Gamma imaging device and imaging method thereof

Abstract

The disclosure provides a gamma imaging device and an imaging method thereof, wherein the gamma imaging device comprises a detector comprising a single crystal bar for detecting incident gamma photons of an imaging field of view relative to movement of the imaging field of view, collimation of the incident gamma photons is achieved for realizing gamma imaging, and a length-width ratio of the single crystal bar is greater than 10:1. Therefore, based on the above-mentioned gamma imaging device, a brand-new detector mode is established, an existing external mechanical collimator with low detection efficiency and being bulky and cumbersome is completely abandoned, limitations of a traditional complex detector structure and multiple electronic structures are greatly simplified, and a high-sensitivity minimalist design gamma imaging detection device can be simultaneously achieved.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of radiation imaging, and in particular to a gamma imaging device and an imaging method thereof. BACKGROUND

[0002] Gamma imaging requires that the detector unit has a significant response difference 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 has a large change. Traditionally, a mechanical collimator is usually used to achieve the response difference in different directions, but since the mechanical collimator blocks a large part of the photons from entering the detector, it will cause a serious decline in the overall detection efficiency, and the mechanical collimator is large in volume and weight, making the overall detector heavy and not portable, and the use scene is also more limited. The existing way of using multiple layers of detector units to block "self-collimation" from front to back will cause the response difference, although it avoids the decline in efficiency, but the detector structure is complex, the number of electronic readout channels is large, which often leads to a large volume or high cost of the imaging device. SUMMARY

[0003] (I) Technical problems to be solved

[0004] To solve at least one of the above technical problems in ensuring the significant response difference of photons in the existing gamma imaging technology, the present disclosure provides a gamma imaging device and an imaging method thereof.

[0005] (II) Technical solutions

[0006] One aspect of the present disclosure provides a gamma imaging device, comprising a detector, the detector comprising a single crystal bar 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 gamma imaging, wherein the single crystal bar has an aspect ratio greater than 10:1.

[0007] Preferably, the detection efficiency of the single crystal bar for the normally incident gamma photons near the front end of the imaging field of view is less than that for the obliquely incident gamma photons in other parts away from the imaging field of view; wherein the spacing between the front end surface of the single crystal bar near the imaging field of view and the imaging field of view is less than or equal to 100 mm.

[0008] Preferably, the detector further comprises a first photoelectric device. The first photoelectric device is coupled to the far end of the single crystal bar away from the imaging field of view, for reading out the gamma photon deposition data in the single crystal bar.

[0009] Preferably, the surface roughness of at least one side surface of the single crystal bar is less than or equal to 0.01 microns.

[0010] Preferably, the detector further comprises a second photoelectric device. The second photoelectric device is coupled on the front end of the single crystal bar close to the imaging field of view, for cooperating with the first photoelectric device to read out the gamma photon deposition data for obtaining the energy spectrum in different directions of the depth of the gamma photon deposition.

[0011] According to an embodiment of the present disclosure, the detector further comprises at least one third photoelectric device. The at least one third photoelectric device is coupled on at least one side surface of the single crystal bar.

[0012] 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 are arranged staggered with the plurality of first crystal blocks to form a crystal bar structure.

[0013] Preferably, the first crystal blocks and the second crystal blocks are scintillator materials; or the first crystal blocks are scintillator materials and the second crystal blocks are photoconductive materials; wherein the emission spectrum and the absorption spectrum of the scintillator materials partially overlap, and the refractive index of the photoconductive materials is greater than or equal to 1.5.

[0014] Preferably, the single crystal bar can comprise a column structure with a quadrilateral, rhombus, triangle, heart, or V-shaped side view.

[0015] Preferably, the detector further comprises a refractive layer and / or an absorption layer. The refractive layer is covered on the front end surface 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, for refracting the scintillation photons generated by the incident gamma photons to increase the loss of the scintillation photons on the front end surface; the absorption layer is covered on the front end surface of the single crystal bar close to the imaging field of view, or covered on the refractive layer, for absorbing the scintillation photons generated by the incident gamma photons to increase the loss of the scintillation photons on the front end surface.

[0016] Preferably, the doping ion concentration and / or the dopant material of the first crystal blocks and the second crystal blocks of the single crystal bar are different, and the doping ion concentration is 0.01% to 0.6%.

[0017] Preferably, the detector further comprises a blocking layer. The blocking layer is coupled on the front end surface of the single crystal bar close to the imaging field of view to block the normally incident gamma photons toward the front end surface.

[0018] Another aspect of the present disclosure provides a gamma imaging device, comprising at least one single crystal bar constituting a crystal bar array and a first circuit board. The at least one single crystal bar constituting the crystal bar array is used for moving relative to the imaging field of view to detect the incident gamma photons of the imaging field of view, and for realizing the collimation of the incident gamma photons for realizing the gamma imaging, wherein the aspect ratio of the single crystal bar is greater than 10:1; the first circuit board is coupled with the far end of the crystal bar array away from the imaging field of view, and is used for outputting the detection data of the crystal bar array on the imaging field of view.

[0019] Preferably, the gamma imaging device further comprises a second circuit board coupled with the array of crystal strips at a front end away from the imaging field of view, for cooperating with the first circuit board to output the detection data of the array of crystal strips on the imaging field of view.

[0020] Preferably, the gamma imaging device further comprises a scintillation crystal layer between the first circuit board and the distal end surface of the array of crystal strips, for receiving the remaining scintillation photons passing through the array of crystal strips.

[0021] Another aspect of the present disclosure provides an imaging method of the above-mentioned gamma imaging device.

