The Effect of Dissolved Oxygen on the Susceptibility of Blood

Purpose: It has been predicted that, during hyperoxia, excess O-2 dissolved in arterial blood will significantly alter the blood's magnetic susceptibility. This would confound the interpretation of the hyperoxia-induced blood oxygenation level-dependent signal as arising solely from changes in deoxyhemoglobin. This study, therefore, aimed to determine how dissolved O-2 affects the susceptibility of blood. Theory and Methods: We present a comprehensive model for the effect of dissolved O-2 on the susceptibility of blood and compare it with another recently published model, referred to here as the ideal gas model (IGM). For validation, distilled water and samples of bovine plasma were oxygenated over a range of hyperoxic O-2 concentrations and their susceptibilities were determined using multiecho gradient echo phase imaging. Results: In distilled water and plasma, the measured changes in susceptibility were very linear, with identical slopes of 0.062 ppb/mm Hg of O-2. This change was dramatically less than previously predicted using the IGM and was close to that predicted by our model. The primary source of error in the IGM is the overestimation of the volume fraction occupied by dissolved O-2. Conclusion: Under most physiological conditions, the susceptibility of dissolved O-2 can be disregarded in MRI studies employing hyperoxia. (C) 2015 Wiley Periodicals, Inc.