Gamma camera, detector and CT machine

Abstract

The utility model discloses a gamma camera, a detector and a CT machine. The gamma camera comprises a scintillator, a collimator, an S < iPM > array, a signal transmission unit, an analog-to-digital conversion unit and a data processing unit. The collimator is arranged in the light incident direction of the scintillator, comprises N light through holes arranged in a matrix manner, and is used for shielding non-vertical incident rays; the S iPM array is matched with the scintillator and the collimator to ensure that photons excited by rays emitted from each light through hole after passing through the scintillator are captured by at least one S iPM; the analog-to-digital conversion unit comprises a Q-V conversion circuit, a single-ended-differential voltage conversion circuit, a differential voltage amplification circuit and an AD conversion circuit, so that a two-stage integrator and a converter are formed, and the signal precision is improved; and the signal transmission unit can adopt a multi-channel connector or a diode array, so that resource occupation is reduced. The detector is formed by splicing gamma cameras into a whole ring and is applied to a CT machine, high-precision detection can be achieved under low-dose rays, and the imaging resolution ratio and accuracy are improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to a gamma camera, also relates to a detector including the gamma camera, and further relates to a CT machine including the detector, belong to radiation imaging technical field. BACKGROUND

[0002] SiPM (Silicon Photomultiplier) is a new type of high-performance semiconductor photodetector, which is composed of multiple avalanche photodiodes (APD) working in Geiger mode. It has single-photon sensitivity and can detect photons from near-ultraviolet (UV) to near-infrared (IR). The main advantages of SiPM include high gain, fast response, low operating voltage, anti-magnetic field interference and mechanical impact resistance, and is widely used in extremely weak light detection fields such as high-energy physics, radiation measurement, biomedical imaging, etc.

[0003] SPECT (Single Photon Emission Computed Tomography) is a nuclear medical imaging technology used to detect the distribution of radioactive tracers in the body. The core function of the SPECT detector is to detect the radiation emitted by the radioactive tracer and convert it into a measurable electrical signal. Through the SPECT detector, two-dimensional or three-dimensional images of internal organs or tissues of the human body can be generated for diagnosis and research of various diseases.

[0004] The working principle of the SPECT detector is as follows: after applying a reverse bias voltage to the P-N junction of the avalanche photodiode, the incident light is absorbed by the P-N junction to form a photocurrent. Through voltage control, applying appropriate reverse bias voltage will cause the avalanche photodiode to produce "avalanche" phenomenon, and the photocurrent will be multiplied, reaching the avalanche multiplication state, thereby realizing the technology of SiPM. SiPM has very high sensitivity and can reach the level of photons, and is often used in photon counters and other applications. By adding a scintillator outside the SiPM, the radiation can be effectively converted into a weak current, and after passing through an analog-to-digital conversion circuit, a digital signal is formed, and then the FPGA performs data processing and output, finally realizing the purpose of the radiation detector. SUMMARY

[0005] The primary technical problem to be solved by the utility model is to provide a gamma camera.

[0006] Another technical problem to be solved by the utility model is to provide a detector including the gamma camera.

[0007] Still another technical problem to be solved by the utility model is to provide a CT machine including the detector.

[0008] To achieve the above technical purposes, the utility model adopts the following technical solutions:

[0009] According to the first aspect of the embodiment of the utility model, a gamma camera is provided, comprising a scintillator, a collimator, a SiPM array, a signal transmission unit, an analog-digital conversion unit, a data processing unit, wherein,

[0010] The collimator is arranged in the light-in direction of the scintillator and comprises N light transmission holes arranged in a matrix, for shielding rays other than the vertical incidence, N being a positive integer;

[0011] The SiPM array comprises N SiPMs arranged in a matrix, and the SiPM array, the scintillator and the collimator are arranged such that the photons excited by the rays emitted by each light transmission hole after passing through the scintillator are captured by at least one SiPM;

[0012] The SiPM array is connected to the analog-digital conversion unit through the signal transmission unit, the analog-digital conversion unit is connected to the data processing unit, and the data processing unit integrates data and outputs image gray values.

[0013] Preferably, the analog-digital conversion unit comprises a Q-V conversion circuit, a single-ended-differential voltage conversion circuit, a differential voltage amplification circuit and an AD conversion circuit connected in series, constituting a two-stage integrator and converter.

[0014] Preferably, the Q-V conversion circuit serves as a first-stage integrator and converter, converts the energy accumulated by the weak current from the SiPM array into a voltage signal, and is used for subsequent signal amplification and signal processing; the single-ended-differential voltage conversion circuit serves as a second-stage integrator and converter, converts the single-ended signal into a differential signal to eliminate common-mode interference.

[0015] Preferably, the single-ended-differential voltage conversion circuit is an operational amplifier integrator circuit, wherein the inverting input terminal of the first operational amplifier is connected to two parallel capacitors, and the non-inverting input terminal is grounded; the other end of the capacitor is connected to the output terminal of the first operational amplifier, forming a negative feedback loop.

[0016] Preferably, the differential voltage amplification circuit comprises a second operational amplifier and a plurality of resistors; the two input terminals of the differential voltage amplification circuit are connected to the non-inverting input terminal and the inverting input terminal of the second operational amplifier through two resistors, respectively; and the output terminal of the second operational amplifier is connected to the inverting input terminal of itself, forming a negative feedback loop.

[0017] Preferably, among the two output terminals of the first operational amplifier, one is connected to the non-inverting input terminal of the second operational amplifier through a resistor, and the other is connected to the inverting input terminal of the second operational amplifier through a resistor.

[0018] Preferably, the signal transmission unit is an N-channel connector that establishes a one-to-one link connection between the SiPM array and the analog-to-digital conversion unit.

[0019] Preferably, the signal transmission unit employs one or more dual-input single-output diode arrays, each diode array containing 8×8 diode units; each diode unit consists of two diodes connected in parallel, wherein the anodes of the two diodes are connected together and connected to a SiPM.

[0020] According to a second aspect of the present invention, a detector is provided, wherein the aforementioned gamma cameras are stitched together to form a complete ring.

[0021] According to a third aspect of the present invention, a CT scanner is provided, including the detector as described above.

[0022] Compared with existing technologies, this invention achieves efficient gamma ray detection and signal processing by using a SiPM as the core component, combined with a scintillator and collimator, and a specific circuit design. The two-stage integrator and converter design of the analog-to-digital conversion unit effectively improves signal accuracy and reduces circuit complexity. The signal transmission unit offers two design options: a one-to-one link via a multi-channel connector or a diode array to reduce resource consumption. This design reduces radiation dose while improving imaging resolution and accuracy, enabling the detector to perform high-precision image detection under low-dose radiation conditions. Furthermore, each functional module supports independent disassembly, facilitating debugging and maintenance, thereby improving the practicality and reliability of the equipment. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the gamma camera provided in the first embodiment of the present invention;

[0024] Figure 2 for Figure 1 A schematic diagram of the collimator structure in the image;

[0025] Figure 3 for Figure 1 A schematic diagram showing the connection between the scintillator and the SiPM array;

[0026] Figure 4 for Figure 3 Right view of the structure shown;

[0027] Figure 5 for Figure 1 A schematic diagram of the diode array connection in the diagram;

[0028] Figure 6 This is a circuit connection diagram of the gamma camera in the first embodiment of the present invention. DETAILED DESCRIPTION

[0029] The technical content of the utility model will be explained in detail with specific embodiments and the accompanying drawings.

[0030] The technical concept of the embodiment of the utility model is: using SiPM (silicon photomultiplier) as the core element, combining the scintillator and the collimator to detect gamma rays, and processing and converting signals through specific circuit design. Among them, the analog-to-digital conversion unit adopts two-stage integrator and converter to improve signal accuracy and reduce circuit complexity. In addition, the signal transmission unit has two designs: one is a one-to-one link of a multi-channel connector, and the other is a diode array to reduce resource occupation. The detector is spliced into a ring shape by multiple gamma cameras, and is applied to a CT machine. It can reduce the dose of rays while improving the resolution and accuracy of imaging, so as to realize high-precision detection under low-dose rays.

[0031] First embodiment

[0032] As shown in Figure 1 The gamma camera provided by the first embodiment of the utility model comprises a collection board and a processing board. Among them, the collection board is integrated with a scintillator 10, an SiPM array 11, a signal transmission unit and a power supply 14. The light entrance direction of the scintillator 10 is provided with a collimator 101, which is used to shield the rays other than the vertical incidence (perpendicular to the scintillator 10), limit the angle of the rays entering the scintillator, exclude the interference of scattered rays, and realize light collimation.

