High-resolution depth coding PET detector device

Abstract

The invention provides a high-resolution depth coding PET detector device, and the device comprises a SiPM pixel module which comprises a SiPM pixel array; the scintillation crystal module comprises a scintillation crystal array, and the SiPM pixel array is optically coupled with the scintillation crystal array; the prismoid light guide module comprises a prismoid light guide array, the prismoid light guide array is optically coupled with the scintillation crystal array, the spatial resolution and DOI resolution of the PET detector module are remarkably improved, meanwhile, good energy resolution and timing resolution are kept, and commercialized popularization is facilitated.

Description

Technical Field

[0001] This invention relates to the medical field, and more particularly to a high-resolution depth-coded PET detector device. Background Technology

[0002] Positron emission tomography (PET), a powerful molecular imaging technique, is widely used in cancer diagnosis, treatment selection, treatment monitoring, and research on neuropsychiatric diseases. However, PET's relatively poor spatial resolution (currently around 3-6 mm) limits its ability to measure target density in small nodules and many human and rodent brain regions associated with disease etiology.

[0003] The development of depth-coded PET detector modules aims to mitigate the parallax error (mislocalization of response lines) of long scintillation crystals. This allows for smaller PET ring diameters, lower costs, and greater solid angle coverage to improve sensitivity, while also reducing the impact of annihilation gamma-ray noncollinearity on spatial resolution. Dual-end readout depth-coded detectors can achieve continuous DOI resolution of <2 mm, but their high cost due to the large number of readout electronics hinders commercialization.

[0004] Single-ended readout detector modules are an alternative, such as multilayer scintillator blocks, monolithic scintillator retroreflector designs, and other custom reflector designs. However, these designs involve trade-offs in depth encoding, cost, scintillator-readout coupling ratio, crystal recognition accuracy, energy resolution, and temporal resolution. In existing technologies, depth-encoded PET detector modules using single-ended readout typically employ uniform glass light guides to achieve light sharing between crystals to acquire depth information (DOI), which presents several key challenges: First, uneven crystal recognition: Because the light sharing of a uniform light guide is isotropic and random, crystals located at the edges and corners of the detector array lack sufficient light sharing units, leading to a significant decrease in their crystal recognition performance. Furthermore, edge and corner crystals account for a high proportion in the array (e.g., 75% and 44% in 4x4 and 8x8 readout chips, respectively), resulting in uneven spatial resolution across the entire detector module.

[0005] Second, the light sharing efficiency is low and nondeterministic: a uniform light guide will randomly scatter upward-propagating photons with a Gaussian intensity distribution onto multiple neighboring SiPMs (silicon photomultiplier tubes). This low-intensity signal distribution across multiple SiPMs is highly susceptible to noise such as dark counting in the SiPMs, thus degrading the energy resolution and DOI resolution.

[0006] Third, performance trade-offs: In order to achieve acceptable crystal recognition with single-ended readout, a glass light guide is often inserted between the crystal and the SiPM. This increases photon loss at the interface, reduces photon detection efficiency, and is therefore detrimental to time-of-flight (TOF) resolution.

[0007] Fourth, cost and complexity: Although single-ended readout has significantly reduced cost and electronic complexity compared to double-ended readout, existing single-ended DOI schemes still face the aforementioned inherent problems when pursuing high performance (such as submillimeter crystals), which limits their widespread application in low-cost, high-resolution clinical PET systems (such as whole-body and brain-specific PET).

[0008] Existing solutions to the above problems include dual-end readout technology, specifically a scheme that places photodetectors at both ends of a scintillation crystal array for readout. This is currently the best-performing DOI implementation method, achieving continuous DOI resolution of <2mm. However, it is costly (requiring twice the number of readout electronics channels and detectors), complex, and difficult to commercialize. Another example is single-end readout + uniform glass optical guide technology: using energy-weighted averaging and other methods, it utilizes a 1.53x1.53x15mm... 3 Crystal and 3x3 mm 2 SiPM can achieve approximately 9% energy resolution and 3mm DOI resolution; however, it suffers from the core issues of edge / corner performance degradation and light sharing randomness, limiting further performance improvements and uniformity. Other single-end DOI technologies include multilayer crystal structures, monolithic crystal structures with reflective layers of varying heights, and other custom reflector designs.

