WO2024093737A1

WO2024093737A1 - Gamma imaging device and imaging method thereof

Info

Publication number: WO2024093737A1
Application number: PCT/CN2023/126255
Authority: WO
Inventors: 马天予; 吕振雷; 朱艺航; 于泽睿; 刘亚强
Original assignee: 清华大学
Priority date: 2022-10-31
Filing date: 2023-10-24
Publication date: 2024-05-10
Also published as: CN115685305A

Abstract

A gamma imaging device and an imaging method. The gamma imaging device comprises a detector; the detector comprises a single crystal strip (101); the single crystal strip (101) is used for moving relative to an imaging field of view to detect incident gamma photons of the imaging field of view, and realize collimation of the incident gamma photons, so as to realize gamma imaging, wherein the aspect ratio of the single crystal strip is greater than 10:1. A front end face (110) is an end face of the end of the single crystal strip (101) close to a radioactive source, a distal end face (120) is an end face of the end of the single crystal strip (101) farther away from the radioactive source than the front end face (110), and a front end and a distal end respectively form the two ends of the single crystal strip (101).

Description

Gamma imaging device and imaging method thereof

Technical Field

The present disclosure relates to the field of radiation imaging technology, and in particular to a gamma imaging device and an imaging method thereof.

Background technique

Gamma imaging requires that the detector unit has obvious response differences to photons from different directions, that is, when the incident direction of the photons changes, the photon count (detection efficiency) in a certain detector unit also changes greatly. Among them, mechanical collimators are usually used traditionally to achieve response differences in different directions, but because the mechanical collimator blocks a large part of the photons from entering the detector, the overall detection efficiency will be seriously reduced, and the mechanical collimator is large in size and weight, making the overall detector bulky and not light, and the use scenario is also relatively limited; the existing method of using multi-layer detector units to block the front and back "self-collimation" will cause response differences. Although it avoids the decline in efficiency, the detector structure is complex and the number of electronic readout channels is large, which often leads to a large imaging device or high cost.

Summary of the invention

In order to solve at least one of the above-mentioned technical problems existing in the existing gamma imaging technology of ensuring obvious photon response differences, the present disclosure provides a gamma imaging device and an imaging method thereof.

One aspect of the present disclosure provides a gamma imaging device, which includes a detector, the detector including a single crystal bar, the single crystal bar is used to move relative to the imaging field of view to detect incident gamma photons in the imaging field of view, and to collimate the incident gamma photons for gamma imaging, wherein the length-to-width ratio of the single crystal bar is greater than 10:1.

Preferably, the detection efficiency of gamma photons incident normally on the front end of a single crystal bar close to the imaging field of view is lower than the detection efficiency of gamma photons incident obliquely on other parts far from the imaging field of view; wherein, The distance between the front end face of a single crystal bar close to the imaging field of view and the imaging field of view is less than or equal to 100 mm.

Preferably, the detector further comprises a first photoelectric device. The first photoelectric device is coupled to a far end of the single crystal bar away from the imaging field of view and is used to read out the gamma photon deposition data in the single crystal bar.

Preferably, the surface roughness of at least one side surface of a single crystal bar is less than or equal to 0.01 micrometer.

Preferably, the detector further comprises a second photoelectric device, which is coupled to the front end of the single crystal bar near the imaging field of view and is used to cooperate with the first photoelectric device to read out the gamma photon deposition data and obtain the energy spectrum in different gamma photon deposition depth directions.

According to an embodiment of the present disclosure, the detector further comprises at least one third optoelectronic device. The at least one third optoelectronic device is coupled to at least one side surface of the single crystal bar.

Preferably, the single crystal bar comprises a plurality of first crystal blocks and a plurality of second crystal blocks. The plurality of second crystal blocks and the plurality of first crystal blocks are arranged alternately to form a crystal bar structure.

Preferably, the first crystal block and the second crystal block are scintillator materials; or the first crystal block is scintillator material and the second crystal block is photoconductive material; wherein the emission spectrum and absorption spectrum of the scintillator material partially overlap, and the refractive index of the photoconductive material is greater than or equal to 1.5.

Preferably, a single crystal bar may include a columnar structure having a quadrilateral, rhombus, triangle, heart or V shape in a side view.

Preferably, the detector further comprises a refractive layer and/or an absorption layer. The refractive layer is covered on the front end face of the single crystal bar close to the imaging field of view, and the refractive index of the refractive layer is greater than the refractive index of the scintillator material of the single crystal bar, and is used to refract the scintillation photons generated by the incident gamma photons, thereby increasing the loss of the scintillation photons on the front end face; the absorption layer is covered on the front end face of the single crystal bar close to the imaging field of view, or is covered on the refractive layer, and is used to absorb the scintillation photons generated by the incident gamma photons, thereby increasing the loss of the scintillation photons on the front end face.

Preferably, the first crystal block and the second crystal block of a single crystal bar have different doping ion concentrations and/or dopant materials, and the doping ion concentration is 0.01% to 0.6%.

Preferably, the detector further comprises a blocking layer, which is coupled to the front end face of the single crystal bar close to the imaging field of view to block gamma photons incident normally toward the front end face.

Another aspect of the present disclosure provides a gamma imaging device, which includes a crystal bar array composed of at least one single crystal bar and a first circuit board. The crystal bar array composed of at least one single crystal bar is used to move relative to the imaging field of view to detect incident gamma photons in the imaging field of view, and to collimate the incident gamma photons to achieve gamma imaging, wherein the aspect ratio of the single crystal bar is greater than 10:1; the first circuit board is coupled to the far end of the crystal bar array away from the imaging field of view, and is used to output detection data of the crystal bar array on the imaging field of view.

Preferably, the gamma imaging device further comprises a second circuit board, which is coupled to the front end of the crystal bar array away from the imaging field of view and is used to cooperate with the first circuit board to output detection data of the crystal bar array on the imaging field of view.

