CN115685305A

CN115685305A - Gamma imaging device and imaging method thereof

Info

Publication number: CN115685305A
Application number: CN202211353168.1A
Authority: CN
Inventors: 马天予; 朱艺航; 吕振雷
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2022-10-31
Filing date: 2022-10-31
Publication date: 2023-02-03
Also published as: WO2024093737A1

Abstract

The present disclosure provides a gamma imaging device and an imaging method thereof, wherein the gamma imaging device comprises a detector, the detector comprises a single crystal strip, the single crystal strip is used for moving relative to an imaging field of view to detect incident gamma photons of the imaging field of view, collimation of the incident gamma photons is realized, and the gamma imaging is realized, wherein the aspect ratio of the single crystal strip is larger than 10: 1. Therefore, based on the gamma imaging device, a brand-new detector mode is established, the existing external mechanical collimator which is low in detection efficiency, heavy and large is completely abandoned, the limitations of the traditional complex detector structure and a plurality of electronic structures are greatly simplified, and the gamma imaging detection device which is high in sensitivity and has a very simple design can be simultaneously used.

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

Gamma imaging requires significant differences in the response of detector cells to photons from different directions, i.e., when the incident direction of photons changes, the photon count (detection efficiency) in a certain detector cell also changes greatly. The mechanical collimator is used for blocking a large part of photons from entering the detector, so that the overall detection efficiency is seriously reduced, the size and weight of the mechanical collimator are large, the overall detector is heavy and not light, and the use scene is limited; the existing mode of shielding the front and back of the multilayer detector units by auto-collimation can cause response difference, and the efficiency is prevented from being reduced, but the detector has a complex structure and a large number of electronic reading channels, so that an imaging device is large in size or high in cost.

Disclosure of Invention

Technical problem to be solved

In order to solve at least one of the above technical problems in the prior art of gamma imaging, which is to ensure the obvious response difference of photons, the present disclosure provides a gamma imaging device and an imaging method thereof.

(II) technical scheme

One aspect of the present disclosure provides a gamma imaging apparatus comprising a detector including a single crystal strip for movement relative to an imaging field of view to detect incident gamma photons of the imaging field of view to achieve collimation of the incident gamma photons for achieving gamma imaging, wherein an aspect ratio of the single crystal strip is greater than 10: 1.

Preferably, the detection efficiency of the gamma photons which are normally incident at the front end of the single crystal strip close to the imaging field of view is smaller than that of the gamma photons which are obliquely incident at other parts far away from the imaging field of view; the distance between the front end face of the single crystal strip close to the imaging visual field and the imaging visual field is smaller than or equal to 100mm.

Preferably, the detector further comprises a first optoelectronic device. A first optoelectronic device is coupled at a distal end of the single crystal stripe away from the imaging field of view for reading gamma photon deposition data in the single crystal stripe.

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

Preferably, the detector further comprises a second optoelectronic device. The second photoelectric device is coupled at the front end of the single crystal strip close to the imaging visual field and used for being matched with the first photoelectric device to read out gamma photon deposition data and obtaining energy spectrums 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. At least one third optoelectronic device is coupled to at least one side surface of the single crystal stripe.

Preferably, the single crystal strip 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 in a staggered mode to form a crystal strip structure.

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

Preferably, the single crystal strip may comprise a cylindrical structure with a side view of quadrilateral, rhombus, triangle, heart, V-shape.

Preferably, the detector further comprises a refractive layer and/or an absorptive layer. The refraction layer covers the front end face of the single crystal strip close to the imaging view field, the refraction layer has a refractive index larger than that of the scintillator material of the single crystal strip, and is used for refracting scintillation photons generated by incident gamma photons and increasing the loss of the scintillation photons on the front end face; the absorption layer covers on the front end face of a single crystal strip close to the imaging visual field or covers on the refraction layer and is used for absorbing scintillation photons generated by incident gamma photons and increasing the loss of the scintillation photons on the front end face.

Preferably, the first crystal block and the second crystal block of the single crystal strip are different in doping ion concentration and/or dopant material, and the doping ion concentration is 0.01% -0.6%.

Preferably, the detector further comprises a barrier layer. The blocking layer is coupled on the front end face of the single crystal strip close to the imaging view field to block gamma photons which are normally incident towards the front end face.

Another aspect of the present disclosure provides a gamma imaging apparatus, which includes a crystal bar array of at least one single crystal bar and a first circuit board. The crystal strip array formed by at least one single crystal strip is used for detecting incident gamma photons of the imaging field of view through movement relative to the imaging field of view, collimation of the incident gamma photons is achieved, and gamma imaging is achieved, wherein the aspect ratio of the single crystal strip is larger than 10:1; the first circuit board is coupled with the far end of the crystal strip array far away from the imaging field of view and used for outputting detection data of the crystal strip array on the imaging field of view.

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

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

Still another aspect of the present disclosure provides an imaging method of the above gamma imaging apparatus.

(III) advantageous effects

The present disclosure provides a gamma imaging device and an imaging method thereof, wherein the gamma imaging device comprises a detector, the detector comprises a single crystal strip, the single crystal strip is used for moving relative to an imaging visual field to detect incident gamma photons of the imaging visual field, collimation of the incident gamma photons is realized, and the gamma imaging is realized, wherein the aspect ratio of the single crystal strip is more than 10: 1. Therefore, based on the gamma imaging device, a brand-new detector mode is established, the existing external mechanical collimator which is low in detection efficiency, heavy and large is completely abandoned, the limitations of the traditional complex detector structure and a plurality of electronic structures are greatly simplified, and the gamma imaging detection device which is high in sensitivity and has a very simple design can be simultaneously used.

