Wide-energy gamma ray imaging system of strip-shaped orthogonal self-coding detector and method of wide-energy gamma ray imaging system

Abstract

The invention discloses a wide energy gamma ray imaging system of a strip-shaped orthogonal self-coding detector and a method thereof. An adopted imaging detector carries out coding through a strip-shaped scintillator detector. A plurality of strip-shaped scintillator detectors are arranged and combined to form a strip-shaped array similar to a coding plate, wherein the projection pattern of the strip-shaped array has uniqueness (anisotropy) to response in all directions, and the imaging efficiency (aperture ratio) is considered. The detector system has fewer electronic channels, larger sensitive volume and lower cost. The MLEM iterative algorithm is fused with the coded aperture imaging method and the Compton imaging method, wide-energy and high-efficiency gamma ray imaging is achieved, and the gamma ray imaging device has large sensitive volume and few electronic reading channels.

Description

Technical Field

[0001] The invention relates to the field of nuclear radiation imaging, and in particular to a wide-energy gamma-ray imaging system of a strip-shaped orthogonal self-encoding detector and a method thereof. Background Art

[0002] In the current context of globalization, the application of nuclear technology has penetrated into many key areas such as energy, industry, agriculture, and medical care, greatly promoting social and economic development. Traditional dosimeters (instruments) or spectrometers can only obtain "point" radiation information and cannot quickly locate the location of radioactive materials; while radioactive imaging technology can provide visual images of the distribution of radioactive materials, making it play an indispensable role in emergency response, accident investigation, environmental monitoring, and nuclear facility safety management.

[0003] Traditional radiation imaging methods include coded aperture imaging and Compton imaging. Coded aperture imaging is suitable for imaging low-energy areas with energies below about 1000keV, and the imaging resolution of high-energy area rays is poor. The Compton imaging method has a high imaging efficiency only for medium- and high-energy area rays with energies above about 250keV. A single imaging technology cannot cover the wide energy range of 50keV to 3000keV for continuous high-sensitivity imaging, so multiple imaging methods are generally combined to improve the overall imaging performance.

[0004] For gamma imaging in a wide energy range, one method is to "mix" coded aperture imaging and Compton imaging. Generally, an additional coding plate is added to the Compton imaging system to increase the imaging capability in the low energy zone. Although the hybrid imaging scheme can achieve imaging in a wide energy range, it has problems such as low imaging sensitivity of low-energy rays and inability to balance imaging efficiency and imaging quality. Another method for wide energy gamma imaging is similar to the array self-encoding detector system. The imaging detector used in this system abandons the traditional collimation-specific coding plate and uses a block-type detector self-encoding to replace the function of the traditional coding plate to achieve low-energy gamma ray imaging; at the same time, the block-type detector self-encoding can also be used as a scattering detector for high-energy Compton imaging. The combination of the two can achieve wide energy gamma ray imaging, but to achieve the function of the traditional coding plate, more block-type detectors are needed, which means that more electronic processing channels are needed, which increases the cost. Secondly, due to the production cost, the size of the block-type detector is limited, and the detection efficiency and imaging sensitivity are not high. The new position-sensitive strip scintillator detector uses dual-end readout technology, has fewer electronic channels, a larger sensitive volume, and low cost. This makes it possible to realize a low-cost imaging system with a large detection sensitive volume and can achieve imaging in a wide energy range.

[0005] At present, nuclear radiation imaging mainly has the following problems and shortcomings:

[0006] 1. For the existing wide-energy gamma-ray imaging detectors, in order to improve the detection efficiency and imaging sensitivity of the detectors, it is necessary to increase the volume of the detectors. Although the above-mentioned square array self-encoding detectors can realize wide-energy gamma-ray imaging, due to the production cost, the size is limited to a certain range. Therefore, the detection efficiency is not good, the imaging sensitivity is not high, and many electronic channels are required, which is also costly.

