A coded-aperture-based compton scatter tomography system and method

Abstract

The application discloses a kind of based on encoding aperture's Compton scattering tomography system and method.The system includes detection device, one-dimensional displacement platform, data processing device;The detection device includes fan-beam X-ray machine, two-dimensional encoding plate and area array detector;Fan-beam X-ray machine is used to scan each tomography of the object to be measured and generates scattered photon;Two-dimensional encoding plate is placed between the object to be measured and area array detector, for the spatial modulation of scattered photon into area array detector;Area array detector is placed with fan-beam X-ray machine side, for receiving scattered photon and converting it into analog signal and then output to data processing device;Data processing device is used to convert analog signal into digital signal, from digital signal in time sequence extraction each tomography position corresponding Compton scattering imaging information, decoding reconstruction the three-dimensional structure diagram of the object to be measured.The application can realize unilateral in situ, efficient real-time nondestructive imaging, effectively obtain object depth information and three-dimensional structure.

Description

Technical Field

[0001] This invention relates to the field of X-ray imaging technology, and specifically to a Compton scattering tomography system and method based on coded aperture. Background Technology

[0002] Compton scattering imaging is a non-destructive testing technique based on the Compton scattering effect. It reflects the internal electron density distribution of an object by detecting the difference in the scattering intensity of X-rays and gamma rays. It has important applications in medical diagnostics, industrial inspection, public safety, scientific research, and archaeology. Compared with conventional transmission imaging, scattering imaging has advantages such as sensitivity to low-density, low-atomic-number materials and the ability to support in-situ, real-time, and single-sided imaging. It has unique advantages for the non-destructive testing of underground objects, wall materials, and large aerospace components. However, due to the all-space distribution of scattered rays and the limitations of the back-end collimator, the detectable scattering intensity is very low, resulting in a poor signal-to-noise ratio in the scattering images. This greatly limits the practical application of scattering imaging. Therefore, improving the utilization rate of X-rays is crucial for scattering imaging technology.

[0003] After years of technological accumulation, various Compton scattering imaging mechanisms have been developed, among which flying-spot imaging and pushbroom imaging have been widely applied in various two-dimensional imaging scenarios based on Compton scattering technology. Existing Compton scattering imaging systems mostly employ flying-spot scanning, relying on the high-speed rotation of rotating collimators such as choppers to generate high-precision X-ray beams. Their mechanical structures are complex, and they are mostly fixed devices. This method performs point scanning imaging of objects, resulting in low utilization of the X-ray source and low imaging efficiency. While X-rays with a certain energy can penetrate objects and reach a certain depth for scanning, only superimposed information within the entire penetration depth along the incident direction can be obtained, failing to achieve depth resolution. Unlike flying-spot imaging, pushbroom imaging uses fan-beam X-rays for line scanning imaging of objects, effectively improving the utilization of the X-ray source. Furthermore, its simple structure makes it easy to form mobile and portable devices. Combined with linear or area array detectors, it can theoretically achieve two-dimensional and even three-dimensional imaging. However, current applications of pushbroom-based Compton scattering imaging are primarily focused on two-dimensional imaging, with limited research on three-dimensional imaging. One of the main reasons is that current technologies generally use pinhole or grid collimators to locate the back-end scattered rays, which greatly limits the utilization rate of scattered rays, resulting in the overall imaging efficiency of push-broom scanning being at the same level as flying-spot scanning. Summary of the Invention

[0004] The purpose of this invention is to provide a Compton scattering tomography system and method based on coded aperture, which can overcome the limitations of existing transmission technology in non-destructive testing, and provide solutions to key problems such as low utilization of scattered rays and low imaging efficiency in current Compton scattering imaging technology through coded aperture technology, so as to realize in-situ, unilateral depth information acquisition and efficient, real-time three-dimensional structure reconstruction.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A Compton scattering tomography system based on coded aperture is characterized by comprising a detection device, a one-dimensional displacement stage, and a data processing device; the detection device comprises a fan-beam X-ray machine, a two-dimensional coded plate, and an area array detector.

