Atsushi Nambu MD, Presenter: Nothing to Disclose

Jordan Zach, 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, Gilead Sciences, Inc Consultant, InterMune, Inc

Joyce Denise Schroeder MD, Abstract Co-Author: Research grant, Siemens AG

Gongyoung Jin MD, PhD, Abstract Co-Author: Nothing to Disclose

Christina Schnell BA, Abstract Co-Author: Nothing to Disclose

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

Russell Bowler MD, PhD, Abstract Co-Author: Nothing to Disclose

Tsutomu Araki MD, Abstract Co-Author: Nothing to Disclose

To investigate the relationship between DLCO and quantitative CT (QCT) data, including those of each lung lobe, in smokers with and without COPD

The subjects were a total of 121 current and former cigarette smokers who underwent volumetric inspiratory and expiratory CT as part of the COPDGene study, and also had plethysmography, DLCO, and estimated alveolar volume (VA) measurements; DLCO was adjusted by VA ( DLCO/VA). CT quantification was done by using a dedicated workstation, Pulmonary Workstation 2 software (VIDA Diagnostics, Inc, Coralville, IA). Quantitative CT measures of emphysema on inspiratory CT included % voxels < 950 Hounsfield unit (HU) < -910 HU, < -856 HU, mean CT attenuation, calculated mean tissue volume, and 15th percentile HU value at inspiratory CT. Air trapping was determined by % voxels < -856 HU at expiratory CT. Univariate analysis was employed to evaluate the correlation between DLCO/VA and quantitative CT parameters, including those of each pulmonary lobe.

Total lung capacity measured by CT (cTLC) correlated strongly with plethysmographic TLC(pTLC) (R2=0.877, p < 0.001). The DLCO/VA correlated most strongly with % emphysema at the -950 HU threshold (R2=0.459, p <0.001) % air trapping (R2=0.421, p < 0.001) and 15th percentile HU value (R2 =0.468, p < 0.001). Correlations for % emphysema at the -910 and -856 HU threshold were less strong (R2=0.391, p < 0.001 and R2=0.214, p <0.001, respectively). For each lung lobe, DLCO/VA had higher correlations with both emphysema % and air trapping % in upper lobes than in lower or middle lobes .

DLCO adjusted for VA correlates well with the severity of emphysema measured by quantitative CT. Upper lobe emphysema seems to be more closely related to DLCO than lower or middle lobe in smokers. The threshold of - 950HU to define emphysema is warranted. cTLC highly correlates with pTLC and thus spirometric gated CT may be unnecessary.

On QCT, % voxels below -950 HU, and 15th percentile HU value are the most clinically valid measures of emphysema.

Nambu, A, Zach, J, Lynch, D, Schroeder, J, Jin, G, Schnell, C, Wilson, C, Bowler, R, Araki, T, Correlation between Diffusion Capacity for Carbon Monoxide (DLCO) and Quantitative CT in Smokers in a Single Institution Study.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11013392.html