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
Purpose
The most common method for emphysema quantification on computed tomography (CT) is segmenting the lungs and calculating the percentage of voxels with a density below a certain threshold.[Müller 1987, Lowe 2019] High image noise will therefore impact the emphysema quantification. Noise may cause a voxel in a low density region to be above the threshold, causing underestimation, but it can simultaneously cause voxels in a high density region to be below the threshold, causing overestimation of emphysema severity.
Noise can be defined as the standard deviation (SD) of the air inside the trachea. This noise measurement should provide an accurate measure of the image noise for low density areas in the thorax.[Messerli 2017]
Noise measured with a circular region of interest (ROI) of tracheal air may have poor reproducibility, because of the relatively low number of voxels included in the measurement. We explored the use of a spherical volume of interest (VOI), with the SD measured on the full trachea segmentation as the ground truth.