Comparison of standard- and low-radiation-dose CT for quantification of emphysema

OBJECTIVE. This study was performed to compare standard- and low-radiation-dose techniques in the CT quantification of emphysema. MATERIALS AND METHODS. The study population consisted of 36 men and 20 women who were current or former heavy smokers and underwent standard- dose ( effective tube current, 100 - 250 mAs) chest CT at our institution within 6 months of having undergone low-dose ( effective tube current, 30 - 60 mAs) chest CT. All CT scans were reconstructed at 5-mm slice thickness with a smooth filter. CT-measured lung volume, mean and median lung attenuation, and percentage of lung volume with attenuation lower than multiple thresholds ( emphysema index values) were compared by Pearson correlation, two-tailed and paired Student's t tests, and regression analysis. RESULTS. There were no significant differences in mean attenuation ( - 848 vs - 846 H, p >= 0.35) for the low dose and the standard dose or in median lung attenuation ( - 879 vs - 878 H, p > 0.66). Low- and standard-dose emphysema indexes were correlated at all attenuation thresholds ( r = 0.86 - 0.97). Mean emphysema indexes were higher on the low-dose scans, but the mean difference at all thresholds was less than 3%. The differences were significant ( p < 0.05) only at the lower index thresholds, correlated with differences in lung volume ( r = 0.86), and increased with greater differences in dose. CONCLUSION. Low-dose technique has minimal effect on CT quantification of emphysema.