Proceedings Article | 9 March 2011
KEYWORDS: Lung, Emphysema, Computed tomography, Signal attenuation, X-ray computed tomography, Scanners, Clinical trials, Image segmentation, Medicine, Physiology
This study investigated the reproducibility of HRCT densitometric measures of emphysema in patients
scanned twice one week apart. 24 emphysema patients from a multicenter study were scanned at full
inspiration (TLC) and expiration (RV), then again a week later for four scans total. Scans for each patient
used the same scanner and protocol, except for tube current in three patients. Lung segmentation with gross
airway removal was performed on the scans. Volume, weight, mean lung density (MLD), relative area
under -950HU (RA-950), and 15th percentile (PD-15) were calculated for TLC, and volume and an airtrapping
mask (RA-air) between -950 and -850HU for RV. For each measure, absolute differences were
computed for each scan pair, and linear regression was performed against volume difference in a subgroup
with volume difference <500mL. Two TLC scan pairs were excluded due to segmentation failure. The
mean lung volumes were 5802 +/- 1420mL for TLC, 3878 +/- 1077mL for RV. The mean absolute
differences were 169mL for TLC volume, 316mL for RV volume, 14.5g for weight, 5.0HU for MLD,
0.66p.p. for RA-950, 2.4HU for PD-15, and 3.1p.p. for RA-air. The <500mL subgroup had 20 scan pairs
for TLC and RV. The R2 values were 0.8 for weight, 0.60 for MLD, 0.29 for RA-950, 0.31 for PD-15, and
0.64 for RA-air. Our results indicate that considerable variability exists in densitometric measures over one
week that cannot be attributed to breathhold or physiology. This has implications for clinical trials relying
on these measures to assess emphysema treatment efficacy.