[0007] 2. Compton imaging detectors composed of position-sensitive strip scintillator detectors have fewer electronic channels, large sensitive volume, and low cost. However, they can only achieve Compton imaging of medium- and high-energy rays, but not wide-energy gamma-ray imaging. Summary of the invention

[0008] In order to solve the above problems, the present invention proposes a wide-energy gamma-ray imaging system of a strip-shaped orthogonal self-encoding detector, in which the imaging detector used is encoded by the strip-shaped scintillator detector itself. By arranging and combining multiple strip-shaped scintillator detectors, a projection pattern is formed that has uniqueness (anisotropy) in response to each direction, and a strip array similar to a coding plate is formed that takes into account the imaging efficiency (aperture ratio). The detector system has fewer electronic channels, a larger sensitive volume, and a lower cost; a method for realizing wide-energy gamma-ray imaging with a strip-shaped scintillator imaging detector is also provided, which can realize wide-energy gamma-ray imaging while ensuring detection efficiency and imaging sensitivity.

[0009] Compared with the existing wide-energy imaging detector system, the present invention has fewer electronic channels, a larger sensitive area and higher imaging efficiency. The problems solved by the present invention are:

[0010] 1. Use strip scintillator orthogonal self-coding to achieve wide-energy gamma-ray imaging. Use strip scintillator orthogonal self-coding arrangement to replace the traditional encoding plate, which can not only avoid the shielding of rays by the traditional encoding plate and improve the detection efficiency, but also achieve continuous high-sensitivity imaging with a wide energy of 50keV to 3000keV.

[0011] 2. Improve the encoding method based on the existing array self-encoding detector structure, use strip scintillator orthogonal self-encoding to replace the square detector array, and form a strip array similar to the encoding plate with unique (anisotropic) projection pattern response in all directions and imaging efficiency (aperture rate) by arranging and combining multiple strip detectors. Use strip orthogonal self-encoding detectors to effectively reduce the electronic channels of the detector system, increase the sensitive volume, and reduce costs.

[0012] To achieve the above object, the specific technical solution of the present invention is:

[0013] A wide-energy gamma-ray imaging system of a strip-shaped orthogonal self-encoding detector comprises a plurality of strip-shaped position-sensitive strip-shaped scintillator detectors;

[0014] A plurality of position-sensitive strip scintillator detectors are arranged in a certain manner to form a three-layer detector plane, wherein the first and second layers of the detector planes constitute a self-encoding detector, and through the arrangement and combination of the plurality of position-sensitive strip scintillator detectors, a strip array of encoding plates is formed, which has a unique response to each direction of the projection pattern, anisotropic response to the incident angle of the gamma ray, and takes into account the imaging efficiency; the third layer of the detector plane is used as an absorption detector;

[0015] The self-encoding detector blocks part of the rays from entering the absorption detector behind it, realizing low-energy gamma-ray imaging; at the same time, the absorption detector takes into account medium and high-energy Compton imaging. The combination of the self-encoding detector and the absorption detector realizes wide-energy gamma-ray imaging.

[0016] Preferably, the detectors of the first layer and the second layer are arranged vertically and encoded to form self-encoding detectors.

[0017] The projection pattern has uniqueness in response to each direction, which means that the projection patterns in each direction formed by orthogonally coded arrangement of position-sensitive strip scintillator detectors in a certain manner are different from each other.

[0018] The invention discloses a wide-energy gamma-ray imaging method of a strip-shaped orthogonal self-encoding detector, which adopts the wide-energy gamma-ray imaging system of the strip-shaped orthogonal self-encoding detector; realizes wide-energy fusion imaging based on the MLEM iterative algorithm, and divides the response of the detector into single-point action events and two-point action events; wherein the full-energy peak events in the energy spectrum of the single-point event and the energy spectrum of the two-point event are respectively used for coded aperture imaging and Compton imaging; in the image reconstruction process, there is no need to distinguish the imaging method in advance, and the imageable single-point event and the two-point event are directly brought into the equation for iteration to realize wide-energy fusion imaging.

