MRI under hyperbaric air and oxygen: Effects on local magnetic field and relaxation times

Purpose: Hyperbaric oxygen therapy has shown efficacies in the treatment of a number of diseases. The goal of this study was to develop a rodent hyperbaric chamber for MRI studies and to investigate the effects of hyperbaric air and hyperbaric oxygen on local magnetic field (B0) and MRI relaxation parameters in the rat brain. Methods: A hyperbaric chamber, constructed to fit inside an animal MRI scanner, was pressurized with air to four atmospheres, while oxygen was delivered locally via nose cone. B₀, T₂, T₂^∗, and T₁ maps in the rat brain were evaluated under normobaric air, hyperbaric air, and hyperbaric oxygen at 7T. Results: Under hyperbaric oxygen, images exhibited artifacts and temporal instability, attributable to fluctuating oxygen concentration from air and oxygen mixing near the imaging region. Physically shielding the imaging region from fluctuating oxygen concentration resolved the problems. With increasing oxygen at hyperbaric pressure, B₀ was shifted downfield with increased inhomogeneity near the ear canals and nose. Brain T₂ and T₂^∗ were lengthened, and T₁ was shortened. Conclusion: This study establishes the means to perform MRI on rodents under hyperbaric conditions. Hyperbaric air and hyperbaric oxygen have significant effects on B₀ and tissue relaxation parameters compared with normobaric air.