Department of Medical Physics, School of Medicine, University of Patras, Rion 26504, Greece.
Med Phys. 2013 Nov;40(11):112505. doi: 10.1118/1.4824694.
In this work, the authors aim for the estimation of the effect of (176)Lu intrinsic radioactivity on the performance of a dual head PET system dedicated to small animal imaging.
A prototype camera has been used as a reference system in order to validate two GATE simulation models, which were used for the investigation. The first model includes the (176)Lu intrinsic radioactivity, while the second does not. The two models have been designed in order to provide similar sensitivities, in terms of count rate performance and scatter fraction, in the linear range of activities. In addition, the model with the (176)Lu intrinsic radioactivity, has been validated in terms of background count rate. Different acquisition schemes have been examined in order to determine the optimum conditions to minimize the (176)Lu effects, while maintaining a high trues count rate. In addition, the effect on the image quality, in terms of spatial resolution, signal-to-noise ratio, and minimum detectable activity, was investigated.
Both models are in good agreement with the measured data. While, the presence of the (176)Lu altered the dead time of the model, it also affected the singles, trues, and randoms count rates. The noise equivalent count rate curves of the two models indicate that for low activities, the lack of (176)Lu radioactivity leads to better noise properties due to the underestimation of the randoms. Signal-to-noise ratio measurement on coincidence images confirm the aforementioned claim, since the model without the (176)Lu provides better less noisy images. Furthermore, the spatial resolution and the minimum detectable activity are overestimated.
It has been proven that the lack of the (176)Lu intrinsic radioactivity has an impact on the design of the simulation model's dead time. Even if there is an alignment with experimental results still the noise properties, for a wide range of activities, are overestimated. In addition, for low activities, better image quality, is presented, mainly due to the lack of the (176)Lu photons which blur the images. Furthermore, it was shown that the use of a high hardware threshold allows the application of a wide energy window, which improves the statistics without a significant compromise on the quality of the detected photons, mainly, due to the early rejection of the low energy photons and the low scatter factor.
在这项工作中，作者旨在估计（176）Lu 固有放射性对专门用于小动物成像的双头 PET 系统性能的影响。
使用原型相机作为参考系统，以验证两个 GATE 模拟模型，这两个模型用于研究。第一个模型包括（176）Lu 固有放射性，而第二个模型则不包括。这两个模型的设计目的是在活动的线性范围内提供相似的计数率性能和散射分数。此外，还对具有（176）Lu 固有放射性的模型进行了背景计数率验证。为了确定最佳条件以最小化（176）Lu 效应，同时保持高真实计数率，检查了不同的采集方案。此外，还研究了图像质量（空间分辨率、信噪比和最小可探测活性）的影响。
两个模型都与测量数据吻合良好。然而，（176）Lu 的存在改变了模型的死时间，也影响了单计数、真计数和随机计数率。两个模型的噪声等效计数率曲线表明，对于低活动，由于对随机计数的低估，缺乏（176）Lu 放射性会导致更好的噪声特性。对符合图像的信噪比测量证实了上述说法，因为没有（176）Lu 的模型提供了更好的低噪声图像。此外，空间分辨率和最小可探测活性被高估。
已经证明缺乏（176）Lu 固有放射性会对模拟模型死时间的设计产生影响。即使与实验结果一致，对于广泛的活动，噪声特性仍然被高估。此外，对于低活动，呈现出更好的图像质量，这主要是由于缺乏（176）Lu 光子，这些光子会使图像模糊。此外，结果表明，使用高硬件阈值可以应用宽能窗，这可以在不显著影响探测光子质量的情况下提高统计数据，主要是由于早期拒绝低能量光子和低散射因子。
