Automated transfer and injection of hyperpolarized molecules with polarization measurement prior to in vivo NMR
Résumé
yperpolarized magnetic resonance via dissolution dynamic nuclear polarization necessitates the transfer of thehyperpolarized molecules from the polarizer to the imager prior to in vivo measurements. This process leads to unavoid-able losses in nuclear polarization, which are difficult to evaluate once the solution has been injected into an animal. Wepropose a method to measure the polarization of the hyperpolarized molecules inside the imager bore, 3 s following dis-solution, at the time of the injection, using a precise quantification of the infusate concentration. This in situ quantifica-tion allows for distinguishing between signal modulations related to variations in the nuclear polarization at the time ofthe injection and signal modulations related to physiological processes such as tissue perfusion. In addition, our methodincludes a radical scavenging process that leads to a minor reduction in sample concentration and takes place within acouple of seconds following the dissolution in order to minimize the losses due to the presence of paramagnetic polar-izing agent in the infusate. We showed that proton exchange between vitamin C, the scavenging molecule and the deu-terated solvent shortens the long carboxyl13C longitudinal relaxation time in [1-13C]acetate. This additional source ofdipolar relaxation can be avoided by using deuterated ascorbate. Overall, the method allows for a substantial gain inpolarization and also leads to an extension of the time window available for in vivo measurements.