New 133Xe gas trapping index for quantifying severe emphysema before partial lung volume reduction.

UNLABELLED Lung volume reduction (LVR) is an effective therapy for end-stage emphysema. Preliminary and postprocedure imaging is usually limited to CT for anatomic delineation of the location and severity of the most acutely affected lung zones. The purpose of this study was to investigate the potential of using a new quantitative gas trapping index (GTI) derived from a (133)Xe ventilation scan to assess the severity of emphysema. METHODS Using the equilibration and washout phases of a (133)Xe ventilation study, a GTI was compared with visual National Emphysema Treatment Trial (NETT) CT scoring, semiautomated CT densitometry, and (99m)Tc perfusion scintigraphy in 28 patients being evaluated for LVR. The GTI was calculated as the percentage of (133)Xe gas retention in a 3-min washout image compared with the peak equilibrium image for 6 lung zones. RESULTS The GTI correlated best with the percentage of perfusion (-0.39, P<0.0001) and the CT density scoring with the percentage of severe emphysema (0.36, P<0.0001). There was less correlation with visual NETT CT scores (0.25, P<0.001). CONCLUSION This GTI, based on widely available (133)Xe imaging, shows good correlation with other quantitative measures of emphysema that are anatomically based. Because this GTI provides a more functional assessment of gas trapping and airway disease, these results suggest that additional study is warranted to investigate its use as a functional measure of emphysema before and after LVR.