Radiation source positioning method and gamma camera device

Abstract

The application discloses a radiation source positioning method and a gamma camera device. The method is as follows: according to the space-time distribution characteristics of optical signals in a detection medium, first and second action point signals are distinguished; the first action point signal is Cerenkov light and scintillation light generated by backscattered electrons generated by Compton scattering of incident gamma rays in the detection medium, and the second action point signal is scintillation light generated by absorbed photons after Compton scattering in the detection medium; the first action point position of the first interaction of the gamma rays and the backscattered electron energy, and the second action point position of the second interaction and the scattered photon energy are calculated according to the scintillation light in the first action point signal; the spatial distribution of the Cerenkov light is extracted within a preset time window, and a backscattered electron motion direction vector is reconstructed; and the direction vector of the rays is calculated by combining the backscattered electron energy, the scattered photon energy, the first action point position, the second action point position and the backscattered electron motion direction vector.

Description

Technical Field

[0001] This invention belongs to the field of nuclear radiation detection and medical imaging technology, and relates to a radiation source localization method and a gamma camera device based on optical signal coupling of multiple physical mechanisms. Background Technology

[0002] Gamma cameras are core equipment for nuclear medicine imaging, environmental radiation monitoring, and astrophysical observation. Existing gamma camera technologies are mainly divided into three categories, but all have significant technical shortcomings.

[0003] 1. Mechanically collimated type: This type relies on heavy metal mechanical collimators, such as lead, to confine the direction of photons. Its disadvantages include extremely low detection efficiency, and the fact that spatial resolution and sensitivity are mutually restrictive and cannot be simultaneously achieved.

[0004] 2. Traditional Compton scattering (no electron direction): The scattering angle is calculated using the Compton formula by measuring the energy and position of the scattered photon. Its disadvantage is that a single measurement has ambiguity (it can only determine one conical surface), and it must rely on the statistical superposition of a large number of photon events to converge to the radiation source direction, resulting in long imaging time and making it unsuitable for low-dose or rapidly changing scenarios.

[0005] 3. Electron Track Tracking Type (with Electron Direction): This type directly records the trajectory of recoil electrons using silicon pixel detectors or time projection chambers (TPCs). Its disadvantages include high system complexity and high cost. Silicon detectors require multi-layer stacking, and the readout electronics are extremely complex, with limitations in thickness making it difficult to fully absorb energy; gas TPCs are bulky and difficult to compact. Furthermore, overlapping electron tracks make it difficult for algorithms to identify the beginning and end of the track, severely impacting reconstruction accuracy.

[0006] Therefore, how to achieve high-precision single-event-level electronic orientation measurement without increasing the complexity of the system hardware (such as introducing complex track detectors) is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the problems existing in the prior art, the present invention aims to provide a radiation source localization method and a gamma camera device based on optical signal coupling using a multi-physics mechanism. This invention utilizes two optical signals (Cherenkov light and scintillation light) with different temporal-spatial characteristics generated in the medium to jointly calculate the electronic state, and uses the Cherenkov radiation and scintillation fluorescence mechanisms to jointly invert the direction of the Compton recoil electron, thereby achieving single-event-level radiation source localization.

[0008] The core technical concept of this invention is to discover and utilize the physical differences in the time and spatial domains between "Cherenkov light" (with picosecond-level transients and strong directionality) and "scintillation light" (nanosecond-level and isotropic) generated by recoil electrons in a high-refractive-index medium, and to transform them into independent technical variables for electron direction vector reconstruction.

[0009] The main innovative aspects of this invention are as follows: 1. Dual-mode optical signal coupling mechanism: By selecting a high refractive index and high transparency material in the scattering layer, Compton recoil electrons are forced to simultaneously excite Cherenkov light (for direction determination) and scintillation light (for energy and position determination). Through time window separation technology (ps-level vs. ns-level), a single detector can simultaneously capture the two types of information.

[0010] 2. Composite Layered Optical Conduction Architecture: A unique stacked structure of "scattering layer-absorption layer-photodetector array" was designed. The absorption layer not only acts as an energy absorber for secondary photons, but also serves as a "light guide" for the light signal from the scattering layer, enabling the bottom SiPM array to simultaneously read the reaction information from both layers, greatly simplifying the readout circuitry and mechanical structure.

