Coded ray camera response function adaptive correction system and correction method

Abstract

The present invention discloses a coded radiographic camera response function adaptive correction system and correction method. The correction system includes a radiation detector, a coded radiographic shielding assembly, a response function adaptive correction system, an image reconstruction system, and a radioactive source to be measured. The radiation detector detects radioactive particles passing through the coded radiographic shielding assembly and obtains a radioactive particle count. The response function adaptive correction system receives the radioactive particle count information transmitted by the radiation detector and optimizes and corrects a preset response function to ensure that the variance between the normalized radioactive particle count information and the corrected response function remains consistent. The image reconstruction system uses the corrected response function to reconstruct the position of the radioactive source. The present invention improves the spatial resolution of the device and can be used for detection and positioning imaging of uncontrolled radioactive sources. It has important application value in the fields of special nuclear material detection and nuclear proliferation prevention.

Description

Technical Field

[0001] The present invention belongs to the field of radiation detection and imaging, and in particular relates to a coded ray camera response function adaptive correction system and correction method thereof. Background Art

[0002] Coded aperture radiography (CAD) cameras are widely used in deep space exploration, nuclear medicine, and the search for uncontrolled radioactive sources. Based on these, time-series coded radiography cameras have been developed. These cameras utilize a rotating or moving coded aperture plate to differentiate responses to radioactive sources at different spatial locations, eliminating the need for array detectors. In principle, both devices require coded radiation shielding components to shield incident radiation, and the shielding efficiency varies with the energy of the incident radiation.

[0003] The so-called response function of the device, for a coded aperture radiography, refers to the detection efficiency of a pixel unit of the array detector at each position in the field of view of the device; for a time-series coded radiography, it refers to the detection efficiency of the detector at each position in the field of view of the device. In many applications, the energy of the radiation emitted by the radiation source is unknown, but the energy has a great influence on the response function, such as Figure 2 As shown, the ideal model assumes that the shielding efficiency of the radiation shielding component is 100% for all energies at the unperforated locations, and that the detector is a point detector. The point detector model assumes that the shielding efficiency of the radiation shielding component is not 100% and varies with the energy of the radiation, which is more realistic. The real model, based on the point detector model, takes into account the effect of detector size. The figure shows that radiation energy has a significant impact on the shape of the response function, especially its amplitude. When the energy of the measured radiation source is unknown, the device's response function is typically calculated using Monte Carlo simulations of radiation of typical energies. This inevitably differs from the response during the actual measurement process, increasing measurement inaccuracy. The present invention enables adaptive correction of the response function based on a preset response function and measurement results when the radiation source energy is unknown. This overcomes the impact of energy differences on the response function, significantly improving the accuracy of the response function and achieving better image reconstruction. It can be used for adaptive optimization of the response function of radiation-shielded coded radiography cameras and time-series coded radiography cameras. This method has broad and important application prospects in nuclear medicine and the search for uncontrolled radiation sources. Summary of the Invention

[0004] The present invention aims to address the problem of inaccurate response functions of coded radiographic cameras when detecting radioactive sources of unknown energy. The specific solution is as follows:

[0005] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0006] The coded ray camera response function adaptive correction system is characterized by comprising: a radiation detector, a coded ray shielding assembly, a response function adaptive correction system, an image reconstruction system and a radioactive source to be measured, wherein the radioactive source to be measured can emit radioactive particles toward the coded ray shielding assembly, the coded ray shielding assembly is provided with coded bar holes, some of the radioactive particles can pass through the coded ray shielding assembly through the coded bar holes, and the remaining radioactive particles are absorbed by the coded ray shielding assembly, the radiation detector detects the radioactive particles passing through the coded ray shielding assembly and obtains a measurement count of the radioactive particles, the radiation detector is connected to the response function adaptive correction system, the response function adaptive correction system is connected to the image reconstruction system, the response function adaptive correction system receives the measurement count information of the radioactive particles transmitted by the radiation detector, and optimizes and corrects the preset response function so that the variance between the normalized measurement count information of the radioactive particles and the corrected response function is consistent, and the image reconstruction system uses the corrected response function to reconstruct the position of the radioactive source.

[0007] To optimize the above technical solutions, specific measures taken also include:

[0008] The coded ray shielding component is located between a radiation detector and a radioactive source to be detected. The radiation detector is an organic scintillator detector or an inorganic scintillator detector.