[0009] The above-mentioned solutions usually involve unavoidable trade-offs between DOI resolution, cost, coupling ratio, crystal recognition accuracy, energy resolution, and time resolution, and cannot optimize all key performance parameters at the same time. Summary of the Invention

[0010] To overcome the aforementioned technical deficiencies, the present invention aims to provide a high-resolution depth-coded PET detector device, which achieves synchronous optimization of all key performance parameters by employing a segmented prism light guide array and utilizing a deterministic offset-coupled light sharing mode and optical path control mechanism.

[0011] To achieve the above objectives, the present invention provides a high-resolution depth-coded PET detector device, comprising: SiPM pixel module, including SiPM pixel array; A scintillation crystal module, including a scintillation crystal array, wherein the SiPM pixel array is optically coupled to the scintillation crystal array; A prism light guide module includes a prism light guide array that is optically coupled to the scintillation crystal array.

[0012] Preferably, the scintillation crystal array includes a first surface and a second surface located opposite to the first surface, the first surface being optically coupled to the SiPM pixel array and the second surface being optically coupled to the prism light guide array.

[0013] Preferably, the prism light guide array includes multiple segmented prism units. Each prism unit has multiple right-angle prism geometries based on its position within the prism light guide array. These right-angle prism geometries include, but are not limited to, a central prism, an edge prism, and a corner prism, to accommodate the light sharing requirements at the center, edge, and corner positions of the prism light guide array.

[0014] Preferably, the scintillation crystal array includes scintillation crystal units, and the coupling mapping relationship between the crystal units in the scintillation crystal array and the pixels in the SiPM pixel array is a first coupling mapping relationship, and the coupling mapping relationship between the crystal units in the scintillation crystal array and the prism units in the prism light guide array is a second coupling mapping relationship. The first coupling mapping relationship is different from the second coupling mapping relationship and has a fixed offset.

[0015] Preferably, the difference between the optical refractive index of the prism unit in the prism optical guide array and the optical refractive index of the scintillation crystal array is less than 0.2.

[0016] Preferably, the prism unit is a right-angled triangular prism made of SF10 glass.

[0017] Preferably, the coupling relationship between a single scintillation crystal unit in the scintillation crystal array and a single pixel in the SiPM pixel array is N:1, where N is an integer greater than 1.

[0018] Preferably, the scintillation crystal array and the prism light guide array are bonded together with optical adhesive, the optical refractive index of which matches the optical refractive index of the prism units of the prism light guide array and the optical refractive index of the scintillation crystal array.

[0019] Preferably, the device further includes a reflection module disposed between the crystal units of the scintillation crystal array and in the gap between the crystal units and the prism units, the reflection module being a barium sulfate reflection layer.

[0020] Preferably, the coupling ratio between a single scintillation crystal unit in the scintillation crystal array and a single pixel in the SiPM pixel array is 4:1, the coupling ratio between a single scintillation crystal unit in the scintillation crystal array and a single prism unit in the prism light guide array is 4:1, and there is a half-crystal pitch offset between the first coupling mapping relationship and the second coupling mapping relationship.

