Investigation of single, random, and true counts from natural radioactivity in LSO-based clinical PET
Investigation of single, random, and true counts from natural radioactivity in LSO-based clinical PET
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DOI：
10.1007/bf03027389
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发表时间：
2005-04-01
影响因子：
2.6
通讯作者：
Senda, M
中科院分区：
文献类型：
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作者：
Yamamoto, S;Horii, H;Senda, M
目的：原硅酸镥 (LSO) 含有天然放射性，可同时发射 β 粒子和三个伽马光子。这些β粒子和伽马光子增加了正电子发射断层扫描（PET）系统中的单一和随机速率，而在Lu-176的相同衰变中产生并由另一个探测器检测到的β粒子和伽马光子可以是β伽马符合真实事件。这项工作的目的是测量由于 LSO 中的自然放射性而产生的单一、随机和真实计数率，并确定基于 LSO 的临床 PET 中能量窗口的最佳较低能量阈值水平。方法：首先，我们使用单晶测量了LSO中这些β粒子和γ光子的能谱，以获得基础数据。然后，我们根据自然放射性测量了基于 LSO 的临床 PET 的单一、随机和真实计数率，作为较低能量阈值的函数。结果：在 PET 中，随着较低能量阈值水平的增加，由于自然背景活动而导致的单一计数率和随机计数率逐渐降低。由于 β-γ 重合，真实计数率比 250 keV 的较低能量阈值低 10 kcps 以上。然而，由于 LSO 中的自然放射性，在设置为超过 350 keV 的较低能量阈值水平下，这些真实计数率可以降低至小于 1 kcps。结论：考虑到这些因素，在基于 LSO 的临床 PET 中，建议将较低的能量阈值水平设置在 350 keV 以上。
Objective: Lutetium oxyorthosilicate (LSO) contains natural radioactivity that emits beta particles and three gamma photons simultaneously. These beta particles and gamma photons increase the single and random rates in a positron emission tomography (PET) system while a beta particle and gamma photon produced in the same decay of Lu-176 and detected by another detector can be betagamma coincidence true events. The purpose of this work is to measure the single, random, and true count rates due to the natural radioactivity in LSO and determine the optimum lower energy threshold level for an energy window in an LSO-based clinical PET. Methods: First, we measured the energy spectra of these beta particles and gamma photons in LSO using a single crystal to obtain the basic data. Then, we measured single, random, and true count rates of an LSO-based clinical PET from the natural radioactivity as a function of the lower energy threshold. Results: In the PET, single and random count rates due to the natural background activity were gradually decreased as the lower energy threshold level increased. The true count rates due to the beta-gamma coincidence were more than 10 kcps below a lower energy threshold of 250 keV. However, these true count rates due to the natural radioactivity in LSO can be decreased to less than I kcps at a lower energy threshold level set at more than 350 keV. Conclusion: With these considerations, in an LSO-based clinical PET, a lower energy threshold level set at above 350 keV is recommended.