[0007] The fan-beam X-ray machine is used to emit fan-beam X-rays to scan the various sections of the object under test and generate scattered photons.

[0008] The two-dimensional encoding plate is placed between the object under test and the area array detector, and is used to spatially modulate the scattered photons entering the area array detector.

[0009] The array detector is placed behind the two-dimensional encoding plate and on the same side as the fan-beam X-ray machine. It is used to receive the scattered photons modulated by the two-dimensional encoding plate and convert them into analog signals before outputting them to the data processing device.

[0010] The one-dimensional displacement stage is used to carry the object under test or the detection device, and during the scanning process, it drives the carried object under test or the detection device to move unidirectionally at a set interval, so as to realize the relative movement between the object under test and the detection device, so that the fan beam X-ray machine can scan each section of the object under test.

[0011] The data processing device is used to receive the analog signal input by the area array detector and convert it into a digital signal, control and monitor the motion trajectory of the one-dimensional displacement stage, record the scanning time of each fracture of the object under test, and then extract the Compton scattering imaging information corresponding to each fracture position from the digital signal in chronological order, and decode and reconstruct the three-dimensional structural map of the object under test.

[0012] Furthermore, the fan-beam X-ray machine includes an X-ray machine and a front collimator. The front collimator is used to limit the direction of the X-rays emitted by the X-ray machine and collimate the cone-beam X-rays emitted by the X-ray machine into fan-beam X-rays.

[0013] Furthermore, the two-dimensional encoding board is a two-dimensional Singer encoding board.

[0014] Furthermore, the two-dimensional singer code is a two-dimensional singer code with coprime length and width; the two-dimensional singer code is generated by wrapping the one-dimensional singer code with the Proctor diagonal; the one-dimensional singer code is obtained by converting the singer sequence into binary.

[0015] Furthermore, the two-dimensional encoding board is a two-dimensional MURA encoding board based on a modified uniform redundancy array.

[0016] A Compton scattering tomography method based on coded aperture, comprising the following steps:

[0017] 1) Mount the object to be tested or the detection device on a one-dimensional displacement stage; the detection device includes a fan-beam X-ray machine, a two-dimensional encoding plate, and an area array detector; place the two-dimensional encoding plate between the object to be tested and the area array detector, and place the area array detector on the same side as the fan-beam X-ray machine;

[0018] 2) The data processing device controls the one-dimensional displacement stage to move the mounted object under test or detection device in one direction at set intervals to achieve relative motion between the object under test and the detection device; when a test position is reached, the fan-beam X-ray machine is activated to emit fan-beam X-rays to scan the current test position of the object under test and generate scattered photons; the area array detector receives the scattered photons modulated by the two-dimensional encoding plate and converts them into analog signals before outputting them to the data processing device.

[0019] 3) Repeat step 2) so that the fan beam X-ray machine scans each section of the object under test and records the time of scanning each section of the object under test.

[0020] 4) The data processing device converts the analog signal input by the area array detector into a digital signal; then extracts the Compton scattering imaging information corresponding to each fault position from the digital signal in chronological order, and decodes and reconstructs the three-dimensional structural map of the object under test.

[0021] This invention relates to a Compton scattering tomography system based on coded aperture, as follows: Figure 1 As shown, it is divided into three parts: a detection device, a one-dimensional displacement stage, and a data processing device; wherein the detection device includes a fan-beam X-ray machine, a two-dimensional coding plate, and an area array detector.

[0022] The fan-beam X-ray machine is used to emit fan-beam X-rays to scan the various sections of the object being tested.

[0023] The two-dimensional encoding plate is placed between the object under test and the area array detector, and spatially modulates the scattered photons entering the area array detector using a selected encoding method.

[0024] The array detector is placed behind the two-dimensional encoding plate and on the same side as the fan-beam X-ray machine. It is used to receive scattered photons modulated by the two-dimensional encoding plate, and at the same time convert the instantaneously received light signal into an analog signal and output the signal to the data processing device.

