title: T2* and T1 assessment of abdominal tissue response to graded hypoxia and hypercapnia using a controlled gas mixing circuit for small animals.
abstract: To characterize T2* and T1 relaxation time response to a wide spectrum of gas challenges in extracranial tissues of healthy rats.
  
  
  
  A range of graded gas mixtures (hyperoxia, hypercapnia, hypoxia, and hypercapnic hypoxia) were delivered through a controlled gas-mixing circuit to mechanically ventilated and intubated rats. Quantitative magnetic resonance imaging (MRI) was performed on a 3T clinical scanner; T2* and T1 maps were computed to determine tissue response in the liver, kidney cortex, and paraspinal muscles. Heart rate and blood oxygen saturation (SaO2 ) were measured through a rodent oximeter and physiological monitor.
  
  
  
  T2* decreases consistent with lowered SaO2 measurements were observed for hypercapnia and hypoxia, but decreases were significant only in liver and kidney cortex (P < 0.05) for >10% CO2 and <15% O2 , with the new gas stimulus, hypercapnic hypoxia, producing the greatest T2* decrease. Hyperoxia-related T2* increases were accompanied by negligible increases in SaO2 . T1 generally increased, if at all, in the liver and decreased in the kidney. Significance was observed (P < 0.05) only in kidney for >90% O2 and >5% CO2 .
  
  
  
  T2* and T1 provide complementary roles for evaluating extracranial tissue response to a broad range of gas challenges. Based on both measured and known physiological responses, our results are consistent with T2* as a sensitive marker of blood oxygen saturation and T1 as a weak marker of blood volume changes. J. Magn. Reson. Imaging 2016;44:305-316.
authors.affiliation: Translational Biology & Engineering Program, Ted Rogers Centre for Heart Research, Toronto, Canada.|Leslie Dan Faculty of Pharmacy, University of Toronto, Canada.|Physiology & Experimental Medicine, Hospital for Sick Children Research Institute, Toronto, Canada.
authors.forename: Tameshwar
authors.initials: T
authors.lastname: Ganesh
authors.affiliation: Lab Animal Services, Hospital for Sick Children, Toronto, Canada.
authors.forename: Marvin
authors.initials: M
authors.lastname: Estrada
authors.affiliation: Department of Anesthesia, University of Toronto, Canada.
authors.forename: James
authors.initials: J
authors.lastname: Duffin
authors.affiliation: Translational Biology & Engineering Program, Ted Rogers Centre for Heart Research, Toronto, Canada.|Leslie Dan Faculty of Pharmacy, University of Toronto, Canada.|Physiology & Experimental Medicine, Hospital for Sick Children Research Institute, Toronto, Canada.|The Edward S. Rogers Sr. Department of Electrical & Computer Engineering, University of Toronto, Canada.|Institute of Biomaterials & Biomedical Engineering, University of Toronto, Canada.
authors.forename: Hai Ling
authors.initials: HL
authors.lastname: Cheng
mesh_terms: D000005:Abdomen / Q000000981:diagnostic imaging / Q000502:physiology; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood*; D004867:Equipment Design; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012121:Respiration, Artificial / Q000295:instrumentation; D014781:Viscera / Q000000981:diagnostic imaging* / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: blood oxygen level dependent; blood volume; gas challenge; tissue oxygenation; vasoreactivity