Pulmonary Nodules: Interscan Variability of Semiautomated Volume Measurements with Multisection CT—Influence of Inspiration Level, Nodule Size, and Segmentation Performance

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Abstract
Purpose: To prospectively assess the precision of semiautomated volume measurements of pulmonary nodules at low-dose multi-detector row computed tomography (CT) and to investigate the influence of nodule size, segmentation algorithm, and inspiration level. Materials and Methods: This study had institutional review board approval; written informed consent was obtained from all patients. Between June 2004 and March 2005, 20 patients (15 men, five women; age range, 40-84 years; mean age, 57 years) referred for chest CT for known lung metastases under-went two additional low-dose chest CT examinations without contrast material (collimation, 16 x 0.75 mm). Between these examinations, patients got off and on the table to simulate the conditions for a follow-up examination. Noncalcified solid pulmonary nodules between 15 and 500 mm(3) that did not abut vessel or pleura were measured in both studies by using widely applied commercial semiautomated software. Interscan variability was established with the Bland and Altman approach. The impact of nodule shape (spherical or nonspherical) on measurement variability was assessed by using one-way analysis of variance, while the contributions of mean nodule volume and change in lung volume were investigated with univariate linear regression for completely (group A) and incompletely (group B) segmented nodules. Results: Two hundred eighteen eligible nodules (volume range, 16.4-472.7 mm(3); 106 spherical, 112 nonspherical) were evaluated. The 95% confidence interval for difference in measured volumes was -21.2%, 23.8% ( mean difference, 1.3%). The precision of nodule segmentation was highly dependent on nodule shape (P <.001) and was weakly related to inspiration level for completely segmented nodules (r = -0.20; P <.047), while mean nodule volume did not show any effect (P = .15 and P = .81 for group A and B nodules, respectively). Conclusion: Variation of semiautomated volume measurements of pulmonary nodules can be substantial. Segmentation represents the most important factor contributing to measurement variability, while change in inspiration level has only a weak effect for completely segmented nodule