On the origin of paramagnetic inhomogeneity effects in blood

Abstract

Hydrogen, sodium, and fluorine (added F^‐) NMR spectra of venous and oxygenated blood were measured. The fluorine resonance was seen as a single peak in both samples, and all three resonances exhibited the same deoxy‐oxy shift. Because F^‐ exchanges slowly across the red cell membrane, and because sodium is 95% extracellular, these results suggest that the intra‐extracellular field difference ΔB is less than 0.1 ppm. A small value of ΔB tends to rule out transmembrane exchange as an important contributor to relaxation in MRI of blood and hematomas. However, the broadening of the resonances with deoxygenation, by 0.3‐0.4 ppm, indicates that both intra‐ and extracellular gradients are of comparable and sufficient magnitude to produce the T2‐weighted hypointensity seen in clinical magnetic resonance images of hematomas at high fields. © 1989 Academic Press, Inc.