Institute of Neuroscience and Medicine, INM-4, Forschungszentrum Jülich GmbH, Jülich, Germany.
Department of Psychiatry, Psychotherapy and Psychosomatics, RWTH Aachen University, Aachen, Germany.
PLoS One. 2021 Jan 22;16(1):e0245580. doi: 10.1371/journal.pone.0245580. eCollection 2021.
Iterative image reconstruction is widely used in positron emission tomography. However, it is known to contribute to quantitation bias and is particularly pronounced during dynamic studies with 11C-labeled radiotracers where count rates become low towards the end of the acquisition. As the strength of the quantitation bias depends on the counts in the reconstructed frame, it can differ from frame to frame of the acquisition. This is especially relevant in the case of neuro-receptor studies with simultaneous PET/MR when a bolus-infusion protocol is applied to allow the comparison of pre- and post-task effects. Here, count dependent changes in quantitation bias may interfere with task changes. We evaluated the impact of different framing schemes on quantitation bias and its propagation into binding potential (BP) using a phantom decay study with 11C and 3D OP-OSEM. Further, we propose a framing scheme that keeps the true counts per frame constant over the acquisition time as constant framing schemes and conventional increasing framing schemes are unlikely to achieve stable bias values during the acquisition time range. For a constant framing scheme with 5 minutes frames, the BP bias was 7.13±2.01% (10.8% to 3.8%) compared to 5.63±2.85% (7.8% to 4.0%) for conventional increasing framing schemes. Using the proposed constant true counts framing scheme, a stabilization of the BP bias was achieved at 2.56±3.92% (3.5% to 1.7%). The change in BP bias was further studied by evaluating the linear slope during the acquisition time interval. The lowest slope values were observed in the constant true counts framing scheme. The constant true counts framing scheme was effective for BP bias stabilization at relevant activity and time ranges. The mean BP bias under these conditions was 2.56±3.92%, which represents the lower limit for the detection of changes in BP during equilibrium and is especially important in the case of cognitive tasks where the expected changes are low.
迭代图像重建广泛应用于正电子发射断层扫描。然而，它被认为会导致定量偏差，特别是在使用 11C 标记放射性示踪剂进行动态研究时，当采集接近尾声时，计数率会降低。由于定量偏差的强度取决于重建帧中的计数，因此它可能会因采集的每一帧而有所不同。在使用放射性示踪剂的神经受体研究中，这种情况尤其相关，此时应用 bolus-infusion 方案以允许比较任务前后的效应。在这种情况下，定量偏差的依赖于计数的变化可能会干扰任务的变化。我们使用 11C 和 3D OP-OSEM 进行了一个体模衰减研究，评估了不同的帧方案对定量偏差及其在结合势（BP）中的传播的影响。此外，我们提出了一种帧方案，该方案在采集时间内保持每帧的真实计数不变，因为恒定的帧方案和传统的递增帧方案不太可能在采集时间范围内获得稳定的偏差值。对于具有 5 分钟帧的恒定帧方案，BP 偏差为 7.13±2.01%（10.8%至 3.8%），而对于传统的递增帧方案，BP 偏差为 5.63±2.85%（7.8%至 4.0%）。使用提出的恒定真实计数帧方案，在 2.56±3.92%（3.5%至 1.7%）处实现了 BP 偏差的稳定。通过评估采集时间间隔内的线性斜率进一步研究了 BP 偏差的变化。在恒定真实计数帧方案中观察到最低的斜率值。在相关的活性和时间范围内，恒定真实计数帧方案对于 BP 偏差的稳定是有效的。在这些条件下，平均 BP 偏差为 2.56±3.92%，这代表了平衡状态下 BP 变化检测的下限，在认知任务中尤其重要，因为预期的变化较小。