Preferably, the gamma imaging device further comprises a scintillation crystal layer, which is located between the first circuit board and the distal end surface of the crystal bar array to receive the remaining scintillation photons passing through the crystal bar array.

Another aspect of the present disclosure provides an imaging method of the above-mentioned gamma imaging device.

The present disclosure provides a gamma imaging device and an imaging method thereof, wherein the gamma imaging device includes a detector, the detector includes a single crystal bar, the single crystal bar is used to move relative to the imaging field of view to detect incident gamma photons in the imaging field of view, realize collimation of the incident gamma photons, and realize gamma imaging, wherein the aspect ratio of the single crystal bar is greater than 10: 1. Therefore, based on the above-mentioned gamma imaging device, a new detector mode is established, which completely abandons the existing low-efficiency and bulky external mechanical collimator, greatly simplifies the limitations of the traditional complex detector structure and multiple electronic structures, and can also have a highly sensitive minimalist gamma imaging detection device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 schematically shows a composition diagram of a single crystal bar 101 as a detector and an imaging field of view FOV of a gamma imaging device according to an embodiment of the present disclosure;

FIG2 schematically shows an imaging detection principle diagram of a conventional mechanical collimator 201 and a detector 202 of an existing gamma imaging device relative to the radiation source position and a corresponding SRF curve diagram;

FIG3 schematically shows an imaging detection principle diagram of a single crystal bar 301 as a detector relative to a radiation source position of a gamma imaging device according to an embodiment of the present disclosure and a corresponding SRF curve diagram;

FIG4 schematically shows a rotation detection diagram of a single crystal bar 401 according to an embodiment of the present disclosure;

FIG5 schematically shows a top view of a single crystal bar 501 as a detector for movement detection relative to an imaging field of view FOV according to an embodiment of the present disclosure;

FIG6A schematically shows a structural perspective view of a single crystal bar 601 according to an embodiment of the present disclosure;

FIG6B schematically shows a perspective view of the structure of a single crystal bar 602 according to an embodiment of the present disclosure;

7A-7G schematically show side views of the structures of single crystal bars 701a-701g according to an embodiment of the present disclosure;

FIG8A schematically shows an imaging composition diagram of a crystal bar array 801 of a gamma imaging device relative to an imaging field of view FOV according to another embodiment of the present disclosure;

FIG8B schematically shows an imaging composition diagram of a crystal bar array 802 of a gamma imaging device relative to an imaging field of view FOV according to another embodiment of the present disclosure;

FIG9 schematically shows a principle diagram of performing two-dimensional lattice translation sampling of a single crystal bar 901 along a direction parallel to the FOV in a gamma imaging method according to an embodiment of the present disclosure;

FIG10A shows a thermal cylindrical reconstructed image in which the imaging field of view FOV of a gamma imaging device according to an embodiment of the present disclosure meets a diameter of 40 mm and the distance between the detector and the FOV meets a diameter of 45 mm;

FIG10B shows a thermal cylindrical reconstructed image in which the imaging field of view FOV of the gamma imaging device according to an embodiment of the present disclosure satisfies a diameter of 100 mm and the distance between the detector and the FOV satisfies a distance of 45 mm;

FIG. 11 shows a diagram of the reconstructed image effect of a single point source, two point sources, and four point sources with a spacing of 6 mm according to an actual prototype device of a gamma imaging device according to an embodiment of the present disclosure.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present disclosure more clear, the following is a detailed description of the present invention. The present disclosure will be further described in detail with reference to the accompanying drawings and embodiments.

It should be noted that the implementation methods not shown or described in the drawings or the text of the specification are all forms known to ordinary technicians in the relevant technical field and are not described in detail. In addition, the above definitions of various elements and methods are not limited to the various specific structures, shapes or methods mentioned in the embodiments, and ordinary technicians in the field can simply change or replace them.

It should also be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "back", "left", "right", etc., are only reference directions of the drawings and are not intended to limit the scope of protection of the present disclosure. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or configurations will be omitted when they may cause confusion in the understanding of the present disclosure.

Moreover, the shapes and sizes of the components in the figures do not reflect the real size and proportion, but only illustrate the contents of the embodiments of the present disclosure. In addition, in the claims, any reference symbols between brackets shall not be constructed as limiting the claims.

Furthermore, the word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The ordinal numbers used in the specification and claims, such as "first", "second", "third", etc., to modify the corresponding elements, do not themselves mean that the elements have any ordinal numbers, nor do they represent the order of one element and another element or the order of manufacturing methods. The use of these ordinal numbers is only used to clearly distinguish a component with a certain name from another component with the same name.

Those skilled in the art will appreciate that the modules in the devices in the embodiments may be adaptively changed and placed in one or more devices different from the embodiments. The modules or units or components in the embodiments may be combined into one module or unit or component, and further they may be divided into a plurality of sub-modules or sub-units or sub-components. All features disclosed in this specification (including the accompanying claims, abstract and drawings) and all processes or units of any method or device so disclosed may be combined in any combination, except that at least some of such features and/or processes or units are mutually exclusive. Unless expressly stated otherwise, each feature disclosed in this specification (including the accompanying claims, abstract and drawings) may be replaced by an alternative feature that provides the same, equivalent or similar purpose. Furthermore, in a unit claim that lists several devices, several of these devices may be replaced by The same hardware item is used to embody this.

Similarly, it should be understood that in order to streamline the present disclosure and aid in understanding one or more of the various disclosed aspects, in the above description of the exemplary embodiments of the present disclosure, the various features of the present disclosure are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting the following intention: the claimed disclosure requires more features than the features explicitly recited in each claim. More specifically, as reflected in the claims below, the disclosed aspects lie in less than all the features of the single embodiment disclosed above. Therefore, the claims that follow the specific embodiment are hereby expressly incorporated into the specific embodiment, with each claim itself serving as a separate embodiment of the present disclosure.

