title: Probing the regional distribution of pulmonary gas exchange through single-breath gas- and dissolved-phase 129Xe MR imaging.
abstract: Although some central aspects of pulmonary function (ventilation and perfusion) are known to be heterogeneous, the distribution of diffusive gas exchange remains poorly characterized. A solution is offered by hyperpolarized 129Xe magnetic resonance (MR) imaging, because this gas can be separately detected in the lung's air spaces and dissolved in its tissues. Early dissolved-phase 129Xe images exhibited intensity gradients that favored the dependent lung. To quantitatively corroborate this finding, we developed an interleaved, three-dimensional radial sequence to image the gaseous and dissolved 129Xe distributions in the same breath. These images were normalized and divided to calculate "129Xe gas-transfer" maps. We hypothesized that, for healthy volunteers, 129Xe gas-transfer maps would retain the previously observed posture-dependent gradients. This was tested in nine subjects: when the subjects were supine, 129Xe gas transfer exhibited a posterior-anterior gradient of -2.00 ± 0.74%/cm; when the subjects were prone, the gradient reversed to 1.94 ± 1.14%/cm (P < 0.001). The 129Xe gas-transfer maps also exhibited significant heterogeneity, as measured by the coefficient of variation, that correlated with subject total lung capacity (r = 0.77, P = 0.015). Gas-transfer intensity varied nonmonotonically with slice position and increased in slices proximal to the main pulmonary arteries. Despite substantial heterogeneity, the mean gas transfer for all subjects was 1.00 ± 0.01 while supine and 1.01 ± 0.01 while prone (P = 0.25), indicating good "matching" between gas- and dissolved-phase distributions. This study demonstrates that single-breath gas- and dissolved-phase 129Xe MR imaging yields 129Xe gas-transfer maps that are sensitive to altered gas exchange caused by differences in lung inflation and posture.
authors.affiliation: Department of Biomedical Engineering, Duke University, Durham, North Carolina;
authors.forename: S Sivaram
authors.initials: SS
authors.lastname: Kaushik
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Freeman
authors.forename: Zackary I
authors.initials: ZI
authors.lastname: Cleveland
authors.forename: John
authors.initials: J
authors.lastname: Davies
authors.forename: Jane
authors.initials: J
authors.lastname: Stiles
authors.forename: Rohan S
authors.initials: RS
authors.lastname: Virgincar
authors.forename: Scott H
authors.initials: SH
authors.lastname: Robertson
authors.forename: Mu
authors.initials: M
authors.lastname: He
authors.forename: Kevin T
authors.initials: KT
authors.lastname: Kelly
authors.forename: W Michael
authors.initials: WM
authors.lastname: Foster
authors.forename: H Page
authors.initials: HP
authors.lastname: McAdams
authors.forename: Bastiaan
authors.initials: B
authors.lastname: Driehuys
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D021621:Imaging, Three-Dimensional; D008168:Lung / Q000502:physiology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D016684:Prone Position / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D016683:Supine Position / Q000502:physiology; D014979:Xenon Isotopes; D055815:Young Adult
chemical_list: D014979:Xenon Isotopes
keywords: dissolved phase; hyperpolarized 129Xe; prone; radial pulse sequence; supine