 151 is provided for each of a predetermined number of capacitors, and generates a first digital signal by using the accumulation result of each of a predetermined number of capacitors and the first reference information. More specifically, the first LUT 151 shown in FIG. 7C organizes the APD 141 in the row direction and receives the input of the output signal output for each group, as in the example shown in FIG. 7B.

Then, the second LUT 152 generates a second digital signal using the first digital signal generated by the first LUT 151 and the second reference information, and the generated second digital signal is used as a digital signal. And. More specifically, as shown in FIG. 7C, the second LUT 152 is a first digital signal generated by the first LUT 151, LUT-A, LUT-B, ..., LUT-J. A second digital signal is generated using the second reference information. Then, the second LUT 152 outputs the generated second digital signal to the FIFA 170.

In the modified example of the first embodiment described above, the case where the APD 141 is grouped in the row direction has been described, but the embodiment is not limited to this. For example, the APD 141 may be grouped in the column direction.

(Second Embodiment)
In the first embodiment, the LUT 150 is configured with a mask ROM, and by using the reference information, a linear output signal is output with respect to the accumulation result. By the way, in the detector 13, even when X-rays are not incident, an APD within one pixel or one pixel itself may be in a failure state in which photons are always detected. In such a case, it is desirable to correct the output signal from the APD in the faulty state or the pixel in the faulty state.

Therefore, in the second embodiment, the case where the reference information is information in which a non-linear value is related to the number of the output value 1 in binary notation will be described. That is, in the second embodiment, the LUT outputs a non-linear digital signal with respect to the accumulation result by using the reference information.

The overall configuration of the X-ray CT apparatus according to the second embodiment is the same as the configuration example shown in FIG. 1, except that a part of the configuration inside the detector 13 is different. Therefore, the description of the same configuration as in FIG. 1 will be omitted. FIG. 8 is a diagram showing a configuration example of the detector 13 according to the second embodiment.

In the example shown in FIG. 8, the detector 13 is shown in a simplified manner. For example, FIG. 8 shows only the LUT 150 out of each SiPM 130 included in the detector 13. In the second embodiment, the LUT 150 is composed of, for example, a magnetic memory. In the LUT 150 composed of a magnetic memory, the reference information can be rewritten. Further, as shown in FIG. 8, the detector 13 includes a control arithmetic processing unit 180 and a communication module 190.

Further, outside the detector 13, an external communication module 39 that functions under the control of the console 30 is provided. In the example shown in FIG. 8, the case where the external communication module 39 is provided outside the console 30 is shown, but the external communication module 39 may be provided inside the console 30.

The communication module 190 and the external communication module 39 can communicate with each other using NFC (Near Field Communication) or Bluetooth (registered trademark). For example, the external communication module 39 transmits reference information to the communication module 190 under the control of the console 30.

Here, for example, the console 30 detects defects in each pixel or APD 141 in advance, and generates reference information so as not to reflect the output signal from the defective pixels or the defective APD. More specifically, an APD whose output value is always 1 when no X-rays are incident, and a pixel whose output value from all APDs is always 1 when no X-rays are incident are output. Reference information is generated to exclude the signal from the count value. As described above, the reference information indicates a predetermined correction value for the accumulated result.

Then, the communication module 190 transfers the reference information received from the external communication module 39 to the control arithmetic processing unit 180. Then, the control arithmetic processing unit 180 sets the reference information received in each LUT 150. That is, the reference information can be set by accessing from an external device.

Then, the LUT 150 according to the second embodiment uses the reference information to generate an output signal in which the output values from the APD in the failure state and the pixels in the failure state are corrected. In other words, the LUT 150 according to the second embodiment can execute the correction process as the pre-process by using the reference information. It should be noted that these correction processes can also be processed in the subsequent stage. However, when the correction process is executed by software in the subsequent stage, floating-point arithmetic is required for each of several thousand pixels. Therefore, it takes time for the correction process in the subsequent stage. On the other hand, in the LUT 150 according to the second embodiment, since the correction process in the subsequent stage can be omitted for each of several 1000 pixels, the time required for image reconstruction can be shortened. As a result, the X-ray CT apparatus according to the second embodiment can reduce the processing load and increase the throughput.

