Alexander McKenzie BS, Presenter: Nothing to Disclose

Douglas Stinson, Abstract Co-Author: Nothing to Disclose

Carla G. Wilson, Abstract Co-Author: Nothing to Disclose

David Augustine Lynch MD, Abstract Co-Author: Research support, Siemens AG Scientific Advisor, Perceptive Informatics, Inc Consultant, Actelion Ltd Consultant, InterMune, Inc

Quantitative CT (QCT) measurements of inspiratory and end-expiratory lung attenuation measurements are used to quantify and characterize obstructive lung disease. We chose to examine a cohort of healthy non-smokers, smokers, and former smokers to determine if severity of disease impacted the relationship of attenuation measures and lung volumes. We hypothesized that in healthier individuals, mean lung attenuation would change more for a given change in lung volume than in those with COPD.

QCT measurements from volumetric inspiratory and end-expiratory thoracic CT scans for 3164 subjects enrolled in the COPDGene study (98 normal nonsmokers, 1392 smokers without COPD, and 229, 690, 478, and 277 smokers with GOLD stages 1, 2, 3, and 4 COPD, respectively) were made by trained analysts using Pulmonary Workstation 2 software from VIDA Diagnostics, Inc. TLC (total lung capacity), FRC (forced residual capacity) and mean lung attenuation (MLA) values were measured. The ratio of FRC to TLC (FRC/TLC) was compared to the ratios of inspiratory and end-expiratory measurements of MLA (MLA E/I). Results were grouped by GOLD stage, and linear regression analysis was performed.

Analyses were performed across all 3164 subjects and separately by GOLD stage. The mean and standard deviation of FRC/TLC was 0.578 ± 0.128. Across all 3164 subjects, the R2 value, slope and y intercept of the regression equation between FRC/TLC and MLA E/I were 0.791, 2.57 and -1.83 respectively. In nonsmokers without COPD, the R2, slope and y intercept of regression equation were 0.782, 1.92, and -1.11. Corresponding values for smokers without COPD were 0.665, 1.59 and -0.81. Values for smokers with GOLD stages 1-4 were: Stage 1 (0.658, 1.67 and -0.91), Stage 2 (0.663, 1.91 and -1.11), Stage 3 (0.556, 2.08 and -1.26), and Stage 4 (0.707, 3.44 and -2.55).

MLA E/I correlates strongly with FRC/TLC across the range of COPD severity. However, with increasing severity of COPD, the relationship between change in lung attenuation and change in lung volume alters substantially.

Evaluation of the relationship between change in lung volume and change in mean attenuation may facilitate assessment of severity of air trapping in subjects with COPD.

McKenzie, A, Stinson, D, Wilson, C, Lynch, D, Relationship between Change in Lung Volume and Change in Mean Lung Attenuation Across the Range of COPD Severity.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12034424.html