[0022] (III) Beneficial Effects

[0023] The present disclosure provides a gamma imaging device and an imaging method thereof, wherein the gamma imaging device comprises a 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 realize collimation of the incident gamma photons for realizing gamma imaging, wherein the single crystal strip has an aspect ratio greater than 10:1. Therefore, based on the above-mentioned gamma imaging device, a completely new detector mode is established, completely abandoning the existing external mechanical collimator which has low detection efficiency and is bulky and cumbersome, greatly simplifying the limitations of the traditional complex detector structure and multiple electronic structures, and at the same time, a high-sensitivity minimalist gamma imaging detection device can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A schematic diagram of a single crystal strip 101 as a detector of a gamma imaging device according to an embodiment of the present disclosure and an imaging field of view FOV is shown;

[0025] Figure 2 A schematic diagram of an imaging detection principle of a conventional mechanical collimator 201 and a detector 202 of an existing gamma imaging device relative to a radioactive source position and a corresponding SRF curve diagram are shown;

[0026] Figure 3 A schematic diagram of an imaging detection principle of a single crystal strip 301 as a detector of a gamma imaging device according to an embodiment of the present disclosure relative to a radioactive source position and a corresponding SRF curve diagram are shown;

[0027] Figure 4 A schematic diagram of a rotating detection diagram of a single crystal strip 401 according to an embodiment of the present disclosure is shown;

[0028] Figure 5 A schematic diagram of a moving detection principle top view of a single crystal strip 501 as a detector relative to an imaging field of view FOV according to an embodiment of the present disclosure is shown;

[0029] Figure 6A A structural perspective view of a single crystal bar 601 according to an embodiment of the present disclosure is schematically shown;

[0030] Figure 6B A structural perspective view of a single crystal bar 602 according to an embodiment of the present disclosure is schematically shown;

[0031] Figures 7A-7G Structural side views of single crystal bars 701a-701g according to an embodiment of the present disclosure are schematically shown;

[0032] Figure 8A An imaging composition view of a crystal bar array 801 of a gamma imaging device according to another embodiment of the present disclosure relative to an imaging field of view FOV is schematically shown;

[0033] Figure 8B An imaging composition view of a crystal bar array 802 of a gamma imaging device according to another embodiment of the present disclosure relative to an imaging field of view FOV is schematically shown;

[0034] Figure 9 A schematic diagram of a single crystal bar 901 in a gamma imaging method according to an embodiment of the present disclosure performing two-dimensional lattice translation sampling along a direction parallel to a FOV is schematically shown;

[0035] Figure 10A A hot cylinder reconstruction image of a gamma imaging device according to an embodiment of the present disclosure with an imaging field of view FOV satisfying a 40mm diameter and a distance between a detector and the FOV satisfying 45mm is shown;

[0036] Figure 10B A hot cylinder reconstruction image of a gamma imaging device according to an embodiment of the present disclosure with an imaging field of view FOV satisfying a 100mm diameter and a distance between a detector and the FOV satisfying 45mm is shown;

[0037] Figure 11 A reconstruction image effect diagram of a real prototype device of a gamma imaging device according to an embodiment of the present disclosure on a single point source, a two-point source and a four-point source with a 6mm spacing is shown. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to specific embodiments and the accompanying drawings.

[0039] It should be noted that the implementations described in the specification and illustrated in the drawings are presented by way of example only and are not intended to limit the scope of the disclosure. As such, the implementations should not be construed as being limited to the particular forms described. Rather, the implementations described herein are to be understood as being illustrative of the principles and applications of the present disclosure. Numerous modifications and adaptations thereof will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the present disclosure.

[0040] It should also be noted that the directional terms used in the embodiments, such as "upper", "lower", "front", "back", "left", "right", etc., are merely used with respect to the orientation of the drawings and are not intended to limit the scope of the disclosure. Throughout the drawings, the same elements are denoted by the same or similar reference numerals. When it can cause confusion to the understanding of the disclosure, the conventional structure or configuration will be omitted.

[0041] Also, the shapes and sizes of the components in the drawings do not reflect the actual sizes and proportions and are merely intended to illustrate the content of the embodiments of the present disclosure. In addition, in the claims, any reference symbols located between parentheses should not be construed as limiting the claims.

[0042] Furthermore, the word "comprise" does not exclude the presence of elements or steps not listed in the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

[0043] The use of ordinal numbers such as "first", "second", "third", etc. used in the specification and claims is intended to modify a respective element and does not require the element to have any ordinal number, nor does it require the order or sequence of the manufacturing method, and the use of such ordinal numbers is merely intended to distinguish the element having the certain name from another element having the same name.

[0044] Those skilled in the art will understand that the modules in the devices in the embodiments can be adaptively changed and arranged in one or more devices different from the embodiments. The modules or units or components in the embodiments can be combined into one module or unit or component, and furthermore can be divided into multiple sub-modules or sub-units or sub-components. Except that at least some of such features and / or processes or units are mutually exclusive, all combinations of all features disclosed in the specification (including the accompanying claims, abstract and drawings) and all processes or units of any methods or apparatuses disclosed can be used. Unless explicitly stated otherwise, each feature disclosed in the specification (including the accompanying claims, abstract and drawings) can be replaced by an alternative feature providing the same, equivalent or similar purpose. Also, in a unit claim listing several devices, several of these devices can be embodied by one and the same hardware item.

