Recovery and normalization of triple coincidences in PET
Recovery and normalization of triple coincidences in PET
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DOI：
10.1118/1.4908226
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发表时间：
2015-03-01
期刊：
影响因子：
3.8
通讯作者：
Herraiz, Joaquin L.
中科院分区：
文献类型：
--
作者：
Lage, Eduardo;Parot, Vicente;Herraiz, Joaquin L.
目的：正电子发射断层扫描(PET)中的三重符合是指同时检测到三条射线的事件。这些事件虽然可能有助于提高PET扫描仪的灵敏度，但在当前系统中被丢弃或处理，因为没有明确的标准将它们分配到唯一的响应线(LOR)。提出的用于恢复这种事件的方法通常依赖于高度专业化的检测系统的使用，阻碍了普遍采用，和/或基于康普顿散射运动学，因此，受标准PET探测器的能量分辨率的限制，精度受到限制。在这项工作中，作者提出了一种简单而通用的解决方案来恢复三重重合，它不需要专门的探测器或额外的能量分辨率要求。方法：为了恢复三重重合，作者的方法是根据这些重合事件在这些LOR中的相对比例来分配这些事件在可能的LOR中。分析表明，这种分配方案代表了三重重合分布问题的最大似然解。临床前PET/CT扫描仪的PET组件被改装成能够获取和处理三重重合。由于发现在整个扫描仪视野中检测双重和三重事件的效率不同，还开发了专门用于三重重合的归一化程序。使用他们的方法包括三重重合的效果与在可能的LOR中对三重重合进行等权重并丢弃所有三重事件的情况进行了比较。作者使用NEMA NU-4临床前PET扫描仪评估方案中描述的灵敏度、噪声当量计数(NEC)率和图像质量作为该比较的优值系数。结果：对于小鼠和大鼠大小的物体，添加了作者方法中的三重符合事件使扫描仪的峰值NEC率分别增加了26.6%和32%。NEC-Rate性能的这种提高也反映在图像质量指标上。在保持空间分辨率和对比度的情况下，使用他们的方法恢复的双重和三重重合重建的图像比只使用双重重合重建的图像具有更好的信噪比。使用等权方案的三重重合的分布增加了系统的表观灵敏度，但降低了图像质量。通过使用他们的方法包含三重符合项所提供的性能提升允许将标准成像过程的采集时间减少多达25%。结论：使用所提出的方法恢复三重符合项可以有效地提高当前临床和临床前PET系统的灵敏度，而不会影响其他参数，如空间分辨率或对比度。(C)2015年美国医学物理学家协会。
Purpose: Triple coincidences in positron emission tomography (PET) are events in which three.-rays are detected simultaneously. These events, though potentially useful for enhancing the sensitivity of PET scanners, are discarded or processed without special consideration in current systems, because there is not a clear criterion for assigning them to a unique line-of-response (LOR). Methods proposed for recovering such events usually rely on the use of highly specialized detection systems, hampering general adoption, and/or are based on Compton-scatter kinematics and, consequently, are limited in accuracy by the energy resolution of standard PET detectors. In this work, the authors propose a simple and general solution for recovering triple coincidences, which does not require specialized detectors or additional energy resolution requirements.Methods: To recover triple coincidences, the authors' method distributes such events among their possible LORs using the relative proportions of double coincidences in these LORs. The authors show analytically that this assignment scheme represents the maximum-likelihood solution for the triple-coincidence distribution problem. The PET component of a preclinical PET/CT scanner was adapted to enable the acquisition and processing of triple coincidences. Since the efficiencies for detecting double and triple events were found to be different throughout the scanner field-of-view, a normalization procedure specific for triple coincidences was also developed. The effect of including triple coincidences using their method was compared against the cases of equally weighting the triples among their possible LORs and discarding all the triple events. The authors used as figures of merit for this comparison sensitivity, noise-equivalent count (NEC) rates and image quality calculated as described in the NEMA NU-4 protocol for the assessment of preclinical PET scanners.Results: The addition of triple-coincidence events with the authors' method increased peak NEC rates of the scanner by 26.6% and 32% for mouse-and rat-sized objects, respectively. This increase in NEC-rate performance was also reflected in the image-quality metrics. Images reconstructed using double and triple coincidences recovered using their method had better signal-to-noise ratio than those obtained using only double coincidences, while preserving spatial resolution and contrast. Distribution of triple coincidences using an equal-weighting scheme increased apparent system sensitivity but degraded image quality. The performance boost provided by the inclusion of triple coincidences using their method allowed to reduce the acquisition time of standard imaging procedures by up to similar to 25%.Conclusions: Recovering triple coincidences with the proposed method can effectively increase the sensitivity of current clinical and preclinical PET systems without compromising other parameters like spatial resolution or contrast. (C) 2015 American Association of Physicists in Medicine.