Alterations of regional alveolar oxygen tension in asymptomatic current smokers: Assessment with hyperpolarized 3He MR imaging

Purpose: To assess the ability of helium 3 (³He) magnetic resonance (MR) imaging of regional alveolar partial pressure of oxygen (Pao₂) to depict smoking-induced functional alterations and to compare its efficacy to that of current diagnostic techniques. Materials and Methods: This study was approved by the local institutional review board and was compliant with HIPAA. All subjects provided informed consent. A total of 43 subjects were separated into three groups: nonsmokers, asymptomatic smokers, and symptomatic smokers. All subjects underwent a Pao₂ imaging session followed by clinically standard pulmonary function tests (PFTs), the 6-minute walk test, and St George Respiratory Questionnaire (SGRQ). The whole-lung mean and standard deviation of Pao₂ were compared with metrics derived from PFTs, the 6-minute walk test, and the SGRQ. A logistic regression model was developed to identify the predictors of alterations to the lungs of asymptomatic smokers. Results: The whole-lung standard deviation of Pao₂ correlated with PFT metrics (forced expiratory volume in 1 second [FEV1]/forced vital capacity [FVC], Pearson r = 20.69, P <.001; percentage predicted FEV1, Pearson r = 20.67, P <.001; diffusing capacity of lung for carbon monoxide [Dlco], Pearson r = 20.45, P =.003), SGRQ score (Pearson r = 0.67, P <.001), and distance walked in 6 minutes (Pearson r = 20.47, P =.002). The standard deviation of Pao₂ was significantly higher in asymptomatic smokers than in nonsmokers (change in the standard deviation of Pao₂ = 7.59 mm Hg, P =.041) and lower when compared with symptomatic smokers (change in the standard deviation of Pao₂ = 10.72 mm Hg, P =.001). A multivariate prediction model containing FEV1/FVC and the standard deviation of Pao₂ (as significant predictors of subclinical changes in smokers) and Dlco (as a confounding variable) was formulated. This model resulted in an area under the receiver operating characteristic curve with a significant increase of 29.2% when compared with a prediction model based solely on nonimaging clinical tests. Conclusion: The ³He MR imaging heterogeneity metric (standard deviation of Pao₂) enabled the differentiation of all three study cohorts, which indicates that it can depict smoking-related functional alterations in asymptomatic current smokers.