[0025] The one-dimensional displacement stage is used to carry the object under test or the detection device, and during the scanning process, it drives the object under test or the detection device to move unidirectionally at a set interval to realize the relative motion between the object under test and the detection device, so that the fan beam X-ray machine can scan each section of the object under test to obtain Compton scattering imaging information of different sections of the object under test.

[0026] The data processing device receives and processes all signals acquired by the probe during the push-broom process, converts the analog signals input by the area array detector into digital signals, and transmits them to the host computer of the data processing device. During the push-broom process, it controls and monitors the trajectory of the one-dimensional displacement stage and records the scanning time for each fracture of the object under test. Then, it extracts and processes multiple sets of fracture projection data from the digital signals in chronological order, decodes and reconstructs two-dimensional cross-sectional views of each fracture of the object under test, and integrates them into a three-dimensional structural image.

[0027] This invention also provides a Compton scattering tomography method based on coded aperture, the process of which is as follows: Figure 2 As shown, the specific steps are as follows:

[0028] 1. Generate an X-ray fan beam to scan the tomographic cross-section of the object under test;

[0029] 2. The scattered rays modulated by the two-dimensional encoding plate are collected by the detector, and the analog signal is converted into a digital signal and transmitted to the data processing device;

[0030] 3. The host computer decodes and reconstructs the projection data at the fault location of the object in real time, and stores the fault projection data and the reconstructed two-dimensional cross-sectional data after each acquisition.

[0031] 4. After the fault projection data is collected within the set time, the host computer controls the one-dimensional displacement stage to move to the next fault to continue collecting data. Repeat step 3 to collect the projection data and two-dimensional cross-sectional data of each fault layer of the object.

[0032] 5. Integrate the decoded and reconstructed two-dimensional cross-sectional images to generate the three-dimensional structure of the object.

[0033] The advantages of this invention are as follows:

[0034] The Compton scattering tomography system and method based on coded aperture provided by this invention can perform in-situ, one-sided, efficient, and real-time non-destructive testing on low-density, low atomic number materials, and obtain the depth information and three-dimensional structure of the object, providing a new imaging means for three-dimensional non-destructive testing in China.

[0035] This invention employs Compton scattering imaging technology, which is sensitive to low-density, low-atomic-number materials and can effectively supplement transmission imaging (sensitive to high-atomic-number materials such as metals). Furthermore, the scattered rays are distributed throughout space, thus allowing for a change in traditional detection layouts. The detector and ray source can be placed on the same side of the object being measured to achieve single-sided imaging, facilitating the integration of lightweight, mobile, or portable imaging devices for in-situ imaging of the object and effectively solving the imaging problem of large objects. The introduction of coded aperture technology into Compton scattering imaging, through high aperture ratio and multiplexing technology, improves the utilization rate of scattered rays. Combined with a two-dimensional pushbroom imaging mode, this further enhances imaging efficiency, providing the necessary conditions for high-speed, real-time image reconstruction. Moreover, the coding is highly flexible and can adapt to various imaging scenarios, achieving both large-field-of-view imaging and high-resolution imaging. A single frame of two-dimensional cross-sectional image generated from a single sampling can effectively reflect the depth information of the object, and the three-dimensional structure of the object can be reconstructed through multiple layer-by-layer pushbrooms.

[0036] This invention organically combines the advantages of Compton scattering imaging, push-broom imaging, and coded aperture imaging technologies, with the three complementing each other to obtain a highly innovative, practical, and three-dimensional non-destructive testing Compton scattering tomography scheme. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a Compton scattering tomography system based on coded aperture provided in an embodiment of the present invention.

[0038] Figure 2 A flowchart of the Compton scattering tomography method based on coded aperture provided in an embodiment of the present invention.

[0039] Figure 3 The encoding board pattern provided in this embodiment of the invention is based on MURA encoding arrangements with multiple different encoding numbers.

