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 treatment1. Dynamic nuclear polarization is an emerging technique for substantially increasing the sensitivity of magnetic resonance imaging experiments2,3. Here we show that tissue pH can be imaged in vivo from the ratio of the signal intensities of hyperpolarized bicarbonate (H13CO3-) and 13CO2 following intravenous injection of hyperpolarized H13CO3-. 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 patients4, 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.
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We thank R. McLaughlin and T. Witney for comments on the manuscript and S. Vowler for help with statistics. F.A.G. is in receipt of a Cancer Research UK and Royal College of Radiologists (UK) clinical research training fellowship, and S.E.D. a National Institutes of Health-Cambridge studentship. The work was supported by a Cancer Research UK Programme grant (to K.M.B.; C197/A3514). The polarizer and related materials were provided by GE Healthcare.
Author Contributions F.A.G. and S.E.D. operated the polarizer and J.H.A.-L. and K.G. provided advice on its use. M.I.K. conducted the MRI experiments and D.-E.H. prepared the animals. M.I.K. and F.A.G. analysed the data. R.I.Z., P.R.J., M.K. and M.H.L. devised the bicarbonate formulation. F.A.G. and K.M.B. wrote the paper and K.M.B. devised and organized the study.
The hyperpolarizer is on loan from GE Healthcare and is the subject of a research agreement between the University of Cambridge, Cancer Research UK and GE Healthcare. GE Healthcare also supplied the trityl radical used in the hyperpolarization process. Imagnia AB has supplied information about formulations for polarizing bicarbonate.
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Gallagher, F., Kettunen, M., Day, S. et al. Magnetic resonance imaging of pH in vivo using hyperpolarized 13C-labelled bicarbonate. Nature 453, 940–943 (2008). https://doi.org/10.1038/nature07017
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