Drawings

FIG. 1 schematically illustrates 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 disclosure;

FIG. 2 schematically illustrates a conventional mechanical collimator 201 and detector 202 imaging detection schematic diagram of a prior art gamma imaging device with respect to the source position and its corresponding SRF graph;

FIG. 3 schematically illustrates an imaging detection schematic diagram of a single crystal strip 301 as a detector relative to a radiation source position and its corresponding SRF graph of a gamma imaging device according to an embodiment of the disclosure;

FIG. 4 schematically illustrates a rotation detection diagram of a single crystal strip 401 in accordance with an embodiment of the present disclosure;

FIG. 5 schematically illustrates a top view of a single crystal strip 501 as a detector in a motion detection principle relative to the FOV of an imaging field of view in accordance with an embodiment of the present disclosure;

FIG. 6A schematically illustrates a structural perspective view of a single crystal ribbon 601 in accordance with an embodiment of the disclosure;

FIG. 6B schematically illustrates a structural perspective view of a single crystal bar 602, according to an embodiment of the present disclosure;

7A-7G schematically illustrate structural side views of a single crystal ribbon 701a-701G according to an embodiment of the disclosure;

fig. 8A schematically illustrates an imaging composition diagram of a crystal bar array 801 with respect to an imaging field of view FOV of a gamma imaging device according to another embodiment of the present disclosure;

FIG. 8B schematically illustrates an imaging composition diagram of the crystal bar array 802 relative to the imaging field of view FOV of a gamma imaging device according to another embodiment of the disclosure;

fig. 9 schematically illustrates a schematic diagram of two-dimensional lattice translational sampling of a single crystal strip 901 in a direction parallel to the FOV in a gamma imaging method according to an embodiment of the present disclosure;

FIG. 10A shows a thermal cylindrical reconstructed image with an imaging field of view FOV of a gamma imaging device meeting a 40mm diameter and a detector to FOV distance meeting 45mm according to an embodiment of the disclosure;

fig. 10B shows a thermal cylindrical reconstructed image with an imaging field of view FOV meeting 100mm diameter and a detector to FOV distance meeting 45mm in accordance with an embodiment of the disclosure;

fig. 11 shows a graph of reconstructed image effects of an actual prototype device of a gamma imaging device according to an embodiment of the disclosure for a single point source, two point sources, and four point sources at 6mm spacing.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments and the accompanying drawings.

It is to be understood that the implementations not shown or described in the drawings or in the text of this specification are in a form known to those skilled in the art and are not described in detail. Further, the above definitions of the various elements and methods are not limited to the various specific structures, shapes or arrangements of parts mentioned in the examples, which may be easily modified or substituted by those of ordinary skill in the art.

It should also be noted that directional terms, such as "upper", "lower", "front", "rear", "left", "right", and the like, used in the embodiments are only directions referring to the drawings, and are not intended to limit the scope of the present disclosure. Throughout the drawings, like elements are represented by like or similar reference numerals. Conventional structures or constructions will be omitted when they may obscure the understanding of the present disclosure.

And the shapes and sizes of the respective components in the drawings do not reflect actual sizes and proportions, but merely illustrate the contents of the embodiments of the present disclosure. Furthermore, in the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

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 use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify a corresponding element does not by itself connote any ordinal number of the element or any ordering of one element relative to another or relative to a method of manufacture, and the use of such ordinal numbers is only used to clearly distinguish one element having a certain name from another element having a same name.

Those skilled in the art will appreciate that the modules in the device of an embodiment may be adaptively changed and placed in one or more devices different from the embodiment. The modules or units or components in the embodiments may be combined into one module or unit or component, and furthermore, may be divided into a plurality of sub-modules or sub-units or sub-components. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where at least some of such features and/or processes or elements are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Also in the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various disclosed aspects. However, the disclosed method should not be interpreted as reflecting an intention that: that is, the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, disclosed aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this disclosure.

As shown in fig. 1, one aspect of the present disclosure provides a gamma imaging apparatus, including a detector including a single crystal strip for movement relative to an imaging field of view to detect incident gamma photons of the imaging field of view to achieve collimation of the incident gamma photons for achieving gamma imaging, wherein an aspect ratio of the single crystal strip is greater than 10: 1.

For a gamma imaging device, a detector as a part for realizing gamma photon detection between an imager and an imaging field belongs to the most key composition content in the device, and can obviously influence the detection efficiency of gamma photons.

The ordinary detector generally needs to adopt a mechanical collimator to collimate photons before entering the detector, so as to realize the response difference of gamma photons in different directions in the detector. In the gamma imaging device of the embodiment of the disclosure, a traditional collimator design is directly abandoned, only a single crystal strip 101 is arranged between a Field of View (Field of View, FOV for short) and an imager (not shown) as a detector, and differential responses to different gamma photons are realized by moving the single crystal strip relative to the FOV of the imaging Field, so that the composition structure of the gamma imaging device is greatly simplified under the condition of ensuring the detection efficiency. Wherein, the number of the single crystal strip can be only one. The FOV of the imaging field of view may generally be a detectable range of a detector where the object to be imaged is located, and may be understood as a position of the radiation source.