As shown in FIG1 , one aspect of the present disclosure provides a gamma imaging device, which includes a detector including a single crystal bar, the single crystal bar being used to move relative to an imaging field of view to detect incident gamma photons in the imaging field of view, and to collimate the incident gamma photons for gamma imaging, wherein the aspect ratio of the single crystal bar is greater than 10:1.

For gamma imaging devices, the detector, as the part between the imager and the imaging field of view that realizes gamma photon detection, is the most critical component of the device and can have a significant impact on the detection efficiency of gamma photons.

Ordinary detectors generally need to use mechanical collimators to collimate photons before entering the detector, so as to achieve differences in the responses of gamma photons in different directions in the detector. In the gamma imaging device of the present embodiment, the traditional collimator design is directly abandoned, and only a single crystal bar 101 is set as a detector between the gamma imaging field of view (FOV) and the imager (not shown), and the differential response to different gamma photons is achieved by moving the single crystal bar relative to the imaging field of view FOV, thereby greatly simplifying the composition structure of the gamma imaging device while ensuring the detection efficiency. Among them, the number of single crystal bars can be only one. Among them, the imaging field of view FOV can generally be the detectable range of the detector where the object to be imaged is located, which can be understood as the position of the radiation source.

In the embodiment of the present disclosure, the detection efficiency of a single crystal bar 101 that can be used as a detector is related to its solid angle relative to the radiation source (which can be understood as the imaging field of view FOV). Compared with conventional square detector units that are not sensitive enough to changes in the incident direction of gamma photons, after significantly increasing the aspect ratio of the single crystal bar 101 of the disclosed embodiment, the imaging solid angle formed when the gamma photon is incident on the front end face 110 of the single crystal bar is the smallest, and the photon detection efficiency is the lowest at this time; when the incident direction of the photon is deflected from being incident on the front end face to the distal end face 120 of the single crystal bar, the photon detection efficiency will be significantly and rapidly improved, thereby being able to bring about a better direction positioning effect. Among them, at the same time, the front end face 110 is the end face of the end (i.e., the front end) of the single crystal bar that is closer to the radiation source position, and the distal end face 120 is the end face of the end (i.e., the distal end) of the single crystal bar that is farther from the radiation source position relative to the front end face 110, and the front end and the distal end respectively constitute the two ends of the single crystal bar.

Therefore, in order to ensure that the single crystal bar can have a more stable detection effect during the detection process, while taking into account a higher detection efficiency, in the specific detection process, it is necessary to move the detector set for the single crystal bar 101, and the movement can include at least one of translation along a straight line or curve in space, self-rotation or rotation around a fixed point or moving point in space as the center of a circle. As shown in FIG5 , a single crystal bar 501 is translated by a unit sampling step Δx (Translation Step) around an imaging field of view FOV with a diameter size D (Diameter of FOV) in a spatial plane, and combined with a unit sampling angle (Rotation Step) to rotate, and the final rotation angle (Projection Angle) is The rotation range of the mobile detection, where satisfy Therefore, by means of the movement of the above-mentioned single crystal bar 101, its position or angle relative to the radiation source (imaging field of view FOV) can be changed, so that the detection of incident photons can produce more diversified and differentiated detection solid angles, thereby significantly improving its detection efficiency and achieving a more accurate directional positioning effect.

Furthermore, in the disclosed embodiment, the structure of a single crystal bar 101 is slender, and in the side view of the structure in the length direction (understood as a projection figure at a side view angle), the ratio of the length dimension L of the figure and the maximum width dimension W/G (for example, if W>G, then L:W is determined, otherwise, then L:G is determined) is greater than or equal to 10:1, that is, the length-to-width ratio of the single crystal bar is greater than 10:1. Thereby, it can be ensured that during the subsequent movement detection process of the single crystal bar 101, the single crystal bar 101 can have a better imaging solid angle, the difference in photon detection efficiency is increased, and a better directional positioning effect is brought about. In other words, the larger the length-to-width ratio of the single crystal bar, the better the crystal is at detecting the direction. The greater the difference in detection efficiency between normal incident and oblique incident gamma photons, the more sensitive the incident direction of the gamma photons is, thus bringing about a better directional positioning effect. Therefore, a single crystal bar with this aspect ratio value can provide a device for gamma imaging detection with both high sensitivity and a minimalist structural design when used alone as a detector.

Therefore, based on the above-mentioned gamma imaging device, a new detector mode is established, which can use only a single crystal bar 101 as a detector to collimate and detect incident photons, and completely abandons the existing external mechanical collimator with low detection efficiency, bulky and non-portable. It greatly simplifies the traditional complex detector structure, breaks the traditional limitations of multiple electronic structures, and can also have a minimalist design of high sensitivity. The gamma imaging detection device has an extremely simple structural design, is lightweight and portable, and is suitable for various imaging scenarios that require mobile and portable applications.

As shown in Figures 2 and 3, according to an embodiment of the present disclosure, the detection efficiency of gamma photons incident normally on the front end of a single crystal bar 301 close to the imaging field of view FOV is lower than the detection efficiency of gamma photons incident obliquely on other parts far away from the imaging field of view FOV; wherein, the distance between the front end face of the single crystal bar close to the imaging field of view and the imaging field of view is less than or equal to 100 mm.

