High-resolution gamma camera and equipment applied to SPECT (Single Photon Emission Computed Tomography)

Abstract

The invention discloses a high-resolution gamma camera and equipment applied to SPECT (Single Photon Emission Computed Tomography). The high-resolution gamma camera comprises a collimator, a scintillator array, an APD array, an analog circuit unit and a digital processing unit, wherein the scintillator array, the APD array, the analog circuit unit and the digital processing unit are sequentially coupled and connected; the collimator is used for controlling the direction of the detected gamma ray; the scintillator array is used for converting incident gamma rays into visible photons and coupling the visible photons to the APD array; the APD array is used for converting an incident light signal into an electronic charge to form an analog current signal; the analog circuit unit is used for carrying out integration and conversion processing on the analog current signal and then outputting a digital signal; and the digital processing unit is used for acquiring and processing the digital signal to form image data and transmitting the image data to an upper computer. According to the high-resolution gamma camera, the spatial resolution and the energy resolution upper limit of an image reconstructed by the SPCET equipment are improved.

Description

Technical Field

[0001] The present invention relates to a high-resolution gamma camera applied to SPECT, and also relates to a SPECT device comprising the high-resolution gamma camera, belonging to the technical field of radiation imaging. Background Art

[0002] Single photon emission computed tomography (SPECT) is a medical imaging technology that uses a radioactive drug injected into the human body. The drug decays within the body, producing high-energy gamma rays. These gamma rays are then detected by a gamma camera. The distribution of single photons in the gamma rays is then reconstructed using computed tomography into a cross-sectional or three-dimensional image reflecting the physiological status of a specific organ. SPECT is widely used in the medical field to detect and diagnose a variety of diseases, including tumors, cardiovascular diseases, and bone diseases, and is crucial for improving the accuracy and efficiency of medical diagnostics.

[0003] In existing technologies, single-photon emission computed tomography (SPECT) usually has low spatial resolution, which makes the reconstructed image blurry. One important reason is that the scintillator is usually made of a whole crystal or a crystal cut into larger pixel areas. At the same time, the photoelectric converter uses a photomultiplier tube (PMT) or a silicon photomultiplier tube (SiPM) coupled to the scintillator to convert the visible light signal into a digital signal, and then uses an algorithm to infer the position of the scintillator's light emission. High-resolution SPECT requires smaller scintillator pixels (pixel ≤ 1mm). 2 ) while using a smaller photoelectric converter. Due to their internal multiple-reflection structure, photomultiplier tubes (PMTs) are physically difficult to achieve millimeter-scale dimensions. Small-sized silicon PMTs, however, are unable to effectively determine gamma photon energy due to the limited number of micropixels per unit area. Further shrinking the micropixel size will pose significant challenges to the SiPM fabrication process, and the detector cost per unit area will increase exponentially. Therefore, improving the spatial resolution of single-photon emission computed tomography (SPECT) without excessively sacrificing energy resolution to meet the imaging requirements of SPECT has always been a crucial technical research topic in this field.

[0004] Chinese patent application number 202210885057.9 discloses a gamma camera detector with improved spatial resolution. The gamma camera detector comprises a collimator layer, a scintillation crystal layer, a light guide layer, and a PMT array layer, arranged adjacently from the outside inward. A ring of extended light guides is positioned adjacent to the outer sides of the scintillation crystals. The extended light guides and the sides of the scintillation crystals are bonded and coupled together via optical adhesive or silicone oil. A ring of fillers is positioned above the extended light guides, located outside the light guide layer and PMT array layer. Summary of the Invention

[0005] The primary technical problem to be solved by the present invention is to provide a high-resolution gamma camera for SPECT.

[0006] Another technical problem to be solved by the present invention is to provide a SPECT device including the high-resolution gamma camera.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] According to a first aspect of an embodiment of the present invention, a high-resolution gamma camera for SPECT is provided, comprising a collimator, a scintillator array, an avalanche photodiode array, an analog circuit unit, and a digital processing unit; wherein,

[0009] The scintillator array, the avalanche photodiode array, the analog circuit unit and the digital processing unit are coupled and connected in sequence;

[0010] The collimator is used to control the direction of the detected gamma rays;

[0011] The scintillator array is used to convert incident gamma rays into visible photons and couple them to the avalanche photodiode array;

[0012] The avalanche photodiode array converts the incident light signal into electron charge by utilizing the avalanche amplification effect and outputs an analog current signal to the analog circuit unit;

[0013] The analog circuit unit is used to perform integration, voltage conversion and analog-to-digital conversion on the input analog current signal, and then output a digital signal to the digital processing unit;

[0014] The digital processing unit is used to collect and process the input digital signal to form image data and transmit it to the host computer.