[0040] Figure 4 The present invention provides coding board patterns based on Singer coding arrangements with different numbers of codes, different aperture ratios, and different aspect ratios. Detailed Implementation

[0041] 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.

[0042] Example 1:

[0043] This invention proposes a Compton scattering tomography method based on modified uniform redundancy array (MURA) encoding, and the specific implementation steps are as follows:

[0044] 1. Generate an X-ray fan beam to scan the tomographic cross-section of the object under test;

[0045] The collimator of an X-ray machine is a slit collimator, made of high-density materials such as tungsten copper or lead, used to limit the direction of X-rays emitted from the machine. The cone-shaped X-ray beam emitted from the X-ray machine is collimated into a fan-shaped X-ray beam by the slit collimator and then emitted onto the object being measured, interacting with the material of the scanned portion, i.e., the tomographic region. Because the slit collimator has a certain width, and the actual fan beam also has a certain width, a single scan only captures a thin layer of the object, called a tomography.

[0046] 2. The scattered rays modulated by the two-dimensional MURA encoder are collected by the detector, and the analog signal is converted into a digital signal and transmitted to the host computer;

[0047] After the X-rays interact with the tomographic material, some of them are scattered at a certain angle and spatially modulated by a two-dimensional MURA encoding plate before being received by an area array detector. The two-dimensional MURA encoding array used consists of a prime number L encoding themes. MURA The one-dimensional MURA encoded sequence mapping is generated, and its element values ​​can be generated according to the following formula:

[0048]

[0049]

[0050] in This represents the element value corresponding to the i-th element in a one-dimensional MURA encoded sequence. This represents the element value corresponding to the element in the i-th row and j-th column of the two-dimensional MURA code. The element value reflects the opening status of the code plate, where 0 represents a closed hole and 1 represents an open hole.

[0051] A two-dimensional MURA encoding board is generated by cyclic nesting based on the basic two-dimensional MURA encoding matrix. The encoding board consists of a tungsten-copper alloy (or other high-density material) and a photosensitive resin support. The tungsten-copper alloy blocks are arranged according to the two-dimensional MURA encoding method to block scattered rays. The photosensitive resin support allows scattered rays to penetrate and be received by the area array detector, which then converts them into photoelectric signals. These signals are then converted into digital signals by the data acquisition board and transmitted to the host computer.

[0052] 3. The host computer decodes and reconstructs the projection data in real time, and stores the projection data and reconstructed data after each acquisition.

[0053] The MURA encoding matrix can be derived from the following formula. Obtain the corresponding MURA decoding matrix After cross-correlation decoding and reconstruction of the projection data, the reconstructed two-dimensional cross-sectional image can be stored and displayed in real time via a host computer.

[0054]

[0055] 4. After the fault projection data is collected within the set time, the host computer controls the one-dimensional displacement stage to move to the next fault to continue collecting data. Repeat step 3 to collect the object's fault projection data layer by layer and perform decoding and reconstruction.

[0056] By controlling the moving distance and time interval of the one-dimensional moving stage, the object under test can be scanned layer by layer from the initial position to obtain two-dimensional projection data of different faults of the object, and the two-dimensional cross-sectional images of each fault can be reconstructed according to the corresponding MURA decoding matrix.

[0057] 5. Integrate the decoded and reconstructed two-dimensional cross-sectional images to generate the three-dimensional structure of the object.

[0058] Each set of reconstructed data is integrated and subjected to affine transformation, and supplemented with corresponding correction and enhancement algorithms, ultimately yielding a three-dimensional image of the object under test.

[0059] The Compton scattering tomography system based on coded aperture provided in this example employs MURA coded imaging. This coding method boasts excellent characteristics such as a high aperture ratio of 50% and an ideal point spread function, effectively improving X-ray utilization. Furthermore, MURA coding features an antisymmetric square structure, allowing the inverse code plate to be obtained by rotating the positive code plate 90 degrees. This facilitates the reduction of near-field artifacts through superimposed imaging of the positive and inverse code plates.