Since the above-mentioned single crystal bar 301 or 101 is used as a detector alone, and the mechanical collimator is directly omitted, the crystal response function (Scintillator response function, referred to as SRF, which represents the detection efficiency of gamma photons at different positions of the imaging field of view FOV) of the detector of the embodiment of the present disclosure is significantly different from that of a conventional detector. As shown in FIG2 , in the conventional design of a detector 202 composed of a metal mechanical collimator 201 and a plurality of crystal units, the photon detection efficiency is the highest in the direction facing the detector 202, and there is almost no detection efficiency in other directions due to shielding, and the corresponding SRF is the highest when the radiation source is in the middle position. On the contrary, as shown in FIG3 , in the solution in which there is no metal mechanical collimator and only a single crystal bar 301 is used as a detector in the embodiment of the present disclosure, since the detection efficiency of the single slender crystal bar 301 is the lowest when it is collimated directly facing the front end face, the SRF is the lowest, while the detection efficiency in other directions is relatively high and can maintain a relatively high and stable level, that is, the detection efficiency of the single crystal bar for gamma photons incident directly on the proximal end face is lower than the detection efficiency of gamma photons obliquely incident on the proximal end face and other surfaces. It can be seen that the above-mentioned gamma imaging device of the embodiment of the present disclosure has a good response to almost all incident photon directions except the position directly facing the front end face, and the detection efficiency for particles incident at different angles is not exactly the same, which can be determined by the relative response of the detector at different positions. The size of the radiation source activity distribution in different incident directions is judged, thus taking all positions into account instead of limiting the sensitive position to a small angle range of the collimator opening. This makes the relationship between detection efficiency and radiation source position completely opposite to that of conventional designs.

Therefore, based on the above detection principle, a minimalist radioactive source counting and positioning device can be designed, in which the detector is composed of only a thin and long crystal strip. And the detector can move and detect in the 4-pi space, and the position with the lowest count is facing the direction of the radioactive source. Among them, the detection efficiency of the detector is positively correlated with the solid angle of a single crystal to the position of the radioactive source. As the distance between the crystal and the imaging field of view (FOV) increases, the detection efficiency is seriously lost. Therefore, the detector should be as close to the imaging field of view FOV as possible. Specifically, the distance d (Distance between FOV and Crystal) between the single crystal strip of the detector and the imaging field of view FOV can be less than or equal to 100 mm (as shown in Figure 5, d = 40 mm), and the components and tooling settings facing the end face of the imaging field of view FOV should be simplified.

Unlike metal collimator detectors and self-collimation detectors that only respond to photons incident from certain directions, a single slender crystal strip has a low response to the target position while taking into account other positions, with a large sensitivity range. Only a few positions of information combination are needed to reconstruct a complete image, which can greatly reduce the sampling positions. Therefore, the gamma imaging device of the disclosed embodiment can have a more flexible sampling scheme when imaging radioactive sources. Specifically, the sampling step size can be adaptively adjusted according to the detector count, and the number of sampling times and sampling time can be reduced without reducing the imaging accuracy.

According to an embodiment of the present disclosure, the detector further includes a first photoelectric device 402 .

The first optoelectronic device 402 is coupled to a far end of the single crystal bar 401 away from the imaging field of view, and is used to read out the gamma photon deposition data in the single crystal bar 401 .

The radiation source imaging device is composed of only a single thin and long crystal bar 401 and a photoelectric device 402. The distribution of the radiation source in the imaging field of view FOV can be imaged by translation and rotation sampling. The translation can be a translation along a straight line or curve in space, and the rotation can be a self-rotation or rotation around a fixed point or a moving point in space as the center of the circle. As shown in FIG4 , the detector has a single crystal bar 401 and a photoelectric device 402 arranged at the far end of the single crystal bar 401, wherein the detector can be rotated in a spatial plane with the center of the single crystal bar 401 in the length direction as the center of the circle, so as to realize The detection effect in the range of 0-180° relative to the imaging field of view FOV is shown.

The first photoelectric device 402 may be a silicon photomultiplier (SiPM), and coupling the photoelectric device 402 to the end face of the single crystal bar 401 far from the imaging field of view FOV can realize single-end readout of photon deposition data. In addition, the front end face of the single crystal bar 401 close to the imaging field of view FOV can be covered with a thin layer of plastic tooling to achieve mobile protection, so as to achieve the purpose of detection close to the imaging field of view FOV.

According to an embodiment of the present disclosure, the surface roughness of at least one side surface of a single crystal bar is less than or equal to 0.01 micrometer.

For the single crystal bar of the embodiment of the present disclosure, it can be a scintillation crystal bar for detection, which can meet the internal transmission requirements of scintillation photons, and the single crystal bar can be a cylinder, a rectangular parallelepiped or other long columnar structure, as long as the aspect ratio of its side view projection is greater than or equal to 10:1.

In addition, on the basis of the above, the side surface of the column of the single crystal bar can also be processed (such as polishing) to make it have better smoothness, reduce the surface roughness of the side surface of the column, so that the roughness can be less than or equal to 0.01 microns, and specifically, it can be polished with 2000-mesh sandpaper, so that the transmission efficiency of the scintillation photons in the single crystal bar can be further improved by means of the mirror reflection ability of its smooth surface, thereby effectively solving the problem of long transmission distance and serious light loss of scintillation photons in the slender crystal bar, and can significantly improve the photon transmission efficiency, obtain a better detection energy spectrum, thereby improving the detection efficiency and directional positioning accuracy.

Based on the above, in specific imaging applications, the transmission matrix of the imaging device needs to be calibrated. The specific steps are to divide the imaging field of view FOV into grid points with the pixel size as the step size, place a point source at each grid point, and measure the projection data with a single crystal bar of the detector, and combine the projection data of the point source at each position to obtain the transmission matrix. In this calibration process, since the detector is composed of only a single crystal bar, there is no mechanical collimator and complex mutual occlusion between crystals, and its SRF value has a strong symmetry (as shown in Figure 3), so the calibration steps of the transmission matrix can be greatly simplified. Specifically, it is only necessary to measure the projection of a single crystal bar as a detector at the middle position, and then use the translation and rotation of the SRF to extend to other positions, so as to obtain a complete transmission matrix, thereby shortening the measurement time required for each radiation source position, greatly shortening the calibration time of the transmission matrix, speeding up data processing, and improving imaging efficiency.

According to an embodiment of the present disclosure, the detector further includes a second photoelectric device (not shown).

