Lung volume reduction surgery: Analysis of preoperative emphysema distribution and severity using quantitative computed tomography

Purpose: To explore the potential value of quantitative CT (QCT) for assessing the severity and distribution of emphysema in lung volume reduction surgery (LVRS) candidates and predicting clinical outcome. Methods: The entire lung density distribution was measured on preoperative CT scans in 18 patients using Pulmo CT software (Siemens Medical Systems, Iselin, NJ). The mean density, and volume and percent of lung in multiple density ranges and anatomic regions were calculated, and associations with clinical outcome investigated. Results: There was little variability in global mean lung density, but substantial variability in 1) the percent of emphysematous lung calculated using a threshold of -900 Hounsfield Units (HU; water=0, air=-1000), 2) the percent of emphysematous lung in the upper, lower, and upper to lower lung, and 3) the volume of lung in the normal density range: Mean Volume (L) of density (HU) Upper:lower normal density Mean -901 1.34 1.03 Std dev 10 0.39 0.19 Range -916 to -876 0.55 to 1.81 0.70 to 1.41 Comparison with outcome revealed correlations between the lung volume in the normal density range and improvement in PaO2 (r=.65, p<.01), volume of lung < -960 HU and improvement in FEV1 (r=.59, p=.01), and percent of lung < -960 HU and improvement in six minute walk distance (r=.69, p<.01). Conclusion: QCT allows objective determination of the variation in emphysema severity and distribution among LVRS candidates that can be correlated with clinical outcome. Clinical Implications: There is potential for objectively standardizing part of the preoperative imaging assessment in LVRS candidates with QCT.