Naunheim Stephan, Kuhl Yannick, Solf Torsten, Schug David, Schulz Volkmar, Mueller Florian
Department of Physics of Molecular Imaging Systems (PMI), Institute for Experimental Imaging, RWTH Aachen University, Germany.
Philips Digital Photon Counting, Aachen, Germany.
Phys Med Biol. 2023 Jan 9;68(2). doi: 10.1088/1361-6560/aca872.
Positron emission tomography (PET) detectors providing attractive coincidence time resolutions (CTRs) offer time-of-flight information, resulting in an improved signal-to-noise ratio of the PET image. In applications with photosensor arrays that employ timestampers for individual channels, timestamps typically are not time synchronized, introducing time skews due to different signal pathways. The scintillator topology and transportation of the scintillation light might provoke further skews. If not accounted for these effects, the achievable CTR deteriorates. We studied a convex timing calibration based on a matrix equation. In this work, we extended the calibration concept to arbitrary structures targeting different aspects of the time skews and focusing on optimizing the CTR performance for detector characterization. The radiation source distribution, the stability of the estimations, and the energy dependence of calibration data are subject to the analysis.A coincidence setup, equipped with a semi-monolithic detector comprising 8 LYSO slabs, each 3.9 mm × 31.9 mm × 19.0 mm, and a one-to-one coupled detector with 8 × 8 LYSO segments of 3.9 mm × 3.9 mm × 19.0 mm volume is used. Both scintillators utilize a dSiPM (DPC3200-22-44, Philips Digital Photon Counting) operated in first photon trigger. The calibration was also conducted with solely one-to-one coupled detectors and extrapolated for a slab-only setup.All analyzed hyperparameters show a strong influence on the calibration. Using multiple radiation positions improved the skew estimation. The statistical significance of the calibration dataset and the utilized energy window was of great importance. Compared to a one-to-one coupled detector pair achieving CTRs of 224 ps the slab detector configuration reached CTRs down to 222 ps, demonstrating that slabs can compete with a clinically used segmented detector design.This is the first work that systematically studies the influence of hyperparameters on skew estimation and proposes an extension to arbitrary calibration structures (e.g. scintillator volumes) of a known calibration technique.
提供有吸引力的符合时间分辨率（CTR）的正电子发射断层扫描（PET）探测器可提供飞行时间信息，从而提高PET图像的信噪比。在使用为各个通道配备时间戳的光电传感器阵列的应用中，时间戳通常未进行时间同步，由于信号路径不同而引入时间偏差。闪烁体的拓扑结构和闪烁光的传输可能会引发进一步的偏差。如果不考虑这些影响，可实现的CTR会变差。我们研究了基于矩阵方程的凸定时校准。在这项工作中，我们将校准概念扩展到针对时间偏差不同方面的任意结构，并专注于优化用于探测器表征的CTR性能。对辐射源分布、估计的稳定性以及校准数据的能量依赖性进行了分析。使用了一个符合装置，该装置配备了一个半单片探测器，包括8个LYSO板，每个板的尺寸为3.9 mm×31.9 mm×19.0 mm，以及一个与8×8个尺寸为3.9 mm×3.9 mm×19.0 mm的LYSO段一对一耦合的探测器。两种闪烁体均使用在首次光子触发下运行的dSiPM（DPC3200 - 22 - 44，飞利浦数字光子计数）。校准也仅使用一对一耦合探测器进行，并外推到仅使用板的设置。所有分析的超参数对校准都有很大影响。使用多个辐射位置可改善偏差估计。校准数据集的统计显著性和所使用的能量窗口非常重要。与实现CTR为224 ps的一对一耦合探测器对相比，板探测器配置的CTR降至222 ps，表明板可以与临床使用的分段探测器设计相竞争。这是第一项系统研究超参数对偏差估计的影响并提出对已知校准技术的任意校准结构（例如闪烁体体积）进行扩展的工作。
