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Selection of patients for lung volume reduction surgery using a power law analysis of the computed tomographic scan

¹ University of British Columbia, McDonald Research Laboratories, St Paul’s Hospital, Vancouver, BC, Canada V6Z 1Y6
² Department of Radiology, Vancouver General Hospital, Vancouver, BC, Canada V5Z 4E3
³ Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh Medical Center and School of Medicine, Pittsburgh, PA, USA
⁴ Division of Thoracic Surgery, Department of Surgery, University of Pittsburgh Medical Center and School of Medicine

Correspondence to:
Correspondence to:
Dr H O Coxson, Department of Radiology, Vancouver General Hospital, 950 West 10th Avenue, Jim Pattison Pavilion North, Room 3350, Vancouver, BC, Canada V5Z 4E3;
hcoxson{at}vanhosp.bc.ca

Background: A study was undertaken to test the hypothesis that patients respond better to lung volume reduction surgery (LVRS) if their emphysema is confluent and predominantly located in the upper lobes.

Methods: A density mask analysis was used to identify voxels inflated beyond 10.2 ml gas/g tissue (-910 HU) on preoperative and postoperative CT scans from patients receiving LVRS. These hyperinflated regions were considered to represent emphysematous lesions. A power law analysis was used to determine the relationship between the number (K) and size (A) of the emphysematous lesions in the whole lung and two anatomical regions using the power law equation Y=KA^-D.

Results: The analysis showed a positive correlation between the change in the power law exponent (D) and the change in exercise (Watts) after surgery (r=0.47, p=0.03). There was also a negative correlation between the power law exponent D in the upper region of the lung preoperatively and the change in exercise following surgery (r=-0.60, p<0.05).

Conclusions: These results confirm that patients with large upper lobe lesions respond better to LVRS than patients with small uniformly distributed disease. Power law analysis of lung CT scans provides a quantitative method for determining the extent and location of emphysema within the lungs of patients with COPD.

Keywords: computed tomography; emphysema; lung volume reduction surgery; chronic obstructive pulmonary disease

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