Dewaraja Yuni K, Ljungberg Michael, Fessler Jeffrey A
Department of Radiology, University of Michigan, Ann Arbor, MI 48109-0552 USA (
IEEE Trans Nucl Sci. 2006;53(1):181. doi: 10.1109/TNS.2005.862956.
We have implemented highly accurate Monte Carlo based scatter modeling (MCS) with 3-D ordered subsets expectation maximization (OSEM) reconstruction for I-131 single photon emission computed tomography (SPECT). The scatter is included in the statistical model as an additive term and attenuation and detector response are included in the forward/backprojector. In the present implementation of MCS, a simple multiple window-based estimate is used for the initial iterations and in the later iterations the Monte Carlo estimate is used for several iterations before it is updated. For I-131, MCS was evaluated and compared with triple energy window (TEW) scatter compensation using simulation studies of a mathematical phantom and a clinically realistic voxel-phantom. Even after just two Monte Carlo updates, excellent agreement was found between the MCS estimate and the true scatter distribution. Accuracy and noise of the reconstructed images were superior with MCS compared to TEW. However, the improvement was not large, and in some cases may not justify the large computational requirements of MCS. Furthermore, it was shown that the TEW correction could be improved for most of the targets investigated here by applying a suitably chosen scaling factor to the scatter estimate. Finally clinical application of MCS was demonstrated by applying the method to an I-131 radioimmunotherapy (RIT) patient study.
我们已针对碘 - 131单光子发射计算机断层扫描（SPECT），采用基于蒙特卡罗的高精度散射建模（MCS）与三维有序子集期望最大化（OSEM）重建方法。散射作为一个附加项包含在统计模型中，而衰减和探测器响应包含在前向/反向投影器中。在当前的MCS实现中，初始迭代使用基于简单多窗口的估计，在后续迭代中，蒙特卡罗估计在更新之前用于多次迭代。对于碘 - 131，通过对数学模型和临床实际体素模型的模拟研究，对MCS进行了评估，并与三能量窗（TEW）散射补偿进行了比较。即使仅经过两次蒙特卡罗更新，MCS估计值与真实散射分布之间也发现了极好的一致性。与TEW相比，MCS重建图像的准确性和噪声更优。然而，改进幅度不大，在某些情况下，可能无法证明MCS的大量计算需求是合理的。此外，结果表明，通过对散射估计应用适当选择的缩放因子，此处研究的大多数目标的TEW校正都可以得到改善。最后，通过将该方法应用于碘 - 131放射免疫治疗（RIT）患者研究，展示了MCS的临床应用。
