Abstract
Purpose: To study the short‐term reproducibility of lung density measurements by multi‐slice computed tomography (CT) using three different radiation doses and three reconstruction algorithms.
Material and Methods: Twenty‐five patients with smoker's emphysema and 25 patients with α1‐antitrypsin deficiency underwent 3 scans at 2‐week intervals. Low‐dose protocol was applied, and images were reconstructed with bone, detail, and soft algorithms. Total lung volume (TLV), 15th percentile density (PD‐15), and relative area at −910 Hounsfield units (RA‐910) were obtained from the images using Pulmo‐CMS software. Reproducibility of PD‐15 and RA‐910 and the influence of radiation dose, reconstruction algorithm, and type of emphysema were then analysed.
Results: The overall coefficient of variation of volume adjusted PD‐15 for all combinations of radiation dose and reconstruction algorithm was 3.7%. The overall standard deviation of volume‐adjusted RA‐910 was 1.7% (corresponding to a coefficient of variation of 6.8%). Radiation dose, reconstruction algorithm, and type of emphysema had no significant influence on the reproducibility of PD‐15 and RA‐910. However, bone algorithm and very low radiation dose result in overestimation of the extent of emphysema.
Conclusion: Lung density measurement by CT is a sensitive marker for quantitating both subtypes of emphysema. A CT‐protocol with radiation dose down to 16 mAs and soft or detail reconstruction algorithm is recommended.