Department of Radiology and the Molecular Imaging Program at Stanford, Stanford University, Stanford, California 94305-5128, USA.
Med Phys. 2010 Nov;37(11):5838-49. doi: 10.1118/1.3484059.
This study aims to address design considerations of a high resolution, high sensitivity positron emission tomography scanner dedicated to breast imaging.
The methodology uses a detailed Monte Carlo model of the system structures to obtain a quantitative evaluation of several performance parameters. Special focus was given to the effect of dense mechanical structures designed to provide mechanical robustness and thermal regulation to the minuscule and temperature sensitive detectors.
For the energies of interest around the photopeak (450-700 keV energy window), the simulation results predict a 6.5% reduction in the single photon detection efficiency and a 12.5% reduction in the coincidence photon detection efficiency in the case that the mechanical structures are interspersed between the detectors. However for lower energies, a substantial increase in the number of detected events (approximately 14% and 7% for singles at a 100-200 keV energy window and coincidences at a lower energy threshold of 100 keV, respectively) was observed with the presence of these structures due to backscatter. The number of photon events that involve multiple interactions in various crystal elements is also affected by the presence of the structures. For photon events involving multiple interactions among various crystal elements, the coincidence photon sensitivity is reduced by as much as 20% for a point source at the center of the field of view. There is no observable effect on the intrinsic and the reconstructed spatial resolution and spatial resolution uniformity.
Mechanical structures can have a considerable effect on system sensitivity, especially for systems processing multi-interaction photon events. This effect, however, does not impact the spatial resolution. Various mechanical structure designs are currently under evaluation in order to achieve optimum trade-off between temperature stability, accurate detector positioning, and minimum influence on system performance.
本研究旨在探讨专门用于乳房成像的高分辨率、高灵敏度正电子发射断层扫描（PET）扫描仪的设计考虑因素。
该方法使用系统结构的详细蒙特卡罗模型来对几个性能参数进行定量评估。特别关注旨在为微小且对温度敏感的探测器提供机械强度和温度调节的密集机械结构的影响。
对于感兴趣的能量范围（450-700keV 能窗），模拟结果预测在机械结构散布在探测器之间的情况下，单光子探测效率降低 6.5%，符合探测效率降低 12.5%。然而，对于较低的能量，由于背散射，检测到的事件数量会大幅增加（在 100-200keV 能窗下的单光子分别增加约 14%和 7%，在较低的 100keV 能量阈值下的符合事件分别增加约 14%和 7%）。在各种晶体元件中存在多次相互作用的光子事件数量也受到结构存在的影响。对于涉及各种晶体元件中多次相互作用的光子事件，对于视场中心的点源，符合光子灵敏度降低多达 20%。固有和重建空间分辨率和空间分辨率均匀性没有可观察到的影响。
机械结构会对系统灵敏度产生相当大的影响，特别是对于处理多相互作用光子事件的系统。然而，这种影响不会影响空间分辨率。目前正在评估各种机械结构设计，以在温度稳定性、准确的探测器定位和对系统性能的最小影响之间实现最佳折衷。