In the disclosed embodiment, the detection efficiency of a single crystal strip 101, which may act as a detector, is related to its solid angle relative to the position of the source of radiation (which may be understood as the imaging field of view FOV). Compared with a conventional square detector unit which is not sensitive enough to the change of the incidence direction of the gamma photons, after the length-width ratio of the single crystal strip 101 is remarkably increased, the imaging solid angle formed when the gamma photons are normally incident on the front end face 110 of the single crystal strip is the smallest, and the photon detection efficiency is the lowest at the moment; when the incident direction of the photons is deflected from the normal incidence to the distal end face 120 of the single crystal stripe at the front end, the photon detection efficiency is significantly and rapidly improved, thereby bringing about a good direction positioning effect. At the same time, the front end face 110 is an end face of an end (i.e., a front end) of the single crystal strip near the radiation source position, the far end face 120 is an end face of an end (i.e., a far end) of the single crystal strip far from the radiation source position, relative to the front end face 110, and the front end and the far end respectively form two ends of the single crystal strip.

Therefore, in order to ensure that the single crystal strip can have a more stable detection effect in the detection process and also have a higher detection efficiency, in the specific detection process, the detector arranged on the single crystal strip 101 needs to be moved, and the movement may include at least one of translation along a spatial straight line or a spatial curved line direction, self-rotation or rotation around a certain fixed point or a moving point as a circle center in the space. As shown in FIG. 5, a single crystal ribbon 501 is translated in a spatial plane by a unit sampling Step Δ x (Translation Step) around an imaging field of view FOV having a Diameter dimension D (Diameter of FOV) in combination with a unit sampling angle

The rotation is performed, and the final completion rotation Angle (project Angle) is

In a rotational range of the rotary shaft, wherein

Satisfy the requirements of

Therefore, by means of the movement of the single crystal strip 101, the position or angle of the single crystal strip with respect to the radiation source (imaging field of view FOV) can be changed, so that a more diversified and differentiated detection solid angle can be generated for the detection of incident photons, thereby significantly improving the detection efficiency and having a more precise direction positioning effect.

Further, in the embodiment of the present disclosure, the structure of the single crystal stripe 101 is elongated, and in the structure side view pattern (understood as a projected pattern of side view angle) in the length direction, the ratio of the length dimension L of the pattern to the maximum width dimension W/G (for example, W > G, L: W is determined, and conversely, L: G is determined) is greater than or equal to 10:1, i.e. the aspect ratio of the single crystal bar is greater than 10: 1. Borrow this, can guarantee at the follow-up removal detection in-process of this single crystal strip 101, this single crystal strip 101 can have better formation of image solid angle, and the poor opposite sex of photon detection efficiency increases, brings better direction location effect. In other words, the larger the aspect ratio of a single crystal strip is, the larger the difference between the detection efficiency of the crystal for gamma photons with normal incidence and that of gamma photons with oblique incidence is, and the more sensitive the incidence direction of the gamma photons is, so that a better direction positioning effect is brought. Therefore, when the single crystal strip with the length-width ratio value is used as a detector alone, the device for gamma imaging detection with high sensitivity and extremely simple structural design can be provided.

Therefore, based on above-mentioned gamma image device, a brand-new detector mode has been established, can only adopt single crystal strip 101 to carry out the collimation as the detector to incident photon and survey, and abandoned current detection inefficiency and bulky not portable outside mechanical collimator completely, traditional complicated detector structure has been simplified to a great extent, break away the traditional restriction of a plurality of electronics structures, and can have the gamma imaging detection device of the extremely simple design of high sensitivity simultaneously concurrently, structural design is very simple, light weight is portable, be fit for needing portable all kinds of imaging scenes who uses.

As shown in fig. 2 and 3, according to an embodiment of the present disclosure, the detection efficiency of gamma photons of a single crystal stripe 301 that are normally incident near the front end of the imaging field of view FOV is less than the detection efficiency of gamma photons that are obliquely incident away from other portions of the imaging field of view FOV; the distance between the front end face of the single crystal strip close to the imaging visual field and the imaging visual field is smaller than or equal to 100mm.

Due to the fact that the

single crystal strip

301 or 101 is used as the detector independently, and a mechanical collimator is directly omitted, the crystal response function (SRF for short, representing the detection efficiency of gamma photons at different positions of the FOV of the imaging field) of the detector of the embodiment of the present disclosure is significantly different from that of a conventional detector. As shown in fig. 2, in the conventional design of the detector 202 having the metal mechanical collimator 201 and the plurality of crystal units, the photon detection efficiency is highest in the direction facing the detector 202, and the SRF is highest when the radiation source position is at the center position in the other directions because the shielding has almost no detection efficiency. On the contrary, as shown in fig. 3, in the solution of the embodiment of the present disclosure, without a metal mechanical collimator, only using a single crystal strip 301 as a detector, since the single elongated crystal strip 301 has the lowest detection efficiency when being collimated to face the front end face, and the SRF is the lowest, the detection efficiency in other directions is rather higher and can maintain a higher and more stable level, that is, the detection efficiency of the single crystal strip for gamma photons incident on the proximal end face is lower than the detection efficiency of gamma photons obliquely incident on the proximal end face and other surfaces. Therefore, the gamma imaging device disclosed by the embodiment of the disclosure has good response to almost all other incident photon directions except the position facing the front end face, the detection efficiency of incident particles at different angles is not completely the same, and the activity distribution of radioactive sources at different incident directions can be judged according to the relative magnitude of the response of the detector at different positions, so that all positions are considered, not only the sensitive position is limited in a small-angle range of the opening of the collimator, and the relation between the detection efficiency and the position of the radioactive source is completely opposite to that of the conventional design.

