title: Quantification of regional early stage gas exchange changes using hyperpolarized (129)Xe MRI in a rat model of radiation-induced lung injury.
abstract: OBJECTIVE
  To assess the feasibility of hyperpolarized (HP) (129)Xe MRI for detection of early stage radiation-induced lung injury (RILI) in a rat model involving unilateral irradiation by assessing differences in gas exchange dynamics between irradiated and unirradiated lungs.
  
  
  METHODS
  The dynamics of gas exchange between alveolar air space and pulmonary tissue (PT), PT and red blood cells (RBCs) was measured using single-shot spiral iterative decomposition of water and fat with echo asymmetry and least-squares estimation images of the right and left lungs of two age-matched cohorts of Sprague Dawley rats. The first cohort (n = 5) received 18 Gy irradiation to the right lung using a (60)Co source and the second cohort (n = 5) was not irradiated and served as the healthy control. Both groups were imaged two weeks following irradiation when radiation pneumonitis (RP) was expected to be present. The gas exchange data were fit to a theoretical gas exchange model to extract measurements of pulmonary tissue thickness (LPT) and relative blood volume (VRBC) from each of the right and left lungs of both cohorts. Following imaging, lung specimens were retrieved and percent tissue area (PTA) was assessed histologically to confirm RP and correlate with MRI measurements.
  
  
  RESULTS
  Statistically significant differences in LPT and VRBC were observed between the irradiated and non-irradiated cohorts. In particular, LPT of the right and left lungs was increased approximately 8.2% and 5.0% respectively in the irradiated cohort. Additionally, VRBC of the right and left lungs was decreased approximately 36.1% and 11.7% respectively for the irradiated cohort compared to the non-irradiated cohort. PTA measurements in both right and left lungs were increased in the irradiated group compared to the non-irradiated cohort for both the left (P < 0.05) and right lungs (P < 0.01) confirming the presence of RP. PTA measurements also correlated with the MRI measurements for both the non-irradiated (r = 0.79, P < 0.01) and irradiated groups (r = 0.91, P < 0.01).
  
  
  CONCLUSIONS
  Regional RILI can be detected two weeks post-irradiation using HP (129)Xe MRI and analysis of gas exchange curves. This approach correlates well with histology and can potentially be used clinically to assess radiation pneumonitis associated with early RILI to improve radiation therapy outcomes.
authors.affiliation: Department of Medical Biophysics, Western University, London, Ontario N6A5C1, Canada; Imaging Research Laboratories, Robarts Research Institute, London, Ontario N6A5C1, Canada; and Department of Oncology, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, Oxford OX3 7DQ, United Kingdom.
authors.forename: Ozkan
authors.initials: O
authors.lastname: Doganay
authors.affiliation: Peter Gilgan Centre for Research and Learning, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G1X8, Canada.
authors.forename: Elaine
authors.initials: E
authors.lastname: Stirrat
authors.affiliation: Department of Medical Biophysics, Western University, London, Ontario N6A5C1, Canada and Imaging Research Laboratories, Robarts Research Institute, London, Ontario N6A5C1, Canada.
authors.forename: Charles
authors.initials: C
authors.lastname: McKenzie
authors.affiliation: General Electric Global Research, Munich 85748, Germany.
authors.forename: Rolf F
authors.initials: RF
authors.lastname: Schulte
authors.affiliation: Department of Medical Biophysics, Western University, London, Ontario N6A5C1, Canada; Imaging Research Laboratories, Robarts Research Institute, London, Ontario N6A5C1, Canada; Peter Gilgan Centre for Research and Learning, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G1X8, Canada; and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G1L7, Canada.
authors.forename: Giles E
authors.initials: GE
authors.lastname: Santyr
mesh_terms: D000818:Animals; D001810:Blood Volume / Q000528:radiation effects; D015331:Cohort Studies; D003287:Contrast Media; D005240:Feasibility Studies; D008168:Lung / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology / Q000528:radiation effects*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008954:Models, Biological; D011659:Pulmonary Gas Exchange / Q000528:radiation effects*; D011833:Radiation Injuries, Experimental / Q000000981:diagnostic imaging* / Q000503:physiopathology; D017564:Radiation Pneumonitis / Q000473:pathology / Q000503:physiopathology*; D017207:Rats, Sprague-Dawley; D014979:Xenon Isotopes
chemical_list: D003287:Contrast Media; D014979:Xenon Isotopes