[0021] Compared with existing technologies, the above technical solution has the following advantages: 1. The non-readout side of the detector uses a segmented prism light guide array with a specially designed prism light guide array, including center, edge and corner prisms, which fundamentally solves the problem of degradation of edge and corner crystal recognition performance, optimizes the light sharing mode, and has low cost and high commercialization. 2. A deterministic offset-coupled light-sharing mode is employed: the coupling relationship between the crystal array and the SiPM pixel array (e.g., 4:1 or 9:1) is offset from the coupling relationship between the crystal array and the prism light guide array. Through prism geometry, it is ensured that a group of crystals covered by a prism is connected precisely to different SiPM readout paths, thus guaranteeing that light sharing occurs between crystals belonging to different readout paths. This effectively guides the optical signal to the nearest adjacent readout pixel, maximizing the contrast of crystal recognition and forming a deterministic offset-coupled light-sharing mode. 3. Optical path control mechanism: The inclined plane of a prism (especially a right-angled prism) can deflect the optical photon path entering it by about 180 degrees, efficiently guiding it to the target's neighboring crystal, achieving deterministic and anisotropic light sharing, rather than random scattering by a non-uniform light guide, while optimizing DOI, energy and crystal recognition performance. Attached Figure Description

[0022] Figure 1 This is an overall architecture diagram of the PET detector device provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the PET detector device provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a conventional detector provided by the present invention; Figure 4 A 16×16 (256) crystal two-dimensional lattice distribution diagram provided for a preferred embodiment of the present invention; Figure 5 A one-dimensional distribution diagram of 16 × 16 (256) crystals provided for a preferred embodiment of the present invention; Figure 6 A comparison chart of detector DOI resolution provided for a preferred embodiment of the present invention; Figure 7A comparison chart of detector DOI energy distribution curves provided for a preferred embodiment of the present invention.

[0023] Reference numerals: 10-SiPM pixel module; 20-Scintillating crystal module; 30-Pyramid light guide module. Detailed Implementation

[0024] The advantages of the present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments.

[0025] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0026] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0027] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0028] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0029] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two components. They can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0030] In the following description, suffixes such as "module," "part," or "unit" used to denote elements are used only for the convenience of the description of the invention and have no specific meaning in themselves. Therefore, "module" and "part" can be used interchangeably.

[0031] Figure 1 This is an overall architecture diagram of the PET detector device provided in an embodiment of the present invention. Figure 1 As shown, a high-resolution depth-coded PET detector device includes: SiPM pixel module, including SiPM pixel array; A scintillation crystal module, including a scintillation crystal array, wherein the SiPM pixel array is optically coupled to the scintillation crystal array; A prism light guide module includes a prism light guide array that is optically coupled to the scintillation crystal array.

[0032] Specifically, the high-resolution depth-coded PET detector device disclosed in this invention has a layered structure. A SiPM pixel module, a scintillation crystal module, and a prism light guide module are fixedly connected from bottom to top. The SiPM pixel module is directly mounted on a PCB (printed circuit board) to provide bias voltage and output electrical signals. The lower end face of the scintillation crystal module is pressed onto the SiPM pixel module, and the prism light guide module is pressed onto the upper end face of the scintillation crystal module. The scintillation crystal module is coupled not only to the SiPM pixel module but also to the prism light guide module in the non-readout layer. The prism light guide module employs a specific prism light guide array, with the prism's inclined surface guiding optical photons to the target's neighboring crystal, achieving deterministic, anisotropic light sharing and improving the optimization of all key performance parameters. It should be noted that the SiPM is a silicon photomultiplier capable of outputting electrical signals; therefore, the SiPM pixel module is located on the readout side of the entire detector device.

[0033] Furthermore, the device also includes a reflection module disposed between the crystal units of the scintillation crystal array and in the gap between the crystal unit and the prism unit. The reflection module is preferably a barium sulfate reflection layer, used to reflect the escaping photons back into the crystal or light guide to avoid light loss.

[0034] Furthermore, the scintillation crystal module specifically includes: The scintillation crystal array includes a first surface and a second surface opposite to the first surface. The first surface is optically coupled to the SiPM pixel array, and the second surface is optically coupled to the prism light guide array. Specifically, the first surface is the lower end surface of the scintillation crystal module attached to the SiPM pixel array, and the second surface is the lower end surface of the scintillation crystal attached to the prism light guide module.

