NMR relaxation rates and blood oxygenation level

Abstract

A linear relationship between the proton relaxation rates and the fraction of deoxyhemoglobin of circulating whole blood (f_Hb) has been established in vitro at 4.7 T. These results have been interpreted on the basis of the additivity of relaxation rates. The slope of the lines of transverse relaxation rates (R₂) versus f_Hb was found to increase with interpulse delay in Carr-Purcell Meiboom-Gill (CPMG) experiments. The Luz-Mei-boom relation applied to this interpulse delay dependence of R₂ suggests a two-site chemical exchange rather than a diffusion mechanism. The 1-ms water proton exchange time derived from these observations has been interpreted in terms of exchange between exchangeable protons close to the paramagnetic center of hemoglobin and protons of bulk water.