CN114910495A - X-ray fluorescence CT and Compton camera composite imaging system and method - Google Patents
X-ray fluorescence CT and Compton camera composite imaging system and method Download PDFInfo
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Abstract
The invention relates to an X-ray fluorescence CT and Compton camera composite imaging system and a method, wherein the system comprises an X-ray source and a sample stage arranged at an interval with the X-ray source; the system also comprises two sets of Compton camera absorption detectors which are in signal connection with the data processing system; the two sets of Compton camera absorption detectors are arranged between the X-ray source and the sample platform, are symmetrically arranged on two sides of a straight line connecting line of the X-ray source and the sample platform, and are respectively and correspondingly provided with a Compton camera scattering detector; an opening is formed in any one of the Compton camera scattering detectors; the Compton camera absorption detector is made of cadmium zinc telluride so that the Compton camera absorption detector can have the function of an X-ray fluorescence detector at the same time. The invention can obtain the effects of optimizing the spatial resolution and the system sensitivity and shortening the imaging time.
Description
Technical Field
The invention belongs to the technical field of testing or analyzing materials by means of determining chemical or physical properties of the materials in physics, and particularly relates to an X-ray fluorescence CT and Compton camera composite imaging system and method.
Background
The X-ray Computed Tomography (X-CT) technology can be widely used for imaging, detecting and observing the structural information inside a detected sample without damage. However, when the sample to be detected is small or the difference of the absorption of X-ray between the tissue to be detected and other tissues in the sample is small, the conventional CT has poor effect. Then, for example, a Single-Photon Emission Computed Tomography (SPECT) technology and a Positron Emission Tomography (PET) technology are developed, the radioisotope tracer is input into the sample to be detected and purposefully distributed, and the two imaging modes have high specificity, can provide functional information through molecular imaging, have higher sensitivity and lower spatial resolution; furthermore, isotopes have limited their use to some extent, since they decay constantly to produce radiation.
With the development of scientific technology, an X-ray Fluorescence CT (XFCT) technology has also appeared, which is an imaging technology combining an X-ray Fluorescence Analysis (XRFA) technology with an X-CT technology, and can not only realize the function of the conventional X-CT, i.e., imaging the internal structure information of a sample, but also excite the internal high-Z tracer atoms of the sample by irradiating the sample with X-rays to generate X-ray Fluorescence photons through the photoelectric effect and receive the X-ray Fluorescence photons by an X-ray Fluorescence detector, thereby providing the spatial distribution information of the concentration of the tracer in the sample. The tracer of XFCT is nanoparticles made of high-Z elements such as gold (Au), gadolinium (Gd), barium (Ba), iodine (I) and the like, and can overcome the defect that radioactive isotope tracers of SPECT and PET continuously decay.
In order to improve the resolution and contrast, the applicant also filed chinese patent application CN106248705A and disclosed an imaging method and system of hybrid X-ray fluorescence CT and X-ray acoustic CT, which utilizes X-ray fluorescence CT to perform functional imaging and utilizes X-ray acoustic CT to perform structural imaging, thereby improving the resolution and contrast, and only using a single projection X-ray to reduce the dose received by the sample.
In order to improve the accuracy, the applicant also filed chinese patent application of CN109709127A and discloses a low scattering X-ray fluorescence CT imaging method, which utilizes a pinhole on an X-ray fluorescence detector or a special pinhole collimator to avoid the influence of compton scattered photons on the signals received by the detector and prevent the detected data from deviating from the real result and artifacts. The literature "Rayleigh and Compton Scattering constraints to X-Ray Fluorescence Intensity", J.E.Fernandez, X-RAY SPECTROMETRY, 21, 1992, 57-68 discloses the effect of X-Ray Fluorescence on X-Ray Fluorescence signals, and studies the (P, C) interaction contribution of the takeoff angle (the angle between the detector and the incident X-Ray), and how to reduce the effect of Compton scattered photons on the detector acceptance signals. However, a beam limiting effect exists in a small hole or a special pinhole collimator, and a part of fluorescence photons which do not pass through the pinhole cannot be collected by the detector, so that the collection efficiency of the fluorescence photons is limited to a certain extent, and the sensitivity of the system is reduced.