[0009] The radioactive particles emitted by the radioactive source to be tested are gamma rays.

[0010] The coded radiation shielding components are made of lead material.

[0011] The radioactive particles emitted by the radioactive source to be measured are neutrons.

[0012] The coded radiation shielding component is made of boron-containing polyethylene material.

[0013] The radiation detector is a coded radiographic camera.

[0014] The adaptive correction method of the coded ray camera response function is as follows:

[0015] The radiation detector detects the radiation passing through the coded radiation shielding assembly; the field of view of the radiation detector is divided into 1, 2, 3…i…I, with a total of I pixels, where the response function of the radiation detector at the i-th position is recorded as R i The Monte Carlo software simulates and calculates the camera's response function R to this pixel by determining the energy of the ray. i , the average value of each pixel response function value is recorded as During the experimental measurement, when the coded radiation shielding assembly moves i pixel positions and stays for a certain period of time, the number of radioactive particles measured by the radiation detector during this period of time is recorded as C i The average value of the radioactive particle count after moving all positions is recorded as

[0016] Radiation detectors respond differently to radioactive sources at different locations in space. The difference in response amplitude is related to the radiation energy. That is, the radiation source energy in actual measurement is likely to be different from the radiation energy in Monte Carlo simulation. Therefore, it is necessary to optimize and correct the response function of the response function adaptive correction system to make the variance between the radioactive particle measurement count and the corrected response function equal. The response function adaptive correction system corrects the preset response function based on the measurement results according to the following formula:

[0017]

[0018] Where R i is the response value of the device at point i, is the average value of the response function, C i is the measurement count value at position i, is the average value of the measured counts, To obtain the corrected response function, both the response function and the radioactive particle measurement count value should be normalized before correction. The variance between the corrected response function and the count value sequence should be kept consistent, that is, the amplitude of the count value and the corrected response function value should be the same.

[0019] The position of the radiation source is reconstructed using the corrected response function.

[0020] The specific method of reconstructing the position of the radiation source using the corrected response function is:

[0021] The image is reconstructed using the maximum likelihood expectation maximization method:

[0022]

[0023] In the formula, “*” represents convolution operation; Represents related operations; f k (x,y) is the image estimation value after the kth iteration; p(i) is the count sequence measured by the detector.

[0024] The present invention has the following effects:

[0025] This method addresses the inaccurate response function of coded radiography cameras when detecting radioactive sources of unknown energy. By combining measurement counts with adaptive corrections to the response function, this method reduces the impact of radiation energy differences on the accuracy of the response function and improves the spatial resolution of the device. This method can be applied to the detection and localization of uncontrolled radioactive sources, and has significant application value in areas such as special nuclear material detection and nuclear non-proliferation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the device of the present invention;

[0027] Figure 2 It is a schematic diagram of the response function of the present invention;

[0028] Figure 3 is the change in angular resolution before and after correction in the embodiment of the present invention;

[0029] Figure 4 This is the image reconstruction result of the radiation source position before and after correction in the embodiment of the present invention.

[0030] The reference numerals are: radiation detector 1 , coded ray shielding assembly 2 , response function adaptive correction system 3 , image reconstruction system 4 , and radiation source to be measured 5 . DETAILED DESCRIPTION

[0031] The embodiments of the present invention are described in further detail below with reference to the accompanying drawings.

[0032] refer to Figure 1 The example shown includes a radiation detector 1 , a coded radiation shielding assembly 2 , a response function adaptive correction system 3 , an image reconstruction system 4 , and a radiation source 5 to be detected.

[0033] The radiation detector 1 is a CLYC scintillator detector with a diameter of 3 cm and a length of 3 cm. The detector records the neutron and gamma ray counts recorded by the detector when the coded ray shielding assembly moves to different positions.

[0034] The material of the coded radiation shielding component 2 is composed of an inner layer of metal lead and an outer layer of boron-containing polyethylene. The thickness of the inner layer of metal lead is 1 cm and is used to shield gamma rays; the thickness of the outer layer of boron-containing polyethylene is 6 cm and is used to shield gamma rays. The coded radiation shielding component is located between the radiation source to be tested and the radiation detector and moves at a constant speed during the test.