The second photoelectric device is coupled to the front end of the single crystal bar close to the imaging field of view, and is used to cooperate with the first photoelectric device to read out the gamma photon deposition data, so as to obtain the energy spectrum in different gamma photon deposition depth directions.

In addition, while coupling the first optoelectronic device to the far end of the single crystal bar of the detector, another second optoelectronic device can be further coupled to the front end of the single crystal bar of the detector, so that the photon deposition data can be read out from the front end, so that the readout data of the first optoelectronic device can be more effectively combined to more accurately calculate the photon position in the single crystal bar of the detector. The second optoelectronic device can also be a silicon photomultiplier (SiPM).

Furthermore, by coupling a SiPM optoelectronic element at both ends of a single crystal bar as an optoelectronic device, the position of the gamma photon deposition depth direction and other data can be calculated more accurately, so that in the subsequent data processing for imaging, the energy spectrum obtained by statistics at different depths can be segmented and calibrated. For example, for a single crystal bar of 1×1× ^20mm3 , it can be divided into 10 2mm depth segments, and the statistical photon energy spectrum of each segment is calibrated separately to improve the overall energy resolution, wherein the specific calibration steps include: firstly, flood-field irradiation of the single crystal bar, and then energy calibration of the depth direction position of the photon using the scintillation photon energies _Ea and _Eb detected by the two optoelectronic devices coupled at its two ends:

Among them, P(z) is the action position in the depth direction, k and t are fitting coefficients, which can be obtained through experimental calibration fitting.

Afterwards, the energy of each incident photon event is corrected with the corresponding coefficient according to the depth segment where it falls. In this way, the problem of poor energy spectrum measurement caused by serious light loss due to the long transmission distance of scintillation photons in the slender crystal strip can be solved through the double-end coupled optoelectronic device, which significantly improves the detection efficiency.

According to an embodiment of the present disclosure, the detector further includes at least one third photoelectric device.

At least one third optoelectronic device is coupled to at least one side surface of the single crystal strip.

In order to further avoid the problem of serious light loss and poor measured energy spectrum caused by the long transmission distance of scintillation photons in the slender crystal strip, the number of coupled optoelectronic devices can be increased on the side surface of the column of the detector of a single crystal strip to achieve side readout, so that The light-emitting surface is significantly enlarged, the transmission light loss of photons in a single crystal strip is reduced, and the double-end readout design of the first photoelectric device and the second photoelectric device can further improve the poor energy spectrum and significantly improve the photon detection efficiency. The third photoelectric device can also be a silicon photomultiplier (SiPM).

As shown in FIGS. 6A-6B , according to an embodiment of the present disclosure, a single crystal bar includes a plurality of first crystal blocks and a plurality of second crystal blocks.

The plurality of second crystal blocks and the plurality of first crystal blocks are arranged alternately to form a crystal strip structure.

As shown in FIG6A , a single crystal bar 601 used as a detector in the embodiment of the present disclosure may be a whole long cylindrical scintillator crystal bar. The scintillator crystal bar may be made of a scintillator material having an emission spectrum and an absorption spectrum that at least partially overlap, such as cerium-doped Gadolinium Aluminum Gallium Garnet (GAGG (Ce) or GAGG for short), thereby further increasing the difference in detection response capabilities for incident photons from different directions, and indirectly improving the angular resolution of positioning imaging of gamma photons.

On the other hand, the single crystal bar can also be a long columnar structure composed of at least two scintillating crystal material blocks with different characteristics. As shown in FIG6B , the single crystal bar 602 is a crystal bar structure composed of a plurality of first crystal blocks 621 and a plurality of second crystal blocks 622 overlapped and spliced with each other. Among them, there are certain differences in the photon transmission characteristics between the first crystal block 621 and the second crystal block 622. In this way, the single crystal bar of the long straight column can be directly physically divided into a plurality of detection units, so that it is possible to know in which unit the photon is specifically deposited, and the amount of information that can be used for photon direction estimation is further increased without significantly increasing the complexity of the structure, thereby improving the detection accuracy and detection efficiency.

Among them, the above-mentioned single crystal bars for detection are all required to have a size ratio design with the above-mentioned aspect ratio greater than or equal to 10:1, and by using optoelectronic devices coupled at its far end and/or front end, when gamma photons incident from different directions are deposited on the single slender crystal, obvious response differences will be formed and read out on its coupled end face as the irradiation angles change, thereby significantly improving the directional sensitivity of the detection efficiency.

According to an embodiment of the present disclosure, the first crystal block and the second crystal block are scintillator materials; or the first crystal block is scintillator material and the second crystal block is optical waveguide material; wherein the scintillator material The emission spectrum and absorption spectrum of the material partially overlap, and the refractive index of the optical guide material is greater than or equal to 1.5.

As shown in FIG6B , the first crystal block 621 and the second crystal block 622 can both be scintillator materials, and the first crystal block 621 can be a 200ns GAGG material block, while the second crystal block 622 can be a 90ns GAGG material block. As mentioned above, this can significantly improve the directional sensitivity of the detection efficiency.

On the other hand, the first crystal block 621 and the second crystal block 622 can also be two completely different materials, such as the first crystal block 621 can also be a scintillating crystal, and the second crystal block 622 can also be a light-conducting material, such as K9 optical glass (refractive index 1.51, similar to the refractive index of the coupling agent and SiPM element) or HZF-62 optical glass (refractive index 1.92, close to the refractive index of the GAGG crystal). The first crystal block 621 and the second crystal block 622 are staggered with each other, which can also significantly improve the directional sensitivity of the detection efficiency.

