In ordered subsets expectation maximization (OSEM) reconstruction of electrocardiography (ECG)-gated myocardial perfusion single-photon emission computed tomography (SPECT), it is often assumed that the image acquisition time is constant for each projection angle and ECG bin. Due to heart rate variability (HRV), this assumption may lead to errors in quantification of left ventricular mechanical dyssynchrony with phase analysis. We hypothesize that a time-modified OSEM (TOSEM) algorithm provides more robust results. List-mode data of 44 patients were acquired with a dual-detector SPECT/CT system and binned to eight ECG bins. First, activity ratio (AR)—the ratio of total activity in the last OSEM-reconstructed ECG bin and first five ECG bins—was computed, as well as standard deviation SDR-R of the accepted R–R intervals; their association was evaluated with Pearson correlation analysis. Subsequently, patients whose AR was higher than 90% were selected, and their list-mode data were rebinned by omitting a part of the acquired counts to yield AR values of 90%, 80%, 70%, 60% and 50%. These data sets were reconstructed with OSEM and TOSEM algorithms, and phase analysis was performed. Reliability of both algorithms was assessed by computing concordance correlation coefficients (CCCs) between the 90% data and data corresponding to lower AR values. Finally, phase analysis results assessed from OSEM- and TOSEM-reconstructed images were compared. A strong negative correlation (r = -0.749) was found between SDR-R and AR. As AR decreased, phase analysis parameters obtained from OSEM images decreased significantly. On the contrary, reduction of AR had no significant effect on phase analysis parameters obtained from TOSEM images (CCC > 0.88). The magnitude of difference between OSEM and TOSEM results increased as AR decreased. TOSEM algorithm minimizes the HRV-related error and can be used to provide more robust phase analysis results.

中文翻译：

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时间修改的OSEM算法，用于通过心电图门控心肌灌注SPECT的相位分析更稳健地评估左心室不同步

在心电图（ECG）门控的心肌灌注单光子发射计算机断层扫描（SPECT）的有序子集期望最大化（OSEM）重建中，通常假定对于每个投影角度和ECG箱，图像获取时间都是恒定的。由于心率变异性（HRV），此假设可能会导致相位分析量化左心室机械不同步。我们假设时间修改的OSEM（TOSEM）算法可提供更可靠的结果。使用双检测器SPECT / CT系统获取了44位患者的列表模式数据，并将其分装到八个ECG箱中。首先，计算活性比（AR），即最后一个OSEM重建的ECG盒和前五个ECG盒中的总活性之比，以及可接受的R-R间隔的标准差SDR-R。通过皮尔逊相关分析评估他们的关联。随后，选择AR高于90％的患者，并通过省略部分获得的计数来重新组合其列表模式数据，以产生90％，80％，70％，60％和50％的AR值。使用OSEM和TOSEM算法重建这些数据集，并进行相位分析。通过计算90％数据与对应于较低AR值的数据之间的一致性相关系数（CCC），评估了两种算法的可靠性。最后，比较了从OSEM和TOSEM重建图像获得的相位分析结果。在SDR-R和AR之间发现强烈的负相关（r = -0.749）。随着AR的降低，从OSEM图像获得的相位分析参数将显着降低。反之，减少AR对从TOSEM图像获得的相位分析参数没有明显影响（CCC> 0.88）。OSEM和TOSEM结果之间的差异幅度随AR的降低而增加。TOSEM算法可将与HRV相关的误差降至最低，并可用于提供更可靠的相位分析结果。