[0011] 3. Single-event full momentum reconstruction algorithm: Combining energy conservation and momentum conservation, and using Cherenkov rings to fit the initial direction of electrons, the "cone blur" of traditional Compton cameras is completely eliminated, and the unique direction determination of single-photon events is achieved.

[0012] The technical solution of this invention is as follows: A method for locating a radiation source, comprising the following steps: The system receives optical signals from the detection medium and distinguishes between a first point of action signal and a second point of action signal based on the spatiotemporal distribution characteristics of the optical signals. The first point of action signal is the Cherenkov light and scintillation light generated by the Compton scattering of incident gamma rays in the detection medium and the generation of recoil electrons. The second point of action signal is the scintillation light generated by the absorption of photons after Compton scattering in the detection medium. Based on the scintillation light in the first point of action signal, calculate the first point of action position and recoil electron energy of the first interaction of the gamma rays, as well as the second point of action position and scattered photon energy of the second interaction. The spatial distribution of Cherenkov light was extracted within a preset ultrafast time window, and the direction vector of recoil electron motion was reconstructed. The direction vector of the incident ray is calculated by combining the recoil electron energy, the scattered photon energy, the position of the first point of action, the position of the second point of action, and the direction vector of the recoil electron motion.

[0013] Preferably, a photoelectric conversion array is used to receive optical signals from a detection medium, the detection medium comprising stacked scattering layer units and absorption layer units; wherein, the scattering layer units are used to perform Compton scattering of incident gamma rays and generate recoil electrons; the absorption layer units are used to absorb photons after Compton scattering and generate scintillation light, and to allow optical signals from the scattering layer units to penetrate and transmit.

[0014] Preferably, the center of the detection medium is the scattering layer unit, the top of the scattering layer unit is used to receive incident gamma rays; the bottom and each side of the scattering layer unit are respectively provided with an absorption layer unit; each absorption layer unit is connected to a photoelectric conversion array for detecting and receiving the light signal output by the absorption layer unit; the top of the scattering layer unit is connected to a photoelectric conversion array for detecting and receiving the light signal output by the top of the scattering layer unit.

[0015] Preferably, the method for obtaining the first point of action position, the recoil electron energy, the second point of action position where secondary interaction occurs, and the scattered photon energy is as follows: the signals collected by each of the photoelectric conversion arrays are scanned; if there is only one high point that meets the conditions, the second point of action position is calculated based on the position of the high point and the thickness of the absorption layer unit; then the high point is subtracted from the signals collected by each of the photoelectric conversion arrays to obtain the remaining signal set; the first point of action position is calculated based on the remaining signal set.

[0016] Preferably, the Cherenkov light signal is extracted within an ultrafast time window of 0-1 ns; a cone-shaped distribution with the initial electron direction vector of the Cherenkov photon as the axis and a set cone angle is used as a physical constraint; based on the extracted Cherenkov light signal, a likelihood function about the recoil electron motion direction vector is constructed using maximum likelihood estimation; and the electron direction vector that maximizes the probability of observing the Cherenkov light signal is found as the recoil electron motion direction vector.

[0017] Preferably, the recoil electron energy and scattered photon energy are obtained through a pre-defined linear relationship between the number of photons and energy.

[0018] Preferably, the first point of action signal and the second point of action signal are distinguished based on the duration and direction of the optical signal.

[0019] Preferably, based on the laws of conservation of energy and momentum, and combining the recoil electron energy, scattered photon energy, first point of action position, second point of action position, and recoil electron motion direction vector, the direction vector of the incident ray is calculated.

[0020] A gamma camera device, characterized in that it includes a scattering layer unit, an absorption layer unit, and a photoelectric detection array; The scattering layer unit is configured to cause Compton scattering of incident gamma rays and generate recoil electrons. The absorption layer unit, located around the scattering layer unit, is configured to absorb scattered photons from Compton scattering and generate scintillation light, and to allow optical signals from the scattering layer unit to penetrate and transmit. The photodetector array is located on the side of the absorption layer unit away from the scattering layer unit and on top of the scattering layer unit, and is configured to respond to and read out the optical signal output by the absorption layer unit.