Further, the LUT 150 can realize a correction process other than a simple photon count by positively using this reference information. For example, even in a state where X-rays are not incident, an implied current generated by APD may be generated with a certain probability. Therefore, the count value corresponding to the implied current is estimated in advance, and the reference information corrected for the implied current count value is set in the LUT 150. Then, the LUT 150 may output an output signal corrected by the number of counts corresponding to the implied current. Further, for example, when a statistically pseudo count value appears, the reference information obtained by subtracting this pseudo count value may be set in the LUT 150.

(Modified example of the second embodiment)
In the second embodiment described above, the case where the reference information indicates a predetermined correction value for the accumulated result has been described, but the embodiment is not limited to this. For example, the reference information may indicate an energy band according to the accumulation result. More specifically, the count value is further replaced with an energy bin. For example, when the value of the count value α is α1 <α ≦ α2, it is discriminated into energy E1, when α2 <α ≦ α3, it is discriminated into energy E2, and when α3 <α ≦ α4, it is discriminated. It discriminates into the energy E3, and when α4 <α≤α5, the reference information is set so as to discriminate into the energy E4. In such a case, the LUT 150 can generate an output signal indicating a count value for each energy band by using the reference information. That is, since the X-ray CT apparatus can discriminate energy in the detector 13, it is possible to reduce the processing load in the subsequent stage.

Further, in the second embodiment described above, the case where the reference information is set in the LUT 150 by wireless communication such as NFC or Bluetooth (registered trademark) has been described, but the embodiment is not limited to this. For example, the LUT 150 may have a dual port interface. In such a case, the LUT 150 receives the designation of the address and the data for the designated address from the outside, and sets the reference information.

When setting reference information by specifying an address and data from the outside for a LUT150 having a dual port interface, control signals such as CS (Clear To Send), WR, and RD can be either parallel or serial. Is. If the control signal is serial, there are many advantages such as a decrease in signal lines.

Further, in the above-described second embodiment and the modified example of the second embodiment, the case where the reference information is set as the initial value has been described, but the embodiment is not limited to this. For example, the above-described second embodiment and modified examples of the second embodiment can be similarly applied when rewriting the reference information set as the initial value.

In the second embodiment and the modified examples of the second embodiment described above, the case where the LUT 150 is configured by using the magnetic memory has been described, but the embodiment is not limited to this. For example, the above-described second embodiment and modified examples of the second embodiment can be similarly applied to the LUT 150 according to the first embodiment configured by using a mask ROM. The reference information cannot be updated in the LUT 150 according to the first embodiment configured by using the mask ROM.

(Third Embodiment)
In the second embodiment, the case where the reference information of the LUT is set in advance by the external device has been described. By the way, the characteristics of the detector 13 change depending on the temperature. Also, the implied current depends on the temperature. Therefore, the reference information of the LUT may be dynamically rewritten according to the temperature change in the detector 13. Therefore, in the third embodiment, a case where the temperature inside the detector 13 is measured by the temperature sensor and the reference information of the LUT is rewritten in real time according to the change in temperature will be described.

The overall configuration of the X-ray CT apparatus according to the third embodiment is the same as the configuration example shown in FIG. 1, except that a part of the configuration inside the detector 13 is different. Therefore, the description of the same configuration as in FIG. 1 will be omitted. FIG. 9 is a diagram showing a configuration example of SiPM 130 according to the third embodiment. The APD cell 140 and the capacitor group 160 shown in FIG. 9 have the same functions as the APD cell 140 and the capacitor group 160 described in FIG.

As shown in FIG. 9, a temperature sensor 200 is provided in the vicinity of the SiPM 130. In the example shown in FIG. 9, it is assumed that the temperature sensor 200 is provided in the vicinity of each SiPM 130. However, only one temperature sensor 200 may be provided in the detector 13, or the plurality of SiPM 130 may be provided with only one temperature sensor 200. On the other hand, it may be provided at a ratio of one.

