NMR RELAXATION RATES AND BLOOD OXYGENATION LEVEL

A linear relationship between the proton relaxation rates and the frac tion of deoxyhemoglobin of circulating whole blood (f(Hb)) has been es tablished in vitro at 4.7 T. These results have been interpreted on th e basis of the additivity of relaxation rates. The slope of the lines of transverse relaxation rates (R(2)) versus f(Hb) was found to increa se with interpulse delay in Carr-Purcell Meiboom-Gill (CPMG) experimen ts. The Luz-Meiboom relation applied to this interpulse delay dependen ce of R(2) suggests a two-site chemical exchange rather than a diffusi on mechanism. The 1-ms water proton exchange time derived from these o bservations has been interpreted in terms of exchange between exchange able protons close to the paramagnetic center of hemoglobin and proton s of bulk water.