New ¹³³Xe Gas Trapping Index for Quantifying Severe Emphysema Before Partial Lung Volume Reduction

Abstract

Lung volume reduction (LVR) is an effective therapy for endstage 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 (20.39, 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.

Lung ventilation–perfusion imbalance in pulmonary emphysema: assessment with automated V/Q quotient SPECT

“…In lung areas with significant alveolar destruction, perfusion may be more disturbed compared with ventilation, resulting in waste ventilation. Although hypoxic vasoconstriction occurs secondarily to ventilation disturbance, perfusion may not be equally reduced against ventilation, as abnormally low V/Q associated with airway obstruction in asthmatic patients has been demonstrated in previous V-Q positron emission tomographic studies [29,30]. The observed marked variations in the parameters of V/Q profile in our patients with emphysema seem to reflect this complicated lung pathophysiology in individuals.…”

“…Lung V-Q imbalance may proceed to morphologic abnormality in patients with emphysema. Studies have shown that the severity and extent of emphysema can be underestimated by CT, compared with pathologic grading [30]. Mild alveolar destruction and/or small airway obstruction causing lung V-Q imbalance may not be well identified on CT due to the limitation of spatial resolution [31][32][33][34][35].…”

Circulating Endothelial Microparticles as a Measure of Early Lung Destruction in Cigarette Smokers

“…HRCT imaging detects early emphysema by identifying pulmonary tissue with radiologic attenuation below a predetermined threshold, findings that roughly correlate with a low DL CO and pathologic evidence of emphysema (74)(75)(76)(77)(78)(79)(80). Although several studies have shown that a significant proportion of asymptomatic smokers have HRCT evidence of emphysema (78,(81)(82)(83), early HRCT findings of ''emphysema'' are not proven to be correlated directly with lung destruction (84)(85)(86)(87)(88)(89)(90). Hyperpolarized gas diffusion-weighted magnetic resonance imaging has also been used to identify emphysema, with a correlation of elevated levels of the apparent diffusion coefficient with decreased DL CO (91).…”

Influence of CT Reconstruction Settings on Extremely Low Attenuation Values for Specific Gas Volume Calculation in Severe Emphysema

“…There is a recent body of evidence that changes in SVg can be suitably used to study regional ventilation [17] and to define severity thresholds in severe emphysema [18]. We have recently shown that SVg determined at different lung volumes provides a useful method for identifying and quantifying the extent and severity of trapped gas [3].…”