Therefore, based on the above detection principle, a very simple radiation source counting and positioning device can be designed, wherein the detector is only formed by one slender strip-shaped crystal strip. And the detector can move to detect in 4-pi space, and the position with the lowest count faces to the direction of the radioactive source. Wherein, the detection efficiency of the detector is positively correlated with the solid angle of a single crystal to the position of a radioactive source, and the detection efficiency loss is serious along with the increase of the distance between the crystal and an imaging Field of view (FOV). Therefore, the detector is close to the imaging field of view FOV as possible, specifically, the Distance d (Distance between FOV and Crystal) between the single Crystal bar of the detector and the imaging field of view FOV can be less than or equal to 100mm (d =40mm as shown in fig. 5), and the components and tooling arrangement facing the end face of the imaging field of view FOV are simplified.

Different from the characteristic that a metal collimator detector and an auto-collimation detector only respond to photons incident in a plurality of directions, the single slender crystal strip has low response to a target position and also considers other positions, the sensitivity range is large, a complete image can be reconstructed only by combining information of a few positions, and the sampling positions can be greatly reduced. Therefore, the gamma imaging device disclosed by the embodiment of the disclosure can have a more flexible sampling scheme when a radioactive source is imaged, and can specifically adjust the sampling step length in a self-adaptive manner according to the counting height of the detector, so that the sampling times and the sampling time are reduced on the premise of not reducing the imaging precision.

According to an embodiment of the present disclosure, the detector further comprises a first opto-electronic device 402.

A first opto-electronic device 402 is coupled at a distal end of the single crystal stripe 401, away from the imaging field of view, for reading out the gamma photon deposition data in the single crystal stripe 401.

For a radioactive source imaging device, the device only consists of one elongated single crystal strip 401 and one photoelectric device 402. Wherein the distribution of the radioactive source within the FOV of the imaging field of view can be imaged by means of translational and rotational sampling. The translation may be a translation along a spatial straight line or a spatial curved line, and the rotation may be a self-rotation or a rotation around a fixed point or a moving point in space, as shown in fig. 4, the detector has a single crystal bar 401 and an optoelectronic device 402 disposed at a distal end of the single crystal bar 401, wherein, with the center in the length direction of the single crystal bar 401 as a center, the detector can be performed a rotation detection in a spatial plane, and a detection effect in a range of 0 to 180 ° with respect to the FOV of the imaging field of view is achieved.

Wherein the first optoelectronic device 402 may be a silicon photomultiplier (SiPM), coupling the optoelectronic device 402 to a distal facet of the single crystal bar 401 away from the imaging field of view FOV may enable single-ended readout of photon deposition data. In addition, the front end face of the single crystal strip 401, which is close to the imaging field of view FOV, can be coated by a thin plastic tool to realize the moving protection of the crystal strip, so as to achieve the purpose of detecting the crystal strip by clinging to the imaging field of view FOV.

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

For the single crystal strip of the embodiment of the present disclosure, it may be a scintillation crystal strip for detection, which may meet the transmission requirement of scintillation photons inside, and the single crystal strip may be a cylinder, a cuboid, or other long-column structure, and only needs to meet the requirement that the aspect ratio of the side-view projection diagram is greater than or equal to 10: 1.

In addition, on the basis, the side surface of the cylinder of the single crystal strip can be further processed (such as polished), so that the cylinder has better smoothness, the surface roughness of the side surface of the cylinder is reduced, the roughness can be less than or equal to 0.01 micrometer, and specifically 2000-mesh abrasive paper can be adopted for polishing, so that the transmission efficiency of scintillation photons in the single crystal strip can be further improved by means of the specular reflection capacity of the smooth surface of the cylinder, the problems of long transmission distance and serious light loss of the scintillation photons in the slender crystal strip are effectively solved, the photon transmission efficiency can be remarkably improved, a better detection energy spectrum is obtained, and the detection efficiency and the direction positioning accuracy are improved.

Based on the above, in a specific imaging application, a transmission matrix needs to be calibrated for an imaging device, and the specific steps are dividing an imaging field of view FOV into grid points by taking a pixel size as a step length, respectively placing a point source at each grid point, measuring projection data by using a single crystal strip of a detector, and combining the projection data of the point source at each position to obtain the transmission matrix. In the calibration process, because the detector only consists of a single crystal strip, no mechanical collimator and no complex mutual shielding between crystals exist, and the SRF value has extremely strong symmetry (as shown in figure 3), the calibration steps of the transmission matrix can be greatly simplified. Specifically, only need measure the projection of single crystal strip at the intermediate position as the detector, recycle to SRF's translation and rotatory extension to other positions, can be in order to obtain complete transmission matrix, and then make the required measuring time in every radiation source position shorter to shorten transmission matrix calibration time greatly, accelerate data processing speed, improve imaging efficiency.

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

The second photoelectric device is coupled at the front end of the single crystal strip close to the imaging view field and used for being matched with the first photoelectric device to read out gamma photon deposition data and obtain energy spectrums in different gamma photon deposition depth directions.

In addition, while the far end of the single crystal strip of the detector is coupled with the first photoelectric device, the front end of the single crystal strip of the detector can be further coupled with another second photoelectric device so as to read photon deposition data from the front end, thereby more effectively combining the read data of the first photoelectric device and more accurately calculating the photon position in the single crystal strip of the detector. Wherein the second photoelectric device can also be a silicon photomultiplier (SiPM).