[0045] Similarly, it is to be understood that the features of the disclosure sometimes are grouped together in a single embodiment, figure or description thereof for clarity purpose and in order to streamline the disclosure and help promote an understanding of one or more aspects of the disclosure. Nonetheless, the disclosure should not be construed so as to reflect an intention that the claimed disclosure is any less than all aspects reflected in each claim. Rather, the disclosure aspects are in the claims as reflected in the claims section below, less than all features of the single embodiments disclosed earlier. As such, the claims following the detailed description are hereby expressly incorporated into this detailed description, wherein each independent claim stands on its own as a separate embodiment.

[0046] To solve at least one of the above technical problems in ensuring the obvious response difference of photons in the existing gamma imaging technology, the disclosure provides a gamma imaging device and an imaging method thereof.

[0047] As shown in the figure, one aspect of the disclosure provides a gamma imaging device, which includes a detector including a single crystal bar for detecting incident gamma photons of an imaging field of view (FOV) relative to the movement of the imaging FOV, achieving the collimation of the incident gamma photons for realizing gamma imaging, wherein the aspect ratio of the single crystal bar is greater than 10:1. Figure 1 For the gamma imaging device, the detector as the part between the imager and the imaging FOV to achieve gamma photon detection is the most critical component of the device, which can significantly affect the detection efficiency of gamma photons.

[0048] The common detector generally needs to use a mechanical collimator to collimate the photons before entering the detector to achieve the response difference of gamma photons in different directions in the detector. In the gamma imaging device of the embodiment of the disclosure, the traditional collimator design is directly abandoned, and only a single crystal bar 101 is set as the detector between the gamma imaging FOV and the imager (not shown), and the differential response of different gamma photons is realized by moving the single crystal bar relative to the imaging FOV, thereby greatly simplifying the composition structure of the gamma imaging device while ensuring the detection efficiency. The number of single crystal bars can be only one. The imaging 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.

[0049]

[0050] ​In the embodiments of the present disclosure, the detection efficiency of the single crystal bar 101 as a detector is related to the solid angle of its relative position to the radiation source (which can be understood as the imaging field of view FOV). Compared with the conventional square detector unit which is not sensitive to the change of the incident direction of gamma photons, the single crystal bar 101 of the embodiments of the present disclosure has a significantly increased aspect ratio. When the gamma photons are normally incident on the front end surface 110 of the single crystal bar, the imaging solid angle formed by the single crystal bar is the smallest, and the photon detection efficiency is the lowest. When the incident direction of the photons is deflected from the normal incidence on the front end surface to the far end surface 120 of the single crystal bar, the photon detection efficiency will be significantly and rapidly improved, thereby being able to bring a better directional positioning effect. Wherein, at the same time, the front end surface 110 is the end surface of the single crystal bar which is closer to the position of the radiation source (i.e. the front end), and the far end surface 120 is the end surface of the single crystal bar which is farther away from the position of the radiation source (i.e. the far end) relative to the front end surface 110, and the front end and the far end respectively constitute the two ends of the single crystal bar.

[0051] Therefore, in order to ensure that the single crystal bar can have more stable detection effect during the detection process, while taking into account the higher detection efficiency, in the specific detection process, the detector of the single crystal bar 101 needs to be moved. The movement can be at least one of translation including linear or curved direction in space, rotation around a fixed point or moving point as the center in space, or rotation around the rotation. As shown in FIG. 5, the single crystal bar 501 is translated in a unit sampling step Δx (Translation Step) around the imaging field of view FOV with a diameter size of D (Diameter of FOV) in a space plane, and is rotated in combination with a unit sampling angle Figure 5 to complete the movement detection of the rotation range with a rotation angle (Projection Angle) of , wherein satisfies Therefore, by means of the movement of the single crystal bar 101 described above, the position or angle of the single crystal bar relative to the radiation source (imaging field of view FOV) can be changed, thereby being able to detect the incident photons and produce more diversified and differentiated detection solid angles, so as to significantly improve the detection efficiency and have a more accurate directional positioning effect.

[0052] ​Further, in the embodiments of the present disclosure, the single crystal bar 101 has an elongated structure, and in a structure side view of the single crystal bar 101 in the length direction (understood as a projection view of the side view angle), the ratio of the length L of the view to the maximum width dimension W / G (for example, W> G, then L:W is determined, otherwise, L:G is determined) is greater than or equal to 10:1, that is, the aspect ratio of the single crystal bar is greater than 10:1. In this way, it can be ensured that the single crystal bar 101 can have a better imaging solid angle in the subsequent movement detection process of the single crystal bar 101, the difference in photon detection efficiency is increased, and better directional positioning effect is brought. In other words, the greater the aspect ratio of the single crystal bar, the greater the difference in detection efficiency of the crystal to the normal incidence and oblique incidence of the gamma photons, and the more sensitive to the incidence direction of the gamma photons, thereby bringing a better directional positioning effect. Therefore, the single crystal bar with the aspect ratio value can provide a device for gamma imaging detection with high sensitivity and extremely simple structure design when used as a detector alone.

[0053] Therefore, based on the above-mentioned gamma imaging device, a completely new detector mode is established, which can only use a single crystal bar 101 as a detector to collimate and detect incident photons, completely abandoning the existing external mechanical collimator with low detection efficiency and cumbersome and bulky inconvenience, greatly simplifying the traditional complex detector structure, breaking the traditional limitations of multiple electronic structures, and simultaneously providing a gamma imaging detection device with high sensitivity and extremely simple design. The structure design is extremely simple, light and portable, and is suitable for various imaging scenes that require mobile and portable applications.