As shown in FIG. 7A to FIG. 7G, according to an embodiment of the present disclosure, a single crystal bar may include a column structure with a side view of a quadrilateral, a rhombus, a triangle, a heart shape, or a V shape. As shown in FIG. 7A to FIG. 7G, a single crystal bar 701a-701g as a detector in an embodiment of the present disclosure may be various types of long column structures, such as columns 701a and 701g with side view projection figures of slender rectangles, a rhombus column 701b, a triangular column 701c, a parallelogram column 701d, a heart-shaped column 701e, and a V-shaped column 701f, etc. Due to the irregularity of their shapes, they can also play a role in improving the directional sensitivity of the detection efficiency, and only need to meet the corresponding design of a length-to-width ratio greater than or equal to 10:1. At the same time, more variations are provided for the diversification of the single crystal bar, which significantly improves the detection application range of the single crystal bar and makes its applicable scenarios more diverse.

Among them, for a single crystal bar 701g as shown in FIG7G , it can also be composed of an overlapping combination of two materials with different properties, such as the overlap between the aforementioned photoconductive material and the scintillation crystal, so as to further improve its response difference, more accurately realize the detection of photon deposition data, obtain higher detection efficiency, and ensure the accuracy of imaging detection data.

According to an embodiment of the present disclosure, preferably, the detector further includes a refractive layer and/or an absorption layer.

The refractive layer covers the front end face of the single crystal bar close to the imaging field of view, and the refractive index of the refractive layer is greater than the refractive index of the scintillator material of the single crystal bar, and is used to refract the incident gamma photons to increase the loss of gamma photons on the front end face;

The absorption layer is covered on the front end face of a single crystal bar close to the imaging field of view, or on the refractive layer, and is used to absorb incident gamma photons and increase the loss of gamma photons on the front end face.

In the case of coupling optoelectronic devices at the far end face far away from the imaging field of view FOV, gamma photons incident on the front end face of a single crystal bar are more likely to be deposited at its far end, and the generated scintillation photons need to travel a longer optical path to reach the optoelectronic device. Due to the self-absorption of the scintillation crystal, part of the signal will be lost, resulting in a relatively lower detection efficiency, thereby increasing the difference in detection efficiency with photons incident from other directions.

In order to further increase the difference in detection efficiency between gamma photons incident directly on the front end face and gamma photons incident obliquely on the front end face, a high refractive index material can be coated on the front end face close to the imaging field of view FOV (far away from the first optoelectronic device) to form a refractive layer (not shown), wherein the refractive index of the high refractive index material can be greater than or equal to the high refractive index material of a single crystal bar (such as the refractive index of GAGG material is 1.91), and such high refractive index material can be titanium dioxide, Teflon, barium sulfate, etc., so as to increase the loss of scintillation photons generated by gamma photons on the end face, thereby achieving the effect of improving the response difference of photons incident from different directions. Among them, most of the gamma photons incident directly on the front end face of the scintillator are deposited on the front end face and generate scintillation photons on the front end face, so that the loss of scintillation photons on the front end face can reduce the detection efficiency of gamma photons incident directly on the front end face of the scintillator, thereby increasing the difference in detection efficiency between it and gamma photons incident from other directions.

In addition, based on the above-mentioned refractive layer design or directly replacing the above-mentioned refractive layer design, a visible photon absorbing material can also be coated on the front end face as an absorption layer. The visible photon absorbing material can be black tape or other black substances, so as to increase the loss of scintillation photons generated by gamma photons on the end face, thereby achieving the effect of increasing the response difference of incident photons in different directions.

According to an embodiment of the present disclosure, the first crystal block and the second crystal block of the single crystal bar have different doping ion concentrations and/or dopant materials, and the doping ion concentration is 0.01% to 0.6%.

Among them, a single crystal bar can be a staggered arrangement of scintillation crystal blocks with different dopants or staggered arrangement of scintillation crystal blocks with the same dopant but different doping concentrations. Among them, the selected crystal dopant can be Ce, Mg, Ti plasma, etc., which can significantly change the luminous efficiency and luminous decay time of the crystal, and its corresponding dopant concentration range is optional from 0.01% to 0.6%, so that the incident light The difference in photon detection efficiency at different depths of the crystal strip increases. The dopant materials of the first crystal block and the second crystal block can be different. For example, the crystal dopant of the first crystal block can be Ce, and the crystal dopant of the second crystal block can be Mg. The staggered arrangement of the two can form the above-mentioned single crystal strip.

Wherein, if the ion doping operation of the crystal dopant or the ion doping operation of different concentrations is performed at a certain interval in the length direction of a single crystal bar, the staggering of scintillation crystals with different dopants or the staggering of scintillation crystals with the same dopant but different doping concentrations can be formed in the length direction, thereby significantly increasing the photon detection efficiency at different depths, and facilitating the realization of the above-mentioned corresponding effects such as segmented calibration and transmission matrix calibration. Wherein, the first crystal block and the second crystal block can be the same dopant material with different single doping ion concentrations, for example, the crystal dopant of the first crystal block and the second crystal block can both be Ce, and the doping ion concentration of Ce in the first crystal block can be 0.01%, and the doping ion concentration of Ce in the second crystal block can be 0.26%, and the staggered arrangement of the two can constitute the above-mentioned single crystal bar.

Therefore, a single crystal strip can be staggered along its length with different crystal dopants or with the same dopant but at different doping concentrations.

According to an embodiment of the present disclosure, the detector further includes a blocking layer.

The blocking layer is coupled to the end face of the single crystal bar near the front end of the imaging field of view to block the gamma photons incident normally toward the end face of the front end.

A thin layer of high-density material can be covered on the front end face of a single crystal bar near the imaging field of view FOV as a blocking layer, which can significantly block the normally incident gamma photons and reduce the detection efficiency of normally incident gamma photons, thereby increasing the directional response difference. The high-density material can be at least one of heavy metal materials with strong photon blocking ability such as tungsten and lead.