The Compton camera is a novel imaging mode of non-mechanical collimation, and is based on the principle of Compton scattering to perform positioning and imaging of rays in a three-dimensional space, namely tracking the incoming direction of incident photons by virtue of the physical effect of Compton scattering to perform 'electronic collimation'. The applicant considers that the Compton camera imaging technology is applied to XFCT in a brand-new thinking and mode, the system sensitivity reduction caused by pinhole beam limitation is made up, the problem that Compton scattered photons influence the received signals of a detector does not exist, and optimization is achieved in the aspects of spatial resolution, sensitivity and imaging time.
Disclosure of Invention
In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a system and a method for X-ray fluorescence CT and compton camera composite imaging, which achieve the effects of optimizing spatial resolution, system sensitivity and shortening imaging time.
In order to solve the technical problems, the invention adopts the following technical scheme:
the X-ray fluorescence CT and Compton camera composite imaging system comprises an X-ray source and a sample stage arranged at an interval with the X-ray source; the system also comprises two sets of Compton camera absorption detectors which are in signal connection with the data processing system; the two sets of Compton camera absorption detectors are arranged between the X-ray source and the sample platform, are symmetrically arranged on two sides of a straight line connecting line of the X-ray source and the sample platform, and are respectively and correspondingly provided with a Compton camera scattering detector;
an opening is formed in any one of the Compton camera scattering detectors; the Compton camera absorption detector is made of cadmium zinc telluride so that the Compton camera absorption detector can have the function of an X-ray fluorescence detector at the same time.
Further perfecting the technical scheme, the X-ray source is a fan-beam X-ray source.
Further, the included angle between the two sets of Compton camera absorption detectors is 120 degrees.
Furthermore, the material of the Compton camera scattering detector is silicon.
Furthermore, both the absorption detector and the scattering detector of the Compton camera adopt array detectors.
Furthermore, the area of the opening accounts for 1/2-2/3 of the area of the scattering detector of the Compton camera.
Further, a pinhole collimator is installed in the opening hole.
Further, X-ray light emitted by the X-ray source irradiates a detected sample on the sample stage, and the X-ray light interacts with substances in the detected sample to generate fluorescence photons;
fluorescence photons incident on the scattering detector of the Compton camera are subjected to Compton scattering in the scattering detector of the Compton camera, the scattered fluorescence photons are received by the corresponding absorption detector of the Compton camera, and imaging event data of the Compton camera are generated by the data processing system;
the fluorescence photons passing through the aperture are received by a corresponding compton camera absorption detector and X-ray fluorescence CT imaging event data is generated by a data processing system;
and the data processing system performs X-ray fluorescence CT image reconstruction by taking the Compton camera imaging event data as prior information and combining the X-ray fluorescence CT imaging event data through a hybrid iterative algorithm so as to obtain the element distribution structure of the detected sample.
The invention also relates to an X-ray fluorescence CT and Compton camera composite imaging method, which is carried out based on the X-ray fluorescence CT and Compton camera composite imaging system and comprises the following steps:
1) irradiating the X-ray light emitted by the X-ray source to a detected sample on the sample stage, wherein the X-ray light interacts with substances in the detected sample to generate fluorescence photons;
2) the fluorescence photons incident on the scatter detector of the Compton camera are subjected to Compton scattering in the scatter detector of the Compton camera, the scattered fluorescence photons are received by the corresponding absorption detector of the Compton camera, and imaging event data of the Compton camera are generated by the data processing system;
receiving the fluorescence photons passing through the aperture with a corresponding compton camera absorption detector and generating X-ray fluorescence CT imaging event data by a data processing system;
3) and the data processing system takes the imaging event data of the Compton camera as prior information and combines the imaging event data of the X-ray fluorescence CT to carry out image reconstruction on the detected sample through a hybrid iterative algorithm.