[0054] As shown in Figure 2 and Figure 3 According to the embodiments of the present disclosure, the detection efficiency of the single crystal bar 301 for the gamma photons incident at the front end of the imaging field of view FOV is less than that of the gamma photons incident obliquely at other parts away from the imaging field of view FOV; wherein the distance between the front end surface 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.

[0055] Since the above-mentioned single crystal bar 301 or 101 is used alone as a detector, the mechanical collimator is directly omitted, so that the crystal response function (Scintillator response function, abbreviated as SRF, which represents the detection efficiency of the gamma photons at different positions in the imaging field of view FOV) of the detector of the embodiments of the present disclosure is significantly different from that of the conventional detector. As shown in Figure 2 In the conventional design of the detector 202 composed of multiple crystal units with a metal mechanical collimator 201, the photon detection efficiency is the highest in the direction opposite to the detector 202, and the detection efficiency is almost zero in other directions due to shielding. Correspondingly, when the position of the radiation source is in the central position, the SRF is the highest. Conversely, as shown inFigure 3 As shown, in the scheme of the embodiment of the present disclosure without a metal mechanical collimator and only adopting a single crystal bar 301 as a detector, since the single thin elongated crystal bar 301 has the lowest detection efficiency and the lowest SRF when collimating the front end face, the detection efficiency of other directions is relatively high and can maintain a relatively high and stable level, that is, the detection efficiency of the single crystal bar to the gamma photons orthogonally incident on the proximal end face is less than the detection efficiency of the 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 of the front end face, and the detection efficiency of different angle incident particles is not completely the same, and the relative size of the response of the detector at different positions can be used to judge the activity distribution of the radioactive source in different incident directions, so as to take into account all positions instead of limiting the sensitive position to a small angle range of the collimator opening, which makes the relationship between the detection efficiency and the position of the radioactive source completely opposite to the conventional design.

[0056] Therefore, based on the above detection principle, a simple radioactive source counting and positioning device can be designed, in which the detector is only composed of a single thin elongated crystal bar. The detector can move in the 4-pi space for detection, and the position with the lowest counting is directed to the direction of the radioactive source. The detection efficiency of the detector is positively correlated with the solid angle of the single crystal to the position of the radioactive source, and the detection efficiency is seriously lost with the increase of the distance between the crystal and the imaging field of view (FOV). Therefore, the detector should be as close to the imaging FOV as possible, specifically, the distance d between the single crystal bar of the detector and the imaging FOV can be less than or equal to 100 mm (such as d = 40 mm as shown), and the elements and tool settings facing the imaging FOV end face need to be simplified. Figure 5

[0057] Unlike the characteristics that the metal collimator detector and the self-collimating detector only respond to photons incident in certain directions, the single thin elongated crystal bar takes into account other positions while responding low to the target position, has a large sensitive range, and only needs a small amount of position information combination to reconstruct a complete image, which can greatly reduce the sampling positions. Therefore, the gamma imaging device of the embodiment of the present disclosure can have a more flexible sampling scheme when imaging the radioactive source, specifically, the sampling step can be adaptively adjusted according to the counting of the detector, the sampling times are reduced, and the sampling time is reduced without reducing the imaging accuracy.

[0058] According to the embodiment of the present disclosure, the detector further comprises a first photoelectric device 402.

[0059] ​The first photoelectric device 402 is coupled at a distal end of the single crystal strip 401 away from the imaging field of view for reading out the gamma photon deposition data in the single crystal strip 401.

[0060] For the radioactive source imaging device, only one single crystal strip 401 and one photoelectric device 402 are used. The radioactive source distribution in the imaging field of view FOV can be imaged by translational and rotational sampling. The translation can be a linear or curved translation in space, and the rotation can be a rotation around a fixed point or a moving point as the center, such as Figure 4 As shown in the figure, the detector has a single crystal strip 401 and a photoelectric device 402 disposed at the distal end of the single crystal strip 401, and the single crystal strip 401 can be rotated around the center in the length direction to achieve a 0-180° detection effect relative to the imaging field of view FOV.

[0061] The first photoelectric device 402 can be a silicon photomultiplier (SiPM), and coupling the photoelectric device 402 at the distal end of the single crystal strip 401 away from the imaging field of view FOV can achieve single-end reading of photon deposition data. In addition, the front end of the single crystal strip 401 near 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 close detection to the imaging field of view FOV.

[0062] According to an embodiment of the present disclosure, the surface roughness of at least one side surface of the single crystal strip is less than or equal to 0.01 microns.

[0063] For the single crystal strip of the embodiment of the present disclosure, it can be a scintillation crystal strip for detection, which can meet the transmission requirements of scintillation photons inside, and the single crystal strip can be a cylindrical, cuboid or other long column structure, as long as the aspect ratio of its side view is greater than or equal to 10:1.

[0064] In addition, on the basis of the above, the side surface of the column of the single crystal strip can also be treated (such as polished) to have good 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. Specifically, 2000-grit sandpaper can be used for polishing, so that the mirror reflection capability of the smooth surface can be used to further improve the transmission efficiency of scintillation photons in the single crystal strip, thereby effectively solving the problem of long transmission distance of scintillation photons in the long crystal strip and serious light loss, which can significantly improve the photon transmission efficiency and obtain better detection spectrum, thereby improving the detection efficiency and directional positioning accuracy.