[0019] In order to achieve wide energy range imaging, it is necessary to use strip detectors to form a self-encoding structure. Therefore, multiple strip detectors are coded horizontally and vertically in a certain way to form a detector structure similar to a coding plate, which has a unique response to each direction and takes into account imaging efficiency. The orthogonal self-encoding detector will block some rays from entering the absorption detector behind it, acting as a coding plate to achieve low-energy coded aperture imaging. At the same time, the absorption detector can be used as a scattering detector for high-energy Compton imaging. The MLEM iterative algorithm is then used to complete the fusion of the coded aperture and Compton imaging methods to achieve continuous high-sensitivity imaging of wide energy.

[0020] The opening ratio of the present invention refers to the ratio of the total area of ​​holes on the coding plate that allow rays to pass through to the total area of ​​the coding plate.

[0021] The advantages of the present invention are:

[0022] A wide-energy gamma-ray imaging system with a strip-shaped orthogonal self-encoding detector is provided. A plurality of strip-shaped detectors are arranged and combined in a certain manner to form a self-encoding detector and an absorption detector, thereby realizing imaging of high and low-energy gamma rays. While ensuring detection efficiency and imaging sensitivity, wide-energy gamma-ray imaging can also be achieved.

[0023] The gamma-ray imaging method of the strip-shaped orthogonal self-encoding detector integrates the coded aperture imaging and Compton imaging methods through the MLEM iterative algorithm to achieve high-efficiency gamma-ray imaging of a wide energy range with a larger sensitive volume and fewer electronic readout channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of a strip-shaped orthogonal self-encoding detector in an embodiment of the present invention.

[0025] Figure 2 FIG. 2 is a two-dimensional plan view of the self-encoding detector 100 according to an embodiment of the present invention.

[0026] Figure 3 Schematic diagram of the connection between the radiation source distribution and the detector response in an embodiment of the present invention.

[0027] Figure 4 Schematic diagram of simulation using Monte Carlo software in an embodiment of the present invention.

[0028] Figure 5 This is a schematic diagram of the fusion principle of the coded aperture and Compton imaging methods using the MLEM iterative algorithm in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions, advantages and implementation process of the present invention more clearly understood, the present invention is further described in detail below based on the accompanying drawings and examples.

[0030] like Figure 1 As shown, a wide-energy gamma-ray imaging system of a strip-shaped orthogonal self-encoding detector comprises a plurality of strip-shaped position-sensitive strip-shaped scintillator detectors;

[0031] A plurality of position-sensitive strip scintillator detectors are arranged in a certain manner to form a three-layer detector plane, wherein the detectors of the first layer and the second layer are arranged vertically and encoded to form a self-encoding detector 100; through the arrangement and combination of the plurality of position-sensitive strip scintillator detectors, a strip array of encoding plates is formed, which has a unique response to each direction of the projection pattern, anisotropic response to the incident angle of the gamma ray, and takes into account the imaging efficiency; the third layer of the detector plane is used as an absorption detector 200;

[0032] The self-encoding detector 100 blocks part of the rays from entering the absorption detector 200 behind it, realizing low-energy gamma-ray imaging; at the same time, the absorption detector 200 takes into account medium and high-energy Compton imaging. The combination of the self-encoding detector 100 and the absorption detector 200 realizes wide-energy gamma-ray imaging.

[0033] The position-sensitive strip scintillator detector comprises a position-sensitive strip scintillator detector, the four largest surfaces of which are covered with a material having a high light reflectivity, and the remaining two end faces are connected to a SiPM light collection device for light collection.

[0034] The projection pattern has uniqueness in response to each direction, which means that the projection patterns in each direction formed by orthogonally coded arrangement of position-sensitive strip scintillator detectors in a certain manner are different from each other.

