Department of Electronics and Telecommunications, University of Florence, 50134 Florence, Italy.
IEEE Trans Med Imaging. 2010 Feb;29(2):397-409. doi: 10.1109/TMI.2009.2032542.
Nodule growth as observed in computed tomography (CT) scans acquired at different times is the primary feature to malignancy of indeterminate small lung nodules. In this paper, we propose the estimation of nodule size through a scale-space representation which needs no segmentation and has high intra- and inter-operator reproducibility. Lung nodules usually appear in CT images as blob-like patterns and can be analyzed in the scale-space by Laplacian of Gaussian ( LoG ) kernels. For each nodular pattern the LoG scale-space signature was computed and the related characteristic scale adopted as measurement of nodule size. Both in vitro and in vivo validation of LoG characteristic scale were carried out. In vitro validation was done by 40 nondeformable phantoms and 10 deformable phantoms. A close relationship between the characteristic scale and the equivalent diameter, i.e., the diameter of the sphere having the same volume of nodules, (Pearson correlation coefficient was 0.99) and, for nodules undergoing little deformations (obtained at constant volume), small variability of the characteristic scale was observed. The in vivo validation was performed on low and standard-dose CT scans collected from the ITALUNG screening trial (86 nodules) and from the LIDC public data set (89 solid nodules and 40 part-solid nodules or ground-glass opacities). The Pearson correlation coefficient between characteristic scale and equivalent diameter was 0.83-0.93 for ITALUNG and 0.68-0.83 for LIDC data set. Intra- and inter-operator reproducibility of characteristic scale was excellent: on a set of 40 lung nodules of ITALUNG data, two radiologists produced identical results in repeated measurements. The scan-rescan variability of the characteristic scale was also investigated on 86 two-year-stable solid lung nodules (each one observed, on average, in four CT scans) identified in the ITALUNG screening trial: a coefficient of repeatability of about 0.9 mm was observed. Experimental evidence supports the clinical use of the LoG characteristic scale to measure nodule size in CT imaging.
在不同时间获取的计算机断层扫描 (CT) 扫描中观察到的结节生长是确定小肺结节恶性的主要特征。在本文中，我们提出了一种通过尺度空间表示来估计结节大小的方法，该方法不需要分割，并且具有较高的内和间操作员可重复性。肺结节在 CT 图像中通常表现为类圆形模式，可以通过拉普拉斯高斯 (LoG) 核在尺度空间中进行分析。对于每个结节模式，计算了 LoG 尺度空间特征，并采用相关特征尺度作为结节大小的测量。进行了 LoG 特征尺度的体外和体内验证。体外验证是通过 40 个非变形体模和 10 个变形体模进行的。特征尺度与等效直径（即具有相同结节体积的球体直径）之间存在密切关系（皮尔逊相关系数为 0.99），并且对于经历微小变形的结节（在恒定体积下获得），特征尺度的变化很小。体内验证是在从 ITALUNG 筛查试验（86 个结节）和 LIDC 公共数据集（89 个实性结节和 40 个部分实性结节或磨玻璃混浊）收集的低剂量和标准剂量 CT 扫描上进行的。对于 ITALUNG，特征尺度与等效直径之间的 Pearson 相关系数为 0.83-0.93，对于 LIDC 数据集，Pearson 相关系数为 0.68-0.83。特征尺度的内和间操作员可重复性非常好：在 ITALUNG 数据的 40 个肺结节集中，两位放射科医生在重复测量中产生了相同的结果。还在 ITALUNG 筛查试验中确定的 86 个两年稳定的实性肺结节（每个结节平均在四个 CT 扫描中观察到）上研究了特征尺度的扫描-再扫描可变性：观察到大约 0.9 毫米的可重复性系数。实验证据支持在 CT 成像中使用 LoG 特征尺度来测量结节大小的临床应用。