[0033] As shown in Figure 2 The collimator 101 is a honeycomb hole structure composed of a tungsten plate, which comprises N matrix arranged light transmission holes 101n. The light transmission hole 101n divides the incident high-energy rays into N parallel light beams arranged in matrix, which are vertically incident on the scintillator 10. The scintillator 10 converts the incident high-energy rays into photons in the visible light range.

[0034] As shown in Figure 3 And Figure 4 The SiPM array 11 as an example of pixelated photodetector is located on the back surface (the surface opposite to the ray incidence surface) of the scintillator 10. The SiPM array 11 detects the flux of photons and samples them, thereby providing the number of detected photons (for example, every 5ns).

[0035] SiPM array 11 includes N SiPMs arranged in a matrix, and each SiPM has a photosensitive area of 6mm*6mm, and is a S13361-2050 series SiPM of HAMAMATSU Co., Ltd., such as S13361-2050AE-08.

[0036] The scintillator and the SiPM array convert the rays into visible photons, and then convert the visible light into an electric current and output the electric current. The visible photons are captured by each SiPM and converted into an electric signal.

[0037] The SiPM array 11 is connected to a processing board through a signal transmission unit. In an embodiment of the present application, the signal transmission unit is two connectors 111 (as shown in Figure 3 The connector is N channels (N=64 in this embodiment), so that the SiPM array and the analog-digital conversion unit on the processing board are directly connected in a one-to-one manner, realizing one-to-one conversion between each channel of the SiPM array and each channel of the analog-digital conversion unit.

[0038] In another embodiment, the signal transmission unit is a diode array 112 (as shown in Figure 5 Specifically, it is one or more (for example, four) 88-arranged double-input single-output diode arrays. As shown in Figure 5 The diode array 112 includes 88 diode units. These diode units represent pixel points in a photodetector. Each pixel point generates a charge signal proportional to the received light intensity. Each diode unit includes two diodes in parallel, and the anodes (positives) of the two diodes are connected together with a SiPM, and the cathodes (negatives) are respectively led out as pin 1 and pin 2.

[0039] As shown in Figure 5 In the diode array 112, the output pins 1 of diode units in the same row are connected to form a channel of the array. Similarly, the output pins 2 of diode units in the same column are connected to form a channel of the array. In this way, the 64-channel SiPM array is integrated into 16-channel output with 8 channels in row and column. Thus, the embodiment realizes the purpose of inputting 256 SiPM matrix signals to the analog-digital conversion unit by using four 8*8 diode arrays. Therefore, the embodiment converts 64 signals into 16-channel acquisition through the diode array, greatly reducing the occupation of resources.

[0040] The power supply of the acquisition board is a chip of model LT3482IUD#PBF. The chip has a voltage regulation range of 0-90V, and the ripple can be as low as 100uV / DIV when the output is 85V / 2.5mA. The chip is a power supply dedicated chip of the APD series, which can provide stable power supply for the SiPM array. In addition, the power supply voltage can be adjusted by replacing the voltage dividing resistor of the chip.

[0041] The processing board comprises an analog-digital conversion unit and a data processing unit. The analog-digital conversion unit is preferably realized by an integrated integrator and converter ADC chip (such as AD9253, AD9633 or AD7606, etc.). The data processing unit is preferably realized by an FPGA, but is not limited thereto.

[0042] As shown in Figure 6 , the analog-digital conversion unit comprises a Q-V conversion circuit, a single-ended-differential voltage conversion circuit, a differential voltage amplification circuit and an AD conversion circuit connected in series. The Q-V conversion circuit is a first-stage integrator and converter, and its input end is connected to the aforementioned connector or diode array, so as to obtain the weak current of the SiPM array (shown as a PD chip in the figure). Figure 6 The Q-V conversion circuit converts the charge Q generated by each SiPM into a voltage V=Q / Cf, and then outputs to the single-ended-differential voltage conversion circuit.

[0043] The single-ended-differential voltage conversion circuit is a second-stage integrator and converter, and satisfies V d1 =(V-V max / 2)×G1, wherein V is the input single-ended signal voltage; V max is the maximum voltage of the signal; G1 is the gain of the first amplifier, indicating the amplification multiple of the signal in the conversion process; and V d1 is one component of the converted differential signal.