[0060] Example 2:

[0061] This invention proposes a Compton scattering tomography method based on Singer coding, and the specific implementation steps are as follows:

[0062] 1. Generate an X-ray fan beam to scan the tomographic cross-section of the object under test;

[0063] The X-ray machine's front collimator is a slit collimator, made of high-density materials such as tungsten copper or lead, used to limit the direction of the X-rays emitted from the X-ray machine. The cone-beam X-rays emitted from the X-ray machine are collimated into a fan-beam X-ray by the slit collimator and emitted to the object being measured, where they interact with the material of the scanned part, i.e., the tomographic region.

[0064] 2. The scattered rays modulated by the two-dimensional Singer coded plate are collected by the detector, and the analog signal is converted into a digital signal and transmitted to the host computer;

[0065] After the X-rays interact with the tomographic material, some of them are scattered at a certain angle and spatially modulated by a two-dimensional Singer-coded plate before being received by an array detector. The two-dimensional Singer coding employed... It is formed by periodically wrapping one-dimensional Singer codes, where the one-dimensional Singer codes are obtained by binary conversion of the Singer sequence (v,k,λ). The two-dimensional Singer codes with coprime dimensions are generated by wrapping the one-dimensional Singer codes with the Proctor diagonal. To ensure the integrity of the rectangular wrapping, it is usually necessary to pad or prune the last pixels.

[0066] A two-dimensional singer coding board is generated by cyclic nesting based on the basic two-dimensional singer coding matrix. The coding board is composed of tungsten-copper alloy (or other high-density materials) and a photosensitive resin support. The tungsten-copper alloy blocks are arranged according to the two-dimensional singer coding method to block scattered rays. The photosensitive resin support allows scattered rays to penetrate and be received by the area array detector, which then converts them into photoelectric signals. These signals are then converted into digital signals by the data acquisition board and transmitted to the host computer.

[0067] 3. The host computer decodes and reconstructs the projection data in real time, and stores the projection data and reconstructed data after each acquisition.

[0068] The Singer coding matrix can be derived from the following formula. Obtain the corresponding Singer decoding matrix After cross-correlation decoding and reconstruction of the projection data, the reconstructed two-dimensional cross-sectional image can be stored and displayed in real time via a host computer.

[0069]

[0070] 4. After the fault projection data is collected within the set time, the host computer controls the one-dimensional displacement stage to move to the next fault to continue collecting data. Repeat step 3 to collect the object's fault projection data layer by layer and perform decoding and reconstruction.

[0071] By controlling the moving distance and time interval of the one-dimensional moving stage, the object under test can be scanned layer by layer from the initial position to obtain two-dimensional projection data of different faults of the object, and the two-dimensional cross-sectional images of each fault can be reconstructed according to the corresponding Singh decoding matrix.

[0072] 5. Integrate the decoded and reconstructed two-dimensional cross-sectional images to generate the three-dimensional structure of the object.

[0073] Each set of reconstructed data is integrated and subjected to affine transformation, and supplemented with corresponding correction and enhancement algorithms, ultimately yielding a three-dimensional image of the object under test.

[0074] The Compton scattering tomography system based on coded aperture provided in this example employs Singer coding imaging, which can generate rectangular code plates with various aperture ratios and aspect ratios, thereby meeting the imaging requirements for source exposure and field of view in various scenarios. During Compton scattering imaging, due to the low energy of the scattered rays, the penetration depth is typically a few centimeters. The rectangular code plate designed based on Singer coding can flexibly modulate the field of view ratio according to the scattering imaging characteristics, and the long rectangular coding mode achieves efficient and real-time depth information detection over a large field of view. By periodically arranging and achieving self-complete packaging, the Singer code plate's encoding and decoding functions can achieve ideal cross-correlation, effectively reducing the proportion of near-field artifacts in near-field source exposure imaging and improving the image signal-to-noise ratio.

