title: Quantitative analysis of hyperpolarized129Xe gas transfer MRI.
abstract: OBJECTIVE
  Hyperpolarized129Xe magnetic resonance imaging (MRI) using Dixon-based decomposition enables single-breath imaging of129Xe in the airspaces, interstitial barrier tissues, and red blood cells (RBCs). However, methods to quantitatively visualize information from these images of pulmonary gas transfer are lacking. Here, we introduce a novel method to transform these data into quantitative maps of pulmonary ventilation, and129Xe gas transfer to barrier and RBC compartments.
  
  
  METHODS
  A total of 13 healthy subjects and 12 idiopathic pulmonary fibrosis (IPF) subjects underwent thoracic1H MRI and hyperpolarized129Xe MRI with one-point Dixon decomposition to obtain images of129Xe in airspaces, barrier and red blood cells (RBCs).129Xe images were processed into quantitative binning maps of all three compartments using thresholds based on the mean and standard deviations of distributions derived from the healthy reference cohort. Binning maps were analyzed to derive quantitative measures of ventilation, barrier uptake, and RBC transfer. This method was also used to illustrate different ventilation and gas transfer patterns in a patient with emphysema and one with pulmonary arterial hypertension (PAH).
  
  
  RESULTS
  In the healthy reference cohort, the mean normalized signals were 0.51 ± 0.19 for ventilation, 4.9 ± 1.5 x 10-3for barrier uptake and 2.6 ± 1.0 × 10-3for RBC (transfer). In IPF patients, ventilation was similarly homogenous to healthy subjects, although shifted toward slightly lower values (0.43 ± 0.19). However, mean barrier uptake in IPF patients was nearly 2× higher than in healthy subjects, with 47% of voxels classified as high, compared to 3% in healthy controls. Moreover, in IPF, RBC transfer was reduced, mainly in the basal lung with 41% of voxels classified as low. In healthy volunteers, only 15% of RBC transfer was classified as low and these voxels were typically in the anterior, gravitationally nondependent lung.
  
  
  CONCLUSIONS
  This study demonstrates a straightforward means to generate semiquantitative binning maps depicting129Xe ventilation and gas transfer to barrier and RBC compartments. These initial results suggest that the method could be valuable for characterizing both normal physiology and pathophysiology associated with a wide range of pulmonary disorders.
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, 27710, USA.|Department of Biomedical Engineering, Duke University, Durham, NC, 27708, USA.
authors.forename: Ziyi
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, 27710, USA.|Medical Physics Graduate Program, Duke University, Durham, NC, 27705, USA.
authors.forename: Scott Haile
authors.initials: SH
authors.lastname: Robertson
authors.affiliation: School of Medicine, Duke University, Durham, NC, 27710, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Wang
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, 27710, USA.|Department of Electrical and Computer Engineering, Duke University, Durham, NC, 27708, USA.
authors.forename: Mu
authors.initials: M
authors.lastname: He
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, 27710, USA.|Department of Biomedical Engineering, Duke University, Durham, NC, 27708, USA.
authors.forename: Rohan S
authors.initials: RS
authors.lastname: Virgincar
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: Geoffry M
authors.initials: GM
authors.lastname: Schrank
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, 27710, USA.|Medical Physics Graduate Program, Duke University, Durham, NC, 27705, USA.
authors.forename: Elianna A
authors.initials: EA
authors.lastname: Bier
authors.affiliation: Division of Cardiology, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: Sudarshan
authors.initials: S
authors.lastname: Rajagopal
authors.affiliation: Department of Medicine, Division of Pulmonary, Allergy and Critical Care, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: Yuh Chin
authors.initials: YC
authors.lastname: Huang
authors.affiliation: Gilead Sciences, Foster City, CA, 94404, USA.
authors.forename: Thomas G
authors.initials: TG
authors.lastname: O'Riordan
authors.affiliation: Department of Medicine, Division of Pulmonary, Allergy and Critical Care, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: Craig R
authors.initials: CR
authors.lastname: Rackley
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: H Page
authors.initials: HP
authors.lastname: McAdams
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, NC, 27710, USA.|Department of Biomedical Engineering, Duke University, Durham, NC, 27708, USA.|Medical Physics Graduate Program, Duke University, Durham, NC, 27705, USA.|Department of Radiology, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: Bastiaan
authors.initials: B
authors.lastname: Driehuys
mesh_terms: D006801:Humans; D008168:Lung; D008279:Magnetic Resonance Imaging; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging*; D012123:Pulmonary Ventilation; D014979:Xenon Isotopes
chemical_list: D014979:Xenon Isotopes
keywords: COPD; IPF; PAH; binning; gas exchange; hyperpolarized 129Xe MRI; image registration; thoracic cavity segmentation