[0015] Preferably, the scintillator array is composed of pixelated scintillators forming a pixel-level array;

[0016] The avalanche photodiode array is composed of pixelated avalanche photodiode chips forming a pixel-level array;

[0017] The pixelated scintillators in the scintillator array correspond one-to-one to the pixelated avalanche photodiode chips in the avalanche photodiode array.

[0018] Preferably, the pixelated scintillator is made of a high light yield scintillating crystal cut into a square columnar crystal material and then the surface is ground and polished;

[0019] The pixelated scintillators in the scintillator array are separated by a reflective layer; the outer surface of the scintillator array except the coupling surface is also prepared by a reflective layer;

[0020] Preferably, the area of ​​the pixelated avalanche photodiode chip is the same as the area of ​​the square column end of the pixelated scintillator;

[0021] After the surface of the pixelated avalanche photodiode chip in the avalanche photodiode array is scrubbed and dried, a plasma cleaning machine or ozone treatment is used to activate the chip surface;

[0022] The avalanche photodiode array is butt-jointed with the substrate.

[0023] Preferably, the coupling surface of the scintillator array is moistened with transparent optical silicone grease and then coupled with the coupling surface of the avalanche photodiode array using a flip-chip method, and then the entire structure is waterproof packaged using a waterproof layer.

[0024] Preferably, the analog circuit unit includes a charge transfer module, an integral conversion module and an analog-to-digital conversion module; wherein the output end of the avalanche photodiode array is connected to the input end of the charge transfer module, the input and output ends of the charge transfer module, the integral conversion module and the analog-to-digital conversion module are connected in series in sequence, and the output end of the analog-to-digital conversion module is connected to the input end of the digital processing unit.

[0025] Preferably, the charge transfer module is used to sequentially derive and collect the analog current signals output by the avalanche photodiode array and output them to the integral conversion module;

[0026] The integral conversion module is used to integrate the input analog current and convert it into an analog voltage signal, and then output it to the analog-to-digital conversion module;

[0027] The analog-to-digital conversion module is used to convert the input analog voltage signal into a digital signal and output the digital signal to the digital processing unit.

[0028] Preferably, the digital processing unit includes a serial-to-parallel conversion module, a pixel sorting module, a data cache module and a data output module; wherein the output end of the analog circuit unit is connected to the input end of the serial-to-parallel conversion module, the input and output ends of the serial-to-parallel conversion module, the pixel sorting module, the data cache module and the data output module are connected in series in sequence, and the output end of the data output module is the output end of the high-resolution gamma camera.

[0029] Preferably, the serial-to-parallel conversion module is used to convert the input serial digital signal into a parallel data signal and output the parallel data signal to the pixel sorting module;

[0030] The pixel sorting module is used to sort the input parallel data signals according to the physical position arrangement of the pixels to form image data and output the image data to the data buffer module;

[0031] The data cache module is used to store the generated image data;

[0032] The data output module is used to read the image data stored in the data cache module and transmit it to the host computer according to the agreed image transmission protocol.

[0033] According to a second aspect of an embodiment of the present invention, a SPECT device is provided, comprising the above-mentioned high-resolution gamma camera for SPECT.

[0034] Compared to existing technologies, the high-resolution gamma camera provided by the present invention utilizes a technical solution that couples a pixelated APD array with a pixelated scintillator array to convert optical signals into electrical signals. This allows for individual processing of the photoelectric signal at each pixel, resulting in more accurate gamma photon position information. Simultaneously, the analog circuit unit and digital processing unit convert and process the electrical signals into image data, improving the spatial resolution and energy resolution limit of images reconstructed by the SPCET device. Therefore, the high-resolution gamma camera provided by the present invention offers advantages such as a clever and rational structural design, low design cost, and high spatial resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the working principle diagram of the avalanche photodiode;

[0036] Figure 2 A structural block diagram of a high-resolution gamma camera for SPECT provided by the present invention;

[0037] FIG3( a ) is a schematic diagram of the coupling structure of a collimator, a scintillator array, and an APD array in an embodiment of the present invention;

[0038] FIG3( b ) is a schematic diagram of the coupling structure and packaging of the scintillator array and the APD array in an embodiment of the present invention;

[0039] Figure 4 1 is a structural block diagram of an analog circuit unit and a digital processing unit in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The technical content of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] like Figure 1 As shown in Figure 1, an avalanche photodiode (APD) is a photodiode that exhibits an avalanche effect. Its operating principle is that when photons strike the semiconductor material of an APD under a high reverse bias voltage (VCC), they trigger an avalanche amplification effect, generating more electrons and charge carriers than traditional photodiodes, thereby enhancing photoelectric conversion efficiency. APDs offer excellent performance, including high sensitivity, high gain, a wide dynamic range, and a fast response time.

