From the Department of Diagnostic Radiology, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Chuo-ku, Kumamoto 860-8556, Japan.
Radiology. 2020 Aug;296(2):324-332. doi: 10.1148/radiol.2020192227. Epub 2020 May 26.
Background Dual-energy CT allows virtual noncontrast (VNC) attenuation and iodine density measurements from contrast material-enhanced examination, potentially enabling adrenal lesion characterization. However, data regarding diagnostic performance remain limited, and combined diagnostic values have never been investigated. Purpose To determine whether VNC attenuation, iodine density, and combination of the two allow reliable differentiation between adrenal adenomas and metastases. Materials and Methods This retrospective study included patients with adrenal lesions who underwent unenhanced and portal venous phase dual-energy CT between January 2017 and December 2018. Unenhanced, contrast-enhanced, and VNC attenuation, as well as iodine density, were measured for each lesion. Agreement between unenhanced and VNC attenuation was assessed by using Wilcoxon rank-sum test, Pearson correlation coefficient, and Bland-Altman plot. The ratio of iodine density to VNC attenuation was calculated for lesions with positive VNC attenuation. Each parameter was compared between adenomas and metastases; diagnostic performance was evaluated by using the area under the receiver operating characteristic curve (AUC) with sensitivity and specificity. Results A total of 149 patients (mean age, 65 years ± 13 [standard deviation]; 89 men; 98 patients with 104 adenomas; 51 patients with 56 metastases) were evaluated. VNC attenuation showed strong positive correlation with unenhanced attenuation ( = 0.92) but resulted in overestimates of adenoma attenuation (mean bias, +11 HU; < .001) and was less sensitive ( = .03) in the diagnosis of adenomas compared with unenhanced attenuation (sensitivity of 79% [81 of 102] [95% confidence interval {CI}: 70%, 87%] and specificity of 95% [53 of 56] [95% CI: 85%, 99%] versus sensitivity of 85% [87 of 102] [95% CI: 77%, 92%] and specificity of 96% [54 of 56] [95% CI: 88%, 100%], with thresholds of ≤29 HU and ≤22 HU, respectively). Contrast-enhanced attenuation had no discriminatory ability (AUC, 0.54; 95% CI: 0.45, 0.62). Iodine density yielded moderate performance (sensitivity of 78% [80 of 102] [95% CI: 69%, 86%] and specificity of 71% [40 of 56] [95% CI: 58%, 83%], with a threshold of ≥1.82 mg/mL). The iodine-to-VNC ratio was higher in adenomas than in metastases (mean, 14.5 vs 4.6; < .001), with sensitivity of 95% (97 of 102; 95% CI: 89%, 98%) and specificity of 95% (53 of 56; 95% CI: 85%, 99%), with a threshold of 6.7 or greater. Conclusion Contrast-enhanced dual-energy CT during the portal venous phase enabled accurate differentiation between adrenal adenomas and metastases by combining virtual noncontrast attenuation and iodine density. Virtual noncontrast imaging alone led to overestimates of adenoma attenuation, and iodine density alone had limited discriminatory utility. © RSNA, 2020 See also the editorial by Hindman and Megibow in this issue.
背景 双能 CT 可在对比剂增强检查时获得虚拟平扫（VNC）衰减和碘密度值，从而可能有助于肾上腺病变的特征分析。然而，有关诊断性能的数据仍然有限，且尚未研究联合诊断值。 目的 旨在确定 VNC 衰减值、碘密度值及其组合是否能可靠地区分肾上腺腺瘤和转移瘤。 材料与方法 本回顾性研究纳入了 2017 年 1 月至 2018 年 12 月间接受平扫和门静脉期双能 CT 检查的肾上腺病变患者。对每个病变的平扫、增强和 VNC 衰减值以及碘密度值进行测量。采用 Wilcoxon 秩和检验、Pearson 相关系数和 Bland-Altman 图评估平扫和 VNC 衰减值之间的一致性。对 VNC 衰减值为阳性的病变计算碘密度与 VNC 衰减值的比值。比较腺瘤与转移瘤之间各参数的差异；采用受试者工作特征曲线（receiver operating characteristic curve，ROC）下面积（area under the receiver operating characteristic curve，AUC）评估诊断性能，同时评估敏感度和特异度。 结果 共纳入 149 例患者（平均年龄 65 岁±13[标准差]；89 例男性；104 个腺瘤中有 98 例患者，56 个转移瘤中有 51 例患者）。VNC 衰减值与平扫衰减值呈强正相关（ = 0.92），但会导致腺瘤衰减值的高估（平均偏差，+11 HU； <.001），并且在诊断腺瘤时的敏感度较平扫衰减值低（ =.03）（平扫衰减值的敏感度为 79%[81/102] [95%置信区间：70%，87%]和特异度为 95%[53/56] [95%置信区间：85%，99%]，而 VNC 衰减值的敏感度为 85%[87/102] [95%置信区间：77%，92%]和特异度为 96%[54/56] [95%置信区间：88%，100%]，阈值分别为≤29 HU 和≤22 HU）。增强衰减值无鉴别能力（AUC，0.54；95%置信区间：0.45，0.62）。碘密度值的性能为中度（敏感度为 78%[80/102] [95%置信区间：69%，86%]和特异度为 71%[40/56] [95%置信区间：58%，83%]，阈值为≥1.82 mg/mL）。与转移瘤相比，腺瘤的碘- VNC 比值更高（均值，14.5 比 4.6； <.001），其敏感度为 95%（97/102；95%置信区间：89%，98%）和特异度为 95%（53/56；95%置信区间：85%，99%），阈值为 6.7 或更高。 结论 门静脉期对比增强双能 CT 通过结合 VNC 衰减值和碘密度值，能准确区分肾上腺腺瘤和转移瘤。单纯 VNC 成像会导致腺瘤衰减值的高估，而单纯碘密度值的鉴别能力有限。 ©RSNA，2020 参见本期 Hindman 和 Megibow 的述评。