[0065] Based on the above, in a specific imaging application, the imaging device needs to be calibrated with a transmission matrix. The specific steps are to divide the imaging field of view (FOV) into grid points with pixel size as the step, place a point source at each grid point, and measure the projection data with a single crystal bar of the detector. The projection data of each position point source is combined to obtain the transmission matrix. In this calibration process, since the detector is only composed of a single crystal bar without a mechanical collimator and complex mutual shielding between crystals, the SRF value has a strong symmetry (as shown in Figure 3 Therefore, the calibration steps of the transmission matrix can be greatly simplified. Specifically, only the projection of the single crystal bar of the detector at the middle position needs to be measured, and then the translation and rotation of the SRF are used to extend to other positions, so that the complete transmission matrix can be obtained, and the measurement time required for each radiation source position is shorter, thereby greatly shortening the transmission matrix calibration time, speeding up the data processing speed, and improving the imaging efficiency.

[0066] According to an embodiment of the present disclosure, the detector further comprises a second photoelectric device (not shown).

[0067] 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 in cooperation with the first photoelectric device to read out the gamma photon deposition data for obtaining the energy spectrum in the direction of different gamma photon deposition depths.

[0068] In addition, while the first photoelectric device is coupled to the distal end of the single crystal bar of the detector, another second photoelectric device can also be coupled to the front end of the single crystal bar of the detector to read out the photon deposition data from the front end, so that the readout data of the first photoelectric device can be combined more effectively, and the photon position in the single crystal bar of the detector can be calculated more accurately. The second photoelectric device can also be a silicon photomultiplier (SiPM).

[0069] Further, by coupling one SiPM photoelectric element as a photoelectric device at each end of the single crystal bar, the position data in the direction of the gamma photon deposition depth can be calculated more accurately, so that in the subsequent data processing process for imaging, the segmented calibration of the energy spectrum statistically obtained at different depths can be realized. For example, for a single crystal bar of 1×1×20mm 3 , it can be divided into 10 depth segments of 2mm, and the photon energy spectrum of each segment is calibrated separately to improve the overall energy resolution. The specific calibration steps include: first, flood irradiation of the single crystal bar, and then energy calibration of the depth direction position of the photons by detecting the scintillation photon energies E a and E b coupled at both ends of the single crystal bar.

[0070]

[0071] wherein P(z) is the action position in the depth direction, k and t are fitting coefficients, which can be calibrated by experiments.

[0072] Afterwards, the energy correction of the corresponding coefficient is performed on each incident photon event according to its falling position in the depth section. In this way, the problem of poor measured energy spectrum caused by serious light loss due to long transmission distance of scintillation photons in the slender crystal bar can be well solved by the double-end coupled photoelectric device, and the detection efficiency is significantly improved.

[0073] According to an embodiment of the present disclosure, the detector further comprises at least one third photoelectric device.

[0074] The at least one third photoelectric device is coupled on at least one side surface of the single crystal bar.

[0075] To further avoid the problem of serious light loss and poor measured energy spectrum caused by long transmission distance of scintillation photons in the slender crystal bar, the number of photoelectric devices coupled on the side surface of the columnar body of the single crystal bar detector can be increased to realize side reading, thereby significantly increasing the light emitting surface, reducing the transmission light loss of photons in the single crystal bar, and combining the double-end reading design of the first photoelectric device and the second photoelectric device, the poor energy spectrum condition can be further improved, and the photon detection efficiency is significantly improved. The third photoelectric device can also be a silicon photomultiplier (SiPM).

[0076] As shown in Figures 6A-6B According to an embodiment of the present disclosure, the single crystal bar comprises a plurality of first crystal blocks and a plurality of second crystal blocks.

[0077] The plurality of second crystal blocks and the plurality of first crystal blocks are arranged alternately to form a crystal bar structure.

[0078] As shown in Figure 6A In the embodiment of the present disclosure, the single crystal bar 601 as the detector can be a long columnar scintillation crystal bar, which can select a scintillator material with at least partially overlapping emission spectrum and absorption spectrum, such as Cerium-doped Gadolinium Aluminum Gallium Garnet (GAGG(Ce) or GAGG), thereby further increasing the difference in detection response capability of photons incident in different directions, and indirectly improving the angle resolution of gamma photon positioning imaging.

[0079] On the other hand, the single crystal bar can also be a long columnar structure composed of at least two blocks of scintillation crystal materials with different characteristics, as shown in Figure 6BAs shown, the single crystal bar 602 is composed of a crystal bar structure formed by a plurality of first crystal blocks 621 and a plurality of second crystal blocks 622 which are spliced with each other. The first crystal blocks 621 and the second crystal blocks 622 have certain differences in photon transmission characteristics. In this way, the single crystal bar of a long straight column can be directly physically divided into a plurality of detection units, so that it can be known that the photons are deposited in which unit, the amount of information available for photon direction estimation is further increased without significantly increasing the structural complexity, and the detection accuracy and detection efficiency are improved.

[0080] The single crystal bar for detection needs to have a size ratio design with a length-width ratio greater than or equal to 10:1, and a photoelectric device is coupled at the distal end and / or the front end, so that the gamma photons incident in different directions are deposited in the single elongated crystal, and obvious response differences are formed on the coupling end face with different illumination angles, which can significantly improve the detection efficiency and direction sensitivity.

[0081] 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 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.

[0082] As shown in the figure, Figure 6B 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 200 ns GAGG material block, and the second crystal block 622 can be a 90 ns GAGG material block. As mentioned above, it can significantly improve the detection efficiency and direction sensitivity.

[0083] On the other hand, the first crystal block 621 and the second crystal block 622 can also be two completely different materials. For example, the first crystal block 621 can also be a scintillation crystal, and the second crystal block 622 can also be a light guide material, such as K9 optical glass (refractive index 1.51, which is close to the refractive index of the coupling agent and the SiPM element) or HZF-62 optical glass (refractive index 1.92, which is close to the refractive index of the GAGG crystal). The first crystal block 621 and the second crystal block 622 are arranged alternately, which can also significantly improve the detection efficiency and direction sensitivity.

