Keywords:
CT, Thorax, Lung, Chest, Technical aspects, Chronic obstructive airways disease, Not applicable
Authors:
H. J. Wisselink, G. J. Pelgrim, M. Rook, M. P. van den Berge, P. D. G. de bock, R. Vliegenthart; Groningen/NL
DOI:
10.26044/ecr2020/C-11585
Methods and materials
We used ultra-low dose CT scans from a cohort of 50 COPD patients. Scanning was performed with third generation dual-source CT (SOMATOM Force, Siemens Healthineers) at 70 ref-mAs, and 100 kVp with Sn-filter (median CTDIvol 0.38 mGy). Images were reconstructed with slice thickness/increment 1.0/0.7mm, medium-smooth kernel, and filtered backprojection.
The trachea was segmented in a 61x61x61 voxel region, centred 1.5 cm above the carina. To prevent an overestimation due to the partial volume effect, a morphological erosion was used to remove a 2 mm layer. Every segmentation was visually checked, see Figure 1 for an example.
To simulate manual measurement variability, a 1 voxel jitter in each direction was used to measure the SD of a 1 cm² ROI and a same radius (0.75 cm³) VOI, resulting in 1 (segmentation) + 27 (ROI) + 27 (VOI) values per scan. One participant was excluded due to incorrect segmentation. 221 of 1323 jitter-scan-combinations were removed from analysis because either the ROI or the VOI was outside the trachea segmentation (before the morphological erosion). A Bland-Altman analysis was performed on the remaining results.