Stockhoff Mariele, Jan Sebastien, Dubois Albertine, Cherry Simon R, Roncali Emilie
Department of Biomedical Engineering, University of California Davis, One Shields Avenue, Davis, CA 95616, United States of America.
Phys Med Biol. 2017 Jun 21;62(12):L1-L8. doi: 10.1088/1361-6560/aa7007. Epub 2017 Apr 28.
Typical PET detectors are composed of a scintillator coupled to a photodetector that detects scintillation photons produced when high energy gamma photons interact with the crystal. A critical performance factor is the collection efficiency of these scintillation photons, which can be optimized through simulation. Accurate modelling of photon interactions with crystal surfaces is essential in optical simulations, but the existing UNIFIED model in GATE is often inaccurate, especially for rough surfaces. Previously a new approach for modelling surface reflections based on measured surfaces was validated using custom Monte Carlo code. In this work, the LUT Davis model is implemented and validated in GATE and GEANT4, and is made accessible for all users in the nuclear imaging research community. Look-up-tables (LUTs) from various crystal surfaces are calculated based on measured surfaces obtained by atomic force microscopy. The LUTs include photon reflection probabilities and directions depending on incidence angle. We provide LUTs for rough and polished surfaces with different reflectors and coupling media. Validation parameters include light output measured at different depths of interaction in the crystal and photon track lengths, as both parameters are strongly dependent on reflector characteristics and distinguish between models. Results from the GATE/GEANT4 beta version are compared to those from our custom code and experimental data, as well as the UNIFIED model. GATE simulations with the LUT Davis model show average variations in light output of <2% from the custom code and excellent agreement for track lengths with R > 0.99. Experimental data agree within 9% for relative light output. The new model also simplifies surface definition, as no complex input parameters are needed. The LUT Davis model makes optical simulations for nuclear imaging detectors much more precise, especially for studies with rough crystal surfaces. It will be available in GATE V8.0.
典型的正电子发射断层扫描（PET）探测器由与光电探测器耦合的闪烁体组成，该光电探测器可检测高能伽马光子与晶体相互作用时产生的闪烁光子。一个关键的性能因素是这些闪烁光子的收集效率，可通过模拟进行优化。在光学模拟中，光子与晶体表面相互作用的精确建模至关重要，但GATE中现有的统一模型往往不准确，尤其是对于粗糙表面。此前，一种基于测量表面的表面反射建模新方法已通过定制蒙特卡罗代码得到验证。在这项工作中，LUT戴维斯模型在GATE和GEANT4中得以实现并验证，可供核成像研究领域的所有用户使用。基于原子力显微镜获得的测量表面，计算了来自各种晶体表面的查找表（LUT）。这些LUT包括取决于入射角的光子反射概率和方向。我们提供了具有不同反射器和耦合介质的粗糙和抛光表面的LUT。验证参数包括在晶体中不同相互作用深度处测量的光输出和光子轨迹长度，因为这两个参数都强烈依赖于反射器特性并能区分不同模型。将GATE/GEANT4测试版的结果与我们的定制代码和实验数据以及统一模型的结果进行了比较。使用LUT戴维斯模型进行的GATE模拟显示，与定制代码相比，光输出的平均变化<2%，并且对于轨迹长度，R>0.99时具有极好的一致性。实验数据在相对光输出方面的误差在9%以内。新模型还简化了表面定义，因为不需要复杂的输入参数。LUT戴维斯模型使核成像探测器的光学模拟更加精确，特别是对于具有粗糙晶体表面的研究。它将在GATE V8.0中可用。