The LUT 150 according to the third embodiment stores a plurality of reference information. For example, the LUT 150 according to the third embodiment stores a plurality of reference information according to the temperature. Hereinafter, a case where the LUT 150 stores the reference information A, the reference information B, the reference information C, and the reference information D will be described.

When the temperature measured by the temperature sensor 200 is T, the reference information A is the reference information corrected for the implied current assumed when T <T1. Further, the reference information B is reference information in which the implied current assumed when T1 ≦ T <T2 is corrected is corrected. Then, the reference information C is reference information corrected for the implied current assumed when T2 ≦ T <T3. Further, the reference information D is reference information corrected for the implied current assumed when T3 ≦ T. It is assumed that temperature T1 <temperature T2 <temperature T3.

The temperature sensor 200 measures the temperature and outputs the measured temperature to the control arithmetic processing unit 180. Then, the control arithmetic processing unit 180 selects any one of the plurality of reference information according to the temperature measured by the temperature sensor 200. For example, the control arithmetic processing device 180 compares the temperature T measured by the temperature sensor with T1, T2 and T3, and the temperature T measured by the temperature sensor 200 is in the temperature range of the temperatures T1 to T3. Determine if it is close to the temperature range. Then, the control arithmetic processing unit 180 selects appropriate reference information based on the determination result and sets it in the LUT 150. As a result, the LUT 150 uses the selected reference information to generate an output signal. For example, when the temperature T is T2 ≦ T <T3, the control arithmetic processing unit 180 selects the reference information C and sets it in the LUT 150. In such a case, the LUT 150 uses the reference information C to generate an output signal.

The control arithmetic processing unit 180 switches the reference information between views, between slices, or during the reset period of the SiPM 130, and does not switch the reference information during image acquisition.

In the third embodiment described above, the LUT 150 has been described as storing a plurality of reference information, but the embodiment is not limited to this. For example, the control arithmetic processing unit 180 may generate reference information in real time based on the temperature measured by the temperature sensor 200, and set the generated reference information in the LUT 150. In other words, the control arithmetic processing unit 180 rewrites the reference information in real time according to the temperature measured by the temperature sensor 200.

Further, in the third embodiment described above, the count of the temperature and the implied current in the detector 13 has been described, but the embodiment is not limited to this. For example, the reference information may be switched by the same mechanism even if an external factor other than the temperature is used.

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

For example, in the above-described embodiment, the capacitor group 160 is described as having one capacitor for each APD 141, but the embodiment is not limited to this. For example, in the capacitor group 160, a plurality of capacitors may be provided for each APD 141, and the capacitors may be switched within a predetermined period to accumulate an electric signal. In other words, a plurality of capacitors are provided for each APD 141, and the capacitors are switched within a predetermined period to accumulate an electric signal. 10A to 10D are diagrams for explaining the capacitor group 160 according to other embodiments.

FIG. 10A shows a configuration example of a capacitor included in the capacitor group 160 according to another embodiment. In FIG. 10A, only the capacitor C1a and the capacitor C1b will be illustrated and described among the plurality of capacitors included in the capacitor group 160 according to the other embodiment. As shown in FIG. 10A, a capacitor C1a and a capacitor C1b are provided for the APD (D1). Then, either one of the capacitor C1a and the capacitor C1b is selectively connected to the APD (D1). Further, a comparator A1 is provided for the capacitor C1a and the capacitor C1b. Then, either one of the capacitor C1a and the capacitor C1b is selectively connected to the comparator A1.

For example, as shown in FIG. 10B, the capacitor C1a is connected to the APD (D1) by receiving the input of the selection signal and connecting the switch Sw1a and the switch Sw1b to the capacitor C1a. Here, when the switch Sw1c is released by receiving the input of the selection signal, the capacitor C1a accumulates the electric signal output from the APD (D1). Then, the comparator A1 detects the electric signal stored in the capacitor C1a by sense-up and compares it with the comparative potential Vth. Then, when the comparator A1 determines that the accumulated electric signal is Vth or more, it outputs 1 as an output value to the LUT 150 as the accumulation result. In the following, when the storage result of the electric signal stored in the capacitor C1a is output, the output value A1-1 is described. In the example shown in FIG. 10B, Sw1d receives the input of the selection signal and is closed, and the electric signal stored in the capacitor C1b is reset.

