Monitoring blood oxygen state in muscle microcirculation with transverse relaxation

Oxygen uptake from the microcirculation is a direct measure of tissue funct ion, Magnetic resonance is capable of detecting differences between oxygena ted and deoxygenated blood due to the paramagnetic properties of deoxyhemog lobin. At the level of the microcirculation, however, imaging methods canno t directly visualize the vessels. Instead, bulk MR parameters are investiga ted for their ability to monitor blood oxygen saturation (%O-2) changes in the microcirculation of tissue, specifically skeletal muscle. Experiments i n an in vitro model verified the feasibility of detecting changes in expone ntial decay signals, and also verified the prediction of only two distinct decay components. Experiments in a rabbit model demonstrate that T-2' and m onoexponential T-2 decay are not sensitive to blood oxygen changes, but tha t the long-T-2 component in a biexponential fit is correlated to the blood oxygen state. Assuming a two-pool model for water protons in muscle, and wi th knowledge of the T-2-%O-2 relation, estimates of the microcirculation bl ood oxygen state can be made with some reasonable assumptions, Magn Reson M ed 45:662-672, 2001. (C) 2001 Wiley-Liss, Inc.