A detector module for reducing crystal size and improving resolution, and its usage method.

Abstract

The present invention relates to the field of medical imaging, and specifically to a detector module that reduces crystal size and improves resolution, and a method of using the same. The detector module of the present invention includes: a front-end detector module, which is used to capture gamma light generated by positron annihilation, and convert it into an electrical signal and output it to a back-end multi-channel readout electronic circuit system; a back-end multi-channel readout electronic circuit system, which is used to perform back-end processing on the electrical signal output by the front-end detector; the front-end detector module includes a scintillation crystal, a wedge-shaped light guide, and a silicon photomultiplier tube, wherein the scintillation crystal is used to capture gamma photons to form visible light; the wedge-shaped light guide is used to capture visible light and disperse it; the silicon photomultiplier tube is used to output the optical signal as an electrical signal and transmit it to the electronic system. The present invention can achieve sub-micron ultra-high resolution, providing further support for the development of medical imaging.

Description

Technical Field

[0001] The present invention relates to the field of medical imaging, and in particular to a detector module capable of reducing crystal size and improving resolution, and a method for using the same. Background Art

[0002] Positron Emission Computed Tomography (PET) achieves tomographic imaging by detecting the gamma rays produced after the decay of radioactive nuclides. The radioactive nuclides used in PET produce positrons after decay. Positrons are the antiparticles of electrons. When positrons produced after the decay of radioactive nuclides injected into the body pass through the tissues of the living body, they annihilate with negative electrons in the tissues within a very short distance (about 0.5mm, different positron nuclides have different positron annihilation distances), and all the mass is converted into energy release, producing gamma photon pairs with an energy of up to 511keV at an angle of approximately 180 degrees to each other. By detecting this pair of gamma photon pairs along the emission direction, the line integral value of the distribution of radioactive nuclides decaying in that direction can be obtained, thereby reconstructing the tomographic image.

[0003] PET is the only new imaging technology that can display the metabolism of biological molecules, receptors and neurotransmitter activities in living bodies. It is now widely used in the diagnosis and differential diagnosis of various diseases, disease assessment, efficacy evaluation, organ function research and new drug development.

[0004] Spatial resolution is one of the important performances in PET systems and an important indicator of the imaging quality of the system. Reducing the crystal size can improve the spatial resolution of the image, but excessive reduction of the crystal size will expand the reaction depth effect and increase parallax, which may lead to a decrease in the spatial resolution of the system. At present, the spatial resolution of medical whole-body PET systems is about 3-5mm, which is limited to presenting the activity status of the corresponding cells, and cannot show the signal transduction between cells and the specific activities of the neural network in a small range. It can only predict the working status of large cell groups or nuclei, and cannot accurately analyze the state of cell activity in small nuclei. Therefore, the development of PET detectors with high spatial resolution is extremely important. This ultra-high resolution PET detector can improve the spatial resolution of the PET system to the sub-millimeter level, observe the signal transduction between cells and the specific activities of the neural network in a small range, and accurately analyze the activity status of cells in small nuclei, which will promote the study of the pathogenesis of Alzheimer's disease. Before developing human PET, experimental research on small animals such as mice is required.

[0005] As summarized above, the prior art still lacks a detector module that can improve resolution and achieve precise analysis. Summary of the invention

[0006] In view of the improvement scheme of the spatial resolution of the prior art, the present invention provides a detector module that reduces the crystal size and improves the resolution. By studying and designing its key component, the front-end detector, the PET resolution can be significantly improved compared with the corresponding prior art, making it possible to accurately analyze the activity status of cells in small nuclei in the medical field.

[0007] To achieve the above-mentioned object, the present invention provides a detector module that reduces crystal size and improves resolution, including a front-end detector module and a back-end multi-channel readout electronic circuit system, wherein the front-end detector module is used to capture the gamma light generated by positron annihilation and convert it into an electrical signal and output it to the back-end multi-channel readout electronic circuit system, and the back-end multi-channel readout electronic circuit system is used to perform back-end processing on the electrical signal output by the front-end detector;

[0008] The front-end detector module includes a scintillation crystal for capturing gamma photons to form visible light;

[0009] The front-end detector module includes a wedge-shaped light guide for capturing visible light and dispersing it;

[0010] The front-end detector module includes a silicon photomultiplier tube, which is used to output the optical signal as an electrical signal and transmit it to the back-end multi-channel readout electronic circuit system;

[0011] The scintillation crystal is composed of a plurality of crystal bars arranged in a square array, the shape of the crystal bar is a rectangular parallelepiped, and the length and width of the crystal bar are both less than 0.25 mm.

[0012] Preferably, the square array is one of 16*16, 18*18 and 20*20.

[0013] Preferably, the material of the crystal bar is yttrium lutetium silicate scintillator crystal or bismuth silicate crystal.

[0014] Preferably, a barium sulfate coating is provided between the crystal bars.