Further, for example, as shown in FIG. 10C, the capacitor C1b is connected to the APD (D1) by receiving the input of the selection signal and connecting the switch Sw1a and the switch Sw1b to the capacitor C1b. Here, when the switch Sw1d is released by receiving the input of the selection signal, the capacitor C1b accumulates the electric signal output from the APD (D1). Then, the comparator A1 detects the electric signal stored in the capacitor C1b by sense-up and compares it with the comparative potential Vth. Then, when the comparator A1 determines that the accumulated electric signal is Vth or more, it outputs 1 as an output value to the LUT 150 as the accumulation result. In the following, when the storage result of the electric signal stored in the capacitor C1b is output, the output value A1-2 is described. In the example shown in FIG. 10C, Sw1c receives the input of the selection signal and is closed, and the electric signal stored in the capacitor C1a is reset.

FIG. 10D shows the timing of processing by the LUT 150 when a plurality of capacitors are provided for each APD. In the example shown in FIG. 10D, the gate time is from time t1 to time t5, from time t5 to time t9, and from time t9 to time t13. Further, as shown in FIG. 10D, the capacitor group 160 receives the input of the selection signal at time t3, time t5, time t7, time t9, time t11, and time t13.

Further, in the example shown in FIG. 10D, during the period from time t1 to time t5, the LUT 150 receives the input of the output value 1 output from the two comparators, the comparator A1-1 and the comparator Am-1, at t2. , LUT150 generates an output signal based on the output values output from the comparator A1-1 and the comparator Am-1, and outputs the generated output signal to the FIFA 170. Then, the input of the LUT 150 is switched to A1-2 ... Am-2 after receiving the input of the selection signal at time t3, and at the same time, the capacitor of the comparator of the A1-1 ... Am-1 is reset. .. After that, after receiving the input of the output value 1 output from the comparator A1-2 connected to the LUT 150 at t4, the LUT 150 generates an output signal based on the output value output from the comparator A1-2. , The generated output signal is output to the FIFO 170.

Further, in the example shown in FIG. 10D, during the period from time t5 to time t9, the LUT 150 receives the input of the output value 1 output from the comparator A1-1 at t6, and then the LUT 150 starts from the comparator A1-1. An output signal is generated based on the output value, and the generated output signal is output to the FIFO 170. Then, the input of the LUT 150 is switched to A1-2 ... Am-2 after receiving the input of the selection signal at time t7, and at the same time, the capacitor of the comparator of the A1-1 ... Am-1 is reset. .. After that, after receiving the input of the output value 1 output from the two comparators A1-2 and the comparator A2-2 connected to the LUT 150 at t8, the LUT 150 outputs from the comparators A1-2 and the comparator A2-2. An output signal is generated based on the generated output value, and the generated output signal is output to the FIFO 170.

Similarly, in the example shown in FIG. 10D, during the period from time t9 to time t13, the LUT 150 received the input of the output value 1 output from the two comparators, the comparator Am-1 and the comparator A2-1, at t10. After that, the LUT 150 generates an output signal based on the output values output from the comparator Am-1 and the comparator A2-1, and outputs the generated output signal to the FIFA 170. Then, the input of the LUT 150 is switched to A1-2 ... Am-2 after receiving the input of the selection signal at time t11, and at the same time, the capacitor of the comparator of the A1-1 ... Am-1 is reset. .. After that, after receiving the input of the output value 1 output from the comparator A1-2 connected to the LUT 150 at t12, the LUT 150 generates an output signal based on the output value output from the comparator A1-2. , The generated output signal is output to the FIFO 170.

As in the above embodiment, by arranging a plurality of capacitors in one cell and sequentially switching the connection with the sense amplifier, photons can be counted more frequently. As a result, the number of counts that can be counted at high doses can be increased, and pile-up can be suppressed.