[0044] In an embodiment of the present application, the single-ended-differential voltage conversion circuit is an operational amplifier integrator circuit, wherein the inverting input end (-) of the first operational amplifier is connected to two parallel capacitors, and the non-inverting input end (+) is grounded (GND). The other end of the capacitor is connected to the output end of the first operational amplifier, forming a negative feedback loop. The input signal is connected to the inverting input end of the first operational amplifier, and the input signal is integrated through the capacitor, so as to generate a voltage signal proportional to the integral of the input signal at the output end of the first operational amplifier.

[0045] The differential voltage amplification circuit further amplifies the voltage V d1 converted into a differential form through an amplifier, so as to satisfy V d2 =V d1 ·G2, wherein V d2is the amplified differential voltage output; G2 is the gain of the second amplifier.

[0046] In an embodiment of the present application, the differential voltage amplification circuit includes a second operational amplifier and a plurality of resistors. The two input terminals of the differential voltage amplification circuit are connected to the non-inverting input terminal (+) and the inverting input terminal (-) of the second operational amplifier through two resistors, respectively. These resistors are used to set the gain and input impedance. The output terminal of the second operational amplifier is connected to the inverting input terminal of itself, forming a negative feedback loop, which can stabilize the gain and reduce the output drift of the second operational amplifier.

[0047] In an embodiment of the present application, the single-ended-differential voltage conversion circuit and the differential voltage amplification circuit are symmetrically designed. In the single-ended-differential voltage conversion circuit, one of the two output terminals of the first operational amplifier is connected to the non-inverting input terminal of the second operational amplifier of the differential voltage amplification circuit through a resistor, and the other is connected to the inverting input terminal of the second operational amplifier of the differential voltage amplification circuit through a resistor. The output terminal of the second operational amplifier is connected to the AD conversion circuit, which converts the analog electrical signal collected by the SiPM array 11 into a digital signal and inputs it into the data processing unit. The collected data is integrated in the data processing unit, and the image gray value is output.

[0048] In the gamma camera provided in the embodiment of the present application, the high-energy rays emitted by the ray source pass through the collimator for filtering, only the rays in the vertical direction can pass through the collimator and enter the scintillator located above the SiPM. The scintillator is excited by the vertically incident rays to generate visible light, which then enters the SiPM to form a weak current signal. The weak current signal is transmitted to the analog-digital conversion unit through the connector (one-to-one channel) or the 8x8 diode array (16 channels), and finally converted into a digital signal. The digital signal is integrated by the data processing unit and the image gray value is output. Among them, the 8x8 diode array identifies the row and column signals through the data processing unit to determine the position and intensity of the vertically incident rays in the SiPM array.

[0049] The analog-digital conversion circuit in the prior art is composed of a dispersed signal amplification circuit and a conversion circuit. Such a structure is prone to introduce interference in the signal transmission and amplification process, affecting the signal accuracy. In contrast, the analog-digital conversion unit in the present application adopts an integrated ADC chip (such as AD9253, AD9633, or AD7606, etc.) that integrates the operational amplifier and the conversion. The photoelectric signal directly enters the chip, shortening the analog signal path and thus reducing the interference. This design brings the following advantages:

[0050] 1) The analog-to-digital conversion unit comprises two-stage integrators and converters, which effectively improve the signal precision while reducing the circuit complexity. The first-stage integrators and converters convert weak current signals into voltage signals, facilitating subsequent amplification and processing; the second-stage integrators and converters convert single-ended signals into differential signals, eliminating common-mode interference and ensuring the accuracy and stability of the signals during transmission and amplification.

[0051] 2) Two signal transmission links are supported: one is a one-to-one link realized by a 64-way connector, and the other is a 16-way link realized by an 8x8 diode array, effectively reducing resource occupation. Specifically, a one-to-one link requires one ADC chip to collect 64-way signals (four ADC chips to collect 256-way signals), while an 8x8 diode array only needs one ADC chip to collect 256-way signals. In the design of a large-area detector, the 8x8 diode array can save three ADC chips, significantly saving resources and costs, and thus becomes the preferred solution.

