High sensitivity 19F MRI allows dynamic biodistribution study and oxygen tension mapping at pharmaceutical doses of a PFOB emulsion in the mouse reticuloendothelial system

Introduction Perfluorooctylbromide (PFOB) is a promising contrast agent for in vivo F MRI owing to its biocompatibility. After intravenous injection, PFOB emulsions are known to localize in the reticuloendothelial system (RES), mainly the liver and spleen. PFOB nanoparticles (PFOB NP) accumulate within macrophages [1] and thus allow quantitative MRI in these organs. However, the complex multipeak spectrum yielded by PFOB and the scalar J-coupling between the CF2 and the CF3 group complicate the choice of an imaging method. Moreover, when injected at pharmacological dose, the low concentration of PFOB in the RES requires a high sensivity acquisition method. We recently optimized a multi spin echo (MSE) sequence allowing cancellation of J-modulation and T2 enhancement and yielding an excellent sensitivity [2]. Thanks to our method, we show that kinectics of accumulation of a PFOB emulsion in the RES can be quantified within the minutes following injection, allowing the evaluation of the emulsion’s stealth when different quantities of polyethylene glycol (PEG) are grafted. We finally show that partial oxygen pressure (pO2) mapping can be performed in the RES after a single injection, contrary to previous studies [3].