Further, in step 3), the hybrid iterative algorithm includes:
dividing a space area where a detected sample is located into cubic grid-shaped spaces, wherein each cubic grid-shaped space is used as a voxel;
assigning an estimated initial value to the weight of each voxel in the space region;
utilizing formula
Carrying out image reconstruction of a Compton camera;
in the formula (I), the compound is shown in the specification,
representing the calculated weight, s, of the voxel j obtained after n iterations j Representing the probability, t, that a fluorescence photon is detected at an arbitrary position in voxel j ij Representing a weighted probability of event i originating from voxel j;
fourthly, calculating the distribution mu of the attenuation coefficient of the X-ray light in the detected sample according to the image reconstructed by the Compton camera I And the attenuation coefficient distribution mu of the fluorescence photons F ；
Using the reconstructed image of Compton camera as the initial estimated image of X-ray fluorescence CT reconstruction, and applying formula
Carrying out image reconstruction of X-ray fluorescence CT;
in the formula (I), the compound is shown in the specification,
representing the calculated weight of pixel j obtained after n iterations, based on the estimated μ I And mu F Calculation of h by addition of absorption correction ij ，h ij Is an element in the projection matrix representing the contribution of the jth pixel to the ith projection value, I i Representing X-ray fluorescence CT projection data measured by a compton camera absorption detector.
Compared with the prior art, the invention has the following beneficial effects:
1. the X-ray fluorescence CT and Compton camera composite imaging system is added with a Compton camera system capable of performing electronic collimation, and fluorescence photons which do not pass through the opening can also be utilized for imaging, so that the X-ray fluorescence CT and Compton camera composite imaging system can play a role in compensating the sensitivity reduced by the beam limitation of the pinhole collimator and the small hole of the detector to a certain extent. The double-layer detector system formed by one Compton camera scattering detector and one Compton camera absorption detector on each side is a Compton camera, and the Compton camera absorption detector corresponding to the Compton camera with an opening in the middle of the Compton camera scattering detector can also be used as a detector (X-ray fluorescence detector) of the X-ray fluorescence CT system.
2. In the X-ray fluorescence CT and Compton camera composite imaging system and method, X-ray fluorescence CT imaging and Compton camera imaging are not two independent processes which do not influence each other, but can play a role in mutual compensation and supplement each other. Specifically, the effect of the compton camera on XFCT is: compensating the sensitivity of the XFCT system reduced by the beam limiting effect of a pinhole collimator, wherein fluorescent photons which do not directly pass through an opening and reach a detector can also be utilized for image reconstruction; providing prior information for XFCT image reconstruction, namely using the image preliminarily reconstructed by Compton camera as initial value of XFCT iterative reconstruction, and calculating attenuation coefficient distribution mu of incident X-ray from the preliminarily reconstructed image of Compton camera I And the attenuation coefficient distribution mu of fluorescent X-ray F The method is used for absorption correction of the projection matrix of XFCT iterative reconstruction, thereby improving the imaging quality and recovering the concentration distribution information of the tracer in the sample to be detected more accurately. The effect of XFCT on a compton camera is: the spatial resolution of the reconstructed image of the Compton camera is improved, because the spatial resolution obtained by imaging of the single Compton camera is far inferior to that of imaging of the single XFCT under the same other conditions, so that the system uses the XFCT in the subsequent reconstruction step to compensate the spatial resolution of the reconstructed result of the Compton camera, and optimization is realized.
Drawings
FIG. 1 is a block diagram of an X-ray fluorescence CT and Compton camera composite imaging system according to an exemplary embodiment;
FIG. 2 is an analysis diagram of a combined X-ray fluorescence CT and Compton camera imaging method according to an exemplary embodiment;
the device comprises an X-ray source 1, a sample table 2, a Compton camera scattering detector 3, a Compton camera absorption detector 4, a data processing system 5 and an opening 6.
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
Referring to fig. 1 and 2, an X-ray fluorescence CT and compton camera composite imaging system of an embodiment includes an X-ray source 1 and a sample stage 2 spaced apart from the X-ray source 1; the device also comprises two sets of Compton camera absorption detectors 4, wherein the two sets of Compton camera absorption detectors 4 are in signal connection with a data processing system 5; the two sets of Compton camera absorption detectors 4 are arranged between the X-ray source 1 and the sample table 2, the two sets of Compton camera absorption detectors 4 are symmetrically arranged on two sides of an incident X-ray beam, and a Compton camera scattering detector 3 is correspondingly arranged between each set of Compton camera absorption detector 4 and the sample table 2; an opening 6 is formed in one Compton camera scattering detector 3; the Compton camera absorption detector 4 is made of cadmium zinc telluride so that the Compton camera absorption detector can simultaneously have the function of an X-ray fluorescence detector.