[0052] 3) Each functional part can be individually disassembled, facilitating quick positioning and problem solving during debugging and use, improving the timeliness of maintenance and use.

[0053] Second embodiment

[0054] The second embodiment of the utility model provides a detector using the above-mentioned gamma camera, wherein the gamma cameras are spliced into a whole ring. The detector utilizes the analog-to-digital conversion unit in the gamma camera, especially the two-stage integrators and converters, thereby ensuring high-precision signal processing. In addition, since the SiPM array itself has high sensitivity and high signal conversion rate, the detector can complete image detection of the same level as other detectors under low-dose radiation conditions. Therefore, the detector provided in the embodiment can meet the requirements of low dose and high precision at the same time.

[0055] Third embodiment

[0056] The third embodiment of the utility model provides a CT machine, which comprises the above-mentioned detector.

[0057] It should be noted that the above-mentioned embodiments are only illustrative. The technical solutions of various embodiments can be combined, and the order of various steps can be changed, all within the protection scope of the utility model.

[0058] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more features. In the description of the utility model, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0059] The gamma camera, the detector and the CT machine are described in detail above. For those skilled in the art, any obvious modification made to the utility model without departing from the essential content of the utility model will constitute an infringement of the utility model patent right and will bear the corresponding legal responsibility.

Claims

1. A gamma camera characterized by The gamma camera comprises a scintillator, a collimator, a SiPM array, a signal transmission unit, an analog-digital conversion unit, and a data processing unit. The collimator is arranged in the light-in direction of the scintillator and comprises N matrix-arranged light transmission holes for shielding rays other than the vertically incident rays, wherein N is a positive integer. The SiPM array comprises N matrix-arranged SiPMs, and the SiPM array, the scintillator, and the collimator are arranged such that the photons excited by the rays emitted from each light transmission hole after passing through the scintillator are captured by at least one SiPM. The SiPM array is connected to the analog-digital conversion unit through the signal transmission unit, the analog-digital conversion unit is connected to the data processing unit, and the data processing unit integrates data and outputs image gray values.

2. The gamma camera of claim 1, wherein: The analog-digital conversion unit comprises a Q-V conversion circuit, a single-ended-differential voltage conversion circuit, a differential voltage amplification circuit, and an AD conversion circuit connected in series, and comprises a two-stage integrator and converter.

3. The gamma camera of claim 2, wherein: The Q-V conversion circuit serves as a first-stage integrator and converter, converts the energy accumulated by the weak current from the SiPM array into a voltage signal, and is used for subsequent signal amplification and signal processing; and the single-ended-differential voltage conversion circuit serves as a second-stage integrator and converter, converts the single-ended signal into a differential signal to eliminate common-mode interference.

4. The gamma camera of claim 3, wherein: The single-ended-differential voltage conversion circuit is an operational amplifier integrator circuit, wherein the inverting input terminal of a first operational amplifier is connected to two parallel capacitors, and the non-inverting input terminal is grounded; the other end of the capacitors is connected to the output terminal of the first operational amplifier, forming a negative feedback loop.

5. The gamma camera of claim 4, wherein: The differential voltage amplification circuit comprises a second operational amplifier and a plurality of resistors; the two input terminals of the differential voltage amplification circuit are connected to the non-inverting input terminal and the inverting input terminal of the second operational amplifier through two resistors, respectively; and the output terminal of the second operational amplifier is connected to the inverting input terminal of itself, forming a negative feedback loop.

6. The gamma camera of claim 5, wherein: One of the two output terminals of the first operational amplifier is connected to the non-inverting input terminal of the second operational amplifier through a resistor, and the other is connected to the inverting input terminal of the second operational amplifier through a resistor.

7. The gamma camera of claim 1, wherein: The signal transmission unit is an N-channel connector that establishes one-to-one link connection between the SiPM array and the analog-digital conversion unit.

8. The gamma camera of claim 7, wherein: The signal transmission unit adopts one or more diode arrays with two inputs and one output, each diode array comprises 8x8 diode units, and each diode unit comprises two parallel diodes with their anodes connected together and connected to a SiPM.

9. A probe, characterized by The gamma camera according to any one of claims 1 to 8, wherein the gamma cameras are tiled into a full ring.

10. A CT machine characterized by The probe according to claim 9.

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