The single crystal strip shown in Figures 1 to 7G above enables the corresponding gamma imaging device to collimate photons using the shape characteristics and properties of the single slender crystal itself, without the need for an external metal collimator or other crystal detector units. The positioning and imaging of the radiation source can be achieved with only a slender scintillation crystal and a coupled optoelectronic device. Compared with the multi-layer detector unit design of the self-collimating detector, the design of the system detector structure is greatly simplified, the number of electronic readout channels is reduced, the weight and volume of the equipment are reduced, and portable imaging can be achieved at a low cost. Moreover, without the blocking of photons by the metal collimator, the The detection efficiency of the device itself is improved, and the radiation source positioning device composed of a single slender crystal can realize the dual functions of counting and positioning, with simple composition and convenient positioning.

It should be noted that the above-mentioned related designs for the single crystal bar of the embodiment of the present disclosure can more or less significantly play a role in improving the directional sensitivity of the detection efficiency, and the details will not be repeated here.

In addition, as shown in FIG9 , a gamma imaging device for a radiation source plane is designed, in which the front end face of a single crystal bar 901 serving as a detector faces the imaging field of view FOV plane, and two-dimensional dot matrix translation sampling is performed on a plane A corresponding to the imaging field of view FOV in a direction parallel to the imaging field of view FOV. Plane A may have a two-dimensional dot matrix composed of multiple sampling points A1, and a radiation source distribution map of the imaging field of view FOV plane may be reconstructed.

As shown in FIG. 8A and FIG. 8B , another aspect of the present disclosure provides a gamma imaging device, which includes a crystal bar array consisting of at least one single crystal bar and a first circuit board.

A crystal bar array composed of at least one single crystal bar is used to move relative to an imaging field of view to detect incident gamma photons in the imaging field of view, and to collimate the incident gamma photons to achieve gamma imaging, wherein the aspect ratio of the single crystal bar is greater than 10:1;

The first circuit board is coupled to the far end of the crystal bar array away from the imaging field of view, and is used to output detection data of the crystal bar array to the imaging field of view.

As shown in FIG8A and FIG8B , a plurality of single crystal bars can be combined in space along the plane where the front end face of each single crystal bar is located close to the imaging field of view FOV (the size meets 200×200×200 mm ³ ) to form crystal bar arrays 801 and 802. When a layer of circuit board 803 and 804 are coupled to the distal end faces of the crystal bar arrays 801 and 802 as single-layer detectors, they are respectively used as the first circuit board. The first circuit boards 803 and 804 can be arranged with a plurality of the first optoelectronic devices coupled to the distal end faces of the crystal bar arrays 801 and 802, so as to achieve high integration and simple structure gamma imaging with only a single-layer detector + circuit board.

As shown in FIG8B , according to an embodiment of the present disclosure, the gamma imaging device further includes a second circuit board, which is coupled to the front end of the crystal bar array away from the imaging field of view, and is used to cooperate with the first circuit board to output detection data of the crystal bar array on the imaging field of view.

As shown in FIG8B , a layer of electric current is coupled to each of the distal end faces of the crystal bar arrays 801 and 802. On the basis of the circuit boards 803 and 804, a layer of circuit boards 805 and 806 are coupled to the front end faces of the crystal bar arrays 801 and 802, respectively, as the second circuit board. The second circuit boards 803 and 804 can be arranged with a plurality of the second optoelectronic devices coupled to the front end faces of the crystal bar arrays 801 and 802. Therefore, with the cooperation of the second circuit board, the design of a gamma imaging device with a single-layer detector + front and rear two-layer circuit boards can be realized, so as to further improve its imaging accuracy without significantly increasing the structural complexity.

The crystal bar arrays 801 and 802 shown in Figures 8A and 8B can be composed of a single thin scintillation crystal to form a detector module. Multiple thin single crystals are arranged at intervals to form the detector array, and sampling at different angles is obtained through translation and rotation detection, so as to obtain better gamma images.

As shown in FIG8B , according to an embodiment of the present disclosure, the gamma imaging device further includes a scintillation crystal layer, which is located between the first circuit board and the distal end surface of the crystal bar array to receive the remaining scintillation photons passing through the crystal bar array.

As shown in FIG8B , based on the array detector module formed by the above-mentioned multiple crystal bars, a complete scintillation crystal layer 807 can be coupled at the far end of the crystal module. The scintillation crystal layer 807 can be located between the first circuit board 803 and the source end face of the crystal bar array 801 to receive the remaining penetrating photons, thereby forming a "comb-tooth-type" detector array, thereby further improving the imaging quality.

Among them, the single crystal bar unit in the above-mentioned crystal bar arrays 801 and 802 can be the single crystal bar shown in the above-mentioned Figures 1-7G, so that the corresponding gamma imaging device can utilize the shape characteristics and properties of the single slender crystal itself to achieve collimation of photons, without the need for an additional metal collimator or the use of other crystal detector units. It can only be composed of a series of slender scintillation crystals arranged with each other to form an array, so as to further realize the positioning and imaging of the radiation source during the mobile detection process of the array, which greatly simplifies the design of the system, reduces the weight and volume of the equipment, and can achieve portable imaging with low cost.

It can be seen that the above-mentioned gamma imaging device of the embodiment of the present disclosure can be designed as a brain SPECT imaging device, which uses multiple crystal array detector modules to form a single-layer detector to form a helmet that surrounds the human brain. It is light, flexible and wearable, and has extremely high commercial value and scientific research value.

Another aspect of the present disclosure provides an imaging device applied to the above-mentioned gamma imaging device. method.

As shown in FIG5 , the gamma imaging device of the embodiment of the present disclosure may be composed of only one slender strip scintillation crystal and one optoelectronic device. The distribution of the radiation source within the imaging field of view FOV is imaged by translational and rotational sampling. At the same time, an adaptive sampling algorithm is designed to reduce the sampling step length Δx at low counts and increase the sampling step length Δx at high counts, thereby minimizing the number of sampling times and reducing the sampling time while ensuring the imaging accuracy.