When the detector is used, X-ray light emitted by the X-ray source 1 irradiates a detected sample on the sample table 2, and the X-ray light interacts with substances in the detected sample to excite a high-Z tracer in the detector to generate fluorescence photons; the part of the fluorescence photons incident on the Compton camera scattering detector 3 generates one-time Compton scattering in the Compton camera scattering detector 3, the scattered fluorescence photons are received by a Compton camera absorption detector 4 corresponding to the back of the Compton camera scattering detector 3, and a data processing system 5 is used for carrying out image reconstruction on the Compton camera; the fluorescence photons passing through the opening 6 are received by a Compton camera absorption detector 4 behind a Compton camera scattering detector 3 where the opening 6 is located, and are processed by a data processing system 5 to obtain X-ray fluorescence CT projection data, the data processing system 5 takes an image reconstructed by the Compton camera image as an initial estimation image reconstructed by the X-ray fluorescence CT image, and the image reconstruction is carried out on the detected sample by combining the X-ray fluorescence CT projection data.
The X-ray fluorescence CT and Compton camera composite imaging system of the embodiment is added with a Compton camera system capable of performing electronic collimation, and fluorescence photons which do not pass through the opening 6 can also be utilized for imaging, so that the X-ray fluorescence CT and Compton camera composite imaging system can play a role in compensating the sensitivity reduced by the beam limitation of the pinhole collimator and the small hole of the detector to a certain extent. The double-layer detector system formed by one Compton camera scattering detector 3 and one Compton camera absorption detector 4 on each side is a Compton camera, and the Compton camera absorption detector 4 corresponding to the Compton camera with the opening 6 in the middle of the Compton camera scattering detector 3 can also be used as a detector (X-ray fluorescence detector) of the X-ray fluorescence CT system.
The system is provided with two groups of Compton cameras, one group is respectively arranged at two sides symmetrical about incident X-rays, and because fluorescence photons radiated from a sample are isotropic, projection data under double incident photon number can be equivalently obtained by receiving superposition of fluorescence signals, the scanning time is shortened, and the radiation dose is reduced.
Wherein, the X-ray source 1 is a fan-beam X-ray source.
Therefore, the imaging mode of the fan-beam X-ray source scanning can scan the whole fault at one time, compared with the pen-beam scanning mode of performing light source translation line-by-line scanning at each angle, the scanning speed can be greatly increased, and particularly, the X-ray fluorescence CT system matched with the pinhole collimator and the array detector can shorten the scanning time of an object to within minutes or even seconds, so that the full-field quick imaging is realized.
Wherein, the included angle between the two sets of Compton camera absorption detectors 4 is 120 degrees.
Because the system adopts the conventional X-ray tube as the ray source, compared with a synchronous radiation source, the system has the advantages of low ray intensity, wide energy spectrum and weak generated fluorescent signal, a great amount of Compton scattering noise is mixed in a projection signal obtained by the detector, the signal-to-noise ratio of the fluorescent signal to the scattering noise is lower, and relatively speaking, the highest signal-to-noise ratio can be obtained when the detection angle is 120 degrees. The energy resolution of the detector is reasonably set, and fluorescent photons and primary Compton scattered photons with different energies can be distinguished as much as possible.
Wherein, the material of the Compton camera scattering detector 3 is silicon.
For a compton camera system, the fluorescent photons radiated from the sample are the incident photons. Under normal temperature conditions, considering that when fluorescence photons interact with the Compton camera scattering detector 3, the probability of Compton scattering is expected to be higher than the probability of absorption, and therefore, a low-Z material silicon (Si) is selected as the material of the Compton camera scattering detector 3; in interaction with the compton camera absorption detector 4, however, it is desirable that the probability of absorption be higher than the probability of compton scattering, so that the high Z material Cadmium Zinc Telluride (CZT) is chosen as the material for the compton camera absorption detector 4.
