Fast 3D kernel computation method for positron range correction in PET
Fast 3D kernel computation method for positron range correction in PET
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DOI：
10.1088/1361-6560/acaa84
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发表时间：
2022-12
影响因子：
3.5
通讯作者：
Chong Li;J. Scheins;L. Tellmann;A. Issa;Long Wei;N. Shah;C. Lerche
中科院分区：
文献类型：
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作者：
Chong Li;J. Scheins;L. Tellmann;A. Issa;Long Wei;N. Shah;C. Lerche
Objective.正电子范围是正电子发射断层扫描（PET）中空间分辨率的基本的、与探测器无关的物理限制，因为它导致重建图像中潜在活性分布的显著模糊。正电子距离校正方法的主要挑战是提供精确的距离核，其固有地包含通常不均匀的阻止本领，特别是在组织边界处。在这项工作中，我们提出了一种新的方法来生成准确的三维（3D）模糊内核在均匀和异质介质，以提高PET的空间分辨率。Approach.在所提出的方法中，正电子能量沉积大致沿沿着直线路径跟踪，这取决于底层材料的正电子阻止本领。根据可用的PET衰减图，从511 keV伽马光子的衰减系数导出正电子阻止本领。因此，在核的范围内考虑能量沉积的历史。特别强调的是，在每个体素中的正电子湮灭概率的非常快速的计算。结果18 F在低密度聚氨酯中的正电子路径分布与Geant 4模拟高度一致，湮没概率大于最大湮没概率的10−2 <$10 −3。Geant 4模拟进一步验证了在这些聚氨酯体模中测量的18F深度分布。水与皮质骨和肺的组织边界被正确地建模。数值计算的残留伪影在1%的范围内。体素中计算出的湮灭概率与Geant 4模拟相比显示出小于20%的总体差异。意义所提出的方法预计显着提高空间分辨率的非标准同位素提供足够准确的范围内核，即使在显着的组织不均匀性的情况下。
Objective. The positron range is a fundamental, detector-independent physical limitation to spatial resolution in positron emission tomography (PET) as it causes a significant blurring of underlying activity distribution in the reconstructed images. A major challenge for positron range correction methods is to provide accurate range kernels that inherently incorporate the generally inhomogeneous stopping power, especially at tissue boundaries. In this work, we propose a novel approach to generate accurate three-dimensional (3D) blurring kernels both in homogenous and heterogeneous media to improve PET spatial resolution. Approach. In the proposed approach, positron energy deposition was approximately tracked along straight paths, depending on the positron stopping power of the underlying material. The positron stopping power was derived from the attenuation coefficient of 511 keV gamma photons according to the available PET attenuation maps. Thus, the history of energy deposition is taken into account within the range of kernels. Special emphasis was placed on facilitating the very fast computation of the positron annihilation probability in each voxel. Results. Positron path distributions of 18F in low-density polyurethane were in high agreement with Geant4 simulation at an annihilation probability larger than 10−2 ∼ 10−3 of the maximum annihilation probability. The Geant4 simulation was further validated with measured 18F depth profiles in these polyurethane phantoms. The tissue boundary of water with cortical bone and lung was correctly modeled. Residual artifacts from the numerical computations were in the range of 1%. The calculated annihilation probability in voxels shows an overall difference of less than 20% compared to the Geant4 simulation. Significance. The proposed method is expected to significantly improve spatial resolution for non-standard isotopes by providing sufficiently accurate range kernels, even in the case of significant tissue inhomogeneities.