Furthermore, the two ends of a single crystal strip are respectively coupled with an SiPM photoelectric element as a photoelectric device, so that data such as positions in the deposition depth direction of gamma photons can be more accurately calculated, and the energy spectrum obtained by counting at different depths can be calibrated in sections in the subsequent imaging data processing process. For example, for 1X 20mm ³ The single crystal strip can be divided into 10 depth sections of 2mm, and the statistical photon energy spectrum of each section is calibrated separately to improve the overall energy resolution, wherein the specific calibration steps comprise: firstly, a single crystal strip is irradiated by a field, and then scintillation photon energy E detected by two photoelectric devices respectively coupled at two ends of the single crystal strip is utilized _a And E _b Energy calibration is carried out on the depth direction position of the photon:

wherein, P (z) is the action position in the depth direction, k and t are fitting coefficients, and can be obtained by calibration fitting through experiments.

Each incident photon event is then energy corrected for its corresponding coefficient in turn according to its location in the depth segment. Therefore, the problem of poor measured energy spectrum caused by serious light loss due to long transmission distance of scintillation photons in the slender crystal strips can be well solved through the double-end coupling photoelectric device, and the detection efficiency is remarkably improved.

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

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

In order to further avoid the problems of serious light loss and poor measured energy spectrum caused by long transmission distance of scintillation photons in the slender crystal strip, the number of the coupled photoelectric devices can be increased on the side surface of the cylinder of the detector of a single crystal strip to realize side surface reading, so that the light emitting surface can be obviously increased, the transmission light loss of photons in the single crystal strip can be reduced, and the poor energy spectrum condition can be further improved and the photon detection efficiency can be obviously improved by combining the double-end reading design of the first photoelectric device and the second photoelectric device. Wherein the third photoelectric device can also be a silicon photomultiplier (SiPM).

As shown in fig. 6A-6B, a single crystal strip includes a plurality of first crystal blocks and a plurality of second crystal blocks according to embodiments of the present disclosure.

The plurality of second crystal blocks and the plurality of first crystal blocks are arranged in a staggered mode to form a crystal bar structure.

As shown in fig. 6A, a single crystal strip 601 serving as a detector in the embodiment of the present disclosure may be a scintillation crystal strip of a whole long column, and the scintillation crystal strip may be made of a scintillator material whose emission spectrum and absorption spectrum at least partially overlap, such as Cerium-doped Gallium Aluminum Garnet (GAGG (Ce) or GAGG for short), so as to further increase the difference in detection response capability of incident photons in different directions, and indirectly improve the angular resolution of positioning imaging of gamma photons.

On the other hand, the single crystal stripe can also be a long column structure formed by splicing at least two different types of scintillator crystal material blocks, as shown in fig. 6B, the single crystal stripe 602 is a crystal stripe structure formed by splicing a plurality of first crystal blocks 621 and a plurality of second crystal blocks 622 overlapping each other. Here, there is a certain difference in photon transmission characteristics between the first crystal block 621 and the second crystal block 622. Therefore, the single crystal bar of the long straight cylinder can be directly and physically divided into a plurality of detection units, so that the unit in which photons are specifically deposited can be known, the information quantity which can be used for estimating the photon direction is further increased on the premise of not remarkably increasing the structural complexity, and the detection accuracy and the detection efficiency are improved.

The single crystal strips for detection are required to have the size ratio design of the length-width ratio being greater than or equal to 10:1, and the photoelectric devices coupled at the far end and/or the front end of the single crystal strips are utilized, so that when gamma photons incident in different directions are deposited on the single elongated crystal, obvious response differences can be formed on the coupling end faces of the single elongated crystal along with different irradiation angles and the gamma photons are read out, and therefore the effect of improving the detection efficiency on the direction sensitivity can be remarkably played.

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

As shown in fig. 6B, the first and second crystal blocks 621 and 622 may be scintillator materials, and the first crystal block 621 may be a 200ns block of GAGG material, while the second crystal block 622 may be a 90ns block of GAGG material, which may significantly contribute to the improvement of detection efficiency versus directional sensitivity, as previously described.

On the other hand, the first crystal block 621 and the second crystal block 622 may be two completely different materials, such as the first crystal block 621 may also be a scintillator crystal, and the second crystal block 622 may also be a photoconductive material, such as K9 optical glass (refractive index 1.51, similar to that of the coupler and SiPM element) or HZF-62 optical glass (refractive index 1.92, similar to that of the GAGG crystal). The first crystal blocks 621 and the second crystal blocks 622 are staggered with each other, and can also significantly contribute to the improvement of the detection efficiency with respect to the directional sensitivity.

As shown in fig. 7A-7G, a single crystal bar may include a cylindrical structure with a side view of a quadrilateral, a rhombus, a triangle, a heart, a V, according to embodiments of the present disclosure. As shown in fig. 7A to 7G, the single crystal stripes 701a to 701G of the detector in the embodiment of the present disclosure may be various long pillar structures, such as the pillars 701a and 701G with elongated rectangles in side view projection pattern, the diamond-shaped pillar 701b, the triangular pillar 701c, the parallelogram-shaped pillar 701d, the heart-shaped pillar 701e, the V-shaped pillar 701f, and the like, and due to the irregularity of the shapes thereof, the effect of improving the detection efficiency on the directivity sensitivity can also be achieved, and only the design that the corresponding aspect ratio is greater than or equal to 10:1 needs to be satisfied. Meanwhile, more change forms are provided for the diversification of the single crystal strip, the detection application range of the single crystal strip is remarkably improved, and the application scene of the single crystal strip is more diversified.

