Fat emulsification measured using NMR transverse relaxation

This paper presents a novel method of measuring the droplet size in oil-in- water emulsions. It is based on changes in the NMR transverse relaxation ra te due to the effect of microscopic magnetic susceptibility differences bet ween fat droplets and the surrounding water. The longitudinal and transvers e relaxation rates of a series of emulsions with constant oil volume fracti on and five different mean droplet sizes, in the range 0.4-20.9 mum, were m easured in vitro at 37 degreesC using EPI. While the longitudinal relaxatio n rate 1/T-1 did not change significantly, 1/T-2 was observed to increase w ith mean droplet size. The measured changes in 1/T-2 were found to be in go od agreement with results predicted from proton random walk simulations, an d were also consistent with analytical solutions based on an outer sphere r elaxation model. Measurements of 1/T-2 on emulsions with a higher oil volum e fraction, and on emulsions of a fixed size where the water phase was dope d with gadolinium to modulate the susceptibility difference between the pha ses, also showed the predicted behavior. As part of this study the suscepti bility difference between olive oil and water was measure toe 1.55 ppm. (C) 2001 Academic Press.