Classification of emphysema in candidates for lung volume reduction surgery: A new objective and surgically oriented model for describing CT severity and heterogeneity

Objective: To elaborate a surgically oriented and objective model for classification of emphysema heterogeneity. Patients and interventions: CT examinations of 66 candidates for lung volume reduction surgery. Design: Emphysema severity was calculated by computer as the emphysema index (EI), a commonly used computer-based quantification that accurately assesses the extent of emphysema of a CT image. The distribution of the EI in different parts of each lung was illustrated in a diagram with the position in the lung (from cranial to caudal) on the x-axis and the EI on the y-axis. The slope of the fitted line was calculated. As a measure of the variation of the EI within each lung, the EI difference was calculated. Results: A diagram was constructed with the absolute value of slope, k, on the x-axis and EI difference on the y-axis. This resulted in a diagram differentiating markedly heterogeneous, intermediately heterogeneous, and homogeneous emphysema. Nineteen patients fulfilled the criteria of bilateral markedly heterogeneous emphysema, 3 patients filled the criteria of bilateral intermediately heterogeneous emphysema, and 18 patients filled the criteria of bilateral homogeneous emphysema. Twenty-six patients had different types of emphysema in the right and left lung. Conclusion: We present a method for classification of emphysema heterogeneity that is (1) objective, (2) surgically oriented, and (3) classifies both lungs separately.