For a single crystal bar 701G shown in fig. 7G, it may also be formed by overlapping and combining two materials with different characteristics, such as the aforementioned overlapping between the light guide material and the scintillation crystal, so as to further improve the response difference, more accurately realize the detection of the photon deposition data, obtain higher detection efficiency, and ensure the accuracy of the imaging detection data.

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

The refraction layer covers the front end face of the single crystal strip close to the imaging view field, the refraction layer has a refractive index larger than that of the scintillator material of the single crystal strip, and is used for refracting incident gamma photons and increasing the loss of the gamma photons on the front end face;

the absorption layer covers on the front end face of the single crystal strip close to the imaging visual field or covers on the refraction layer and is used for absorbing incident gamma photons and increasing the loss of the gamma photons on the front end face.

For the case that the photoelectric device is coupled at the far end face far away from the FOV of the imaging field of view, more gamma photons incident on the front end face of a single crystal strip are deposited at the far end of the photoelectric device, and the generated scintillation photons can reach the photoelectric device only through a longer optical path.

In order to further increase the difference between the detection efficiency of the gamma photons which are normally incident on the front end face and the detection efficiency of the gamma photons which are obliquely incident on the front end face, a refractive layer (not shown) may be formed by coating a high refractive index material on the front end face close to the FOV of the imaging field (far away from the first photoelectric device), wherein the refractive index of the high refractive index material may be greater than or equal to that of a single crystal stripe (for example, the refractive index of the GAGG material is 1.91), and the high refractive index material may be titanium dioxide, teflon, barium sulfate, or the like, so as to increase the loss of scintillation photons generated by the gamma photons on the end face and achieve the effect of increasing the response difference of incident photons in different directions. The gamma photons which are normally incident on the front end face of the scintillator are mostly deposited on the front end face and generate scintillation photons on the front end face, so that the loss of the scintillation photons on the front end face can reduce the detection efficiency of the gamma photons which are normally incident on the front end face of the scintillator, and the difference of the detection efficiency of the gamma photons which are incident in other directions is increased.

In addition, on the basis of the design of the refraction layer or directly replacing the design of the refraction layer, a visible photon absorption material can be coated on the end face of the front end to serve as an absorption layer, and the visible photon absorption material can be black adhesive tape or other black substances and the like, so that the loss of scintillation photons generated by gamma photons on the end face is increased, and the effect of improving the response difference of incident photons in different directions is achieved.

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

The single crystal strip can be formed by staggering scintillation crystal blocks with different dopants or staggering scintillation crystal blocks with the same dopant but different doping concentrations. The selected crystal dopant can be Ce, mg, ti and the like, the luminous efficiency and the luminous decay time of the crystal can be obviously changed, and the concentration range of the corresponding dopant can be selected from 0.01-0.6%, so that the difference of the photon detection efficiency of incident photons deposited at different depth positions of the crystal strip is increased. The dopant material of the first crystal block and the second crystal block may be different, for example, the crystal dopant of the first crystal block may be Ce, and the crystal dopant of the second crystal block may be Mg, which are staggered to form the single crystal stripe.

If the ion doping operation of the crystal dopant or the ion doping operation of different concentrations is performed at intervals in the length direction of a single crystal strip, the interleaving of the scintillation crystals with different dopants or the interleaving of the scintillation crystals with the same dopant but different doping concentrations can be formed in the length direction, so that the photon detection efficiency of different depths can be obviously increased, and the corresponding effects of the segmented calibration and the transmission matrix calibration can be conveniently realized. The first crystal block and the second crystal block can be the same dopant material, and the single doping ion concentration can be different, for example, the crystal dopant of the first crystal block and the crystal dopant of the second crystal block can be Ce, the doping ion concentration of Ce of the first crystal block can be 0.01%, and the doping ion concentration of the second crystal block can be 0.26%, and the first crystal block and the second crystal block can be staggered to form the single crystal strip.

Thus, a single crystal strip may be formed with an alternation of different crystal dopants or of the same dopant but different doping concentrations along its length.

According to an embodiment of the present disclosure, the detector further comprises a barrier layer.

The blocking layer is coupled on the end face of the single crystal strip close to the front end of the imaging field of view to block gamma photons which are normally incident towards the end face of the front end.

The front end face of a single crystal strip close to the FOV of the imaging field of view can be covered with a thin sheet layer formed by a high-density material to serve as a blocking layer, normal incidence gamma photons can be blocked remarkably, the detection efficiency of the normal incidence gamma photons is reduced, and therefore the directional response difference is increased. The high-density material may be at least one of heavy metal materials having strong photon-blocking ability, such as tungsten and lead.

The single crystal strip shown in fig. 1 to 7G enables the corresponding gamma imaging device to realize the collimation of photons by using the shape characteristics and properties of the single elongated crystal, and the positioning and imaging of the radioactive source can be realized by only one elongated scintillation crystal and one coupled photoelectric device without using an additional metal collimator or using other crystal detector units. And moreover, the metal collimator does not block photons, the detection efficiency of the device is greatly improved, and the radioactive source positioning device consisting of a single long and thin crystal can realize the double functions of counting and positioning, and is simple in composition and convenient to position.

It should be noted that, the above-mentioned related designs for the single crystal strip according to the embodiments of the present disclosure can more or less significantly improve the detection efficiency and the directional sensitivity, and details are not repeated.

