Kadrmas Dan J, Oktay M Bugrahan, Casey Michael E, Hamill James J
Utah Center for Advanced Imaging Research (UCAIR), Department of Radiology, University of Utah, Salt Lake City, UT 84108-1218 USA.
IEEE Trans Nucl Sci. 2012 Oct;59(5):1940-1947. doi: 10.1109/TNS.2012.2197414.
Lesion-detection performance in oncologic PET depends in part upon count statistics, with shorter scans having higher noise and reduced lesion detectability. However, advanced techniques such as time-of-flight (TOF) and point spread function (PSF) modeling can improve lesion detection. This work investigates the relationship between reducing count levels (as a surrogate for scan time) and reconstructing with PSF model and TOF. A series of twenty-four whole-body phantom scans was acquired on a Biograph mCT TOF PET/CT scanner using the experimental methodology prescribed for the Utah PET Lesion Detection Database. Six scans were acquired each day over four days, with up to 23 (68)Ge shell-less lesions (diam. 6, 8, 10, 12, 16 mm) distributed throughout the phantom thorax and pelvis. Each scan acquired 6 bed positions at 240 s/bed in listmode format. The listmode files were then statistically pruned, preserving Poisson statistics, to equivalent count levels for scan times of 180 s, 120 s, 90 s, 60 s, 45 s, 30 s, and 15 s per bed field-of-view, corresponding to whole-body scan times of 1.5-24 min. Each dataset was reconstructed using ordinary Poisson line-of-response (LOR) OSEM, with PSF model, with TOF, and with PSF+TOF. Localization receiver operating characteristics (LROC) analysis was then performed using the channelized non-prewhitened (CNPW) observer. The results were analyzed to delineate the relationship between scan time, reconstruction method, and strength of post-reconstruction filter. Lesion-detection performance degraded as scan time was reduced, and progressively stronger filters were required to maximize performance for the shorter scans. PSF modeling and TOF were found to improve detection performance, but the degree of improvement for TOF was much larger than for PSF for the large phantom used in this study. Notably, the images using TOF provided equivalent lesion-detection performance to the images without TOF for scan durations 40% shorter, suggesting that TOF may offset, at least in part, the need for longer scan times in larger patients.
肿瘤PET中的病灶检测性能部分取决于计数统计，扫描时间越短，噪声越高，病灶可检测性越低。然而，诸如飞行时间（TOF）和点扩散函数（PSF）建模等先进技术可以改善病灶检测。这项工作研究了降低计数水平（作为扫描时间的替代指标）与使用PSF模型和TOF进行重建之间的关系。使用为犹他州PET病灶检测数据库规定的实验方法，在Biograph mCT TOF PET/CT扫描仪上进行了一系列24次全身体模扫描。在四天内每天进行6次扫描，在体模胸部和骨盆中分布有多达23个（68）锗无壳病灶（直径6、8、10、12、16毫米）。每次扫描以列表模式格式在每个床位240秒的时间内采集6个床位位置。然后对列表模式文件进行统计修剪，保留泊松统计，使其等效计数水平对应于每个床位视野180秒、120秒、90秒、60秒、45秒、30秒和15秒的扫描时间，对应于1.5 - 24分钟的全身扫描时间。每个数据集使用普通泊松响应线（LOR）OSEM、PSF模型、TOF以及PSF + TOF进行重建。然后使用通道化非白化（CNPW）观察者进行定位接收器操作特性（LROC）分析。对结果进行分析以描绘扫描时间、重建方法和重建后滤波器强度之间的关系。随着扫描时间的减少，病灶检测性能下降，对于较短的扫描，需要更强的滤波器来使性能最大化。发现PSF建模和TOF可提高检测性能，但对于本研究中使用的大体模，TOF的改善程度远大于PSF。值得注意的是，使用TOF的图像在扫描持续时间缩短40%的情况下提供了与不使用TOF的图像等效的病灶检测性能，这表明TOF至少在一定程度上可以抵消较大患者对更长扫描时间的需求。