[0084] As shown in the figure, Figures 7A-7G According to an embodiment of the present disclosure, the single crystal bar can include a column structure with a quadrilateral, rhombus, triangle, heart, or V-shaped side view. Figures 7A-7GAs shown, the single crystal bar 701a-701g of the present disclosure as a detector can be various long column structures, such as the column 701a and 701g with a long and narrow rectangular shape, the column 701b with a rhombus shape, the column 701c with a triangle shape, the column 701d with a parallelogram shape, the column 701e with a heart shape, and the column 701f with a V shape, etc. Due to the irregularity of the shape, the single crystal bar can also improve the detection efficiency and directionality sensitivity, as long as the corresponding length-width ratio is greater than or equal to 10:1.

[0085] As shown, the single crystal bar 701g can also be composed of the overlapping combination of two different characteristic materials, such as the overlapping between the light guide material and the scintillation crystal as described above, so as to further improve the response difference, more accurately realize the detection of photon deposition data, and obtain higher detection efficiency while ensuring the accuracy of imaging detection data. Figure 7G

[0086] According to the embodiments of the present disclosure, preferably, the detector further comprises a refractive layer and / or an absorption layer.

[0087] The refractive layer is covered on the front end surface of the single crystal bar close to the imaging field of view, and the refractive index of the refractive layer is greater than that of the scintillator material of the single crystal bar, for refracting the incident gamma photons and increasing the loss of the gamma photons on the front end surface.

[0088] The absorption layer is covered on the front end surface of the single crystal bar close to the imaging field of view, or covered on the refractive layer, for absorbing the incident gamma photons and increasing the loss of the gamma photons on the front end surface.

[0089] For the case of coupling the photoelectric device on the far end surface away from the imaging field of view FOV, more gamma photons incident on the front end surface of the single crystal bar are deposited on the far end thereof, and the generated scintillation photons need to pass through a longer optical path to reach the photoelectric device. Due to the self-absorption of the scintillation crystal, part of the signal will be lost, resulting in a relatively reduced detection efficiency, thereby increasing the difference in detection efficiency of the photons incident from other directions.

[0090] ​To further increase the difference between the detection efficiency of the gamma photons normally incident on the front end surface and the gamma photons obliquely incident on the front end surface, a high refractive index material can be coated on the front end surface (far from the first photoelectric device) near the imaging field of view FOV 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), which can be titanium dioxide, Teflon, barium sulfate, etc. to increase the loss of scintillation photons generated by gamma photons on the end surface, so as to improve the response difference of photons incident in different directions. Among them, the gamma photons normally incident on the front end surface of the scintillator are mostly deposited on the front end surface and generate scintillation photons on the front end surface, so that the loss of scintillation photons on the front end surface can reduce the detection efficiency of gamma photons normally incident on the front end surface of the scintillator, thereby increasing the detection efficiency difference of gamma photons incident in other directions.

[0091] In addition, on the basis of the above refractive layer design or directly replacing the above refractive layer design, a visible photon absorbing material can be coated on the front end surface as an absorbing layer, which can be black tape or other black substances, etc. to increase the loss of scintillation photons generated by gamma photons on the end surface, so as to improve the response difference of photons incident in different directions.

[0092] According to embodiments of the present disclosure, the first crystal block and the second crystal block of the single crystal bar are different in doping ion concentration and / or dopant material, and the doping ion concentration is 0.01% to 0.6%.

[0093] The single crystal bar can be an alternating arrangement of scintillation crystal blocks of different dopants or an alternating arrangement of scintillation crystal blocks of the same dopant but different doping concentrations. The selected crystal dopant can be Ce, Mg, Ti ions, which can significantly change the light emission efficiency and light emission decay time of the crystal, and the corresponding dopant concentration range is 0.01% to 0.6% selectable, so that the photon detection efficiency difference of incident photons deposited at different depths of the crystal bar is increased. 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, and the alternating arrangement of the two can form the above-mentioned single crystal bar.

[0094] Wherein, if the ion doping operation of the crystal dopant or the ion doping operation of different concentrations is carried out at a certain interval in the length direction of the single crystal strip, the staggered scintillation crystals of different dopants or the staggered scintillation crystals of the same dopant but different doping concentrations can be formed in the length direction, so that the photon detection efficiency at different depths can also be significantly increased, and the corresponding effects of the above-mentioned such as segmented calibration and transmission matrix calibration can be easily realized. Wherein, 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 dopants of the first crystal block and the second crystal block can both 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%. The staggered arrangement of the two can constitute the above-mentioned single crystal strip.

[0095] Therefore, the single crystal strip can form a staggered arrangement of different crystal dopants or a staggered arrangement of the same dopant but different doping concentrations along the length direction thereof.

[0096] According to an embodiment of the present disclosure, the detector further comprises a blocking layer.

[0097] The blocking layer is coupled to the end surface of the single crystal strip near the front end of the imaging field of view to block the normally incident gamma photons toward the end surface of the front end.

[0098] A sheet layer formed of a high-density material can be covered on the front end surface of the single crystal strip near the imaging field of view FOV as the blocking layer, which can significantly block the normally incident gamma photons and reduce the detection efficiency of the normally incident gamma photons, thereby increasing the directional response difference. Wherein, the high-density material can be at least one of tungsten, lead and other heavy metal materials with strong photon blocking ability.