[0035] like Figure 2As shown, it is a two-dimensional plane view of the self-encoding detector 100. Each layer is composed of four quadrant strip detectors, wherein the first and third quadrants of the first layer are composed of 16 strip detectors arranged horizontally in sequence, and the second and fourth quadrants are composed of 16 strip detectors arranged vertically in sequence. On this basis, the 1st, 3rd, 4th, 6th, 9th, 10th, 14th and 16th strip detectors of the first quadrant are sequentially extracted from top to bottom, and the 1st, 3rd, 7th, 8th, 11th, 13th, 14th and 16th strip detectors of the third quadrant are sequentially extracted from top to bottom; the 1st, 3rd, 7th, 8th, 9th, 12th, 13th and 16th strip detectors of the second quadrant are sequentially extracted from left to right, and the 1st, 4th, 5th, 8th, 9th, 10th, 14th and 16th strip detectors of the fourth quadrant are sequentially extracted from left to right. The first and third quadrants of the second layer are arranged vertically by 16 strip detectors, and the second and fourth quadrants are arranged horizontally by 16 strip detectors. On this basis, the 1st, 3rd, 4th, 7th, 8th, 11th, 13th and 16th strip detectors of the second quadrant are extracted from top to bottom, and the 1st, 4th, 6th, 9th, 10th, 13th, 14th and 16th strip detectors of the fourth quadrant are extracted from top to bottom; the 1st, 3rd, 5th, 8th, 11th, 12th, 14th and 15th strip detectors of the first quadrant are extracted from left to right, and the 2nd, 3rd, 5th, 6th, 9th, 12th, 14th and 16th strip detectors of the third quadrant are extracted from left to right. The first and third quadrants of the third layer are arranged horizontally by 16 strip detectors, and the second and fourth quadrants are arranged vertically by 16 strip detectors. The first layer of detectors and the second layer of detectors are stacked vertically to form a structure similar to the coding plate, which has a high opening rate. The first and second layers of detectors will block some rays from entering the absorption detector behind, replacing the coding plate to achieve low-energy gamma-ray imaging; at the same time, the combination of three layers of detectors can also take into account high-energy Compton imaging, and the combination of the two can achieve wide-energy gamma-ray imaging.

[0036] It should be noted that the aperture ratio, extraction order and detector type of the coded detector in this embodiment are merely exemplary, that is, the aperture ratio and extraction order of the self-encoding detector composed of multiple strip detectors are not limited to the above methods. Those skilled in the art can adjust the aperture ratio and extraction order according to actual conditions.

[0037] like Figure 3As shown in the figure, when measuring radioactivity, the raw data obtained by the detector contains information such as time, position and energy, which is called the detector response. Image reconstruction is to convert the detector response into an image of the distribution of incident gamma rays in space. Its mathematical relationship can be expressed by the following formula. The distribution of the radiation source can be a two-dimensional sphere or a three-dimensional space. The detector response contains the position and energy information of the action point, which can be expressed by (x1, y1, z1, e1), (x2, y2, z2, e2)...

[0038]

[0039] The actual detector response is a statistic that follows a Poisson distribution, that is, the number of counts d observed by the detector for each event n Obey is a Poisson distribution with mean:

[0040]

[0041] Then based on the maximum likelihood expectation method, the distribution of the radiation source can be estimated through the objective function:

[0042]

[0043] Using the expected maximum (EM) iteration equation, the possible radiation source distribution can be estimated:

[0044]

[0045] like Figure 4 As shown, Monte Carlo simulation is used to obtain the sensitivity matrix of two-dimensional space. The sensitivity matrix of two-dimensional imaging space is solved as the imaging efficiency in each direction, so it can be obtained through Monte Carlo simulation. Secondly, the Monte Carlo simulation method can be used as a method to obtain the system response matrix instead of the analytical method by repeatedly randomly sampling the transmission probability model of rays and matter. Monte Carlo software is used to simulate the measurement of gamma rays, simulate all processes of tracking photons and electrons in the detector, and record the energy deposition in the detector when the gamma rays pass through the detector. By Gaussian broadening the energy deposition in the detector, the energy spectrum of gamma rays in the detector is finally obtained.