[0021] Preferably, the top of the scattering layer unit is used to receive incident gamma rays; the bottom and each side of the scattering layer unit are respectively provided with an absorption layer unit; each absorption layer unit is connected to a photoelectric conversion array for detecting and receiving the light signal output by the absorption layer unit; the top of the scattering layer unit is connected to a photoelectric conversion array for detecting and receiving the light signal output by the top of the scattering layer unit.

[0022] The advantages of this invention are as follows: This invention can obtain electronic orientation without complex track-tracking hardware, which greatly reduces cost and size; it achieves single-event-level imaging and significantly improves detection sensitivity under low statistics. Attached Figure Description

[0023] Figure 1 This is a flowchart of the method of the present invention.

[0024] Figure 2 This is a schematic diagram of a Cherenkov-based optical gamma camera.

[0025] Figure 3 This is a schematic diagram of the detection principle based on the Cherenkov optical Compton camera.

[0026] Figure 4 This is a design drawing for a single-sided absorption layer. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0028] like Figure 1 As shown, an embodiment of the present invention proposes a radiation source localization method based on optical signal coupling using multiple physical mechanisms, which includes the following steps: S1. Signal acquisition step: A photoelectric conversion array is used to receive an optical signal from a detection medium, the detection medium comprising a scattering layer unit and an absorption layer unit stacked together; wherein, the scattering layer unit is used to perform Compton scattering of incident gamma rays and generate recoil electrons; the absorption layer unit is used to absorb photons after Compton scattering and generate scintillation light, and to allow the optical signal from the scattering layer unit to penetrate and transmit. S2. First point of action location and signal separation step: Based on the spatiotemporal distribution characteristics of the optical signal, distinguish the second point of action signal from the absorption layer unit and the first point of action signal from the scattering layer unit, which contains Cherenkov light and scintillation light components; wherein, the first point of action signal is the Cherenkov light and scintillation light generated by the incident gamma rays undergoing Compton scattering in the detection medium and generating recoil electrons; the second point of action signal is the scintillation light generated by the absorption of photons after Compton scattering in the detection medium.

[0029] S3. Energy and Position Calculation Steps: Based on the scintillation light component separated from the first point of action signal, calculate the position coordinates of the incident ray during its first interaction with the scattering layer unit. ) and recoil electron energy ( ), and the coordinates of the positions where secondary interactions occur in the absorbing layer units ( ) and scattered photon energy ( ); 1) Second point of application location r 2 (Absorption layer) a. Input signal: Distribution of fluorescent photons captured by the SiPM array in the absorption layer I (x,y) (time window: >1 ns).

[0030] b. Positioning method: (i) High-brightness filtering: Scan the SiPM pixel signal of each detection surface and filter pixels that meet the following conditions: signal strength I pixel >>Average intensity of the surrounding 8 pixels; only one bright spot in the entire array meets the criteria. (Note: If multiple bright spots exist, they are considered noise or multiple interaction events and are discarded.) (ii) Position calculation: Let the center coordinates of the highlighted pixel be ( x h , y h The thickness of the absorption layer is... t The location of the point of application is: r 2 =( x h , y h ,t / 2).

[0031] 2) First application point location r 1 (Scattering layer) a. Input signal: The remaining signal captured by the SiPM array of the scattering layer (i.e., the signal of the high point in the previous step is subtracted).

[0032] b. Location method: Any of the following well-known algorithms can be used: (1) Center of gravity method: ; (2) Maximum likelihood estimation method; (3) Machine learning: Pre-trained models directly output coordinates.

[0033] 3) Energy calibration and deposition energy acquisition Calibration method: Establish photon number through experimental or simulation calibration. N With deposited energy E Relationship: E = k N + b High-brightness photon counting N 2 It can be converted into energy according to the scattering crystal calibration formula. E 2. This energy is the energy of the scattered photons; the remaining number of photons is obtained by subtracting the number of photons in the high-spot area from the total number of photons. N 1. Convert into energy according to the formula for measuring the absorption crystal. E 1. This energy is the recoil electron energy. The sum of the two is the incident photon energy. E 0.