[0075] Although specific embodiments of the invention have been disclosed for illustrative purposes 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 coded-aperture based Compton scatter tomography system, characterized by, It includes a detection device, a one-dimensional displacement stage, and a data processing device; the detection device includes a fan-beam X-ray machine, a two-dimensional encoding plate, and an area array detector. The fan-beam X-ray machine is used to emit fan-beam X-rays to scan the various sections of the object under test and generate scattered photons. The two-dimensional encoding plate is placed between the object under test and the area array detector, and is used to spatially modulate the scattered photons entering the area array detector. The array detector is placed behind the two-dimensional encoding plate and on the same side as the fan-beam X-ray machine. It is used to receive the scattered photons modulated by the two-dimensional encoding plate and convert them into analog signals before outputting them to the data processing device. The one-dimensional displacement stage is used to carry the object under test or the detection device, and during the scanning process, it drives the carried object under test or the detection device to move unidirectionally at a set interval, so as to realize the relative movement between the object under test and the detection device, so that the fan beam X-ray machine can scan each section of the object under test. The data processing device is used to receive the analog signals input by the area array detector and convert them into digital signals, control and monitor the motion trajectory of the one-dimensional displacement stage, and record the scanning time of each layer of the object under test. Then, Compton scattering imaging information corresponding to each fault location is extracted from the digital signal in chronological order, and the three-dimensional structure map of the object under test is decoded and reconstructed.

2. The system of claim 1, wherein, The fan-beam X-ray machine includes an X-ray machine and a front collimator. The front collimator is used to limit the direction of the X-rays emitted by the X-ray machine and collimate the cone-beam X-rays emitted by the X-ray machine into fan-beam X-rays.

3. The system of claim 1, wherein, The two-dimensional encoding board is a two-dimensional Singer encoding board.

4. The system of claim 3, wherein, The two-dimensional singer code is a two-dimensional singer code with coprime length and width; the two-dimensional singer code is generated by wrapping the one-dimensional singer code with the Proctor diagonal; the one-dimensional singer code is obtained by converting the singer sequence into binary.

5. The system of claim 1, wherein, The two-dimensional encoding board is a two-dimensional MURA encoding board based on a modified uniform redundancy array.

6. A Compton scattering tomography method based on coded aperture, comprising the following steps: 1) Mount the object to be measured or the detection device on a one-dimensional displacement stage; The detection device includes a fan-beam X-ray machine, a two-dimensional encoding plate, and an area array detector; A two-dimensional encoding plate is placed between the object to be tested and the area array detector, with the area array detector placed on the same side as the fan-beam X-ray machine. 2) The data processing device controls the one-dimensional displacement stage to move the mounted object under test or detection device in one direction at set intervals to achieve relative motion between the object under test and the detection device; when a test position is reached, the fan-beam X-ray machine is activated to emit fan-beam X-rays to scan the current test position of the object under test and generate scattered photons; the area array detector receives the scattered photons modulated by the two-dimensional encoding plate and converts them into analog signals before outputting them to the data processing device. 3) Repeat step 2) so that the fan beam X-ray machine scans each section of the object under test and records the time of scanning each section of the object under test. 4) The data processing device converts the analog signal input by the area array detector into a digital signal; then extracts the Compton scattering imaging information corresponding to each fault position from the digital signal in chronological order, and decodes and reconstructs the three-dimensional structural map of the object under test.

7. The method of claim 6, wherein, The fan-beam X-ray machine includes an X-ray machine and a front collimator. The front collimator is used to limit the direction of the X-rays emitted by the X-ray machine and collimate the cone-beam X-rays emitted by the X-ray machine into fan-beam X-rays.

8. The method of claim 6, wherein, The two-dimensional encoding board is a two-dimensional Singer encoding board.

9. The method of claim 8, wherein, The two-dimensional singer code is a two-dimensional singer code with coprime length and width; the two-dimensional singer code is generated by wrapping the one-dimensional singer code with the Proctor diagonal; the one-dimensional singer code is obtained by converting the singer sequence into binary.

10. The method of claim 6, wherein, The two-dimensional encoding board is a two-dimensional MURA encoding board based on a modified uniform redundancy array.

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