Perflurooctyl bromide emulsions as in vivo carriers for laser-polarized xenon-129 for magnetic resonance imaging: The effect of phosphatidylcholine chain-length and oxygenation of the emulsion on longitudinal relaxation time (T(1)) and line-width

Hyperpolarized 129Xe (HXe) can be dissolved in biologically compatible Perfluorooctylbromide (PFOB) emulsions while maintaining sufficient polarization for in vivo magnetic resonance imaging. Increasing the longitudinal (T₁) and the transverse (T₂*) relaxation times of HXe dissolved in PFOB emulsions is critical if it is to be used for in vivo Magnetic Resonance Imaging. The effects of emulsion droplet size and oxygenation were studied to determine if these times might be increased. Emulsion droplet sizes were controlled by changing the amount of phosphatidylcholine (PC) used to stabilize the emulsion and by changing the chain-length of the PCs' hydrocarbon tail. It was found that the average droplet size could be decreased from 3.05 μm to 2.42 μm by using a PC with a 4 carbon tail (DBPC) rather than one with an 18 carbon tail (DOPC). With this decrease in size, line-width decreased significantly from 4.74 ppm to 2.42 ppm. There was no correlation between T₁ and droplet size. Oxygenation did not affect line-width but had a destructive effect on T₁. It was possible to increase T₁s by over 100 s through the rigorous elimination of oxygen.