Magnetic resonance imaging of pH in vivo using hyperpolarized 13C-labelled bicarbonate

As alterations in tissue pH underlie many pathological processes, the capability to image tissue pH in the clinic could offer new ways of detecting disease and response to treatment(1). Dynamic nuclear polarization is an emerging technique for substantially increasing the sensitivity of magnetic resonance imaging experiments(2,3). Here we show that tissue pH can be imaged in vivo from the ratio of the signal intensities of hyperpolarized bicarbonate ((HCO3-)-C-13) and (CO2)-C-13 following intravenous injection of hyperpolarized (HCO3-)-C-13. The technique was demonstrated in a mouse tumour model, which showed that the average tumour interstitial pH was significantly lower than the surrounding tissue. Given that bicarbonate is an endogenous molecule that can be infused in relatively high concentrations into patients(4), we propose that this technique could be used clinically to image pathological processes that are associated with alterations in tissue pH, such as cancer, ischaemia and inflammation.