[0035] Furthermore, the prism-shaped light guide module specifically includes: This prism-shaped optical guide array is composed of multiple segmented prism units; specifically, Figure 3 This is a schematic diagram of the structure of a conventional detector provided by the present invention. The conventional detector uses a uniform and continuous light guide. Figure 2 This is a schematic diagram of the PET detector device provided in an embodiment of the present invention. See also: Figure 2 One embodiment of the present invention proposes to use a segmented prism light guide array on the non-readout side of the PET detector module to replace the uniform glass light guide of the conventional technology, thereby optimizing the light sharing mode.

[0036] The right-angle prism geometry of the prism unit varies according to its position in the prism light guide array to accommodate the light sharing requirements at the center, edge, and corner positions. The right-angle prism geometry includes, but is not limited to, center prisms, edge prisms, and corner prisms. Specifically, one embodiment of the present invention provides a differentiated prism design for different positions (center, edge, and corner) of the detector array, fundamentally solving the problem of degraded crystal recognition performance at the edges and corners. Furthermore, by using prism geometry, especially the bevel of the right-angle prism, deterministic optical path guidance close to 180 degrees is achieved, efficiently redirecting upward-propagating photons that do not contribute to timing information to the predetermined crystal unit, simulating the light collection behavior of double-ended readout, thereby simultaneously optimizing DOI, energy, and crystal recognition performance.

[0037] Furthermore, the coupling mapping relationship between the crystal unit in the scintillation crystal array and the pixel in the SiPM pixel array, i.e., the first coupling mapping relationship, is different from the coupling mapping relationship between the crystal unit in the scintillation crystal array and the prism unit in the prism light guide array, i.e., the second coupling mapping relationship, and has a fixed offset amount. Specifically, one embodiment of the present invention proposes to adopt a specific offset coupling method between the crystal unit and the pixel in the SiPM pixel array, and between the crystal unit and the prism, so as to ensure that light sharing occurs between crystals belonging to different readout paths.

[0038] Specifically, the difference between the first coupling mapping relationship and the second coupling mapping relationship means that the coupling grouping of the crystal unit and the SiPM pixel is different in space from the coupling grouping of the crystal unit and the prism unit, and has a specific offset.

[0039] Furthermore, the coupling relationship between a single crystal unit in the scintillation crystal array and a single pixel in the SiPM pixel array is N:1, where N is an integer greater than 1, and preferably, N is 4 or 9.

[0040] Furthermore, the difference between the optical refractive index of the prism unit and the optical refractive index of the scintillation crystal array is less than 0.2, to ensure that the optical refractive indices of both are as small as possible.

[0041] Furthermore, the scintillation crystal array and the prism light guide array are bonded together with optical adhesive. The optical refractive index of the optical adhesive matches the optical refractive index of the prism unit and the scintillation crystal array to ensure minimal optical loss.

[0042] Example 1: 4:1 Coupled Prism-PET Detector Module In this embodiment, the detector device has a layered structure, comprising, from bottom to top: Readout layer (SiPM pixel module): an 8×8 array of silicon photomultiplier (SiPM) pixels, with an effective area of ​​3.2×3.2 mm per pixel. 2 The array is mounted on a PCB and is used to provide bias voltage and output electrical signals.

[0043] Scintillation crystal layer (scintillation crystal module): A 16×16 array of lutetium yttrium bromide orthorhombic silicate (LYSO) scintillation crystals. Each crystal unit has a cross-section of 1.4×1.4 mm. 2 The crystal array is 20 mm in length. All six faces of the crystal array are polished to optimize light output. The lower face (first surface) of the crystal array is optically coupled to the SiPM array through a layer of transparent optical adhesive, the optical refractive index of which matches the optical refractive index of the prism unit and the scintillation crystal array.

