Department of Radiology, University of Pennsylvania, Philadelphia, PA, 19104, USA.
Med Phys. 2017 Jul;44(7):3534-3544. doi: 10.1002/mp.12311. Epub 2017 Jun 9.
To improve the precision of multicenter clinical trials, several efforts are underway to determine scanner-specific parameters for harmonization using standardized phantom measurements. The goal of this study was to test the correspondence between quantification in phantom and patient images and validate the use of phantoms for harmonization of patient images.
The National Electrical Manufacturers' Association image quality phantom with hot spheres was scanned on two time-of-flight PET scanners. Whole-body [ F]-fluorodeoxyglucose (FDG)-PET scans were acquired of subjects on the same systems. List-mode events from spheres (diam.: 10-28 mm) measured in air on each scanner were embedded into the phantom and subject list-mode data from each scanner to create lesions with known uptake with respect to the local background in the phantom and each subject's liver and lung regions, as a proxy to characterize true lesion quantification. Images were analyzed using the contrast recovery coefficient (CRC) typically used in phantom studies and serving as a surrogate for the standardized uptake value used clinically. Postreconstruction filtering (resolution recovery and Gaussian smoothing) was applied to determine if the effect on the phantom images translates equivalently to subject images. Three postfiltering strategies were selected to harmonize the CRC or CRC values between the two scanners based on the phantom measurements and then applied to the subject images.
Both the average CRC and CRC values for lesions embedded in the lung and liver in four subjects (BMI range 25-38) agreed to within 5% with the CRC values for lesions embedded in the phantom for all lesion sizes. In addition, the relative changes in CRC and CRC resulting from the application of the postfilters on the subject and phantom images were consistent within measurement uncertainty. Further, the root mean squared percent difference (RMS ) between CRC values on the two scanners calculated over the three sphere sizes was significantly reduced in the subjects using postfiltering strategies chosen to harmonize CRC or CRC based on phantom measurements: RMS of the CRC values in subjects was reduced from 36% to < 8% after harmonizing CRC , while RMS for CRC was reduced from ~33% to < 6% after harmonizing CRC with a different strategy. However, with this strategy designed to harmonize CRC , the RMS for CRC only improved to ~14% in subjects.
The consistency of the CRC measurements between the phantom and subject data demonstrates that harmonization strategies defined with phantom studies track well to patient images. However, quantitative agreement between different scanners as represented by the RMS depends on the metric chosen for harmonization.
为了提高多中心临床试验的精度，人们正在努力通过使用标准化体模测量来确定特定于扫描仪的参数以实现协调。本研究的目的是检验体模定量与患者图像之间的一致性，并验证体模用于协调患者图像的可用性。
使用 National Electrical Manufacturers' Association（NEMA）体模对两个飞行时间 PET 扫描仪进行了带有热球的扫描。在相同的系统上对受试者进行了全身 [ F]-氟脱氧葡萄糖（FDG）-PET 扫描。将每个扫描仪上空气中的球体（直径：10-28mm）的列表模式事件嵌入到体模和每个扫描仪的受试者列表模式数据中，以创建具有相对于体模和每个受试者的肝和肺区域的局部背景的已知摄取的病变，作为对真实病变定量的特征。使用通常用于体模研究的对比恢复系数（CRC）来分析图像，并将其用作临床上使用的标准化摄取值的替代物。应用后重建滤波（分辨率恢复和高斯平滑）以确定该滤波对体模图像的影响是否等效于对受试者图像的影响。根据体模测量，选择了三种后滤波策略来协调两个扫描仪之间的 CRC 或 CRC 值，然后将其应用于受试者图像。
对于四个受试者（BMI 范围 25-38）的肺和肝中嵌入的病变的平均 CRC 和 CRC 值与所有病变大小的体模中嵌入的病变的 CRC 值相差在 5%以内。此外，应用后滤波器后，受试者和体模图像中 CRC 和 CRC 的相对变化在测量不确定度内是一致的。此外，通过使用基于体模测量的后滤波策略来协调 CRC 或 CRC，在选择的三个球体尺寸上，两个扫描仪之间的 CRC 值的均方根百分比差异（RMS）显著降低：受试者的 CRC 值的 RMS 从 36%降低到<8%，而在协调 CRC 时，CRC 的 RMS 从约 33%降低到<6%。但是，使用这种策略来协调 CRC 时，在受试者中，CRC 的 RMS 仅改善至约 14%。
体模和受试者数据之间 CRC 测量的一致性表明，使用体模研究定义的协调策略可以很好地追踪患者图像。但是，不同扫描仪之间的定量一致性，如 RMS 所表示的，取决于为协调而选择的指标。