[0035] The preset response function of the system builds a Monte Carlo model based on the size and relative position of the radiation detector and the coded radiation shielding component. The gamma radiation source and neutron source in the Monte Carlo simulation are set as Cs-137 source and Cf-252 neutron source, respectively.

[0036] The adaptive correction method of the coded ray camera response function is as follows:

[0037] The radiation detector 1 detects the radiation passing through the coded radiation shielding assembly 2; the field of view of the radiation detector 1 is divided into 1, 2, 3…i…I, with a total of I pixels, where the response function of the radiation detector 1 at the i-th position is recorded as R i The Monte Carlo software simulates and calculates the camera's response function R to this pixel by determining the energy of the ray. i , the average value of each pixel response function value is recorded as During the experimental measurement, when the coded radiation shielding assembly moves i pixel positions and stays for a certain period of time, the number of radioactive particles measured by the radiation detector (1) during this period of time is recorded as C i The average value of the radioactive particle count after moving all positions is recorded as

[0038] The radiation detector (1) responds differently to radioactive sources at different locations in space, and the difference in response amplitude is related to the energy of the radiation. That is, the energy of the radiation source in actual measurement is likely to be different from the energy of the radiation in Monte Carlo simulation. Therefore, it is necessary to optimize and correct the response function of the response function adaptive correction system 3 so that the variance between the radioactive particle measurement count and the corrected response function is equal. The response function adaptive correction system 3 corrects the preset response function according to the measurement results according to the following formula:

[0039]

[0040] Where, i is the response value of the device at point i, is the mean value of the response function, i is the measurement count value at position i, is the average value of the measured counts, To obtain the corrected response function, both the response function and the radioactive particle measurement count value should be normalized before correction. The variance between the corrected response function and the count value sequence should be kept consistent, that is, the amplitude of the count value and the corrected response function value should be the same.

[0041] The position of the radiation source is reconstructed using the corrected response function.

[0042] The specific method of reconstructing the position of the radiation source using the corrected response function is:

[0043] The image is reconstructed using the maximum likelihood expectation maximization method:

[0044]

[0045] In the formula, “*” represents convolution operation; Represents related operations; f k (x,y) is the image estimation value after the kth iteration; p(i) is the count sequence measured by the detector.

[0046] Spatial resolution describes a system's ability to discern the location of a radioactive source. To mitigate the effects of distance from the system, angular resolution is often used as an evaluation metric. The full width at half maximum (FWHM) of the radioactive source hotspot in the reconstructed image is often used as the angular resolution. For 2D time-series coded aperture radiography cameras, angular resolution is further divided into horizontal and vertical angular resolutions.

[0047] A σ =FWHM(S)

[0048] Among them, S is the distribution of hot spots in the reconstructed image, FWHM is the calculation of its half-maximum width, and the half-maximum width of the hot spot S in the horizontal and vertical directions is used as the angular resolution A in the horizontal and vertical directions respectively. σ .

[0049] Sensitivity describes the detection efficiency of the system and its ability to measure the minimum value of the measurand. The contrast-to-noise ratio (CNR) of the reconstructed image is usually used to evaluate the sensitivity of the system. The contrast-to-noise ratio of the image can be calculated as follows:

[0050]

[0051] Among them, N max is the maximum pixel value in the image, N min is the minimum pixel value in the image, σ Nmax is the standard deviation of the maximum pixel value.

[0052] By comparing the spatial resolution and sensitivity indicators of the reconstructed images before and after correction, it was found that the angular resolution and contrast-to-noise ratio were greatly improved after correction, indicating that the adaptive correction of the response function by this method significantly improved the image reconstruction quality.

[0053] Example:

[0054] Positioning and imaging measurement of a neutron source of unknown energy at a distance of 100m

[0055] This example performs positioning imaging on an Am-Be neutron source shielded by an unknown material at a distance of 100m. The radiation source is located at a position 260° relative to the device, and the radiation source activity is approximately 1Ci. During the measurement process, due to the difference between the energy of neutrons and gamma rays emitted by the measured neutron source and the energy in the response function simulation, after a cycle of measurement, the preset response function is corrected according to the measurement count. The image is reconstructed using the response functions before and after the correction. During the reconstruction process, the angular resolution changes with the number of iterations as shown in the figure below. Figure 3 As shown in , it can be seen that after the response function is corrected, the image angular resolution is significantly improved. The optimal number of iterations before and after correction is selected, and the reconstructed image is shown as Figure 4 As shown, the sensitivity and signal-to-noise ratio of the visible image have also been significantly improved.

