Department of Nuclear Medicine, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, Ohio, 44195, USA.
Med Phys. 2018 Mar;45(3):1118-1122. doi: 10.1002/mp.12779. Epub 2018 Feb 16.
Evaluating gamma camera image quality is a routine task required for annual physics surveys and laboratory accreditation. A common method is visual assessment of a planar view of the American College of Radiology (ACR) phantom, for which a satisfactory result is to resolve 7.9 mm diameter cold rods with high contrast. The objective was to investigate an automated quantitative measure of planar image quality for more precise evaluation of gamma camera performance.
Planar images were automatically co-registered to a template of the phantom's cold rod pattern. Contrast-to-noise ratio (CNR) was measured for each cold rods sector by automatic placement of regions of interests on each rod and on each gap between rods. A quadratic fit to CNR vs. rod diameter yielded the Minimum Detectable Rod Diameter (MDRD) corresponding to a CNR threshold of 4. This methodology was applied to planar images acquired on a variety of gamma cameras according to ACR guidelines and also to planar images generated by Monte Carlo simulation.
The automated MDRD analysis had reproducibility of 0.1 mm in repeat phantom scans with random repositioning between scans. The MDRD was 5.8 mm for modern fully digital gamma cameras and 6.2 mm for an older analog gamma camera, whereas visual assessment was identical for all cameras. Simulated Monte Carlo images had MDRD of 5.6 mm using the following parameters: 3.5 mm FWHM intrinsic detector resolution, LEHR collimators, 9.0% FWHM energy resolution, and 15% energy window. Further simulations revealed that collimator design and detector resolution have a substantial impact on MDRD but that energy window width and energy resolution have a minor or negligible impact. The small difference between the Monte Carlo simulations and the modern fully digital gamma cameras was attributed to nonlinearities associated with event positioning and depth-of-interaction effects, which were not modeled in the simulations.
Automated MDRD analysis of planar phantom images is a robust technique that provides more precise and meaningful evaluation of camera performance than visual assessment. MDRD is a suitable measure for quality assurance and for annual physics surveys of gamma cameras.
评估伽玛相机的图像质量是年度物理测量和实验室认证所必需的常规任务。一种常见的方法是对美国放射学院（ACR）体模的平面视图进行视觉评估，其满意的结果是解析直径为 7.9 毫米的冷棒，具有高对比度。目的是研究一种自动定量测量平面图像质量的方法，以便更精确地评估伽玛相机的性能。
平面图像自动与冷棒模式模板配准。通过在每个棒和棒之间的每个间隙上自动放置感兴趣区域，测量每个冷棒扇区的对比度噪声比（CNR）。CNR 与棒直径的二次拟合得出最小可检测棒直径（MDRD），对应于 CNR 阈值为 4 的值。根据 ACR 指南，该方法应用于各种伽玛相机的平面图像，也应用于蒙特卡罗模拟生成的平面图像。
随机重新定位在重复体模扫描之间，自动 MDRD 分析具有 0.1 毫米的可重复性。现代全数字伽玛相机的 MDRD 为 5.8 毫米，旧的模拟伽玛相机的 MDRD 为 6.2 毫米，而所有相机的视觉评估均相同。使用以下参数的模拟蒙特卡罗图像的 MDRD 为 5.6 毫米：3.5 毫米 FWHM 固有探测器分辨率、LEHR 准直器、9.0% FWHM 能量分辨率和 15%能量窗。进一步的模拟表明，准直器设计和探测器分辨率对 MDRD 有很大影响，但能量窗宽度和能量分辨率的影响较小或可以忽略不计。蒙特卡罗模拟与现代全数字伽玛相机之间的微小差异归因于与事件定位和相互作用深度效应相关的非线性，这些非线性在模拟中未建模。
平面体模图像的自动 MDRD 分析是一种稳健的技术，比视觉评估更能精确和有意义地评估相机性能。MDRD 是伽玛相机质量保证和年度物理测量的合适指标。