Further, in the above-described embodiment, the capacitor group 160 has been described as controlling individual switches to reset the electric signal stored in the capacitor when the input of the reset signal is received. By the way, since the reset switch is generally composed of transistors, a soft error may occur. In such a case, the reset switch may be switched from off to on. Therefore, an embodiment for preventing a soft error in the reset switch will be described. FIG. 11 is a diagram showing a configuration example of SiPM 130 according to another embodiment.

As shown in FIG. 11, a reset timing control circuit 210 is provided outside the SiPM 130. Here, the reset timing control circuit 210 is provided in the radiation blocking area. The reset timing control circuit 210 erases the accumulated electric signal after a predetermined period of time. Here, the predetermined period is set based on the light emission period of the scintillator provided in the indirect conversion type X-ray detection element. For example, the predetermined period is longer than the time during which the light emission of the scintillator is halved. Then, the reset timing control circuit 210 outputs a reset signal to each capacitor to erase the electric signal accumulated in each capacitor at a predetermined timing. Then, each reset switch for erasing the electric signal stored in each capacitor is controlled based on the reset signal output from the reset timing control circuit 210.

For example, as shown in FIG. 11, in the capacitor group 160, each reset switch for erasing the electric signal stored in each capacitor is connected in series with another reset switch. Then, the capacitor group 160 erases the electric signal accumulated in synchronization with the other reset switches based on the reset signal output from the reset timing control circuit 210. In other words, each reset switch erases the electric signal accumulated by each capacitor in synchronization with the other switches based on the reset signal output from the reset timing control circuit 210. This makes it possible for the X-ray CT apparatus to prevent soft errors in the reset switch. In the example shown in FIG. 11, the case where the reset timing control circuit 210 is provided in the radiation blocking area has been described, but the embodiment is not limited to this. For example, the reset timing control circuit 210 may be provided outside the radiation blocking area as long as the reset processing cannot be performed unless the reset switches are turned on at the same time.

In the above-described embodiment, the detector 13 is supported by the rotating frame 15 and is described as rotating at high speed in a circular orbit centered on the subject P, but the embodiment is not limited to this. For example, the above-described embodiment is also applicable when a plurality of photon counting detectors (PCDs) are arranged in a fourth generation array. Here, in the fourth generation X-ray CT apparatus, a predetermined number of photon counting detectors (PCDs) are sparsely arranged at fixed positions along a predetermined circle around the subject to be scanned. In addition, it is a hybrid type X-ray CT apparatus equipped with both an energy integral detector arranged in a 3rd generation geometric shape and a photon counting type detector (PCD) sparsely arranged in a 4th generation geometric shape. However, the above-described embodiment is applicable.

Further, in the above-described embodiment, the case where the detector 13 is an indirect conversion type photon counting type detector has been described, but the embodiment is not limited to this. For example, the X-ray detection element of the detector 13 may be a direct conversion type. In such a case, the X-ray detection element is composed of, for example, a cadmium telluride (CdTe: cadmium telluride) semiconductor, a cadmium zinc telluride (CdZnTe) semiconductor, or the like.

In the description of the above-described embodiment, each component of each of the illustrated devices is a functional concept, and does not necessarily have to be physically configured as shown in the figure. That is, the specific form of distribution / integration of each device is not limited to the one shown in the figure, and all or part of the device is functionally or physically dispersed / physically distributed 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 realized by a CPU and a program analyzed and executed by the CPU, or may be realized as hardware by wired logic.

Further, the control method described in the above embodiment can be realized by executing a control program prepared in advance on a computer such as a personal computer or a workstation. This control program can be distributed via a network such as the Internet. Further, this control program can also be executed by being recorded on a computer-readable recording medium such as a hard disk, flexible disk (FD), CD-ROM, MO, or DVD, and being read from the recording medium by the computer.

According to at least one embodiment described above, the accuracy of the photon counting process can be improved.