[0034] S4. Electron Direction Reconstruction Steps: Extract the spatial distribution of Cherenkov light components within a preset ultrafast time window, and reconstruct the recoil electron motion direction vector based on the Cherenkov radiation geometry model. ); a. Input parameters: Step 1 r 2 and step 2 r 1; Photon information captured by the SiPM array within a 0-1 ns time window.

[0035] b. Reconstruction method: Cherenkov cone angle calculation: Where n: the refractive index of the crystal. , It is the electron velocity. It is the speed of light in a vacuum.

[0036] Based on the electron energy information obtained in step 3 After obtaining the electron velocity, the corresponding Cherenkov angle is calculated using the formula above. Combined with the origin position information from the first step, the spatial distribution points of Cherenkov photons are extracted within a time window of 0-1 ns. The electron motion direction vector is determined by fitting the distribution to the theoretical light cone surface using maximum likelihood estimation (MLE). Although the recoil electrons change direction due to collisions during their motion, causing changes in the intensity and direction of the Cherenkov ring, the Cherenkov ring with the strongest initial direction has the greatest intensity, and its direction is consistent with the initial direction of the recoil electrons. Therefore, by analyzing the position and intensity of the strongest Cherenkov ring, the initial direction of the recoil electrons can be accurately determined.

[0037] S5. Radiation source direction inversion steps: Based on the laws of conservation of energy and momentum, combined with the energy of the recoil electrons ( ), scattered photon energy ( ), location of the first point of action ( ), second point of action location ( ) and the direction vector of recoil electron motion ( ), calculate the direction vector of the incident ray.

[0038] a. Input parameter: recoil electron energy ( ), scattered photon energy ( ), location of the first point of action ( ), second point of action location ( ) and the direction vector of recoil electron motion ( ).

[0039] b. Calculation method: Conservation of energy and momentum in: For the momentum of the incident photon ; Incident gamma photon energy; Direction of incident gamma; For the momentum of the scattered photon ; Direction of scattered photons .

[0040] Finally, the direction of incident gamma was obtained. .

[0041] In an optional embodiment of the present invention, the scattering layer unit is a transparent medium with a high refractive index, so that recoil electrons with energies above a threshold generate Cherenkov radiation.

[0042] In an optional embodiment of the present invention, in step S4, the preset ultrafast time window is the interval of 0 to 1 nanosecond (ns) after the arrival of the optical signal; the electronic orientation reconstruction is achieved by fitting the matching degree between the projection distribution of Cherenkov photons on the photoelectric conversion array (i.e., the spatial distribution of Cherenkov light components) and the theoretical light cone surface (i.e., the theoretical Cherenkov radiation geometry model) through known methods such as maximum likelihood estimation or machine learning.

[0043] In an optional embodiment of the present invention, the method for distinguishing signals in step S2 includes: firstly scanning the photoelectric conversion array to identify high-intensity spots with signal strength significantly higher than surrounding pixels, and determining the position corresponding to the high-intensity spot as the second point of action. The high-spot signal is subtracted from the total signal, and the remaining signal is determined to be the first action point signal from the scattering layer unit.

[0044] like Figure 2 As shown, an embodiment of the present invention provides a gamma camera device for implementing the above method, comprising: The scattering layer unit is configured to cause Compton scattering of incident gamma rays and generate recoil electrons; the material of the scattering layer unit has high refractive index characteristics, so that the recoil electrons can simultaneously generate Cherenkov light and scintillation light. An absorption layer unit, located around the scattering layer unit, is configured to absorb Compton-scattered photons and generate scintillation light; the absorption layer unit has optical transparency or a specific light-guiding structure to allow light signals from the scattering layer unit to penetrate and transmit. A photodetector array, located on the side of the absorption layer unit away from the scattering layer unit and on top of the scattering layer unit, is configured to simultaneously respond to and read out the aforementioned Cherenkov light and scintillation light signals. Specifically, the SiPM array on top of the scattering layer unit is used to detect and receive the light signal output from the top of the scattering layer unit; the SiPM arrays on the bottom and sides of the scattering layer unit are used to detect the light signal output from the absorption layer unit.

[0045] In an optional embodiment of the present invention, the absorption layer unit is composed of an array of scintillator modules, each scintillator module having an optical isolation layer on its sidewall for light confinement, and the top and bottom of the scintillator modules being light-transmitting interfaces.