In addition, as shown in fig. 9, a gamma imaging device of a radiation source plane is designed, a front end face of a single crystal strip 901 serving as a detector faces a plane of an imaging field of view FOV, and two-dimensional lattice translation sampling is performed on a plane a corresponding to the imaging field of view FOV along a direction parallel to the imaging field of view FOV, the plane a may have a two-dimensional lattice formed by a plurality of sampling points A1, and a radiation source distribution diagram of the imaging field of view FOV plane may be reconstructed.

As shown in fig. 8A and 8B, another aspect of the present disclosure provides a gamma imaging apparatus, wherein a crystal bar array of at least one single crystal bar and a first circuit board are included.

The crystal strip array formed by at least one single crystal strip is used for detecting incident gamma photons of the imaging field of view through movement relative to the imaging field of view, collimation of the incident gamma photons is achieved, and gamma imaging is achieved, wherein the aspect ratio of the single crystal strip is larger than 10:1;

the first circuit board is coupled with the far end of the crystal strip array far away from the imaging field of view and used for outputting detection data of the crystal strip array on the imaging field of view.

As shown in FIGS. 8A and 8B, the FOV of the imaging field of view (the size of which satisfies 200X 200 mm) may be approached along each single crystal strip ³ ) The front end face of the

crystal strip array

801 and 802 are formed by combining a plurality of single crystal strips in space. When the far end faces of the

crystal bar arrays

801 and 802 as the single-layer detectors are respectively coupled with a layer of

circuit board

803 and 804, the first circuit board is used. A plurality of corresponding first photoelectric devices coupled to the distal end surfaces of the

crystal stripe arrays

801 and 802 may be disposed on the

first circuit boards

803 and 804, so that gamma imaging with high integration and simple structure is realized only by using a single-layer detector + circuit board.

As shown in fig. 8B, according to the embodiment of the disclosure, the gamma imaging apparatus further includes a second circuit board, coupled to a front end of the crystal strip array away from the imaging field of view, for cooperating with the first circuit board to output the detection data of the crystal strip array on the imaging field of view.

As shown in fig. 8B, a layer of

circuit board

803, 804 is coupled to the distal end surface of each of the

crystal stripe arrays

801, 802, and a layer of

circuit board

805, 806 is coupled to the front end surface of each of the

crystal stripe arrays

801, 802 as a second circuit board. A plurality of second photoelectric devices coupled to the front end faces of the

crystal stripe arrays

801 and 802 may be disposed on the

second circuit boards

803 and 804. Therefore, by means of the matching of the second circuit board, the design of the gamma imaging device with the single-layer detector and the front and rear circuit boards can be realized, so that the imaging precision is further improved without obviously increasing the structural complexity.

The

crystal bar arrays

801 and 802 shown in fig. 8A and 8B may be formed by a single elongated scintillation crystal to form a detector module. A plurality of slender single crystals are arranged at intervals to form the detector array, and sampling at different angles is obtained through translational, rotational and other movement detection, so that a better gamma image can be obtained.

As shown in fig. 8B, according to an embodiment of the present disclosure, the gamma imaging device further includes a scintillation crystal layer positioned between the first circuit board and the distal end face of the array of crystal bars to receive remaining scintillation photons passing through the array of crystal bars.

As shown in fig. 8B, on the basis of the array detector module formed by the plurality of crystal bars, a complete scintillation crystal layer 807 may be further coupled to the far end of the crystal module, and the scintillation crystal layer 807 may be located between the first circuit board 803 and the source end face of the crystal bar array 801 to receive the residual penetrating photons, so that a "comb-tooth type" detector array can be formed, thereby further improving the imaging quality.

The single crystal strip unit in the

crystal strip arrays

801 and 802 may be the single crystal strip shown in fig. 1 to 7G, so that the gamma imaging device corresponding to the single crystal strip can collimate photons by using the shape characteristics and properties of the single elongated crystal itself, and only one elongated scintillation crystal can be arranged with each other to form an array without using an additional metal collimator or using other crystal detector units, so as to further realize the positioning and imaging of a radioactive source in the moving detection process of the array, thereby greatly simplifying the design of the system, reducing the weight and volume of the device, and realizing portable imaging, and having low cost.

Therefore, the gamma imaging device can be designed as a brain SPECT imaging device, a single-layer detector is formed by a plurality of crystal array detector modules to form a helmet surrounding the brain of a human body, and the gamma imaging device is portable, flexible and wearable and has extremely high commercial value and scientific research value.

Still another aspect of the present disclosure provides an imaging method applied to the above-described gamma imaging apparatus.

As shown in fig. 5, the gamma imaging device according to the embodiment of the disclosure may be composed of only one elongated scintillation crystal and one photoelectric device. The distribution of the radiation source within the FOV of the imaging field of view is imaged by translational and rotational sampling. And meanwhile, a self-adaptive sampling algorithm is designed, the sampling step length delta x is reduced at the low counting position, and the sampling step length delta x is increased at the high counting position, so that the imaging precision is ensured, the sampling times are reduced as far as possible, and the sampling time is reduced.

For image reconstruction, the SRF of the detector formed by a single crystal strip is in an undershoot shape (as shown in fig. 3), and contrary to a conventional metal collimator detector, filtering is performed by using a Siddon algorithm, and when reconstruction is performed by back projection analysis, the bright part of the reconstructed image represents that the activity of a radioactive source is low, and the dark part represents that the activity of the radioactive source is high, and a forward image representing the distribution of the radioactive source can be obtained by performing value size conversion on the image:

wherein, y' _i Represents the forward distribution graph obtained after transformation, max { y } represents the maximum value in the original reverse graph, and max { y } represents the minimum value in the original reverse graph. If the ML-EM iterative image reconstruction algorithm is adopted, the obtained image is a forward image, and size transformation processing is not needed.

