From the Departments of Physics (S.T., G.D.C.), Biomedical Engineering (W.J.G., J.P.M., G.W.M.), Radiology and Medical Imaging (J.P.M., J.F.M., E.E.d.L., A.M.R., G.W.M.), and Medicine (Y.M.S.), University of Virginia, Box 801339, Charlottesville, VA 22908; Department of Radiology, University of Missouri, Columbia, Mo (T.A.A.); and Department of Science and Engineering, University of Nottingham, Ningbo, China (C.W.).
Radiology. 2020 Oct;297(1):201-210. doi: 10.1148/radiol.2020192804. Epub 2020 Aug 11.
Background Apparent diffusion coefficient (ADC) maps of inhaled hyperpolarized gases have shown promise in the characterization of emphysema in patients with chronic obstructive pulmonary disease (COPD), yet an easily interpreted quantitative metric beyond mean and standard deviation has not been established. Purpose To introduce a quantitative framework with which to characterize emphysema burden based on hyperpolarized helium 3 (He) and xenon 129 (Xe) ADC maps and compare its diagnostic performance with CT-based emphysema metrics and pulmonary function tests (PFTs). Materials and Methods Twenty-seven patients with mild, moderate, or severe COPD and 13 age-matched healthy control subjects participated in this retrospective study. Participants underwent CT and multiple value diffusion-weighted He and Xe MRI examinations and standard PFTs between August 2014 and November 2017. ADC-based emphysema index was computed separately for each gas and value as the fraction of lung voxels with ADC values greater than in the healthy group 99th percentile. The resulting values were compared with quantitative CT results (relative lung area <-950 HU) as the reference standard. Diagnostic performance metrics included area under the receiver operating characteristic curve (AUC). Spearman rank correlations and Wilcoxon rank sum tests were performed between ADC-, CT-, and PFT-based metrics, and intraclass correlation was performed between repeated measurements. Results Thirty-six participants were evaluated (mean age, 60 years ± 6 [standard deviation]; 20 women). ADC-based emphysema index was highly repeatable (intraclass correlation coefficient > 0.99) and strongly correlated with quantitative CT ( = 0.86, < .001 for He; = 0.85, < .001 for Xe) with high AUC (≥0.93; 95% confidence interval [CI]: 0.85, 1.00). ADC emphysema indices were also correlated with percentage of predicted diffusing capacity of lung for carbon monoxide ( = -0.81, < .001 for He; = -0.80, < .001 for Xe) and percentage of predicted residual lung volume divided by total lung capacity ( = 0.65, < .001 for He; = 0.61, < .001 for Xe). Conclusion Emphysema index based on hyperpolarized helium 3 or xenon 129 diffusion MRI provides a repeatable measure of emphysema burden, independent of gas or value, with similar diagnostic performance as quantitative CT or pulmonary function metrics. © RSNA, 2020 See also the editorial by Schiebler and Fain in this issue.
背景 吸入超极化气体的表观扩散系数 (ADC) 图已显示出在慢性阻塞性肺疾病 (COPD) 患者肺气肿特征描述方面的潜力，但尚未建立出一种简单可解释的、超出均值和标准差的定量指标。目的 引入一种定量框架，用于根据超极化氦 3 (He) 和氙 129 (Xe) ADC 图描述肺气肿负担，并比较其与基于 CT 的肺气肿指标和肺功能测试 (PFT) 的诊断性能。材料与方法 本回顾性研究纳入了 27 例患有轻度、中度或重度 COPD 的患者和 13 名年龄匹配的健康对照者。参与者在 2014 年 8 月至 2017 年 11 月期间接受了 CT 和多次 值扩散加权 He 和 Xe MRI 检查以及标准 PFT。针对每个气体和 值，分别计算 ADC 基于的肺气肿指数，定义为 ADC 值大于健康组第 99 百分位数的肺体素分数。将这些值与定量 CT 结果（相对肺区<-950 HU）作为参考标准进行比较。诊断性能指标包括受试者工作特征曲线下面积 (AUC)。对 ADC、CT 和 PFT 基于的指标进行 Spearman 秩相关和 Wilcoxon 秩和检验，并对重复测量进行组内相关系数分析。结果 共评估了 36 名参与者（平均年龄 60 岁±6[标准差]；20 名女性）。ADC 基于的肺气肿指数具有高度可重复性（组内相关系数>0.99），与定量 CT 高度相关（He： = 0.86， <.001；Xe： = 0.85， <.001），AUC 较高（≥0.93；95%置信区间[CI]：0.85，1.00）。ADC 肺气肿指数也与一氧化碳弥散量预计值的百分比呈负相关（He： = -0.81， <.001；Xe： = -0.80， <.001），与残气量预计值与肺总量的比值呈负相关（He： = 0.65， <.001；Xe： = 0.61， <.001）。结论 基于超极化氦 3 或氙 129 扩散 MRI 的肺气肿指数可提供一种重复性肺气肿负担测量方法，该方法独立于气体或 值，与定量 CT 或肺功能指标具有相似的诊断性能。 ©2020RSNA 本期 Schiebler 和 Fain 的社论也有相关内容。
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