Hyperhole collimator for gamma photon detection and nuclear medicine imaging system

Abstract

The super-hole collimator for gamma photon detection and the nuclear medicine imaging system provided by the utility model are provided with the collimator plate, the plurality of collimating holes which are irregularly distributed or randomly distributed are formed in the collimator plate, and when radioactive rays in an imaging view pass through the collimating holes and then form projection overlapping on a gamma photon detector, the radioactive rays are irradiated by the gamma photon detector. The orientation of the collimation hole should meet the requirement that the normal vector of the central plane of the collimation hole passes through the center of the imaging view, and the field angle of the collimation hole should meet the requirement that the extension lines of the two edges of the collimation hole are tangent to the imaging view. According to the multi-pinhole collimator, the limitation of a pinhole arrangement mode in a traditional multi-pinhole collimator on the number of pinholes is effectively overcome, a certain number of collimation holes are randomly arranged on the collimator, and the number of the collimation holes is far larger than that of the pinholes in the existing multi-pinhole collimator; the projection overlapping area of radioactive rays on the detector after passing through all the collimation holes in the imaging view field is improved, a super-hole collimator is formed, and the detection efficiency is remarkably improved on the premise that the image resolution is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of nuclear medicine imaging technology, and specifically relates to a super-aperture collimator for gamma photon detection used to improve the sensitivity of single-photon emission computed tomography (SPECT) in nuclear medicine imaging systems, and a nuclear medicine imaging system having the super-aperture collimator. Background Technology

[0002] Single-photon emission computed tomography (SPECT) is an important nuclear medicine imaging technique, widely used in preclinical drug research and clinical disease diagnosis. Spatial resolution and detection efficiency are two important technical indicators for evaluating SPECT imaging performance. SPECT imaging requires a collimator to collimate gamma rays, thereby determining the incident direction of gamma photons detected by the detector. Commonly used collimators include parallel-aperture collimators and multi-pinhole collimators. The radiation source in the imaging field of view emits gamma photons uniformly in all directions. The collimator only allows gamma photons with specific incident directions to pass through the collimator and be received by the detector. This allows the determination of the incident direction of the detected gamma photons, which can then be used for image reconstruction to obtain the three-dimensional distribution of the radiation source within the imaging field of view. Utility Model Content

[0003] This utility model aims to solve at least one of the technical problems existing in the prior art.

[0004] Although parallel-aperture collimators are widely used in clinical practice, their spatial resolution and detection efficiency are insufficient to meet higher clinical demands as nuclear medicine advances. Multi-aperture collimators can improve detection efficiency and spatial resolution by narrowing the imaging field of view and designing appropriate pinhole magnification and arrangement. They are particularly advantageous for imaging small organs such as the heart, thyroid, and brain. Therefore, multi-aperture SPECT imaging systems represent an important development direction for current emission computed tomography (ECT) technology. In traditional multi-aperture collimator designs, multiple pinholes are arranged on the collimator to improve detection efficiency. Currently, regular arrangements are used, but this limits the number of pinholes, resulting in low overlap of projections from different holes / pinholes on the detector. This leads to low detection efficiency in existing multi-aperture collimators, typically around 0.05%. In clinical applications, longer data acquisition times are still required to obtain sufficient statistical counts for image reconstruction.

[0005] Therefore, this utility model provides a super-aperture collimator for gamma photon detection and a nuclear medicine imaging system having the super-aperture collimator, which significantly improves detection efficiency while ensuring image resolution.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of this utility model provides a super-aperture collimator for gamma photon detection. The super-aperture collimator has a collimator plate on which multiple collimator holes are formed in an irregular or random distribution. When a radioactive ray in the imaging field of view passes through the collimator holes, it forms a projection overlap on the gamma photon detector. The orientation of the collimator holes should satisfy the condition that the normal vector of the center plane of the collimator hole passes through the center of the imaging field of view, and the angle of the collimator holes should satisfy the condition that the extension lines of the two edges of the collimator holes are tangent to the imaging field of view.

[0008] In some embodiments, the projected area of ​​the radioactive rays within the imaging field of view onto the gamma photon detector through each collimating aperture is superimposed to be 6 to 12 times the detection area of ​​the gamma photon detector.

[0009] In some embodiments, the collimator plate is divided into several sub-regions arranged in an array, and at least two sub-regions have different collimation hole arrangements. The arrangement of each collimation hole on the collimator plate also satisfies any one or a combination of the following requirements:

[0010] Requirement A: Within each sub-region, the center points of any three or more of the collimating holes are not collinear;

[0011] Requirement B: Within each sub-region, the coordinate increments of each collimating hole along the first direction are at least partially different, and the coordinate increments of the three adjacent collimating holes along the first direction are different; the coordinate increments of each collimating hole along the second direction are at least partially different, and the coordinate increments of the three adjacent collimating holes along the second direction are different; the first direction intersects the second direction.

