Background: The detection and quantification of solid components in pulmonary subsolid nodules (SSN) are of vital importance on differential diagnosis, pathological speculation and prognosis prediction. However, no objective and wide-accepted criterion has been built up to now. The purpose of this study is to explore the optimal threshold that can be used for the detection and quantification of solid components in SSNs by using threshold segmentation method on computed tomography (CT) images.
Methods: CT images of 102 SSNs were retrospectively analyzed. To establish a reference standard, the observers made judgments on whether the solid component existed in every SSN and did manual measurements of the volume of solid component with the help of software. Threshold segmentations of every nodule were then performed using different threshold settings and all of the measured volumes were assumed to be solid volumes, then solid-to-total volume ratios were calculated. The results were compared with the reference standards using the receiver operating characteristic curve and Wilcoxon test.
Results: The application of thresholds as -250 HU or -300 HU resulted in high diagnostic value on the detection of solid component, with area under curve values as 0.982 and 0.977, respectively; the cut-off values of solid-to-total volume ratio were 1.10% and 6.14%, respectively; the median volumes of solid components were 202.7 mm3 (598.2 mm3), 247.1 mm3(696.0 mm3), which were not significantly different from the reference standard[199.5 mm3 (743.1 mm3)](P=0.125,1, 0.061,3).
Conclusions: Threshold segmentation on chest CT images is valuable to detect and quantify the solid component on SSNs, the thresholds as -250 HU and -300 HU are recommended. .
背景与目的 肺内亚实性结节（subsolid nodule, SSN）实性成分的识别与定量对SSN的鉴别诊断，病理预测和预后评估具有重要价值，但目前缺乏公认且客观的标准。本研究旨在应用计算机断层扫描（computed tomography, CT）阈值分割方法确定用于SSN实性成分识别与定量的最佳阈值。方法 回顾性分析102例SSN的CT图像。由观察者确定SSN内是否存在实性成分并借助软件确定实性成分的体积，以此作为参照标准。应用CT阈值分割方法对所有SSN进行分析，测量其内不同CT阈值对应的体素体积，假定该体积即为实性成分体积，计算实性成分与结节整体的体积比率。所得结果与相应参照标准进行比较，应用受试者工作特征曲线及Wilcoxon检验筛选最佳阈值。结果 阈值设为-250 HU时，识别SSN内实性成分的诊断价值最大（曲线下面积为0.982），以体积比率1.10%作为确认实性成分存在的界限值，其诊断效能最高。阈值设为-300 HU时诊断效能次之，对应曲线下面积和体积比率界限值分别为0.977、6.14% 。阈值设为-250 HU、-300 HU时所得实性成分中位体积分别为202.7 mm3（598.2 mm3）、247.1 mm3（696.0 mm3），与参照标准199.5 mm3（743.1 mm3）间无显著差异（P=0.125,1, 0.061,3）。结论 CT阈值分割方法可对SSN实性成分进行准确识别与定量，阈值可设为-250 HU或-300 HU。.