[0046] 1. System Core Architecture Logic This device consists of a scattering layer, an absorption layer, and a SiPM array. The scattering layer is designed with a high refractive index. The material. The physical logic lies in: the threshold velocity for the generation of Cherenkov radiation is... , Speed ​​of light. High refractive index. Reduce threshold speed This ensures that Compton recoil electrons can effectively generate directional Cherenkov light (duration on the order of ps), accompanied by isotropic scintillation light (duration on the order of nanoseconds). Optical signal transmission path: This invention utilizes the absorption layer's property as a "light guide." The Cherenkov light and scintillation light generated by the scattering layer directly penetrate the top interface of the absorption layer and reach the bottom SiPM; while the scintillation light generated by the absorption layer itself is transmitted to the SiPM via total internal reflection. There are significant differences in their arrival time and spatial distribution patterns (the two photons differ slightly in time; the Cherenkov light duration is on the order of ps, while the scintillation light duration is on the order of nanoseconds, forming a time-domain separated signal. Spatially, the Cherenkov light is emitted in a cone shape with the electron direction as the axis, while the scintillation light is isotropically emitted, resulting in different spatial distributions). Therefore, the Cherenkov light is a photon signal with a time window of 0-1 ns, providing a physical basis for signal separation.

[0047] 2. The mathematical and physical process of electron orientation reconstruction Location and Energy Acquisition: Photon Distribution Acquired Using SiPM Array First, use the high-brightness screening method ( (Surrounding average) Location of absorption layer action point After removing this signal, the point of action of the scattering layer is located from the remaining signal using the centroid method or machine learning algorithms. .energy (Electronics) and (Photons) are linked by a pre-defined linear relationship between photon number and energy. get.

[0048] Direction Vector Extraction: Cherenkov light signals are extracted within an ultrafast time window of 0-1 ns. Although electron motion causes scattering, the Cherenkov ring intensity is highest and the direction is most accurate at the initial moment. A likelihood function is constructed using maximum likelihood estimation (MLE), and the electron direction vector that maximizes the photon distribution probability of the extracted Cherenkov light signal is identified as the recoil electron motion direction vector. : This step transforms the physical distribution of the light cone into a mathematically optimal solution.

[0049] Model the observed spatial distribution of Cherenkov photons.

[0050] Input data: The set of photon impact locations recorded by the detector within a 0-1 ns time window { }

[0051] Physical constraint: Cherenkov photons obey the initial direction vector of the electron. A conical distribution with a fixed axis and cone angle θ (θ is calculated from the refractive index n and electron velocity v).

[0052] Construct the direction vector of recoil electron motion Likelihood function: in: Given the direction vector of recoil electron motion At that time, the photon is in position The probability density function of occurrence.

[0053] in Photon position With the direction vector of recoil electron motion The included angle.

[0054] Generate a set of candidate direction vectors on the unit sphere. , }, for each candidate direction vector Calculate its likelihood value. And solve for the electron direction vector that maximizes the likelihood function: The initial direction vector of the electron is the one that best matches the geometric characteristics of the Cherenkov ring.

[0055] 3. Final determination of the incident gamma direction Based on the momentum conservation equation: The direction of the incident photon momentum It can be uniquely determined by the following formula, without the need for statistical analysis of multiple cases: Here Depend on Sure, The electron orientation reconstructed from Cherenkov light.

[0056] 4. Expanding Applications: Electron-pair effect mode: For high-energy gamma rays (>1.02 MeV), this device can also operate in electron-pair effect mode. In this mode, orientation reconstruction is performed by detecting the Cherenkov light point cloud generated by annihilation photon pairs at 511 keV and electron-positron pairs, using the dual-mode optical signal coupling mechanism of this invention.

[0057] Although specific embodiments of the invention have been disclosed for illustrative purposes and to aid in understanding and implementing the invention, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the content disclosed in the preferred embodiments, and the scope of protection claimed by the invention is defined by the claims.

