Macdonald Lawrence R, Schmitz Ruth E, Alessio Adam M, Harrison Robert L, Lewellen Thomas K, Kinahan Paul E
Dept. of Radiology, Univ. of Washington, Seattle, WA 98195 USA.
IEEE Nucl Sci Symp Conf Rec (1997). 2007;4:2880-2884. doi: 10.1109/NSSMIC.2007.4436736.
We present the derivation of a live-time model for predicting count rates in computer simulations of PET scanners. Computer models are frequently used to investigate new PET scanner configurations, but they typically do not account for the count losses caused by scanner-specific electronics and processing. The live-time fraction depends strongly on the photon flux incident on the detector. We modeled the live-time of a clinical PET scanner by relating measured and simulated single photon fluxes. Our model used data from a specific scanner, but the approach is generally applicable.We applied the live-time model to partial collimation on a PET scanner; in particular, a scanner with septa positioned between every third detector ring ("2.7D" acquisition mode). The photon flux was measured and simulated for conventional acquisition modes (2D, 3D), and simulated for partial collimation (2.7D). These data were used in the model to predict live-time for partial collimation. The model was then validated against measurements in 2.7D mode. At low activity the model was very accurate at predicting the live-time fraction. Over-estimation of count-rates by the simulations lead to an uncertainly in the live-model. The uncertainty increased with activity concentration, reaching 0.9% and 2.2% at 20 kBq/mL for singles and coincidence live-time, respectively. When applied to 2.7D mode, the model predicted coincidence live-time accurate to 2.2% and 10% at 5 kBq/mL and 20 kBq/mL in the phantom, respectively. The 2.7D singles-counting live-time was predicted to within 0.2% of the measured value for up to 20 kBq/mL in the phantom.
我们展示了一种用于在正电子发射断层扫描（PET）扫描仪的计算机模拟中预测计数率的实时模型的推导过程。计算机模型经常被用于研究新型PET扫描仪配置，但它们通常没有考虑特定扫描仪的电子设备和处理过程所导致的计数损失。实时分数强烈依赖于入射到探测器上的光子通量。我们通过关联测量的和模拟的单光子通量来对临床PET扫描仪的实时进行建模。我们的模型使用了来自特定扫描仪的数据，但该方法具有普遍适用性。我们将实时模型应用于PET扫描仪上的部分准直；特别是对于在每隔第三个探测器环之间设置隔板的扫描仪（“2.7D”采集模式）。针对传统采集模式（2D、3D）测量并模拟了光子通量，并针对部分准直（2.7D）进行了模拟。这些数据被用于模型中以预测部分准直的实时。然后根据2.7D模式下的测量结果对该模型进行了验证。在低活度下，该模型在预测实时分数方面非常准确。模拟对计数率的高估导致了实时模型的不确定性。不确定性随着活度浓度的增加而增大，在活度浓度为20 kBq/mL时，单光子实时和符合实时的不确定性分别达到0.9%和2.2%。当应用于2.7D模式时，该模型在体模中5 kBq/mL和20 kBq/mL时分别将符合实时预测到精确至2.2%和10%。对于体模中高达20 kBq/mL的情况，2.7D单光子计数实时被预测到与测量值相差在0.2%以内。