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

10 gantry 13 detector 140 APD cell 141 APD
150 LUT

Claims (21)

Multiple X-ray detectors that detect X-rays and generate electrical signals,
A capacitor provided for each X-ray detection element and accumulating an electric signal generated by each X-ray detection element,
By using the accumulated result of the electrical signal in the capacitor of the multiple, with a previously stored reference information, and a generator for generating a digital signal,
Equipped with a,
An integrator is not provided between each X-ray detector and the generator.
Photon counting type detector. The photon counting type detector according to claim 1, wherein the generation unit outputs a linear digital signal with respect to the accumulation result by using the reference information. The X-ray detection element has a plurality of photoelectric conversion units and has a plurality of photoelectric conversion units.
The photon counting type according to claim 2, wherein the generation unit receives inputs of output values from the plurality of photoelectric conversion units and generates the digital signal corresponding to the total value of the input values based on the reference information. Detector. The photon counting type detector according to claim 1, wherein the generation unit outputs a non-linear digital signal with respect to the accumulation result by using the reference information. The photon counting type detector according to claim 4, wherein the reference information indicates a predetermined correction value for the accumulation result. The photon counting type detector according to claim 4, wherein the reference information indicates an energy band according to the accumulation result. The photon counting type detector according to claim 1, wherein the generation unit is composed of a mask ROM (Read Only Memory). The photon counting type detector according to claim 1, wherein the generation unit is composed of a magnetic memory. The photon counting type detector according to claim 8, wherein the reference information can be set by accessing from an external device. Equipped with a temperature sensor
The photon counting type detector according to claim 9, wherein the external device rewrites the reference information in real time according to the temperature measured by the temperature sensor. The generator stores a plurality of reference information and stores a plurality of reference information.
The photon counting type detector according to claim 10, wherein the external device selects any one of the plurality of reference information according to the temperature measured by the temperature sensor. Further, a control unit for outputting a control signal for erasing the electric signal accumulated in each capacitor at a predetermined timing to each capacitor is provided.
The photon counting type detector according to claim 1, wherein each switch for erasing the electric signal stored in each capacitor is controlled based on the control signal output from the control unit. The photon counting type detector according to claim 12, wherein the control unit is provided in a radiation blocking area. The control unit erases the accumulated electric signal after a predetermined period of time.
The photon counting type detector according to claim 12, wherein the predetermined period is set based on a light emitting period of a scintillator provided in the indirect conversion type X-ray detection element. The photon counting type detector according to claim 14, wherein the predetermined period is longer than the time during which the light emission of the scintillator is halved. The photon counting type detector according to claim 1, wherein each X-ray detection element is an indirect conversion type X-ray detection element having a plurality of photoelectric conversion units. The photon counting type detector according to claim 16, wherein a plurality of the capacitors are provided for each photoelectric conversion unit, and the capacitors are switched within a predetermined period to accumulate an electric signal. Each switch for erasing the electric signal accumulated in each capacitor is connected in series with another switch, and each capacitor synchronizes with the other switch based on the control signal output from the control unit. The photon counting type detector according to claim 12, which erases an accumulated electric signal. The photon counting type detector according to claim 1, wherein the generation unit is provided for each of a predetermined number of capacitors, and generates a digital signal by using the accumulation result of each of a predetermined number of capacitors and the reference information. The generator
A first generator, which is provided for each predetermined number of capacitors and generates a first digital signal using the accumulation result of each predetermined number of capacitors and the first reference information,
A second digital signal is generated by using the first digital signal generated by the first generation unit and the second reference information, and the generated second digital signal is used as the digital signal. The photon counting type detector according to claim 1, further comprising a generator. Multiple X-ray detectors that detect X-rays and generate electrical signals,
A capacitor provided for each X-ray detection element and accumulating an electric signal generated by each X-ray detection element,
By using the accumulated result of the electrical signal in the capacitor of the multiple, with a previously stored reference information, and a generator for generating a digital signal,
Photon counting type detector equipped with
A collecting unit that collects the digital signal from each of the X-ray detection elements,
A reconstruction unit that reconstructs an image using the digital signal collected by the collection unit, and a reconstruction unit.
Equipped with a,
An X-ray CT apparatus in which an integrator is not provided between each X-ray detection element and the generation unit.

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