[0056] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. The adaptive correction system of the response function of the coded ray camera is characterized by: Including radiation A detector (1), a coded ray shielding component (2), a response function adaptive correction system (3), an image reconstruction system (4), and a radioactive source to be measured (5). The radioactive source to be measured (5) can emit radioactive particles to the coded ray shielding component (2). The coded ray shielding component (2) is provided with coded bar holes. Some of the radioactive particles can pass through the coded ray shielding component (2) through the coded bar holes, and the remaining radioactive particles are absorbed by the coded ray shielding component (2). The radiation detector (1) detects the radioactive particles passing through the coded ray shielding component (2) to obtain a measurement count of the radioactive particles. The radiation detector (1) is connected to the response function adaptive correction system (3). The response function adaptive correction system (3) is connected to the image reconstruction system (4). The response function adaptive correction system (3) receives the measurement count information of the radioactive particles transmitted by the radiation detector (1) and optimizes and corrects the preset response function so that the variance between the normalized measurement count information of the radioactive particles and the corrected response function remains consistent. The image reconstruction system uses the corrected response function to reconstruct the position of the radioactive source.

2. The coded radiographic camera response function adaptive correction system according to claim 1, characterized in that: The coded ray shielding assembly (2) is located between a radiation detector (1) and a radioactive source (5) to be detected, and the radiation detector (1) is an organic scintillator detector or an inorganic scintillator detector.

3. The coded radiographic camera response function adaptive correction system according to claim 1, characterized in that: The radioactive particles emitted by the radioactive source (5) to be tested are gamma rays.

4. The coded radiographic camera response function adaptive correction system according to claim 1, characterized in that: The coded ray shielding component (2) is made of lead material.

5. The coded radiographic camera response function adaptive correction system according to claim 1, characterized in that: The radioactive particles emitted by the radioactive source (5) to be tested are neutrons.

6. The coded radiographic camera response function adaptive correction system according to claim 1, characterized in that: The coded ray shielding component (2) is made of boron-containing polyethylene material.

7. The coded radiographic camera response function adaptive correction system according to claim 1, characterized in that: The radiation detector (1) is a coded ray camera.

8. A method for adaptively correcting the response function of a coded ray camera, characterized by: The adaptive correction system for the response function of a coded ray camera according to claim 1 is applied, and the specific correction method is as follows: The radiation detector (1) detects the radiation passing through the coded radiation shielding assembly (2); the field of view of the radiation detector (1) is divided into 1, 2, 3…i…I, with a total of I pixels, wherein the response function of the radiation detector (1) at the i-th position is recorded as R i The Monte Carlo software simulates and calculates the camera's response function R to this pixel by determining the energy of the ray. i , the average value of each pixel response function value is recorded as During the experimental measurement, when the coded radiation shielding assembly moves i pixel positions and stays for a certain period of time, the number of radioactive particles measured by the radiation detector (1) during this period of time is recorded as C i The average value of the radioactive particle count after moving all positions is recorded as The radiation detector (1) responds differently to radioactive sources at different locations in space. The difference in response amplitude is related to the energy of the radiation. That is, the energy of the radiation source in actual measurement is likely to be different from the energy of the radiation in Monte Carlo simulation. Therefore, it is necessary to optimize and correct the response function of the response function adaptive correction system (3) so that the variance between the radioactive particle measurement count and the corrected response function is equal. The response function adaptive correction system (3) corrects the preset response function according to the measurement results according to the following formula: Where R i is the response value of the device at point i, is the average value of the response function, C i is the measurement count value at position i, is the average value of the measured counts, To obtain the corrected response function, both the response function and the radioactive particle measurement count value should be normalized before correction. The variance between the corrected response function and the count value sequence should be kept consistent, that is, the amplitude of the count value and the corrected response function value should be the same. The position of the radiation source is reconstructed using the corrected response function.

9. The adaptive correction method for the response function of a coded ray camera according to claim 8, characterized in that: The specific method of reconstructing the position of the radiation source using the corrected response function is: The image is reconstructed using the maximum likelihood expectation maximization method: Where "*" represents convolution operation; " indicates related operations; f k (x,y) is the image estimation value after the kth iteration; p(i) is the count sequence measured by the detector.

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