[0099] The above Figures 1-7G The single crystal strip shown enables the corresponding gamma imaging device to realize collimation of photons by using the shape characteristics and properties of the single thin and long crystal itself, without the aid of an additional metal collimator or the use of other crystal detector units. The positioning and imaging of the radiation source can be realized by only one thin and long scintillation crystal and one coupled photoelectric 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, portable imaging can be realized, and the cost is low. Moreover, without the blocking of the metal collimator to the photons, the detection efficiency of the device itself is greatly improved, and the radiation source positioning device composed of a single thin and long crystal can realize the dual functions of counting and positioning, has a simple structure, and is convenient to position.

[0100] It should be noted that the above-mentioned related designs of the single crystal bar for the embodiments of the present disclosure can more or less significantly improve the detection efficiency and direction sensitivity, which will not be described in detail.

[0101] In addition, as Figure 9 indicated, a gamma imaging device is designed, in which the front end face of the single crystal bar 901 as the detector directly faces the imaging field of view FOV plane, and two-dimensional lattice translation sampling is performed on the plane A corresponding to the imaging field of view FOV in the direction parallel to the imaging field of view FOV, and the plane A can have a two-dimensional lattice composed of multiple sampling points A1, and the radioactive source distribution map of the imaging field of view FOV plane can be reconstructed.

[0102] As Figure 8A and Figure 8B indicated, 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.

[0103] The crystal bar array composed of at least one single crystal bar is used for movement relative to the imaging field of view to detect incident gamma photons of the imaging field of view, and realizes collimation of the incident gamma photons for gamma imaging, wherein the aspect ratio of the single crystal bar is greater than 10:1;

[0104] 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 for outputting the detection data of the imaging field of view by the crystal bar array.

[0105] As Figure 8A and Figure 8B indicated, multiple single crystal bars can be combined in space along the plane where the front end face of each single crystal bar close to the imaging field of view FOV (the size meets 200x200x200mm 3 ) is located to form a crystal bar array 801, 802. A layer of circuit board 803, 804 is coupled to the far end face of the crystal bar array 801, 802 as a single layer detector, respectively, to serve as the first circuit board. Among them, the first circuit board 803, 804 can be arranged with a plurality of first optoelectronic devices corresponding to the far end face of the above-mentioned crystal bar array 801, 802, so as to realize high integration and simple structure of the gamma imaging device with only single layer detector + circuit board.

[0106] As Figure 8B indicated, according to the embodiments of the present disclosure, the above-mentioned 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 for cooperating with the first circuit board to output the detection data of the imaging field of view by the crystal bar array.

[0107] As Figure 8BAs shown, based on the distal end faces of crystal bar arrays 801 and 802, respectively, a circuit board 803 and 804 are coupled, and on the front end faces of the same crystal bar arrays 801 and 802, a circuit board 805 and 806 are coupled, serving as a second circuit board. Multiple second optoelectronic devices coupled to the front end faces of the crystal bar arrays 801 and 802 can be arranged on these second circuit boards 803 and 804. Therefore, by utilizing these second circuit boards, a gamma imaging device design with a single-layer detector and two circuit boards can be realized, further improving its imaging accuracy without significantly increasing structural complexity.

[0108] Among them, the above Figure 8A and Figure 8B The crystal bar arrays 801 and 802 shown can be composed of detector modules made up of slender single scintillation crystals. Multiple slender single crystals are arranged at intervals to form this detector array. By moving and rotating the crystals, samples are obtained from different angles, thus enabling the acquisition of better gamma images.

[0109] like Figure 8B As shown, according to an embodiment of the present disclosure, the gamma imaging device further includes a scintillation crystal layer located between the first circuit board and the distal end face of the crystal bar array to receive residual scintillation photons passing through the crystal bar array.

[0110] like Figure 8B As shown, based on the array detector module formed by the above-mentioned multiple crystal strips, 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 strip array 801 to receive the remaining transmitted photons, thereby forming a "comb-shaped" detector array, which can further improve the imaging quality.

[0111] Among them, the single crystal bar unit in the crystal bar arrays 801 and 802 can be the above-mentioned Figures 1-7G The single crystal strip shown enables the corresponding gamma imaging device to collimate photons using the shape and properties of the single slender crystal itself. It does not require an external metal collimator or other crystal detector units. It can be formed by arranging a series of slender scintillation crystals to form an array. During the moving detection process of this array, the radioactive source can be located and imaged, which greatly simplifies the system design, reduces the weight and size of the equipment, enables portable imaging, and is inexpensive.

[0112] As can be seen, the gamma imaging device described in this embodiment can be designed as a brain SPECT imaging device, using multiple crystal array detector modules to form a single-layer detector to form a helmet surrounding the human brain. It is lightweight, flexible, and wearable, and has extremely high commercial and scientific research value.

[0113] Another aspect of the present disclosure provides an imaging method applied to the above-mentioned gamma imaging device.

[0114] As shown in Figure 5 , the above-mentioned gamma imaging device of the embodiment of the present disclosure can be composed of only one elongated strip-shaped scintillation crystal and one photoelectric device. The distribution of the radioactive source in 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 Δx at low counts and increase the sampling step Δx at high counts, so as to reduce the sampling time as much as possible while ensuring the imaging accuracy.