In order to accurately record the position of each reaction and the energy deposition generated at the position, the Compton camera scattering detector 3 and the Compton camera absorption detector 4 both adopt array detectors.
The area of the opening 6 occupies 1/2-2/3 of the area of the scatter detector 3 of the Compton camera. Thus, the opening 6 is large, and when the types of the detected samples are different, whether the pinhole collimator is additionally arranged in the opening 6 can be flexibly selected.
If the radiation dose received by the sample to be detected needs to be controlled within a lower range, a pinhole collimator (not shown in the figure) needs to be installed at the position of the opening 6, the pinhole collimator can be made of lead (Pb), 9 pinholes are totally arranged and distributed in a 3 x 3 array, and the shape of the pinhole is formed by vertically overlapping two cones with the base angles of 55 degrees; suitable parameters can be set for the size of each pinhole and the vertical distance between the holes according to the overall structure of the system, so that the mutual overlapping of the projections obtained on the absorption detector 4 of the Compton camera is avoided. The pinhole collimator realizes the path positioning of the fluorescent rays incident to each unit of the Compton camera absorption detector 4 in the full field of view by using a pinhole imaging principle, the tracer distribution in the sample can be imaged without rotating the sample, the scanning speed is extremely high, the scanning time is extremely short, and the radiation dose received by the sample can be controlled in a lower range.
If the requirement of the detected sample on the scanning time and the radiation dose is relatively low, a pinhole collimator does not need to be arranged at the position of the opening 6, the beam limiting effect of a pinhole does not exist, all the fluorescence photons which penetrate through the opening 6 and fully deposit the energy on the absorption detector 4 of the Compton camera can be used for X-ray fluorescence CT imaging, and the utilization rate and the collection efficiency of the fluorescence photons are improved. Correspondingly, under the condition that a pinhole collimator is not used, the sample needs to be rotated by a certain fixed angle, then the scanning process is repeated until the sample is rotated by 360 degrees, and the Compton camera absorption detector 4 acquires fluorescence projection data under different angles for X-ray fluorescence CT image reconstruction. Due to the addition of the rotation step, the scanning time is relatively long and the radiation dose is also large.
With continued reference to fig. 2, the system uses a compton camera scatter detector 3 without an aperture 6 and a corresponding compton camera absorption detector 4, connected to a data processing system 5, for imaging only the compton camera; a Compton camera scattering detector 3 with an opening 6 and a corresponding Compton camera absorption detector 4 are connected with a data processing system 5, and not only imaging of the Compton camera but also imaging of X-ray fluorescence CT are required. The compton camera scatter detector 3 and the compton camera absorption detector 4 detectors on both sides are both position and energy sensitive detectors, which record the position where the fluorescence photons interact with them and the energy deposited at that position and upload the data to the data processing system 5. And the data processing system 5 is used for matching and screening qualified compton camera imaging events and X-ray fluorescence CT imaging events according to a preset time window and an energy window, storing relevant data of the events, and finally reconstructing the image of the detected sample by using the data through a hybrid iterative algorithm.
The execution steps of the hybrid iterative algorithm are as follows:
dividing a space region (imaging space) where a detected sample is located into cubic grid-shaped spaces, wherein each cubic grid-shaped space is used as a voxel;
assigning an estimated initial value to the weight of each voxel in the imaging space;
utilizing formula
Carrying out image reconstruction of a Compton camera;
in the formula (I), the compound is shown in the specification,
is expressed byThe calculated weight, s, of the voxel j obtained after n iterations j Representing the probability, t, that a fluorescence photon is detected at an arbitrary position in voxel j ij Representing the weighted probability of event i resulting from voxel j. These data are all obtainable by computational processing of data directly measured in qualified compton camera imaging events; the two-dimensional sectional image obtained by intersecting the updated weight distribution of each voxel in the imaging space obtained after iteration for a certain number of times and the fault scanned by the fan-beam X-ray source 1 is the preliminary result of Compton camera reconstruction, and theoretically, the concentration of the tracer in each pixel is in direct proportion to the weight corresponding to the pixel;
fourthly, calculating the attenuation coefficient distribution mu of the incident X-ray in the detected sample according to the preliminarily reconstructed image of the Compton camera I And the attenuation coefficient distribution mu of fluorescent X-ray F ；
Attenuation coefficient distribution mu of incident X-rays in a sample to be examined for a tracer of a specific high Z element I The concentration distribution of the tracer agent reflected by the primary reconstructed image of the Compton camera is in a linear relation; distribution of attenuation coefficient mu of fluorescent X-ray under the condition of low precision requirement F Can be ignored.