[0044] Prism-shaped light guide layer (prism-shaped light guide module): An 8×8 array of right-angled triangular prism units serves as the light guide. Each prism is precision-machined from optical glass (refractive index n=1.767). This light guide layer achieves optical coupling with the upper surface (second surface, i.e., radiation incident surface) of the crystal array through a high-refractive-index optical adhesive.

[0045] Reflective layer (reflective module): The sides of all LYSO crystals and the non-coupling gap between the top surface of the crystal and the prism are filled with highly reflective barium sulfate (BaSO4) powder or coating to reflect escaping photons back into the crystal or light guide, reducing light loss.

[0046] In this embodiment, a 4:1 coupling scheme, an offset coupling scheme, and a differentiated prism design scheme are used to achieve high uniformity and high depth resolution, as detailed below: First, the 4:1 coupling scheme: four consecutive 2×2 LYSO crystals are coupled to one 3.2×3.2 mm crystal. 2 On the SiPM pixels; at the same time, the crystal array and the prism array also adopt a 4:1 correspondence.

[0047] Offset coupling scheme: such as Figure 2 As shown, the crystal-SiPM coupling grouping and the crystal-prism coupling grouping are spatially offset by half a crystal pitch. Specifically, the 2×2 crystal covered by one prism unit belongs to exactly four different, adjacent SiPM pixel groups. This design ensures that photons collected by a prism are efficiently redistributed to four different readout paths, thereby providing a high-contrast signal pattern for crystal recognition, which is one of the core technical features disclosed in this invention.

[0048] Differentiated Prism Design Scheme: The elements in the prism array are not all identical. Instead, based on their location at the center, edge, or corner of the array, three slightly different right-angle prism geometries (mainly the angle and size of the bevel) are designed. For example: (1) Central prism: Its design aims to distribute photons evenly to its four neighbors; (2) Edge prism: Because it lacks a neighbor on one side, its design will adjust the optical path to allocate more photons that should be shared with the missing neighbor to other existing neighbors in order to compensate for the lack of light sharing; (3) Corner prism: It lacks neighbors on both sides, so its optical design changes the most to ensure that the corner crystal still has enough photons to be guided to the only two neighboring SiPMs, thereby obtaining a clear recognition signal.

[0049] This embodiment also provides a method for assembling the device, including the following steps: Step 1: Assemble the LYSO crystal array, BaSO4 reflective layer and glass support plate into a robust scintillator block; Step 2: Mount and fix the SiPM array onto the PCB; Step 3: Uniformly coat a layer of optical silicone grease onto the surface of the SiPM array; Step 4: Carefully align and press the lower end face (polished) of the scintillator block onto the SiPM array, ensuring the correct 4:1 alignment between the crystal and the pixel, expel excess air bubbles, and allow the adhesive layer to cure. Step 5: Apply optical adhesive evenly to the upper surface (already polished) of the scintillator block; Step six involves precisely aligning and pressing the pre-fabricated array of prisms (different types of prisms have been categorized according to their positions) onto the upper surface of the crystal. The key to this step is ensuring that the coupling between the prism array and the crystal array is offset relative to the SiPM array by a predetermined amount. Step 7: Cure the optical adhesive to complete the module assembly.

[0050] like Figures 4-7 As shown, by using 22 The performance achieved by this embodiment, tested using a Na point source, is as follows: Crystal recognition: such as Figures 4-5 As shown, all 16 × 16 (256) crystal lattices are clearly distinguishable, and the separation at the center, edge and corner of the array is uniform and consistent, with no performance degradation. Depth resolution (DOI): such as Figure 6 As shown, this study uses a plumb collimator (1mm aperture) to collect data at depths of 2, 6, 10, 14, and 18mm, with a DOI resolution of 2.2 mm FWHM, which is superior to the 3.0 mm FWHM of the traditional design. Energy resolution: After applying DOI correction, the average energy resolution is 9%. For example... Figure 7 As shown in figure a, the energy efficiency of traditional detectors is 11%, while Figure 7 As shown in b, the detector energy resolution in this embodiment is 9%.