[0012] Requirement C: A portion of the sub-regions contains the same number of collimating holes, while the remaining sub-regions contain different numbers of collimating holes.

[0013] In some embodiments, the sub-regions on the collimator plate are uniformly distributed and the areas of each sub-region are equal; and / or

[0014] At least 80% of the sub-regions in the collimator plate have different collimation hole arrangements, and two adjacent sub-regions have different collimation hole arrangements.

[0015] In some embodiments, in a single sub-region, at least 80% of the collimating holes have different coordinate increments along the first direction, and three adjacent collimating holes have different coordinate increments along the first direction; at least 80% of the collimating holes have different coordinate increments along the second direction, and three adjacent collimating holes have different coordinate increments along the second direction; and / or

[0016] At least 50% of the sub-regions contain a different number of collimating holes.

[0017] In some embodiments, the number of collimating holes on the collimator plate is determined based on the superposition requirement of the projected areas of all collimating holes on the gamma photon detector and the size of the collimator plate.

[0018] In some embodiments, the cross-sectional shapes of the collimation holes on the collimator plate may be the same or different.

[0019] In some embodiments, the cross-sectional shape of the collimating hole is circular or any regular polygon.

[0020] In some embodiments, the collimator plate is a flat plate or a curved plate.

[0021] The second aspect of this utility model provides a nuclear medicine imaging system, wherein the nuclear medicine imaging system has a super-orifice collimator according to any embodiment of the first aspect of this utility model.

[0022] The super-aperture collimator for gamma photon detection provided by this utility model has the following characteristics and beneficial effects:

[0023] This invention effectively overcomes the limitation on the number of pinholes imposed by the pinhole arrangement in traditional multi-pinhole collimators. By irregularly or randomly arranging a certain number of collimating holes on the collimator, the number is far greater than that in existing multi-pinhole collimators. This ensures that the superimposed projection area of ​​radioactive rays in the imaging field of view onto the detector through each collimating hole meets the requirements, forming a super-aperture collimator. This improves detection efficiency, thereby increasing the gamma photon count collected per unit time and effectively shortening the imaging acquisition time. The number of pinholes is determined by ensuring that the superimposed projection area of ​​the imaging field of view onto the detector through all collimating holes is at least three times the detector area, preferably six to twelve times. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of an 80-pinhole super-hole collimator provided in the first aspect embodiment of the present invention;

[0025] Figure 2 It is the passage of radioactive rays within the imaging field of view Figure 1The diagram shows the superimposed projection of the 80 pinhole super-aperture collimator onto the gamma photon detector.

[0026] Figure 3 (a) and (b) are schematic diagrams of two other pinhole layouts for an 80-pinhole super-hole collimator. Figure 3 In the middle (c) and (d), respectively, are with Figure 3 (a) and (b) are schematic diagrams of the superimposed projections on the corresponding gamma photon detectors;

[0027] Figure 4 This is a schematic diagram illustrating the design requirements of a single collimation hole provided in the first aspect embodiment of this utility model;

[0028] Figure 5 This is a schematic diagram of the super-aperture collimator provided in the first aspect embodiment of the present invention applied to a dual-probe SPECT imaging system;

[0029] Figure 6 (a) is a schematic diagram of the thermal cylinder model established in the embodiment of this utility model. Figure 6 In the middle (b) to (h), the reconstructed images are the corresponding images when the number of pinholes N is 40, 50, 60, 80, 100, 110, and 120, respectively. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the application will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining this application and are not intended to limit this application.

[0031] Conversely, this application covers any alternatives, modifications, equivalent methods, and schemes made within the spirit and scope of this application as defined by the claims. Furthermore, to provide the public with a better understanding of this application, certain specific details are described in detail below. However, this application can be fully understood by those skilled in the art even without these detailed descriptions.

[0032] According to the first aspect of the present invention, a super-aperture collimator for gamma photon detection is provided, wherein N collimator holes are irregularly or randomly distributed on its collimator plate. When radioactive rays in the imaging field of view pass through the randomly distributed collimator holes on the collimator plate, they form a projection overlap on the gamma photon detector. The superimposed projection area of ​​all collimator holes should be much larger than the detection area of ​​the gamma photon detector. Under the premise of ensuring image resolution, the detection efficiency can be significantly improved. Combined with the existing maximum likelihood-expectation-maximization (MLEM) iterative image reconstruction algorithm, the image reconstruction quality is improved.