Using the image primarily reconstructed by Compton camera as the initial estimation image for X-ray fluorescence CT reconstruction, and applying formula
Carrying out image reconstruction of X-ray fluorescence CT;
in the formula (I), the compound is shown in the specification,
representing the calculated weight of pixel j obtained after n iterations, based on the estimated μ I And mu F Calculation of h by addition of absorption correction ij ，h ij Is an element in the projection matrix representing the contribution of the jth pixel to the ith projection value, I i X-ray fluorescence CT projection data representing measurements by the Compton camera absorption detector 4, i.e., all fluorescence light fully absorbed by the Compton camera absorption detector 4 during a qualified X-ray fluorescence CT imaging eventTotal energy of the sub-depositions. And executing certain iteration times until the quality of the reconstructed image can reach a certain standard.
It will be appreciated that since the X-ray source 1 employs fan beam excitation, the image obtained from a "scan, projection, reconstruction" will reflect the tracer concentration distribution of only one slice scanned by the fan beam over the sample. If the three-dimensional distribution of the whole tracer in the sample is required to be obtained, the X-ray source 1 needs to be translated, different faults are scanned for multiple times, then the steps of projection and reconstruction are repeated, tracer distribution images of multiple faults are obtained, and then the tracer distribution images are comprehensively analyzed.
It should be noted that, in the method designed by the present invention, the X-ray fluorescence CT imaging and the compton camera imaging are not two independent processes that do not affect each other, but can compensate each other and supplement each other. Specifically, the effect of the compton camera on XFCT is: compensating the sensitivity of the existing XFCT system reduced by the beam limiting effect of a pinhole collimator, wherein fluorescent photons which do not directly pass through the opening 6 and reach a detector can also be utilized for image reconstruction; providing prior information for XFCT image reconstruction, namely using the image preliminarily reconstructed by Compton camera as initial value of XFCT iterative reconstruction, and calculating attenuation coefficient distribution mu of incident X-ray from the preliminarily reconstructed image of Compton camera I And the attenuation coefficient distribution mu of fluorescent X-ray F The method is used for absorption correction of the projection matrix of XFCT iterative reconstruction, thereby improving the imaging quality and more accurately recovering the concentration distribution information of the tracer in the sample to be detected. The effect of XFCT on a compton camera is: the spatial resolution of the reconstructed image of the Compton camera is improved, because the spatial resolution obtained by imaging of the single Compton camera is far inferior to that of imaging of the single XFCT under the same other conditions, so that the system uses the XFCT in the subsequent reconstruction step to compensate the spatial resolution of the reconstructed result of the Compton camera, and optimization is realized.
Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.
Claims (10)
- An X-ray fluorescence CT and Compton camera composite imaging system comprises an X-ray source and a sample stage arranged at an interval with the X-ray source; the method is characterized in that: the system also comprises two sets of Compton camera absorption detectors which are in signal connection with the data processing system; the two sets of Compton camera absorption detectors are arranged between the X-ray source and the sample platform, are symmetrically arranged on two sides of a straight line connecting line of the X-ray source and the sample platform, and are respectively and correspondingly provided with a Compton camera scattering detector;an opening is formed in any one of the Compton camera scattering detectors; the Compton camera absorption detector is made of cadmium zinc telluride so that the Compton camera absorption detector can have the function of an X-ray fluorescence detector at the same time.
- 2. The X-ray fluorescence CT and compton camera composite imaging system of claim 1, wherein: the X-ray source is a fan beam X-ray source.