[0042] like Figure 2 As shown, an embodiment of the present invention provides a high-resolution gamma camera for SPECT, comprising a collimator, a scintillator array, an APD array, an analog circuit unit, and a digital processing unit, wherein the scintillator array, the APD array, the analog circuit unit, and the digital processing unit are sequentially coupled.

[0043] The collimator is used to control the direction of the detected gamma rays. It consists of a lead plate containing a large number of pinholes and is installed in front of the scintillator array.

[0044] The scintillator array is used to convert incident gamma rays into visible photons and couple the visible photons to the APD array at the rear end. In a preferred embodiment of the present invention, the scintillator array can be made of high-light-yield scintillating crystals such as LYSO, sodium iodide, and GAGG.

[0045] The APD array uses the avalanche amplification effect of the avalanche photodiode to convert the incident light signal into electron charge and output an analog current signal to the analog circuit unit.

[0046] The analog circuit unit is used to perform integration and voltage conversion and analog-to-digital conversion on the input analog current signal, and then output a digital signal to the digital processing unit.

[0047] The digital processing unit is used to collect and process the input digital signals to form image data, and transmit the image data to the host computer.

[0048] In one embodiment of the present invention, the coupling structure of the collimator, scintillator array, and APD array is shown in Figure 3(a). The collimator is mounted at the front end of the scintillator array, and the APD array is mounted at the rear end of the scintillator array. The coupling structure and packaging method of the scintillator array and APD array are shown in Figure 3(b) (using an array with six rows or columns as an example). The scintillator array and APD array coupling structure includes a scintillator array 1, an APD array 2, a reflective layer 3, optical silicone grease 4, a PCB substrate 5, and a waterproof layer 6. The following details the fabrication method and installation process of this coupling structure.

[0049] The scintillator array 1 is an n*m pixel-level array of pixelated scintillators, where n and m are both positive integers. The pixelated scintillators are made of high-light-yield scintillator crystals cut into extremely small square-shaped prisms, for example, 1mm*1mm*3mm square-shaped prisms. The six sides of the square-shaped prisms are polished to form the pixelated scintillators. The pixelated scintillators are then arranged into an n*m pixel-level array. Titanium dioxide or ESR reflective tape is used as a reflective layer 3 to separate the pixelated scintillators in the array. A reflective layer 3 of titanium dioxide is also formed on the top and side surfaces (excluding the coupling surface) of the scintillator array 1.

[0050] The APD array 2 is composed of pixelated APD chips in an n*m pixel-level array. The size of the pixelated APD chip area is the same as the area of ​​the square column end of the pixelated scintillator. For example, the pixelated scintillator is a square column crystal material of 1mm*1mm*3mm, and the size of the pixelated APD chip area is 1mm 2 Before installation, the dust on the chip surface of the APD array 2 is first gently wiped with an alcohol swab, then dried at 60°C for 30 minutes. Then, the chip surface is activated using a plasma cleaner or ozone treatment for 10 minutes to prepare for coupling and installation with the scintillator array 1. The other side of the APD array 2 is provided with external interfaces, including output interfaces and power supply interfaces. Therefore, the docking installation of the APD array 2 and the PCB substrate 5 uses corresponding base connections or direct welding connections.

[0051] When coupling the scintillator array 1 and the APD array 2, the lower surface (i.e., the coupling surface) of the scintillator array 1 is first moistened with an appropriate amount of transparent optical silicone grease 4. The scintillator array 1 and the upper surface of the APD array 2 are then coupled and mounted using a flip-chip method, ensuring a one-to-one correspondence between the pixelated scintillators in the scintillator array 1 and the pixelated APDs in the APD array 2. Finally, a waterproof layer 6 of parylene is used to waterproof the entire structure.

