Design and Simulation of Three-dimensional Position Sensitive Detector with Monolithic Scintillation Crystal Based on Lens Array for Multiple Focus Points
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摘要: 连续晶体闪烁体探测器可以实现γ射线作用点的三维位置定位。本文提出一种新的探测器结构，引入透镜阵列实现作用点定位。探测器采集多元聚焦图像，从而改变对连续晶体闪烁光分布探测的需求。文中建立连续晶体、透镜阵列和光子计数器阵列的模型进行模拟研究，建立多元聚焦的光路反演重建算法定位γ射线作用点的三维位置。通过重建结果分析评估基于透镜阵列的连续晶体探测器性能，这种结构具有较好的定位能力和位置分辨。对于尺寸为48 mm×48 mm×45 mm的硅酸钇镥（LYSO）闪烁晶体，实现了xy平面位置分辨优于1.54 mm，z方向位置分辨优于3.13 mm。基于连续晶体和透镜阵列结构的探测器还可对多作用点的情形进行重建，分析三组选定位置的重建结果，该结构对双作用点定位具有可行性。Abstract: The monolithic scintillation crystal detector has the ability to position the three-dimension interaction location of the gamma ray in the detector depending on accurate acquisition of scintillation light distribution. Depth estimation of light field can be solved by a lens array in light field technology. A new detector model was designed in the paper which introduced a lens array for positioning the interaction in the monolithic detector. The scintillation light is focused by each lens unit in the lens array. Photons in some discrete pixels of the photon counter array where the scintillation light is focus on are detected to form an image of multiple focus points instead of the scintillation light distribution detection based on continuous crystal. The position of the scintillation light source in the crystal can be reconstructed from the focus image through optical path inversion. The detector model consisting of a monolithic crystal, a lens array and a multi-pixel photon counter was established in the paper. The monolithic scintillator was a lutetium-yttrium silicate (LYSO) scintillator with dimensions 48 mm×48 mm×45 mm. The lens was hemispherical with a radius of 15 mm supposed to be uniformly distributed in 3×3 array and the material was as same as the crystal. The crystal and the lens array were considered as a whole in the simulation. The multi-pixel photon counter was set at 44.4 mm from the crystal surface. The pixel size of the photon counter array was 3 mm and the quantum efficiency was 30%. The axis of symmetry of the three parts was same. The reconstruction algorithm was based on optical path inversion from multiple focus points for locating the 3D position of gamma-ray interaction. The intersection points of the inverted optical paths and the set z plane with different depths in the crystal was calculated in the reconstruction process. When the intersection points converged towards the same point in the z0 plane, the depth of interaction was z0 and the intersection point in the z0 plane was the interaction point. The reconstruction results were analyzed to evaluate the performance of the monolithic scintillation crystal detector based on the lens array. The x/y resolution is better than 1.54 mm and the z resolution is better than 3.13 mm. The two interaction points when coincidence occurs are reconstruced in the condition that the energy is the same. The detector is feasible for the positioning of two interaction points by the reconstruction results of three groups of selected positions. The monolithic scintillation detector based on a lens array has both good positioning ability and position resolution. The detector is suitable for the position reconstruction of multiple interaction points.
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