- 3. The X-ray fluorescence CT and compton camera composite imaging system of claim 2, wherein: the included angle between the two sets of Compton camera absorption detectors is 120 degrees.
- 4. The X-ray fluorescence CT and compton camera composite imaging system according to claim 1, characterized in that: the Compton camera scattering detector is made of silicon.
- 5. The X-ray fluorescence CT and compton camera composite imaging system of claim 1, wherein: the Compton camera absorption detector and the Compton camera scattering detector both adopt array detectors.
- 6. The X-ray fluorescence CT and compton camera composite imaging system of claim 1, wherein: the area of the opening accounts for 1/2-2/3 of the area of the scattering detector of the Compton camera.
- 7. The X-ray fluorescence CT and compton camera composite imaging system of claim 6, wherein: a pinhole collimator is mounted in the opening.
- 8. The X-ray fluorescence CT and compton camera composite imaging system according to any one of claims 1 to 7, wherein: x-ray light emitted by the X-ray source irradiates a detected sample on the sample table, and the X-ray light interacts with substances in the detected sample to generate fluorescence photons;fluorescence photons incident on the scattering detector of the Compton camera are subjected to Compton scattering in the scattering detector of the Compton camera, the scattered fluorescence photons are received by the corresponding absorption detector of the Compton camera, and imaging event data of the Compton camera are generated by the data processing system;the fluorescence photons passing through the aperture are received by a corresponding compton camera absorption detector and X-ray fluorescence CT imaging event data is generated by a data processing system;and the data processing system takes the imaging event data of the Compton camera as prior information and combines the imaging event data of the X-ray fluorescence CT to carry out image reconstruction on the detected sample through a hybrid iterative algorithm.
- The X-ray fluorescence CT and Compton camera composite imaging method is characterized by comprising the following steps: the method is based on the X-ray fluorescence CT and Compton camera composite imaging system of any one of claims 1-8, and comprises the following steps:1) irradiating the X-ray light emitted by the X-ray source to a detected sample on the sample stage, wherein the X-ray light interacts with substances in the detected sample to generate fluorescence photons;2) the fluorescence photons incident on the scatter detector of the Compton camera are subjected to Compton scattering in the scatter detector of the Compton camera, the scattered fluorescence photons are received by the corresponding absorption detector of the Compton camera, and imaging event data of the Compton camera are generated by the data processing system;receiving the fluorescence photons passing through the aperture with a corresponding compton camera absorption detector and generating X-ray fluorescence CT imaging event data by a data processing system;3) and the data processing system takes the imaging event data of the Compton camera as prior information and combines the imaging event data of the X-ray fluorescence CT to carry out image reconstruction on the detected sample through a hybrid iterative algorithm.
- 10. The X-ray fluorescence CT and compton camera composite imaging method as claimed in claim 9, characterized in that: in step 3), the hybrid iterative algorithm includes:dividing a space area where a detected sample is located into cubic grid-shaped spaces, wherein each cubic grid-shaped space is used as a voxel;assigning an estimated initial value to the weight of each voxel in the space region;utilizing formulaCarrying out image reconstruction of a Compton camera;
in the formula (I), the compound is shown in the specification,representing the calculated weight, s, of the voxel j obtained after n iterations j Representing the probability, t, that a fluorescence photon is detected at an arbitrary position in voxel j ij Representing the weighted probability of event i resulting from voxel j;
fourthly, calculating the attenuation coefficient distribution mu of the X-ray light in the detected sample according to the image reconstructed by the Compton camera I And the attenuation coefficient distribution mu of the fluorescence photons F ；Using the reconstructed image of Compton camera as the reconstructed image of X-ray fluorescence CTInitially estimating the image, applying a formulaCarrying out image reconstruction of X-ray fluorescence CT;
in the formula (I), the compound is shown in the specification,representing the calculated weight of pixel j obtained after n iterations, based on the estimated μ I And mu F Calculation of h by addition of absorption correction ij ，h ij Is an element in the projection matrix representing the contribution of the jth pixel to the ith projection value, I i X-ray fluorescence CT projection data representing compton camera absorption detector measurements.
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