For image reconstruction, the SRF of the detector composed of a single crystal strip is in a downward-thrusting shape (as shown in FIG3 ). In contrast to conventional metal collimator detectors, when Siddon algorithm is used for filtering and back-projection analytical reconstruction, the bright areas of the reconstructed image represent low activity of the radiation source, and the dark areas represent high activity of the radiation source. The image needs to be transformed in value to obtain a forward image representing the distribution of the radiation source:

Among them, y′ _i represents the forward distribution map obtained after transformation, max{y} represents the maximum value in the original reverse map, and max{y} represents the minimum value in the original reverse map. Among them, if the ML-EM iterative image reconstruction algorithm is used, the image obtained is a forward map, and no size transformation is required.

As shown in FIG10A and FIG10B , in the Monte Carlo simulation verification, when the FOV diameter D is 40 mm and the distance d between the detector and the FOV is 45 mm, the average detection efficiency is 4.3×10 ^-5 , and the thermal cylinder with a diameter of 3 mm and a center distance of 6 mm can be distinguished; when the FOV diameter D is 100 mm and the distance d between the detector and the FOV is 45 mm, the average detection efficiency is 3.0×10 ^-5 , and the thermal cylinder with a diameter of 3 mm and a center distance of 6 mm can be distinguished.

Accordingly, in the actual experimental verification, a single crystal detector prototype device was built as an actual prototype to test its imaging performance. A single GAGG (Ce) scintillating crystal strip of 1×1×20 mm ³ was selected as the detector, two SiPM elements were coupled at both ends, and a translation and rotation platform was used to realize the scanning trajectory and the imaging of simulated point sources at different positions. As shown in Figure 11, the reconstruction results show the reconstructed image effects of single point sources, two point sources and four point sources with a spacing of 6 mm. When the FOV diameter is 20 mm and the distance d between the detector and the FOV is 45 mm, the average detection efficiency can reach 1.8×10 ^-5 , and two point sources 6 mm apart can be clearly distinguished, and the distribution of multiple point sources also shows excellent resolution.

So far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings.

The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

A gamma imaging device, comprising a detector, the detector comprising:

A single crystal bar is used to move relative to an imaging field of view to detect incident gamma photons in the imaging field of view and to collimate the incident gamma photons for gamma imaging, wherein the aspect ratio of the single crystal bar is greater than 10:1.
The gamma imaging device according to claim 1, wherein the detection efficiency of gamma photons incident normally on the front end of the single crystal bar close to the imaging field of view is less than the detection efficiency of gamma photons incident obliquely on other parts away from the imaging field of view; wherein the distance between the front end face of the single crystal bar close to the imaging field of view and the imaging field of view is less than or equal to 100 mm.
The gamma imaging device according to claim 1, wherein the detector further comprises:

A first optoelectronic device is coupled to a far end of the single crystal bar away from the imaging field of view and is used to read out gamma photon deposition data in the single crystal bar.
The gamma imaging device according to claim 1, wherein the surface roughness of at least one side surface of the single crystal bar is less than or equal to 0.01 micrometer.
The gamma imaging device according to claim 3, wherein the detector further comprises:

A second photoelectric device is coupled to the front end of the single crystal bar close to the imaging field of view, and is used to cooperate with the first photoelectric device to read out the gamma photon deposition data to obtain energy spectra in different gamma photon deposition depth directions.
The gamma imaging device according to claim 3 or 5, wherein the detector further comprises:

At least one third optoelectronic device is coupled to at least one side surface of the single crystal strip.
The gamma imaging device according to claim 1, wherein the single crystal bar comprises:

a plurality of first crystal blocks,

A plurality of second crystal blocks are arranged alternately with the plurality of first crystal blocks to form a crystal Strip structure.
The gamma imaging device according to claim 7, wherein:

The first crystal block and the second crystal block are scintillator materials; or

The first crystal block is a scintillator material, and the second crystal block is a light-conducting material;

The emission spectrum and absorption spectrum of the scintillator material partially overlap, and the refractive index of the optical waveguide material is greater than or equal to 1.5.
The gamma imaging device according to claim 1, wherein the single crystal bar may include a columnar structure having a quadrilateral, a diamond, a triangle, a heart, or a V shape in a side view.
The gamma imaging device according to claim 2, wherein the detector further comprises:

a refractive layer covering the front end face of the single crystal bar close to the imaging field of view, the refractive layer having a refractive index greater than the refractive index of the scintillator material of the single crystal bar, and being used for refracting scintillation photons generated by the incident gamma photons to increase the loss of scintillation photons on the front end face; and/or

The absorption layer is covered on the front end face of the single crystal bar close to the imaging field of view, or on the refractive layer, and is used to absorb the scintillation photons generated by the incident gamma photons to increase the loss of the scintillation photons on the front end face.
The gamma imaging device according to claim 7, wherein the doping ion concentration and/or dopant material of the first crystal block and the second crystal block of the single crystal bar are different, and the doping ion concentration is 0.01% to 0.6%.
The gamma imaging device according to claim 3, wherein the detector further comprises:

A blocking layer is coupled to the front end face of the single crystal bar close to the imaging field of view to block gamma photons incident normally toward the front end face.
A gamma imaging device, comprising:

A crystal bar array consisting of at least one single crystal bar, used to move relative to an imaging field of view to detect incident gamma photons in the imaging field of view, and to collimate the incident gamma photons to achieve gamma imaging, wherein the aspect ratio of the single crystal bar is greater than 10:1;

A first circuit board is coupled to the far end of the crystal bar array away from the imaging field of view, and is used to Output detection data of the crystal strip array to the imaging field of view.
The gamma imaging device according to claim 13, further comprising:

The second circuit board is coupled to the front end of the crystal bar array away from the imaging field of view, and is used to cooperate with the first circuit board to output detection data of the crystal bar array on the imaging field of view.
The gamma imaging device according to claim 13, further comprising:

The scintillation crystal layer is located between the first circuit board and the distal end surface of the crystal bar array to receive the remaining scintillation photons passing through the crystal bar array.
An imaging method for a gamma imaging device according to any one of claims 1 to 15.