[0015] Preferably, the thickness of the barium sulfate coating is less than 0.1 mm.

[0016] Preferably, the wedge-shaped light guide is made of a light guide material, and the light guide material is acrylic or transparent resin.

[0017] Preferably, the back-end multi-channel readout electronic circuit system includes a field programmable gate array and a circuit simulation board, wherein the circuit simulation board is used to receive the electrical signal of the silicon photomultiplier tube and obtain the energy value after performing an integral operation, and then transmit the energy value to the field programmable gate array for back-end processing to obtain a data stream. The field programmable gate array is cyclone10.

[0018] According to another aspect of the present invention, a method for using the detector module is provided, comprising the following steps:

[0019] (S1) placing the assembled detector module and the radiation source 5-10 cm in front of the front detector module, powering the rear multi-channel readout electronic circuit system, connecting the electronic circuit system with a computer, and completing data acquisition;

[0020] (S2) Screening, analyzing and decoding the collected data to obtain a decoded image.

[0021] Preferably, during the decoding process in (S2), a threshold method is used to remove background noise, specifically, all energy signals collected by the silicon photomultiplier tube are subtracted from the mode of the energy values, positive values ​​remain unchanged, and negative values ​​become 0, and then a center of gravity method is used to obtain a clear decoded image.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention sets the length and width of the scintillation crystal bar to be less than 0.25 mm. 0.25 mm has a higher discreteness, and the reaction point position of each crystal bar can be clearly analyzed, which can significantly improve the resolution, and the spatial resolution reaches the sub-millimeter level.

[0024] (2) The present invention adopts a wedge-shaped light guide to solve the edge effect problem, so that a many-to-one coupling method can be adopted. Further, with the same number of crystal bars, fewer SIPMs can be used to meet the decoding requirements, effectively reducing the equipment cost.

[0025] (3) The crystal structure of the present invention is compact and small in size, and the number of SIPM arrays required can be reduced under the same number of crystal bars, thereby greatly reducing the cost of the system.

[0026] (4) The front-end detector modules of the present invention are relatively small in size. When forming a circular array, the discreteness is high, and more front-end detector modules can be placed, which greatly improves the imaging effect of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of a front-end detector module according to the present invention;

[0028] Figure 2 is a front view of a front detector module according to the present invention;

[0029] Figure 3 is a top view of the front-end detector module according to the present invention;

[0030] Figure 4 This is a decoding diagram of a 0.25 mm crystal made according to Example 1 of the present invention;

[0031] Figure 5 This is a decoding diagram of a 0.5 mm crystal made according to Comparative Example 1 of the present invention.

[0032] In all the drawings, the same reference numerals are used to denote the same elements or structures, including: scintillator crystal 1 , wedge-shaped light guide 2 , silicon photomultiplier tube 3 , silicon photomultiplier tube array 4 , barium sulfate coating 5 , crystal bar 6 . DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] Example 1

[0035] A detector module that reduces crystal size and improves resolution includes a front-end detector module and a back-end multi-channel readout electronic circuit system. Figure 1-3 As shown, it includes a scintillation crystal 1, a wedge-shaped light guide 2 and a high-sensitivity silicon photomultiplier tube sipm array 4, and the silicon photomultiplier tube array 4 is composed of a 6x6 silicon photomultiplier tube 3 array.

[0036] The scintillator crystal 1 is composed of 16x16 crystal bars 6, each of which has a length and width of 0.5 mm and a size of 0.25 mmx0.25 mm, thereby achieving higher resolution requirements. There is a 0.1 mm barium sulfate coating 5 between each crystal bar 6, and the reflective material has a certain light transmittance.

[0037] The wedge-shaped light guide 2 is made of a material with good light-guiding properties, such as acrylic, transparent resin, etc. Its function is to disperse light and solve the edge effect problem caused by the many-to-one coupling between the crystal bar and the SIPM.

[0038] The silicon photomultiplier tube array 4 receives the visible light generated by the reaction of the scintillation crystal, outputs the optical signal as an electrical signal, and transmits it to the electronic system.

[0039] The smaller the size of the crystal bar divided by the scintillating crystal 1, the higher the resolution of the photoreaction position. However, the smaller the crystal bar 6, the more silicon photomultiplier tubes 3 are required to receive it. The present invention proposes a many-to-many coupling method, that is, multiple crystal bars 6 correspond to multiple silicon photomultiplier tubes 3.

[0040] The present invention proposes to use a wedge-shaped light guide 2 for light splitting operation. The wedge-shaped light guide 2 is made of a material with good light-conducting properties. Visible light is emitted from the crystal bar 6 to the surroundings. Since there is a reflective material barium sulfate 5 with a certain light transmittance between each crystal bar 6, the position where the reaction occurs in the figure will form a peak in the view of the silicon photomultiplier tube array. Through the light splitting operation of the wedge-shaped light guide 2, when the visible light generated by the reaction at the two edge positions of the crystal bar 6 is received by the silicon photomultiplier tube 3, the two positions can be solved by the centroid algorithm.

