Two-compartment radial diffusive exchange analysis of the NMR lineshape of (129)Xe dissolved in a perfluorooctyl bromide emulsion.

Hyperpolarized (129)Xe (xenon) gas dissolved in a perfluorooctyl bromide (PFOB) emulsion stabilized with egg yolk phospholipid (EYP) is a possible contrast agent for quantitative blood flow measurements using magnetic resonance imaging. The NMR line shape of xenon dissolved in PFOB emulsion depends strongly on the exchange of spins between PFOB and water. The exchange in this system depends on three factors: the geometrical factors (i.e., droplet size and surrounding water volume), the permeability of the EYP monolayer surrounding the droplet, and the diffusion coefficients of xenon in the two media. A theoretical model which predicts the line shape of xenon in the emulsion based on the Bloch-Torrey equations is presented. Fitting the full width at half maximum (FWHM) of the theoretical line shapes with the FWHM of the experimental spectra obtained from emulsions with different water dilutions allows estimation of the volume-weighted average diameter of the PFOB droplets (3.5+/-0.8) microm and the permeability of the EYP membrane surrounding the droplet (58+/-14) microm / s.