Ghaly Michael, Links Jonathan M, Frey Eric C
The Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, USA.
Phys Med Biol. 2015 Jul 7;60(13):5083-101. doi: 10.1088/0031-9155/60/13/5083. Epub 2015 Jun 17.
Dual-isotope simultaneous-acquisition (DISA) rest-stress myocardial perfusion SPECT (MPS) protocols offer a number of advantages over separate acquisition. However, crosstalk contamination due to scatter in the patient and interactions in the collimator degrade image quality. Compensation can reduce the effects of crosstalk, but does not entirely eliminate image degradations. Optimizing acquisition parameters could further reduce the impact of crosstalk. In this paper we investigate the optimization of the rest Tl-201 energy window width and relative injected activities using the ideal observer (IO), a realistic digital phantom population and Monte Carlo (MC) simulated Tc-99m and Tl-201 projections as a means to improve image quality. We compared performance on a perfusion defect detection task for Tl-201 acquisition energy window widths varying from 4 to 40 keV centered at 72 keV for a camera with a 9% energy resolution. We also investigated 7 different relative injected activities, defined as the ratio of Tc-99m and Tl-201 activities, while keeping the total effective dose constant at 13.5 mSv. For each energy window and relative injected activity, we computed the IO test statistics using a Markov chain Monte Carlo (MCMC) method for an ensemble of 1,620 triplets of fixed and reversible defect-present, and defect-absent noisy images modeling realistic background variations. The volume under the 3-class receiver operating characteristic (ROC) surface (VUS) was estimated and served as the figure of merit. For simultaneous acquisition, the IO suggested that relative Tc-to-Tl injected activity ratios of 2.6-5 and acquisition energy window widths of 16-22% were optimal. For separate acquisition, we observed a broad range of optimal relative injected activities from 2.6 to 12.1 and acquisition energy window of widths 16-22%. A negative correlation between Tl-201 injected activity and the width of the Tl-201 energy window was observed in these ranges. The results also suggested that DISA methods could potentially provide image quality as good as that obtained with separate acquisition protocols. We compared observer performance for the optimized protocols and the current clinical protocol using separate acquisition. The current clinical protocols provided better performance at a cost of injecting the patient with approximately double the injected activity of Tc-99m and Tl-201, resulting in substantially increased radiation dose.
双同位素同时采集（DISA）静息-负荷心肌灌注单光子发射计算机断层扫描（MPS）协议相较于单独采集具有诸多优势。然而，患者体内散射以及准直器中的相互作用导致的串扰污染会降低图像质量。补偿可减少串扰的影响，但无法完全消除图像退化。优化采集参数可进一步降低串扰的影响。在本文中，我们使用理想观察者（IO）、现实的数字体模群体以及蒙特卡罗（MC）模拟的锝-99m和铊-201投影，研究静息态铊-201能量窗宽度和相对注射活度的优化，以此作为提高图像质量的一种手段。我们比较了对于一台能量分辨率为9%的相机，在以72keV为中心、宽度从4keV到40keV变化的铊-201采集能量窗宽度下，灌注缺损检测任务的性能。我们还研究了7种不同的相对注射活度，定义为锝-99m与铊-201活度之比，同时将总有效剂量保持在13.5mSv不变。对于每个能量窗和相对注射活度，我们使用马尔可夫链蒙特卡罗（MCMC）方法，针对1620组固定且可逆的有缺损和无缺损噪声图像（模拟现实背景变化）的三联体，计算IO测试统计量。估计了三类接收器操作特性（ROC）曲面下的体积（VUS），并将其用作品质因数。对于同时采集，IO表明锝与铊的相对注射活度比为2.6 - 5且采集能量窗宽度为16% - 22%时是最优的。对于单独采集，我们观察到最优相对注射活度范围很广，从2.6到12.1，采集能量窗宽度为16% - 22%。在这些范围内观察到铊-201注射活度与铊-201能量窗宽度之间呈负相关。结果还表明，DISA方法有可能提供与单独采集协议所获得的图像质量相当的图像质量。我们比较了优化协议与当前使用单独采集的临床协议的观察者性能。当前的临床协议以向患者注射大约两倍于锝-99m和铊-201的注射活度为代价，提供了更好的性能，这导致辐射剂量大幅增加。
