Mapping of oxygen by imaging lipids relaxation enhancement: A potential sensitive endogenous MRI contrast to map variations in tissue oxygenation

Abstract

Purpose Because of its paramagnetic properties, oxygen may act as an endogenous magnetic resonance imaging contrast agent by changing proton relaxation rates. Changes in tissue oxygen concentrations have been shown to produce changes in relaxation rate R₁ of water. The aim of the study was to improve the sensitivity of oxygen enhanced R₁ imaging by exploiting the higher solubility of oxygen in lipids (as compared with water) to sensitively monitor changes in tissue oxygen levels by selectively measuring the R₁ of lipids. Methods The method, with the acronym “MOBILE” (mapping of oxygen by imaging lipids relaxation enhancement), was applied in different mouse models of hypoxic processes on a 11.7 T magnetic resonance imaging system. MOBILE was compared with R*₂, R₁ of water, and with pO₂ measurements (using electron paramagnetic resonance oximetry). MOBILE was also applied in the brain of healthy human volunteers exposed to an oxygen breathing challenge on a 3 T magnetic resonance imaging system. Results MOBILE was shown to be able to monitor changes in oxygenation in tumor, peripheral, liver, and brain tissues. The clinical translation was demonstrated in human volunteers. Conclusion MOBILE arises as a promising noninvasive and sensitive tool for diagnosis and therapeutic guidance in disorders involving hypoxia. Magn Reson Med 70:732–744, 2013.