[0051] In summary, the high-resolution depth-coded PET detector device disclosed in this embodiment of the invention employs a segmented prism light guide array on the non-readout side of the detector module, uses prisms to control the optical path, and significantly improves the spatial resolution and DOI resolution of the PET detector module through a deterministic offset-coupled light sharing mode, while maintaining good energy resolution and timing resolution, and has a low cost, which is conducive to commercial promotion.

[0052] It should be noted that the embodiments of the present invention have better implementability and are not intended to limit the present invention in any way. Any person skilled in the art may use the above-disclosed technical content to change or modify it into equivalent effective embodiments. However, any modifications or equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A high-resolution depth-coded PET detector device, characterized in that, include: SiPM pixel module, including SiPM pixel array; A scintillation crystal module includes a scintillation crystal array, wherein the SiPM pixel array is optically coupled to the scintillation crystal array; A prism light guide module includes a prism light guide array, wherein the prism light guide array is optically coupled to the scintillation crystal array.

2. The high-resolution depth-coded PET detector device as described in claim 1, characterized in that, The scintillation crystal array includes a first surface and a second surface located opposite the first surface. The first surface is optically coupled to the SiPM pixel array, and the second surface is optically coupled to the prism light guide array.

3. The high-resolution depth-coded PET detector device as described in claim 1, characterized in that, The prism light guide array includes multiple segmented prism units. Each prism unit has multiple right-angle prism geometries at its position in the prism light guide array. The right-angle prism geometries include, but are not limited to, central prisms, edge prisms, and corner prisms, to adapt to the light sharing requirements at the center, edge, and corner positions of the prism light guide array.

4. The high-resolution depth-coded PET detector device as described in claim 1, characterized in that, The scintillation crystal array includes scintillation crystal units. The coupling mapping relationship between the crystal units in the scintillation crystal array and the pixels in the SiPM pixel array is a first coupling mapping relationship. The coupling mapping relationship between the crystal units in the scintillation crystal array and the prism units in the prism light guide array is a second coupling mapping relationship. The first coupling mapping relationship is different from the second coupling mapping relationship and has a fixed offset.

5. The high-resolution depth-coded PET detector device as described in claim 1, characterized in that, The difference between the optical refractive index of the prism unit in the prism optical guide array and the optical refractive index of the scintillation crystal array is less than 0.

2.

6. The high-resolution depth-coded PET detector device as described in claim 3, characterized in that, The prism unit is a right-angled triangular prism made of SF10 glass.

7. The high-resolution depth-coded PET detector device as described in claim 1, characterized in that, The coupling relationship between a single scintillation crystal unit in the scintillation crystal array and a single pixel in the SiPM pixel array is N:1, where N is an integer greater than 1.

8. A high-resolution depth-coded PET detector device as described in claim 1 or 5, characterized in that, The scintillation crystal array and the prism light guide array are bonded together with optical adhesive, the optical refractive index of which matches the optical refractive index of the prism units of the prism light guide array and the optical refractive index of the scintillation crystal array.

9. A high-resolution depth-coded PET detector device as described in claim 1, characterized in that, The device further includes a reflection module, which is disposed between the crystal units of the scintillation crystal array and in the gap between the crystal units and the prism units. The reflection module is a barium sulfate reflection layer.

10. A high-resolution depth-coded PET detector device as described in claim 4, characterized in that, The coupling ratio between a single scintillation crystal unit in the scintillation crystal array and a single pixel in the SiPM pixel array is 4:1, and the coupling ratio between a single scintillation crystal unit in the scintillation crystal array and a single prism unit in the prism light guide array is 4:

1. There is a half-crystal pitch offset between the first coupling mapping relationship and the second coupling mapping relationship.

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