Department of Radiology, Stanford University School of Medicine, Stanford, CA, USA.
AJR Am J Roentgenol. 2011 Sep;197(3):623-30. doi: 10.2214/AJR.10.5288.
The purpose of the study was to quantify and compare the effect of CT dose and of size and density of nodules on the detectability of lung nodules and to quantify the influence of CT dose on the size of the nodules.
From 50 patients a total of 125 cuboidal regions of interest (3 × 3 × 1.5 cm volumes) showing a single nodule (≤ 8 mm) and 27 normal cuboids were selected. Image sets were reconstructed with the software from raw data simulating different dose levels: 300 (original dose), 220, 180, 140, 100, 80, 60, 50, 40, 30, 20, 10, and 5 reference mAs. A logistic regression model was used to analyze detectability for three blinded readers. Odds ratios were calculated for nodule size smaller than 3 mm versus 3 mm and larger and for nodule attenuation of -300 HU and greater versus less than -300 HU.
Tube current-time settings of 10 mAs and greater were not associated with a significant difference in individual reader sensitivity compared with the standard setting of 300 mAs. At 5 mAs only one reader had a significant decrease in sensitivity, from 82% to 77% (p = 0.0035). According to the odds ratios and logistic regression results, the strongest negative effect on sensitivity can be assumed for low nodule density followed by small nodule size and dose level. The mean nodule volume measurement error between 5 and 300 mAs was 2.2% ± 18% (SD) and much lower than the interobserver volume measurement error rate of 38% ± 45%.
The results show the feasibility of a low-dose CT protocol at 10 mAs for follow-up of lung nodules. Computer-aided volume measurement in follow-up of lung nodules decreases interobserver variability.
本研究旨在定量比较 CT 剂量、结节大小和密度对肺结节检测的影响，并定量评估 CT 剂量对结节大小的影响。
从 50 名患者中，共选择了 125 个立方感兴趣区（3×3×1.5cm 体积），这些区域均显示单个结节（≤8mm）和 27 个正常立方。使用软件从原始数据中重建图像集，模拟不同剂量水平：300（原始剂量）、220、180、140、100、80、60、50、40、30、20、10 和 5 参考 mAs。使用逻辑回归模型对三位盲法读者的可检测性进行分析。对于小于 3mm 和大于 3mm 的结节大小以及衰减值小于-300HU 和大于-300HU 的结节，计算了比值比。
与 300mAs 的标准设置相比，10mAs 及以上的管电流时间设置与个体读者的敏感性差异无显著相关性。在 5mAs 时，只有一位读者的敏感性显著下降，从 82%降至 77%（p=0.0035）。根据比值比和逻辑回归结果，对敏感性的最强负面影响可归因于低结节密度，其次是结节大小和剂量水平。在 5 至 300mAs 之间，平均结节体积测量误差为 2.2%±18%（标准差），远低于观察者间体积测量误差率 38%±45%。
结果表明，10mAs 的低剂量 CT 方案在肺结节随访中是可行的。肺结节随访中的计算机辅助体积测量降低了观察者间的变异性。