[0046] like Figure 5 As shown, the MLEM iterative algorithm is used to complete the fusion of coded aperture and Compton imaging methods.

[0047] The raw data required for the two imaging methods are determined by screening single-point and two-point cases, and used as the detector response. The detector system is then irradiated in all directions with a radiation source to obtain the energy spectrum of gamma rays in the detector at each coordinate point of the radiation source, and the system response matrix can be obtained by statistical calculation.

[0048] According to the detector response (x 1 ,y 1 ,z 1 ,e 1 )、(x 2 ,y 2 ,z 2 ,e 2 )... indicates that the detector response is divided into single-point action cases and two-point action cases. The energy spectrum of the single-point case and the full-energy peak event in the two-point case spectrum are used for coded aperture imaging and Compton imaging, respectively. The imaging single-point case and the two-point case are brought into the equation iteration together without selecting the energy in advance. In the iterative process, the optimal imaging method is automatically approached, thereby achieving continuous high-sensitivity imaging with a wide energy range.

[0049] Compton imaging can use the List-mode MLEM algorithm, which iterates only the detected events. A single event only adds one row to the system matrix T, and the different detector responses D are all 1. If the number of imaging events reaches several thousand and iterates several times, a good image can be obtained. Using the built simulation platform, the system matrix of all detector responses is simulated and stored in advance, avoiding a lot of time-consuming calculation processes. In addition, the complete system response matrix is ​​obtained, and the sensitivity matrix can be calculated more accurately.

[0050] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the implementation methods of the present invention, and should be understood that the protection scope of the present invention is not limited to such special statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A wide energy gamma ray imaging system with a strip-shaped orthogonal self-encoding detector, characterized in that: A position-sensitive strip scintillator detector including a plurality of strips; A plurality of position-sensitive strip scintillator detectors are arranged in a certain manner to form a three-layer detector plane, wherein the first and second layers of the detector plane form a self-encoding detector (100), and a projection pattern is formed by arranging and combining the plurality of position-sensitive strip scintillator detectors to form a strip array of encoding plates having unique responses in all directions, anisotropic responses to incident angles of gamma rays, and taking imaging efficiency into consideration; The third detector plane is used as an absorption detector (200); The self-encoding detector (100) blocks part of the rays from entering the absorption detector (200) behind it, thereby realizing low-energy gamma-ray imaging; meanwhile, the absorption detector (200) takes into account medium- and high-energy Compton imaging, and the combination of the self-encoding detector (100) and the absorption detector (200) realizes wide-energy gamma-ray imaging.

2. The wide energy gamma ray imaging system of the strip-shaped orthogonal self-encoding detector according to claim 1, characterized in that: The detectors of the first layer and the second layer are arranged vertically and encoded to form a self-encoding detector (100).

3. The wide energy gamma ray imaging system of the strip-shaped orthogonal self-encoding detector according to claim 1, characterized in that: The projection pattern has uniqueness in response to each direction, which means that the projection patterns in each direction formed by orthogonally coded arrangement of position-sensitive strip scintillator detectors in a certain manner are different from each other.

4. A wide energy gamma ray imaging method using a strip-shaped orthogonal self-encoding detector, characterized in that: A wide-energy gamma-ray imaging system using the strip orthogonal self-encoding detector described in any one of claims 1 to 3; realizing wide-energy fusion imaging based on the MLEM iterative algorithm, dividing the detector response into single-point action events and two-point action events; wherein the full-energy peak events in the single-point event spectrum and the two-point event spectrum are used for coded aperture imaging and Compton imaging, respectively; during the image reconstruction process, there is no need to distinguish the imaging method in advance, and the imageable single-point events and two-point events are directly brought into the equation for iteration to realize wide-energy fusion imaging.

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