Accurate determination of pH via hyperpolarized $^{129}$Xe NMR

International audienceMeasuring non-invasively and in a local way the in vivo extra-cellular pH is of importance for the diagnosis of insidious pathologies such as various cancers. For one decade, the use of hyperpolarized agents has been proposed; each method possesses its own advantage and inconvenience, and their applicability in the in vivo domain is not always straightforward. For instance,~ome years ago, we proposed the use of cage-molecules, bearing ionizable groups, in which laser-polarized xenon exhibits a pH-dependentchemical shift.' However extracting pH from measurement of the absolute chemical shift of caged xenon or even of the chemical shift difference between free and caged xenon is susceptible to be biased by external parameters such as temperature andmagnetic susceptibility fluctuation