Blood NMR relaxation in the rotating frame: mechanistic implications

The rotating frame nuclear magnetic resonance relaxation rate R1ρ in the blood and cell lysate was studied at 4.7 T to provide reference values for in vivo modeling and to address the mechanisms contributing to net relaxation. A strong dependence on oxygenation, hematocrit, and spin lock field strength B1 (0.2–1.6 G) was observed in whole blood, whereas in lysate the effects were severely attenuated. The results were further compared to transverse relaxation rate R2. A good agreement in low-field asymptotes of these two relaxation rates was found. R1ρ field dispersion was fitted to Lorenzian line shape and resulted in correlation times around 40 μs. The dispersion behavior was related to motional properties of intracellular hemoglobin and effects of susceptibility shift interface across the cell membrane induced by compartmentalization of Hb into cells in blood.