title: MRI of brain tissue oxygen tension under hyperbaric conditions.
abstract: The brain depends on a continuous supply of oxygen to maintain its structural and functional integrity. This study measured T1 from MRI under normobaric air, normobaric oxygen, hyperbaric air, and hyperbaric oxygen (HBO) conditions as a marker of tissue pO2 since dissolved molecular oxygen acts as an endogenous contrast agent. Brain tissue T1 decreased corresponding to increased pO2 with increasing inhaled oxygen concentrations, and tissue oxygenation was estimated from the T1 changes between different inhaled oxygen levels. Tissue pO2 difference maps between different oxygen conditions showed heterogeneous pO2 changes in the brain. MRI-derived tissue pO2 was markedly lower than the arterial pO2 but was slightly higher than venous pO2. Additionally, for comparison with published extracellular tissue pO2 data obtained using oxygen electrodes and other invasive techniques, a model was used to estimate extracellular and intracellular pO2 from the MRI-derived mean tissue pO2. This required multiple assumptions, and so the effects of the assumptions and parameters used in modeling brain pO2 were evaluated. MRI-derived pO2 values were strongly dependent on assumptions about the extra- and intracellular compartments but were relatively less sensitive to variations in the relaxivity constant of oxygen and contribution from oxygen in the cerebral blood compartment. This approach may prove useful in evaluating tissue oxygenation in disease states such as stroke.
authors.affiliation: Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, United States; Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX, United States. Electronic address: muire@uthscsa.edu.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Muir
authors.affiliation: Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, United States; Graduate School of Biomedical Science, University of Texas at San Antonio, San Antonio, TX, United States.
authors.forename: Damon P
authors.initials: DP
authors.lastname: Cardenas
authors.affiliation: Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, United States; Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX, United States; South Texas Veterans Health Care System, Department of Veterans Affairs, San Antonio, TX, United States. Electronic address: duongt@uthscsa.edu.
authors.forename: Timothy Q
authors.initials: TQ
authors.lastname: Duong
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D006931:Hyperbaric Oxygenation / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D057054:Molecular Imaging / Q000379:methods; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D010100:Oxygen
keywords: Hyperbaric oxygen; MRI; T(1); Tissue oxygenation