42 AJR:188, January 2007 AJR 2007; 188:42–47 0361–803X/07/1881–42 © American Roentgen Ray Society 042.fm — 11/30/06 Gierada et al. CT in Emphysema Chest Imaging • Original Research Comparison of Standard- and Low-Radiation-Dose CT for Quantification of Emphysema David S. Gierada 1 Thomas K. Pilgram 1 Bruce R. Whiting 1 Cheng Hong 1,2 Andrew J. Bierhals 1 Jin Hwan Kim 1,3 Kyongtae T. Bae 1,2 Gierada DS, Pilgram TK, Whiting BR, et al. Keywords: CT technique, lung diseases Supported by National Institutes of Health grant R01HL72369 and NIH contract N01CN25516. DOI:10.2214/AJR.05.1498 Received August 25, 2005; accepted after revision December 7, 2005. 1 Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S Kingshighway Blvd., St. Louis, MO 63110. Address correspondence to D. S. Gierada (gieradad@wustl.edu). 2 Present address: University of Pittsburgh Medical Center, Pittsburgh, PA 15213. 3 Present address: Radiology Department, Chungnam National University School of Medicine, Dae Jon, Korea 301-721. 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 at- tenuation, and percentage of lung volume with attenuation lower than multiple thresholds (em- physema 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. uantification of emphysema with CT methods [1–3] may be a means of learning more about the preva- lence and natural history of emphy- sema, phenotyping in clinical trials involving patients with chronic obstructive pulmonary disease [4, 5], identifying risk factors related to emphysema progression rates, and evaluating the response to pharmacologic therapies for slowing emphysema progression [6, 7]. The use of CT to quantify emphysema has been lim- ited in part by the requirement for ionizing ra- diation. Results of ongoing clinical trials [8–12] are showing that low-dose CT may be a clini- cally acceptable and diagnostically adequate technique for lung cancer screening. Because of the reduction in radiation exposure, low-dose CT also is potentially more acceptable than standard-dose scanning for applications related to emphysema quantification. On CT images, lung tissues of different compositions are mapped onto pixels with dif- ferent attenuation values. The volume of em- physema is typically calculated as the sum of pixels with attenuation values below a specific threshold value. The studies that established the lung attenuation threshold values used for defining emphysema with quantitative CT (QCT) analysis [1, 2, 13–15] were performed before the introduction of low-dose CT tech- niques. These studies were conducted with X- ray tube currents up to eight times greater than those commonly used in lung cancer screening studies. Although areas of emphysema on low- dose CT images may be as perceptible as those on standard-dose CT images, reduction of ra- diation dose lowers the signal-to-noise ratio. The effect of this decrease on the frequency distribution of lung attenuation values in vary- ing degrees of emphysema has not been estab- lished. This study was performed to compare QCT measurements of emphysema obtained from standard- and low-dose CT scans. Materials and Methods Subjects A total of 56 subjects (36 men, 20 women; mean age ± SD, 62 ± 6 years; age range, 47–74 years) were included in this retrospective study. Fifty of the subjects were volunteer participants in Q Downloaded from www.ajronline.org by 52.73.204.196 on 05/17/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved