Volumetric analysis of pulmonary nodules: reducing the discrepancy between the diameter-based volume calculation and voxel-counting method

Sung Hyun Yoon; Jihang Kim; Kyong Joon Lee; Chang-Mo Nam; Junghoon Kim; Kyung Hee Lee; Kyung Won Lee

doi:10.21037/qims-21-485

Volumetric analysis of pulmonary nodules: reducing the discrepancy between the diameter-based volume calculation and voxel-counting method

Quant Imaging Med Surg. 2022 Mar;12(3):1674-1683. doi: 10.21037/qims-21-485.

Authors

Sung Hyun Yoon¹, Jihang Kim¹, Kyong Joon Lee^{1

2}, Chang-Mo Nam², Junghoon Kim¹, Kyung Hee Lee^{1

3}, Kyung Won Lee¹

Affiliations

¹ Department of Radiology, Seoul National University Bundang Hospital, Seongnam, Korea.
² Monitor Corporation, Seoul, Korea.
³ Department of Radiology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.

Abstract

Background: When assessing the volume of pulmonary nodules on computed tomography (CT) images, there is an inevitable discrepancy between values based on the diameter-based volume calculation and the voxel-counting method, which is derived from the Euclidean distance measurement method on pixel/voxel-based digital image. We aimed to evaluate the ability of a modified diameter measurement method to reduce the discrepancy, and we determined a conversion equation to equate volumes derived from different methods.

Methods: Two different anthropomorphic phantoms with subsolid and solid nodules were repeatedly scanned under various settings. Nodules in CT images were detected and segmented using a fully automated algorithm and the volume was calculated using three methods: the voxel-counting method (V_vc ), diameter-based volume calculation (V_d ), and a modified diameter-based volume calculation (V_d+ ₁), in which one pixel spacing was added to the diameters in the three axes (x-, y-, and z-axis). For each nodule, V_d and V_d ₊₁ were compared to V_vc by computing the absolute percentage error (APE) as follows: APE =100 × (V - V_vc )/V_vc . Comparisons between APE_d and APE_d+1 according to CT parameter setting were performed using the Wilcoxon signed-rank test. The Jonckheere-Terpstra test was used to evaluate trends across the four different nodule sizes.

Results: The deep learning-based computer-aided diagnosis (DL-CAD) successfully detected and segmented all nodules in a fully automatic manner. The APE was significantly less with V_d+1 than with V_d (Wilcoxon signed-rank test, P<0.05) regardless of CT parameters and nodule size. The APE median increased as the size of the nodule decreased. This trend was statistically significant (Jonckheere-Terpstra test, P<0.001) regardless of volume measurement method (diameter-based and modified diameter-based volume calculations).

Conclusions: Our modified diameter-based volume calculation significantly reduces the discrepancy between the diameter-based volume calculation and voxel-counting method.

Keywords: Pulmonary nodules; computer-aided diagnosis; volumetry.