The performance of MLEM for dynamic imaging from simulated few-view, multi-pinhole SPECT.
The performance of MLEM for dynamic imaging from simulated few-view, multi-pinhole SPECT.
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DOI：
10.1109/tns.2012.2214235
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发表时间：
2013-02
影响因子：
1.8
通讯作者：
Schmidt TG
中科院分区：
文献类型：
--
作者：
Ma D;Wolf P;Clough AV;Schmidt TG
正在开发固定小动物 SPECT 系统，用于从有限的角度视图进行快速动态成像。本文通过模拟量化了最大似然期望最大化 (MLEM) 的性能，用于从静止的三相机多针孔 SPECT 系统重建几秒的摄取持续时间的时间活动曲线 (TAC)。该研究还量化了启发式方法的好处，该方法使用从传统数量的视图重建的先前图像来初始化重建，例如从动态 TAC 的后期研究部分期间获取的数据。我们将由先验图像初始猜测 (IG) 初始化的 MLEM 重建称为 MLEMig。在一系列角度采样方案中量化了先验图像初始猜测对静态体模两个区域之间对比度的描述的影响。 TAC 根据实验测量的大鼠肺中 99mTc-六甲基丙烯胺肟 (HMPAO) 的摄取进行建模。根据估计的指数清洗和清洗参数的准确性对所得到的模拟图像的时间序列进行定量分析。在静态和动态模型研究中，先验图像初始猜测改进了模型的空间描述，例如改进了圆柱体边界的定义以及更准确地量化圆柱体之间的相对对比度。例如，在动态研究中，MLEM 重建的相对对比度误差约为 50%，而 MLEMig 的相对对比度误差约为 25-30%。在静态模型研究中，初始猜测的好处随着观看次数的增加而减少。先验图像初始猜测在重建的动态图像中引入了附加偏移，这可能是由于先验图像引入的偏差造成的。使用统一的初始猜测进行初始化的 MLEM 生成的图像忠实地再现了模拟 TAC 的时间依赖性；与真实值相比，MLEM 重建估计的平均指数冲洗/冲洗参数没有统计学上的显着差异。 MLEMig 重建估计的冲洗参数与真实值没有显着差异，但在某些情况下，估计的冲洗参数与真实值存在显着差异。总体而言，从几个视图和统一的初始猜测进行的 MLEM 重建准确地量化了 TAC 的时间依赖性，同时在对象的空间描述中引入了错误。使用后期研究的初始猜测来初始化重建可以提高空间精度，同时在某些情况下降低时间精度。
Stationary small-animal SPECT systems are being developed for rapid dynamic imaging from limited angular views. This paper quantified, through simulations, the performance of Maximum Likelihood Expectation Maximization (MLEM) for reconstructing a time-activity curve (TAC) with uptake duration of a few seconds from a stationary, three-camera multi-pinhole SPECT system. The study also quantified the benefits of a heuristic method of initializing the reconstruction with a prior image reconstructed from a conventional number of views, for example from data acquired during the late-study portion of the dynamic TAC. We refer to MLEM reconstruction initialized by a prior-image initial guess (IG) as MLEMig. The effect of the prior-image initial guess on the depiction of contrast between two regions of a static phantom was quantified over a range of angular sampling schemes. A TAC was modeled from the experimentally measured uptake of 99mTc-hexamethylpropyleneamine oxime (HMPAO) in the rat lung. The resulting time series of simulated images was quantitatively analyzed with respect to the accuracy of the estimated exponential washin and washout parameters. In both static and dynamic phantom studies, the prior-image initial guess improved the spatial depiction of the phantom, for example improved definition of the cylinder boundaries and more accurate quantification of relative contrast between cylinders. For example in the dynamic study, there was ~50% error in relative contrast for MLEM reconstructions compared to ~25-30% error for MLEMig. In the static phantom study, the benefits of the initial guess decreased as the number of views increased. The prior-image initial guess introduced an additive offset in the reconstructed dynamic images, likely due to biases introduced by the prior image. MLEM initialized with a uniform initial guess yielded images that faithfully reproduced the time dependence of the simulated TAC; there were no statistically significant differences in the mean exponential washin/washout parameters estimated from MLEM reconstructions compared to the true values. Washout parameters estimated from MLEMig reconstructions did not differ significantly from the true values, however the estimated washin parameter differed significantly from the true value in some cases. Overall, MLEM reconstruction from few views and a uniform initial guess accurately quantified the time dependance of the TAC while introducing errors in the spatial depiction of the object. Initializing the reconstruction with a late-study initial guess improved spatial accuracy while decreasing temporal accuracy in some cases.