[0033] To better understand the above-mentioned super-orifice collimator, the following will combine... Figures 1-4 The super-orifice collimator of this embodiment will be explained.

[0034] See Figure 1 , Figure 2 This embodiment provides a super-aperture collimator for gamma photon detection, comprising a collimator plate 101 on which N=80 collimating apertures 102 are formed in an irregular or randomly distributed manner. The imaging field of view and the gamma photon detector 201 are located on opposite sides of the collimator plate 101. The imaging field of view should form an envelope around the object being detected. When radioactive rays within the imaging field of view pass through the collimating apertures 102, they form a projection overlap on the gamma photon detector 201. The superposition of the projection areas of all the collimating apertures 102 within the imaging field of view should be at least three times the detection area of ​​the gamma photon detector 201.

[0035] Preferably, the projected area of ​​all collimation holes 102 on a single collimator plate 101 within the imaging field of view is superimposed to 6 to 12 times the detection area of ​​the gamma photon detector 201 corresponding to the collimator plate 101, so as to significantly improve the detection efficiency at the center of the imaging field of view.

[0036] See Figure 2 In this embodiment, the imaging field of view is the superposition of projections formed on the gamma photon detector 201 by all collimating holes 102 on the collimator plate 101, and 202 is the projection of the imaging field of view after passing through one collimating hole 102. The sum of all projected areas is calculated to be 8.82 times the detection area of ​​the gamma photon detector 201, which is within the range of 6 to 12 times required by the design of this super-aperture collimator. The detection efficiency at the center of the imaging field of view is 0.32%, which significantly exceeds the detection efficiency of 0.05% of the traditional multi-pinhole collimator.

[0037] Furthermore, the number of collimating holes 102 contained on the collimator plate 101 is determined based on the superposition requirement of the projected areas of all collimating holes 102 on the gamma photon detector 201 and the size of the collimator plate 101.

[0038] As a specific embodiment of this utility model, it is applied to a device with an outer contour dimension of 345.6×256.6mm. 2 When the collimator plate 101 is collimator plate 101, and the superposition of the projected area of ​​the imaging field of view through all the collimating holes 102 on the gamma photon detector 201 is required to be 6 to 12 times the detection area of ​​the gamma photon detector 201, the number N of collimating holes 102 arranged on the collimator plate 101 is 60 to 100.

[0039] Furthermore, this invention overcomes the limitation on the number of collimating holes in traditional collimators by providing multiple collimating holes that are irregularly or randomly distributed on the collimator plate 101. The irregular or random distribution defined in this invention is achieved by dividing the collimator plate 101 into several sub-regions arranged in an array, each sub-region containing at least three collimating holes 102, with at least two sub-regions having different arrangements of the collimating holes 102. The arrangement of the collimating holes 102 on the collimator plate 101 also satisfies any one or a combination of the following requirements:

[0040] Requirement A: Within each sub-region, the center points of any three or more collimating holes 102 are not collinear;

[0041] Requirement B: Within each sub-region, the coordinate increments of each collimating hole 102 along the first direction are at least partially different, and the coordinate increments of three adjacent collimating holes 102 along the first direction are different; the coordinate increments of each collimating hole 102 along the second direction are at least partially different, and the coordinate increments of three adjacent collimating holes 102 along the second direction are different, wherein the first direction intersects the second direction.

[0042] Requirement C: A portion of the sub-regions contains the same number of collimating holes 102, while the remaining sub-regions contain different numbers of collimating holes 102.

[0043] Optionally, the collimator plate 101 is uniformly divided into several sub-regions, each with an equal area.

[0044] Preferably, at least 80% of the sub-regions in the collimator plate 10 have different collimation hole arrangements, and two adjacent sub-regions have different collimation hole arrangements.

[0045] Preferably, for requirement B, in a single sub-region, at least 80% of the collimation holes 102 have different coordinate increments along the first direction and the three adjacent collimation holes 102 have different coordinate increments along the first direction, and at least 80% of the collimation holes 102 have different coordinate increments along the second direction and the three adjacent collimation holes 102 have different coordinate increments along the second direction; optionally, two directions perpendicular to each other on the collimation plate are respectively designated as the first direction and the second direction.

[0046] Preferably, for requirement C, at least 50% of the sub-regions contain a different number of collimating holes 102.