[0041] Comparative Example 1

[0042] The difference between the comparative example and the example 1 is that the length and width of each crystal bar 6 are both 0.5 mm.

[0043] According to the technical solution of the present invention, the components are assembled and tested, including the following steps:

[0044] S1. Front-end detector coupling, assembling the scintillation crystal 1, the wedge-shaped light guide 2 and the high-sensitivity 6x6 array SIPM 4 in sequence.

[0045] S2. The back-end multi-channel readout electronic circuit system is connected to the front-end detector, and the front-end detector and the back-end multi-channel readout electronic circuit system are connected together by a flexible cable to complete electronic data transmission;

[0046] S3. Place the radiation source near the detector, power the back-end multi-channel readout electronic circuit system, use computer software to connect the electronic circuit system, and complete data acquisition.

[0047] S4. Use MATLAB analysis program to filter and analyze the collected data.

[0048] Analysis program, refer to the application CN112656439A of the inventor, a method and system for position decoding of positron emission imaging. The method includes obtaining multiple energy array diagrams using visible light generated by positron emission; judging whether a Compton event occurs in the energy array diagram, if so, removing the energy array diagram, if not, retaining the energy array diagram; finding the peak of the energy array diagram after filtering out the Compton event, dividing a local area of ​​a preset size with the peak as the center, and setting the energy outside the local area to zero; locating the position where the positron actually reacts in the local area using a centroid decoding algorithm.

[0049] Since the 0.25mm size is too small, the background noise is relatively large. The present invention proposes to use a threshold method to remove the background noise. Specifically, all energy signals collected by the silicon photomultiplier tube are subtracted from the mode of the energy values. The positive values ​​remain unchanged and the negative values ​​become 0. Then the centroid method is used to obtain a clear decoded image.

[0050] Figure 4 This is a decoding diagram of a 0.25 mm crystal made according to Example 1 of the present invention. Figure 5 This is a 0.5mm crystal decoding diagram made according to comparative example 1 of the present invention. Both can clearly resolve the reaction point position of each crystal bar. Since the 0.25mm crystal has a higher discreteness, it can resolve radiation events within 0.5mm. Compared with the 0.5mm crystal, the resolution is improved, and the resolution applied to the overall system is improved.

[0051] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A detector module that reduces crystal size and improves resolution, characterized in that: include: A front-end detector module and a back-end multi-channel readout electronic circuit system, wherein the front-end detector module is used to capture the gamma light generated by positron annihilation and convert it into an electrical signal and output it to the back-end multi-channel readout electronic circuit system, and the back-end multi-channel readout electronic circuit system is used to perform back-end processing on the electrical signal output by the front-end detector; The front-end detector module includes a scintillation crystal for capturing gamma photons to form visible light; The front-end detector module includes a wedge-shaped light guide for capturing visible light and dispersing it; The front-end detector module includes a silicon photomultiplier tube, which is used to output the optical signal as an electrical signal and transmit it to the back-end multi-channel readout electronic circuit system; The scintillation crystal is composed of a plurality of crystal bars arranged in a square array, the shape of the crystal bar is a rectangular parallelepiped, and the length and width of the crystal bar are both less than 0.25 mm.

2. The detector module according to claim 1, characterized in that: The square array is one of 16*16, 18*18 and 20*20.

3. The detector module according to claim 1 or 2, characterized in that: The material of the crystal bar is yttrium lutetium silicate scintillating crystal or bismuth silicate crystal.

4. The detector module according to claim 3, characterized in that: A barium sulfate coating is arranged between the crystal bars.

5. The detector module according to claim 4, characterized in that: The thickness of the barium sulfate coating is less than 0.1 mm.

6. The detector module according to claim 1, characterized in that: The wedge-shaped light guide is made of a light guide material, and the light guide material is acrylic or transparent resin.

7. The detector module according to claim 1, characterized in that: The back-end multi-channel readout electronic circuit system includes a field programmable gate array and a circuit simulation board. The circuit simulation board is used to receive the electrical signal of the silicon photomultiplier tube and obtain an energy value after performing an integration operation, and then transmit the energy value to the field programmable gate array for back-end processing to obtain a data stream.

8. The method for using the detector module according to any one of claims 1 to 7, characterized in that: The following steps are involved: (S1) placing the assembled detector module and the radiation source 5-10 cm in front of the front detector module, powering the rear multi-channel readout electronic circuit system, connecting the electronic circuit system with a computer, and completing data acquisition; (S2) Screening, analyzing and decoding the collected data to obtain a decoded image.

9. The method for using the detector module according to claim 8, characterized in that: In the decoding process of (S2), the threshold method is used to remove the background noise. Specifically, all energy signals collected by the silicon photomultiplier tube are subtracted from the mode of the energy value, the positive value remains unchanged, and the negative value becomes 0, and then the centroid method is used to obtain a clear decoded image.

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