title: Pulmonary hyperpolarized (129) Xe morphometry for mapping xenon gas concentrations and alveolar oxygen partial pressure: Proof-of-concept demonstration in healthy and COPD subjects.
abstract: OBJECTIVE
  Diffusion-weighted (DW) hyperpolarized (129) Xe morphometry magnetic resonance imaging (MRI) can be used to map regional differences in lung tissue micro-structure. We aimed to generate absolute xenon concentration ([Xe]) and alveolar oxygen partial pressure (pA O2 ) maps by extracting the unrestricted diffusion coefficient (D0 ) of xenon as a morphometric parameter.
  
  
  METHODS
  In this proof-of-concept demonstration, morphometry was performed using multi b-value (0, 12, 20, 30 s/cm(2) ) DW hyperpolarized (129) Xe images obtained in four never-smokers and four COPD ex-smokers. Morphometric parameters and D0 maps were computed and the latter used to generate [Xe] and pA O2 maps. Xenon concentration phantoms estimating a range of values mimicking those observed in vivo were also investigated.
  
  
  RESULTS
  Xenon D0 was significantly increased (P = 0.035) in COPD (0.14 ± 0.03 cm(2) /s) compared with never-smokers (0.12 ± 0.02 cm(2) /s). COPD ex-smokers also had significantly decreased [Xe] (COPD = 8 ± 7% versus never-smokers = 13 ± 8%, P = 0.012) and increased pA O2 (COPD = 18 ± 3% versus never-smokers = 15 ± 3%, P = 0.009) compared with never-smokers. Phantom measurements showed the expected dependence of D0 on [Xe] over the range of concentrations anticipated in vivo.
  
  
  CONCLUSIONS
  DW hyperpolarized (129) Xe MRI morphometry can be used to simultaneously map [Xe] and pA O2 in addition to providing micro-structural biomarkers of emphysematous destruction in COPD. Phantom measurements of D0 ([Xe]) supported the hypotheses that differences in subjects may reflect differences in functional residual capacity.
authors.affiliation: Imaging Research Laboratories, Robarts Research Institute, Western University, London, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Ouriadov
authors.affiliation: Imaging Research Laboratories, Robarts Research Institute, Western University, London, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Farag
authors.affiliation: Department of Medical Biophysics, Western University, London, Canada.|James Hogg Research Centre, The University of British Columbia, and The Institute of Heart and Lung Health, St. Paul's Hospital, Vancouver, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Kirby
authors.affiliation: Department of Medicine, Western University, London, Canada.
authors.forename: D G
authors.initials: DG
authors.lastname: McCormack
authors.affiliation: Imaging Research Laboratories, Robarts Research Institute, Western University, London, Canada.|Department of Medical Biophysics, Western University, London, Canada.|Department of Medical Imaging, Western University, London, Canada Western University, London, Canada.
authors.forename: G
authors.initials: G
authors.lastname: Parraga
authors.affiliation: Imaging Research Laboratories, Robarts Research Institute, Western University, London, Canada.|Department of Medical Biophysics, Western University, London, Canada.|Department of Medical Imaging, Western University, London, Canada Western University, London, Canada.|Peter Gilgan Centre for Research and Learning, The Hospital for Sick Children, Toronto, Canada.
authors.forename: G E
authors.initials: GE
authors.lastname: Santyr
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media / Q000493:pharmacokinetics; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D057054:Molecular Imaging / Q000379:methods; D010100:Oxygen / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000378:metabolism* / Q000473:pathology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000378:metabolism* / Q000473:pathology*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D014978:Xenon / Q000378:metabolism*; D014979:Xenon Isotopes / Q000493:pharmacokinetics
chemical_list: D003287:Contrast Media; D019275:Radiopharmaceuticals; D014979:Xenon Isotopes; D014978:Xenon; D010100:Oxygen
keywords: diffusion; hyperpolarized; lung, morphometry; pAO2; xenon concentration