[0115] For image reconstruction, the SRF of the detector composed of a single crystal strip is of a down-convex shape (as shown in Figure 3 ), which is contrary to the conventional metal collimator detector. When the Siddon algorithm is used for filtering and back-projection analytical reconstruction, the bright part of the reconstructed image represents a low radioactive source activity, and the dark part represents a high radioactive source activity. The magnitude transformation processing of the image is required to obtain the forward image representing the radioactive source distribution:

[0116]

[0117] , wherein y' i represents the forward distribution image obtained after transformation, max{y} represents the maximum value in the original back-projection image, and max{y} represents the minimum value in the original back-projection image. If the ML-EM iterative image reconstruction algorithm is used, the obtained image is a forward image, and no magnitude transformation processing is required.

[0118] As shown in Figure 10A and Figure 10B , 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 reaches 4.3×10 -5 , and a hot 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 reaches 3.0×10 -5 , and a hot cylinder with a diameter of 3 mm and a center distance of 6 mm can be distinguished.

[0119] Correspondingly, in the actual experimental verification, a single-crystal detector prototype device is built as an actual prototype to test its imaging performance. A single GAGG(Ce) scintillation crystal strip with a size of 1×1×20 mm 3 is selected as the detector, two SiPM elements are coupled at both ends, and a translational and rotational platform is used to realize the imaging of the scanning track and the simulated point source at different positions. As shown in Figure 11It can be seen from the reconstruction results that the reconstruction image effects of the single-point source, the two-point source and the four-point source with a 6mm interval can be achieved, when the diameter of the FOV is 20mm and the distance d between the detector and the FOV is 45mm, the average detection efficiency can reach 1.8×10 -5 and the two point sources with a 6mm interval can be clearly distinguished, and the multi-point source distribution also shows excellent resolution.

[0120] Thus far, the embodiments of the present disclosure have been described in detail in conjunction with the accompanying drawings.

[0121] The above-described specific embodiments further specifically describe the purposes, technical solutions and beneficial effects of the present disclosure, and it should be understood that the above-described specific embodiments are merely specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A gamma imaging device, wherein, The detector comprises: a single crystal bar for detecting incident gamma photons of an imaging field of view relative to movement of the imaging field of view to realize collimation of the incident gamma photons for realizing gamma imaging, wherein an aspect ratio of the single crystal bar is greater than 10:1, the movement comprises translation and rotation; a detection efficiency of a front end of the single crystal bar close to the imaging field of view for normally incident gamma photons is less than a detection efficiency of other surfaces close to the front end of the imaging field of view and other surfaces for obliquely incident gamma photons; the single crystal bar comprises: a plurality of first crystal blocks, and a plurality of second crystal blocks staggered with the plurality of first crystal blocks to form a crystal bar structure.

2. The gamma imaging device of claim 1, wherein, A spacing 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.

3. The gamma imaging apparatus of claim 1, wherein, The detector further comprises: a first photoelectric device coupled to a far end of the single crystal bar away from the imaging field of view for reading out gamma photon deposition data in the single crystal bar.

4. The gamma imaging device of claim 1, wherein, A surface roughness of at least one side surface of the single crystal bar is less than or equal to 0.01 microns.

5. The gamma imaging apparatus of claim 3, wherein, The detector further comprises: a second photoelectric device coupled to the front end of the single crystal bar close to the imaging field of view for reading out the gamma photon deposition data in cooperation with the first photoelectric device to obtain energy spectra in different gamma photon deposition depth directions.

6. The gamma imaging apparatus of claim 3 or 5, wherein, The detector further comprises: at least one third photoelectric device coupled to at least one side surface of the single crystal bar.

7. The gamma imaging apparatus of claim 1, wherein: the first crystal blocks and the second crystal blocks are scintillator materials; or the first crystal blocks are scintillator materials, and the second crystal blocks are light guide materials; wherein an emission spectrum and an absorption spectrum of the scintillator materials partially overlap, and a refractive index of the light guide materials is greater than or equal to 1.

5.

8. The gamma imaging device of claim 1, wherein, The single crystal bar can comprise a column structure with a side view of a quadrilateral, a rhombus, a triangle, a heart shape, or a V shape.

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

10. The gamma imaging apparatus of claim 1, wherein, The first crystal blocks and the second crystal blocks of the single crystal bar are different in a doping ion concentration and / or a dopant material, and the doping ion concentration is 0.01% to 0.6%.

11. The gamma imaging apparatus of claim 3, wherein, The detector further comprises: a blocking layer coupled to the front end face of the single crystal bar close to the imaging field of view to block normally incident gamma photons toward the front end face.

12. A gamma imaging device, wherein, The detector comprises: A crystal bar array of at least one single crystal bar for detecting incident gamma photons of an imaging field of view with respect to movement of the imaging field of view to achieve collimation of the incident gamma photons for gamma imaging, wherein a length to width ratio of the single crystal bar is greater than 10:1, the movement includes translation and rotation; a front end of the single crystal bar proximate to the imaging field of view has a detection efficiency for normally incident gamma photons less than a detection efficiency for obliquely incident gamma photons at other surfaces proximate to the front end of the imaging field of view; a first circuit board coupled to a distal end of the crystal bar array distal to the imaging field of view for outputting detection data of the imaging field of view by the crystal bar array; the single crystal bar includes: a plurality of first crystal blocks, and a plurality of second crystal blocks interleaved with the plurality of first crystal blocks to form a crystal bar structure.

13. The gamma imaging device of claim 12, wherein, Further comprising: a second circuit board coupled to a front end of the crystal bar array proximate to the imaging field of view for outputting detection data of the imaging field of view by the crystal bar array in cooperation with the first circuit board.

14. The gamma imaging device of claim 12, wherein, Further comprising: a scintillation crystal layer between the first circuit board and a distal end surface of the crystal bar array for receiving residual scintillation photons passing through the crystal bar array.

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