As shown in FIGS. 10A and 10B, in the Monte Carlo simulation verification, when the FOV diameter D is 40mm and the distance D between the detector and the FOV is 45mm, 4.3 × 10 is reached ^-5 The average detection efficiency of the system can distinguish a thermal cylinder with the diameter of 3mm and the circle center distance of 6 mm; when the FOV diameter D is 100mm and the distance D between the detector and the FOV is 45mm, 3.0 x 10 is reached ^-5 The average detection efficiency of the thermal detector can distinguish a thermal cylinder with the diameter of 3mm and the distance between the centers of the circles of 6 mm.

Correspondingly, in practical experimental verification, the imaging performance of the single crystal detector prototype device is tested by building the single crystal detector prototype device as a practical prototype, and 1 multiplied by 20mm is selected ³ The single GAGG (Ce) scintillation crystal strip is used as a detector, two ends of the single GAGG (Ce) scintillation crystal strip are coupled with two SiPM elements, and a translation and rotation platform is used for realizing the imaging of a scanning track and a simulation point source at different positions. As shown in FIG. 11It shows that the reconstruction image effect of single point source, two point sources and four point sources with 6mm distance can be seen from the reconstruction result, when the FOV diameter is 20mm, and the distance d between the detector and the FOV is 45mm, the FOV can reach 1.8 multiplied by 10 ^-5 And two point sources 6mm apart can be clearly resolved, and excellent resolving power is also demonstrated for the distribution of multi-point sources.

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

The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present invention, and should not be construed as limiting the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A gamma imaging apparatus comprising a detector, the detector comprising:

a single crystal strip for movement relative to an imaging field of view to detect incident gamma photons of the imaging field of view, to effect collimation of the incident gamma photons for effecting gamma imaging, wherein the single crystal strip has an aspect ratio greater than 10: 1.

2. The gamma imaging device of claim 1 wherein the single crystal stripe has a detection efficiency for gamma photons at normal incidence near the front of the imaging field of view that is less than the detection efficiency for gamma photons at oblique incidence away from other portions of the imaging field of view; the distance between the front end face of the single crystal strip close to the imaging visual field and the imaging visual field is smaller than or equal to 100mm.

3. The gamma imaging device of claim 1 wherein the detector further comprises:

a first optoelectronic device coupled at a distal end of the single crystal stripe away from the imaging field of view for reading out gamma photon deposition data in the single crystal stripe.

4. The gamma imaging device of claim 1 wherein at least one side surface of the single crystal bar has a surface roughness of 0.01 microns or less.

5. The gamma imaging device of claim 3 wherein the detector further comprises:

and the second photoelectric device is coupled at the front end of the single crystal strip close to the imaging view field, is used for being matched with the first photoelectric device, reads out the gamma photon deposition data and is used for acquiring energy spectrums in different gamma photon deposition depth directions.

6. The gamma imaging device of claim 3 or 5 wherein the detector further comprises:

at least one third optoelectronic device coupled to at least one side surface of the single crystal stripe.

7. The gamma imaging device of claim 1 wherein the single crystal bar comprises:

a plurality of first crystal masses of a first crystal,

the second crystal blocks and the first crystal blocks are arranged in a staggered mode to form a crystal strip structure.

8. The gamma imaging device of claim 7,

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 guide material;

wherein the emission spectrum and the absorption spectrum of the scintillator material partially overlap, and the refractive index of the light guide material is greater than or equal to 1.5.

9. The gamma imaging device of claim 1 wherein the single crystal bar may comprise a cylindrical structure with a side view of a quadrilateral, diamond, triangle, heart, V-shape.

10. The gamma imaging device of claim 2 wherein the detector further comprises:

the refraction layer covers the front end face, close to the imaging view field, of the single crystal strip, the refraction layer is larger than the refraction index of a scintillator material of the single crystal strip and used for refracting the scintillation photons generated by the incident gamma photons and increasing the loss of the scintillation photons on the front end face; and/or

And the absorption layer covers the front end face of the single crystal strip close to the imaging view field or the refraction layer and is used for absorbing scintillation photons generated by the incident gamma photons and increasing the loss of the scintillation photons on the end face of the front end.

11. The gamma imaging device of claim 7 wherein the first and second crystal blocks of the single crystal strip differ in dopant ion concentration and/or dopant material, the dopant ion concentration being between 0.01% and 0.6%.

12. The gamma imaging device of claim 3 wherein the detector further comprises:

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

13. A gamma imaging apparatus, comprising:

an array of crystal stripes of at least one single crystal stripe for movement relative to an imaging field of view to detect incident gamma photons of the imaging field of view, to effect collimation of the incident gamma photons for effecting gamma imaging, wherein the single crystal stripe has an aspect ratio greater than 10:1;

14. The gamma imaging device of claim 13, further comprising:

and the second circuit board is coupled with the front end of the crystal strip array, which is far away from the imaging visual field, and is used for being matched with the first circuit board to output the detection data of the crystal strip array to the imaging visual field.

15. The gamma imaging device of claim 13, further comprising:

a scintillation crystal layer positioned between the first circuit board and the distal end face of the array of crystal bars to receive remaining scintillation photons that pass through the array of crystal bars.

16. A method of imaging by the gamma imaging device of any one of claims 1 to 15.