[0052] The working principle of the scintillator array and APD array coupling structure is that when a gamma ray hits the scintillator array, the pixelated scintillator at the incident point lights up, and the generated visible light reaches the corresponding pixelated APD photosensitive surface directly or through reflection, causing an avalanche amplification effect to generate a large number of carrier electrical signals, and at the same time generates an after pulse with a dead time of about 10ns. The electrical signal is transmitted to the subsequent analog circuit unit for corresponding processing. Since the light sensor composed of the pixelated APD corresponds to the scintillator pixel one by one, the physical position of the gamma ray source can be accurately obtained during imaging processing without algorithm calculation, making the final imaging resolution higher. At the same time, the adjacent pixelated APDs will not be affected by the presence of the reflective layer and can receive the incident photons normally, avoiding the inaccurate judgment of the incident point caused by the simultaneous incidence of gamma photons at adjacent positions. Furthermore, due to the smaller size of the pixelated scintillator and pixelated APD, the probability of a radiation source of the same activity re-entering the same pixel within the dead time is extremely low. Therefore, compared to existing gamma cameras, the APD dead time requirements and scintillator afterglow requirements are relatively lower, allowing for resolution of higher-density gamma rays. Furthermore, compared to existing photoelectric converters using small-area photomultiplier tubes or silicon photomultiplier tubes, pixelated APDs can be used with scintillators with higher light yields, enabling accurate determination of gamma photon energy, thereby raising the detector's overall energy resolution limit.

[0053] In one embodiment of the present invention, the structures of the analog circuit unit and the digital processing unit are as follows: Figure 4 The analog circuit unit includes a charge transfer module, an integral conversion module, and an analog-to-digital conversion module. The output of the APD array is connected to the input of the charge transfer module. The input and output of the charge transfer module, integral conversion module, and analog-to-digital conversion module are connected in series. The output of the analog-to-digital conversion module is connected to the input of the digital processing unit.

[0054] The charge transfer module sequentially extracts and collects the analog current signals output by the APD array and outputs them to the integral conversion module. The integral conversion module integrates the input analog current, converts it into an analog voltage signal, and outputs it to the analog-to-digital conversion module. The analog-to-digital conversion module converts the input analog voltage signal into a digital signal and outputs it to the digital processing unit. This analog-to-digital conversion module can be implemented using a high-speed ADC.

[0055] All circuits in the analog circuit unit are made of integrated circuit technology into a dedicated integrated circuit chip, namely an ASIC chip. Its working timing is controlled by the control signal provided by the digital processing unit. It can simultaneously collect and convert the analog current signal output by the APD array and output the digital signal to the digital processing unit.

[0056] The digital processing unit includes a serial-to-parallel conversion module, a pixel sorting module, a data buffer module, and a data output module. The output of the analog circuit unit is connected to the input of the serial-to-parallel conversion module. The input and output of the serial-to-parallel conversion module, pixel sorting module, data buffer module, and data output module are connected in series. The output of the data output module serves as the output of the high-resolution gamma camera and is connected to the host computer.

[0057] The serial-to-parallel conversion module is used to convert the input serial digital signal into a parallel data signal and output it to the pixel sorting module. The pixel sorting module is used to sort the input parallel data signal according to the physical position of the pixel points to form image data, and output the image data to the data cache module. The data cache module is used to store the generated image data, and when the stored image data reaches a complete frame of data, it is provided to the data output module for reading. The data cache module can be implemented using internal memory or external memory. The data output module is used to read the image data stored in the data cache module and transmit the image data to the host computer according to the agreed image transmission protocol.

[0058] In a high-resolution gamma camera, the scintillator array and APD array coupling structure convert the detected light signal into an analog electrical signal. The analog circuit unit and digital processing unit convert the analog electrical signal into image data, completing all the work of the gamma camera. The image data is provided to the host computer for tomographic reconstruction into a cross-sectional image or a three-dimensional image.

[0059] The above describes in detail the structure and operating principle of a high-resolution gamma camera for SPECT provided by an embodiment of the present invention. Based on the aforementioned high-resolution gamma camera, an embodiment of the present invention further provides a SPECT device comprising one or more high-resolution gamma cameras, a rotating motion gantry, and a host computer. The high-resolution gamma camera is used to detect gamma rays emitted by radioactive elements and transmit the distribution data of single photons in the gamma rays to the host computer for reconstruction via computed tomography into a cross-sectional or three-dimensional image reflecting the physiological condition of a human organ. The specific structure and operating principle of the high-resolution gamma camera in the SPECT device will not be further elaborated here.

[0060] In summary, compared with the prior art, the high-resolution gamma camera provided by the embodiments of the present invention utilizes a technical solution that couples a pixelated APD array with a pixelated scintillator array to convert optical signals into electrical signals, enabling the photoelectric signal at each pixel to be processed independently, more accurately obtaining the position information of gamma photons. Simultaneously, the analog circuit unit and digital processing unit are used to convert and process the electrical signals into image data, thereby improving the spatial resolution and energy resolution limit of the image reconstructed by the SPCET device. Therefore, the high-resolution gamma camera provided by the present invention has the advantages of a clever and reasonable structural design, low design cost, and high spatial resolution.

