Division of Cyclotron Nuclear Medicine, Cyclotron and Radioisotope Center, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan.
Ann Nucl Med. 2010 Jul;24(6):461-8. doi: 10.1007/s12149-010-0381-y. Epub 2010 Apr 20.
Positron emission tomography (PET) scanners require periodic monitoring in order to maintain scanner performance. The aim of the present study was to examine the deterioration of PET scanner performance caused by aging.
We retrospectively examined PET scanner performance alterations in terms of sensitivity, spatial resolution, false coincidences due to scatter and random coincidences based on 13 years of follow-up data, including data when the PET scanner underwent an overhaul at the 10th year after installation. Sensitivity and scatter fraction were calculated by using cross calibration factor (CCF) measurement data, which are collected routinely. Efficacy of the examining the sensitivity and scatter was confirmed by NEMA measurements. Trans-axial resolution was measured as full width at half-maximum (FWHM) and full width at tenth-maximum (FWTM) at 0-20 cm offset from the field of view (FOV) center at the time of installation, 8 years after installation, and immediately after the overhaul. Random coincidence rate fraction was measured in a wide range of count rates before and after the overhaul.
The results indicated that the total reduction of sensitivity during the first 10 years was 41% of the initial value in terms of NEMA measurement, and that the annual reduction of sensitivity progressed at a rate of 4.7% per year in terms of CCF measurement data. The changes in sensitivity can be calculated using CCF measurement data. Regarding the spatial resolution, mean FWHM and FWTM values were increased by 1.7 and 3.6%, respectively, in 8 years after installation. The relative scatter fraction was significantly increased compared with that before the overhaul. The random fraction decreased by 10-15% after the overhaul within a certain range of random count rates (1-120 kcps). In the case of our scanner, the parameter that displayed the largest change was the sensitivity, and this change was thought to be caused by the reduction of photomultiplier tube (PMT) gain, although the changes in PMT gain can cause various types of performance deterioration, as investigated in this study.
We observed that the sensitivity of our PET scanner generally deteriorated due to aging. Sensitivity monitoring using CCF measurements can be an easy and useful method for monitoring and maintaining the performance of PET scanners against aging. Since the data were obtained from a single scanner, the authors would encourage the initiation of a follow-up study involving various scanners.
正电子发射断层扫描（PET）扫描仪需要定期监测以维持扫描仪的性能。本研究的目的是研究由于老化导致的 PET 扫描仪性能的下降。
我们通过 13 年的随访数据，包括安装后第 10 年进行全面检修的数据，回顾性地检查了灵敏度、空间分辨率、由于散射引起的假符合和随机符合等 PET 扫描仪性能的变化。灵敏度和散射分数是通过使用常规采集的交叉校准因子（CCF）测量数据来计算的。通过 NEMA 测量来验证检查灵敏度和散射的效果。在安装时、安装 8 年后以及全面检修后，测量视野（FOV）中心 0-20cm 处的 trans-axial 分辨率作为半高全宽（FWHM）和十分之九全宽（FWTM）。在全面检修前后的宽计数率范围内测量随机符合率分数。
结果表明，在 NEMA 测量中，前 10 年的灵敏度总衰减为初始值的 41%，而在 CCF 测量数据中，灵敏度的年衰减率为每年 4.7%。灵敏度的变化可以使用 CCF 测量数据来计算。关于空间分辨率，安装 8 年后平均 FWHM 和 FWTM 值分别增加了 1.7%和 3.6%。与全面检修前相比，相对散射分数显著增加。在一定的随机计数率（1-120kcps）范围内，全面检修后随机分数下降了 10-15%。在我们的扫描仪中，变化最大的参数是灵敏度，虽然 PMT 增益的变化会导致各种类型的性能下降，如本研究中所调查的那样，但认为这是由于光电倍增管（PMT）增益的降低所致。
我们观察到我们的 PET 扫描仪的灵敏度通常会因老化而恶化。使用 CCF 测量进行灵敏度监测可以是一种简单而有用的方法，用于监测和维护 PET 扫描仪的性能，防止老化。由于数据来自单个扫描仪，作者鼓励开展涉及各种扫描仪的后续研究。