[0047] See Figure 3Figures (a) to (d) show two other pinhole layouts of the 80-pinhole super-aperture collimator provided in this embodiment of the present invention and their corresponding projection superimposed diagrams formed on the gamma photon detector 201. The dashed lines in the figures represent the boundaries of the sub-regions divided in this embodiment, which uniformly divide the collimator plate 101 into 2×5 array sub-regions, with each sub-region having a relative shape and area.

[0048] Furthermore, the collimation hole on the collimator plate 101 should ensure that the projection of the imaging field of view through the collimation hole at least partially covers the detection range of the detector.

[0049] Furthermore, the shapes of the collimation holes 102 on the collimator plate 101 can be the same or different, and the specific cross-sectional shape can be circular or any regular polygon. The aperture of each collimation hole 102 is set according to the target spatial resolution requirements.

[0050] Further, see Figure 4 This diagram illustrates the spatial relationship between a single collimator aperture 102 and the imaging field of view 108. T represents the thickness of the collimator plate 101, D is the diameter of the collimator aperture (at its central plane), α is the angle of the collimator aperture, R is the radius of the imaging field of view, and L is the distance from the central plane 103 of the collimator aperture to the center 107 of the imaging field of view. The orientation of the collimator aperture 102 should satisfy the condition that the normal vector 104 of the central plane 103 of the collimator aperture passes through the center 107 of the imaging field of view, and the angle of the collimator aperture should satisfy the condition that the two extended edges 105 and 106 of the collimator aperture are tangent to the imaging field of view 108, thus enabling the imaging field of view 108 to be imaged by the collimator aperture 102.

[0051] Furthermore, the collimator plate 101 is made of heavy metal alloys with high atomic number and high density, such as tungsten and lead, to shield the radiation emitted by SPECT nuclides.

[0052] Furthermore, the collimator plate 101 can be a flat plate or a curved plate, and the appropriate plate type can be selected according to the specific imaging application scenario.

[0053] See Figure 5 The nuclear medicine imaging system with the above-described super-orifice collimator is provided according to the second aspect of the present invention.

[0054] Furthermore, the nuclear medicine imaging system is the SPECT system.

[0055] It is understood that the nuclear medicine imaging system provided in the second aspect of this utility model has an ultra-aperture collimator that can significantly improve detection efficiency, thereby increasing the gamma photon count collected per unit time and effectively shortening the imaging acquisition time.

[0056] The effectiveness of this utility model embodiment will be verified below with specific experimental data:

[0057] like Figure 5 As shown, this is a commonly used dual-probe SPECT system in clinical practice. It has two gamma photon detectors 201 arranged at 90°. Each gamma photon detector 201 is connected to a corresponding collimator plate 101 on the side facing the imaging field of view 108 via a connector 203. The object being detected is located in the area of ​​the imaging field of view 108. In this embodiment, the inherent spatial resolution of the gamma photon detector 201 is 3.4 mm, and the effective detection area of ​​the gamma photon detector 201 is 540 × 400 mm. 2 The outer dimensions of the collimator plate 101 are 345.6 × 256.6 mm. 2 The vertical distance between the gamma photon detector 201 and the collimator plate 101 is 148.1 mm, and the imaging field of view 108 is a sphere with a diameter of 19 cm.

[0058] First, based on the above data and the geometric optics model of gamma photons, the relationship between target spatial resolution and collimating aperture diameter was constructed. Then, according to the target spatial resolution requirement, the collimating aperture diameter of 102 was determined to be 4.5 mm. Next, a simulation model with this super-aperture collimator and a gamma photon detector was built based on a real detection scenario. On the collimator plate of this simulation model, N=40, 50, 60, 80, 100, 110, and 120 collimating apertures were randomly designed, with a diameter of 4.5 mm. The orientation and angle of the collimating apertures, as well as the radioactive rays within the imaging field of view, were determined after passing through each collimating aperture and entering the gamma photon field of view. The superposition of projected areas formed on the sub-detectors all met the set requirements, resulting in seven super-aperture collimators with different numbers of collimating holes. The cumulative sum of the projected surfaces of all collimating holes within the imaging field of view of the radioactive rays was approximately 457.8%, 566.6%, 674.0%, 882.4%, 1107.4%, 1212.2%, and 1317.7% of the detection area of ​​the gamma photon detector, respectively. The calculated detection efficiencies at the center of the imaging field of view (the specific calculation method is a well-known method in the art) were 0.15%, 0.24%, 0.32%, 0.41%, 0.44%, and 0.48%, respectively. Finally, Monte Carlo simulation and image reconstruction based on a thermal cylinder model were performed on a dual-probe SPECT system (the specific implementation process is a well-known technique in the art), see [link to documentation]. Figure 6 In the constructed thermal cylinder model (a), the diameters of the thermal cylinders, from smallest to largest, are 6mm, 9mm, 12mm, 15mm, 18mm, and 21mm, and the same acquisition time of 30s is set. Figure 6 Images (b) to (h) are the reconstructed images corresponding to N = 40, 50, 60, 80, 100, 110, and 120, respectively. It can be seen that when N is between 60 and 100, the reconstructed image has fewer artifacts, and this is taken as the optimal collimation hole layout scheme in this embodiment.