[0061] It should be noted that the terms "upper," "lower," and "horizontal," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, in the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0062] The above describes in detail the high-resolution gamma camera and apparatus for SPECT provided by the present invention. Any obvious modification to the present invention without departing from its essence would constitute an infringement of the present invention's patent rights and would incur corresponding legal liability.

Claims

1. A high-resolution gamma camera for SPECT, characterized by It includes a collimator, a scintillator array, an avalanche photodiode array, an analog circuit unit and a digital processing unit; wherein, The scintillator array, the avalanche photodiode array, the analog circuit unit and the digital processing unit are coupled and connected in sequence; The collimator is used to control the direction of the detected gamma rays; The scintillator array is used to convert incident gamma rays into visible photons and couple them to the avalanche photodiode array; The avalanche photodiode array converts the incident light signal into electron charge by utilizing the avalanche amplification effect and outputs an analog current signal to the analog circuit unit; The analog circuit unit is used to perform integration, voltage conversion and analog-to-digital conversion on the input analog current signal, and then output a digital signal to the digital processing unit; The digital processing unit is used to collect and process the input digital signal to form image data and transmit it to the host computer.

2. The high-resolution gamma camera for SPECT according to claim 1, wherein: The scintillator array is composed of pixelated scintillators forming a pixel-level array; The avalanche photodiode array is composed of pixelated avalanche photodiode chips forming a pixel-level array; The pixelated scintillators in the scintillator array correspond one-to-one to the pixelated avalanche photodiode chips in the avalanche photodiode array.

3. The high-resolution gamma camera for SPECT according to claim 2, wherein: The pixelated scintillator is made of high light yield scintillating crystals cut into square columnar crystal materials and then surface-polished; The pixelated scintillators in the scintillator array are separated by a reflective layer; the outer surface of the scintillator array except the coupling surface is also prepared by a reflective layer.

4. The high-resolution gamma camera for SPECT according to claim 2, wherein: The area of ​​the pixelated avalanche photodiode chip is the same as the area of ​​the square column end of the pixelated scintillator; After the surface of the pixelated avalanche photodiode chip in the avalanche photodiode array is scrubbed and dried, a plasma cleaning machine or ozone treatment is used to activate the chip surface; The avalanche photodiode array is butt-jointed with the substrate.

5. The high-resolution gamma camera for SPECT according to claim 1, wherein: The coupling surface of the scintillator array is moistened with transparent optical silicone grease and then coupled with the coupling surface of the avalanche photodiode array using a chip flip-chip method for mounting. The entire structure is then waterproofed and packaged using a waterproof layer.

6. The high-resolution gamma camera for SPECT according to claim 1, wherein: The analog circuit unit includes a charge transfer module, an integral conversion module and an analog-to-digital conversion module; wherein the output end of the avalanche photodiode array is connected to the input end of the charge transfer module, the input and output ends of the charge transfer module, the integral conversion module and the analog-to-digital conversion module are connected in series in sequence, and the output end of the analog-to-digital conversion module is connected to the input end of the digital processing unit.

7. The high-resolution gamma camera for SPECT according to claim 6, wherein: The charge transfer module is used to sequentially derive and collect the analog current signals output by the avalanche photodiode array and output them to the integral conversion module; The integral conversion module is used to integrate the input analog current and convert it into an analog voltage signal, and then output it to the analog-to-digital conversion module; The analog-to-digital conversion module is used to convert the input analog voltage signal into a digital signal and output the digital signal to the digital processing unit.

8. The high-resolution gamma camera for SPECT according to claim 1, wherein: The digital processing unit includes a serial-to-parallel conversion module, a pixel sorting module, a data cache module, and a data output module; wherein the output end of the analog circuit unit is connected to the input end of the serial-to-parallel conversion module, the input and output ends of the serial-to-parallel conversion module, the pixel sorting module, the data cache module, and the data output module are connected in series in sequence, and the output end of the data output module is the output end of the high-resolution gamma camera.

9. The high-resolution gamma camera for SPECT according to claim 8, wherein: The serial-to-parallel conversion module is used to convert the input serial digital signal into a parallel data signal and output it to the pixel sorting module; The pixel sorting module is used to sort the input parallel data signals according to the physical position arrangement of the pixels to form image data and output the image data to the data buffer module; The data cache module is used to store the generated image data; The data output module is used to read the image data stored in the data cache module and transmit it to the host computer according to the agreed image transmission protocol.

10. A SPECT device, characterized in that A high-resolution gamma camera for SPECT according to any one of claims 1 to 9.

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