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A Cluster Analysis of CT Scans Predicts Patients Who Respond to Lung Volume Reduction Surgery*

Harvey O. Coxson, PhD; Kenneth P. Whittall, PhD; Robert M. Rogers, MD, FCCP; Frank C. Sciurba, MD, FCCP; Robert J. Keenan, MD; James C. Hogg, MD
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*From the UBC Pulmonary Research Lab (Drs. Coxson, Whittall, and Hogg), St. Paul’s Hospital, Vancouver, BC, Canada; and from the University of Pittsburgh Medical Center, Division of P/A/CCM (Drs. Rogers and Sciurba), and the Division of Surgery (Dr. Keenan), Pittsburgh, PA.

Correspondence to: Harvey O. Coxson, PhD, Department of Radiology LSP3350, Vancouver General Hospital, 950 West 10th Ave, Vancouver, BC V5Z 4E3, Canada



Chest. 2000;117(5_suppl_1):247S-248S. doi:10.1378/chest.117.5_suppl_1.247S
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Abbreviations: HU = Hounsfield units; LVRS = lung volume reduction surgery

We postulated that patients having the greatest response to lung volume reduction surgery (LVRS) have the distribution of their emphysema characterized by large, predominantly upper lobe lesions. This study uses quantitative analysis of pre- and postoperative CT scans in 21 patients following bilateral LVRS to assess the distribution of emphysematous lesions and the surface area to volume ratio (SA/V) of the lung. The SA/V is calculated using a previously described prediction equation (Am J Respir Crit Care Med 1999; 159: 851–856) and the emphysematous lesions are quantified using a cluster analysis. Voxels with attenuation values below − 910 Hounsfield units (HU) are described as “emphysematous lesions.” Clusters are defined as one or more contiguous voxels below − 910 HU. The number, size, and location of the clusters are quantified and presented as a cumulative fraction of the lung as well as a “fractal dimension” which takes into account the number and size of all clusters within the image (smaller fractal dimensions characterize larger and fewer lesions). Cardiopulmonary exercise performance (maximal watts) is performed using symptom- limited incremental bicycle ergometry. Following LVRS both the total lung volume (− 888 mL) and the volume of emphysema decreases (− 909 mL) and surface area to volume ratio increases (+ 2.6 m2/L) significantly (p < 0.05). There is a negative correlation between the fractal number in the upper regions of the lung pre-operatively and the change in exercise tolerance (r = − 0.62, p = 0.01). There is also positive correlation between the change in the fractal number and the change in exercise tolerance after surgery (r = 0.64, p < 0.001). This supports the hypothesis that patients with primarily large, upper lobe emphysematous lesions will respond better to LVRS than patients with small uniformly distributed clusters. We conclude that cluster analyses of lung CT scans provide quantitative information on the extent and location of emphysema within the lungs of patients with COPD, and we propose that it could be further evaluated as a selection tool for LVRS.

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