Claims

1. A method for locating a radiation source, comprising the following steps: The system receives optical signals from the detection medium and distinguishes between a first point of action signal and a second point of action signal based on the spatiotemporal distribution characteristics of the optical signals. The first point of action signal is the Cherenkov light and scintillation light generated by the Compton scattering of incident gamma rays in the detection medium and the generation of recoil electrons. The second point of action signal is the scintillation light generated by the absorption of photons after Compton scattering in the detection medium. Based on the scintillation light in the first point of action signal, calculate the first point of action position and recoil electron energy of the first interaction of the gamma rays, as well as the second point of action position and scattered photon energy of the second interaction. The spatial distribution of Cherenkov light was extracted within a preset ultrafast time window, and the direction vector of recoil electron motion was reconstructed. The direction vector of the incident ray is calculated by combining the recoil electron energy, the scattered photon energy, the position of the first point of action, the position of the second point of action, and the direction vector of the recoil electron motion.

2. The method according to claim 1, characterized in that, An optical signal from a detection medium is received using a photoelectric conversion array, the detection medium comprising stacked scattering layer units and absorption layer units; wherein, the scattering layer units are used to perform Compton scattering of incident gamma rays and generate recoil electrons; the absorption layer units are used to absorb the photons after Compton scattering and generate scintillation light, and to allow the optical signal from the scattering layer units to penetrate and transmit.

3. The method according to claim 2, characterized in that, The center of the detection medium is the scattering layer unit, the top of which is used to receive incident gamma rays; the bottom and each side of the scattering layer unit are respectively provided with an absorption layer unit; each absorption layer unit is connected to a photoelectric conversion array for detecting and receiving the light signal output by the absorption layer unit; the top of the scattering layer unit is connected to a photoelectric conversion array for detecting and receiving the light signal output by the top of the scattering layer unit.

4. The method according to claim 2 or 3, characterized in that, The method for obtaining the first point of action position, the recoil electron energy, the second point of action position where secondary interaction occurs, and the scattered photon energy is as follows: the signals collected by each of the photoelectric conversion arrays are scanned. If there is only one high point that meets the conditions, the second point of action position is calculated based on the position of the high point and the thickness of the absorption layer unit. Then, the high point is subtracted from the signals collected by each of the photoelectric conversion arrays to obtain the remaining signal set. The first point of action position is calculated based on the remaining signal set.

5. The method according to claim 1, 2, or 3, characterized in that, Cherenkov light signals are extracted within an ultrafast time window of 0-1 ns. A cone-shaped distribution with the initial electron direction vector of Cherenkov photons as the axis and a set cone angle is used as a physical constraint. Based on the extracted Cherenkov light signals, a likelihood function about the recoil electron motion direction vector is constructed using maximum likelihood estimation. The electron direction vector that maximizes the probability of observing the Cherenkov light signal is then identified as the recoil electron motion direction vector.

6. The method according to claim 1, 2, or 3, characterized in that, The recoil electron energy and scattered photon energy are obtained by pre-calibrating the linear relationship between photon number and energy.

7. The method according to claim 1, 2, or 3, characterized in that, Based on the duration and direction of the optical signal, the first point of action signal and the second point of action signal are distinguished.

8. The method according to claim 1, characterized in that, Based on the laws of conservation of energy and momentum, and combining the energy of the recoil electron, the energy of the scattered photon, the position of the first point of action, the position of the second point of action, and the direction vector of the recoil electron, the direction vector of the incident ray is calculated.

9. A gamma camera device, characterized in that, Includes scattering layer units, absorption layer units, and photoelectric detection arrays; The scattering layer unit is configured to cause Compton scattering of incident gamma rays and generate recoil electrons. The absorption layer unit, located around the scattering layer unit, is configured to absorb scattered photons from Compton scattering and generate scintillation light, and to allow optical signals from the scattering layer unit to penetrate and transmit. The photodetector array is located on the side of the absorption layer unit away from the scattering layer unit and on top of the scattering layer unit, and is configured to respond to and read out the optical signal output by the absorption layer unit.

10. The gamma camera device according to claim 9, characterized in that, The top of the scattering layer unit is used to receive incident gamma rays; the bottom and each side of the scattering layer unit are respectively provided with an absorption layer unit; each absorption layer unit is connected to a photoelectric conversion array for detecting and receiving the light signal output by the absorption layer unit; the top of the scattering layer unit is connected to a photoelectric conversion array for detecting and receiving the light signal output by the top of the scattering layer unit.

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