[0059] It should be noted that, in this embodiment of the invention, the superimposed projection area of ​​the radioactive rays within the imaging field of view through all the collimating holes in the collimator plate onto the gamma photon detector is 6 to 12 times the detection area of ​​the gamma photon detector, which is applicable to most commonly used SPECT systems in clinical practice. Furthermore, experiments have shown that, provided the above-mentioned projection superposition area requirement is met, the number of openings has a more significant impact on image reconstruction results than the location of the openings.

[0060] In summary, this utility model embodiment increases the overlapping area of ​​the projection by setting a large number of randomly or irregularly arranged pinholes, while constraining the aperture, orientation, and angle of the aligned pinholes as well as the overlapping area of ​​the projection, so as to avoid the generation of artifacts in the reconstructed image, thereby greatly improving the detection efficiency while ensuring image resolution.

[0061] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0062] Although embodiments of this disclosure have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this disclosure, the scope of which is defined by the claims and their equivalents.

Claims

1. A super-aperture collimator for gamma photon detection, characterized in that, The super-aperture collimator has a collimator plate with multiple collimator holes that are irregularly or randomly distributed. When radioactive rays in the imaging field of view pass through the collimator holes, they form overlapping projections on the gamma photon detector. The orientation of the collimator holes should satisfy the condition that the normal vector of the center plane of the collimator hole passes through the center of the imaging field of view, and the angle of the collimator holes should satisfy the condition that the extension lines of the two edges of the collimator holes are tangent to the imaging field of view.

2. The super-orifice collimator according to claim 1, characterized in that, The projected area of ​​the radioactive rays within the imaging field of view onto the gamma photon detector through each collimating aperture is superimposed to be 6 to 12 times the detection area of ​​the gamma photon detector.

3. The super-orifice collimator according to claim 1, characterized in that, The collimator plate is divided into several sub-regions arranged in an array, with at least two sub-regions having different collimation hole arrangements. The arrangement of each collimation hole on the collimator plate also satisfies any one or a combination of the following requirements: Requirement A: Within each sub-region, the center points of any three or more of the collimating holes are not collinear; Requirement B: Within each sub-region, the coordinate increments of each collimating hole along the first direction are at least partially different, and the coordinate increments of the three adjacent collimating holes along the first direction are different; the coordinate increments of each collimating hole along the second direction are at least partially different, and the coordinate increments of the three adjacent collimating holes along the second direction are different; the first direction intersects the second direction. Requirement C: A portion of the sub-regions contains the same number of collimating holes, while the remaining sub-regions contain different numbers of collimating holes.

4. The super-orifice collimator according to claim 3, characterized in that, The sub-regions on the collimator plate are uniformly distributed, and the areas of each sub-region are equal; and / or At least 80% of the sub-regions in the collimator plate have different collimation hole arrangements, and two adjacent sub-regions have different collimation hole arrangements.

5. The super-orifice collimator according to claim 3, characterized in that, In a single sub-region, at least 80% of the collimating holes have different coordinate increments along the first direction, and three adjacent collimating holes have different coordinate increments along the first direction; at least 80% of the collimating holes have different coordinate increments along the second direction, and three adjacent collimating holes have different coordinate increments along the second direction; and / or At least 50% of the sub-regions contain a different number of collimating holes.

6. The super-orifice collimator according to claim 1, characterized in that, The number of collimating holes on the collimator plate is determined based on the superposition requirement of the projected areas of all collimating holes on the gamma photon detector and the size of the collimator plate.

7. The super-orifice collimator according to claim 1, characterized in that, The cross-sectional shapes of the collimation holes on the collimator plate may be the same or different.

8. The super-orifice collimator according to claim 1, characterized in that, The cross-sectional shape of the collimation hole can be circular or any regular polygon.

9. The super-orifice collimator according to claim 1, characterized in that, The collimator plate can be a flat plate or a curved plate.

10. A nuclear medicine imaging system, characterized in that, The nuclear medicine imaging system has a super-orifice collimator according to any one of claims 1 to 9.

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