High sensitivity 19F MRI of a perfluoro-octyl bromide emulsion: application to a dynamic biodistribution study and oxygen tension mapping in the mouse liver and spleen

We have recently developed an optimized multi-spin echo (MSE) sequence dedicated to perfluoro-octyl bromide (PFOB) imaging yielding an excellent sensitivity in vitro. The aim of the present study was to apply this sequence to quantitative measurements in the mouse liver and spleen after intravenous (i.v.) injection of PFOB emulsions. We first performed oxygenation maps 25.5 min after a single infusion of emulsion and, contrary to previous studies, shortly after injection. The signal-to-noise ratio (SNR) in the liver and spleen was as high as 45 and 120, respectively, for 3-min images with 11.7-mL pixels. Values of oxygen tension tended to be slightly higher in the spleen than in the liver. Dynamic biodistribution experiments were then performed immediately after intravenous (i.v.) injection of PFOB emulsions grafted with different quantities of polyethylene glycol (PEG) for stealth. Images were acquired every 7 min for 84 min and the SNR measured in the liver and spleen was at least four from the first time point. Uptake rates could be assessed for each PEG amount and, in spite of high standard deviations (SDs) owing to inter animal variability, our data confirmed that increasing quantities of PEG allow more gradual uptake of the emulsion particles by the liver and spleen. In conclusion, our method seems to be a powerful tool to non-invasively perform accurate in vivo quantitative measurements in the liver and spleen using 19 F MRI. (authors)