Abstract #0413

Separation of the contribution of protein concentration and pH to measured APT signal changes in a preclinical model of brain metastases

Kevin J Ray^1,2, Manon Simard², James R Larkin², Michael A Chappell³, and Nicola R Sibson²

¹Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom, ²CRUK & MRC Oxford Institute for Radiation Oncology, University of Oxford, Oxford, United Kingdom, ³Institute of Biomedical Engineering, University of Oxford, Oxford, United Kingdom

Amide proton transfer (APT) studies usually attribute the altered APT signal in tumours to an increased cytosolic protein concentration. However, other concomitant changes in pH, T₁, or water content make absolute quantification of protein concentration or pH from APT signals challenging. In this study, we separate the contributions of protein concentration and pH to APT signal differences in a preclinical model of brain metastases by combining in vivo and ex vivo measurements. We show that 66% of the observed APT signal difference was caused by protein concentration alterations, with the remaining 34% signal change reflecting an increase in tumour pH.

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