Towards Temperature-Corrected pH Mapping using CEST Imaging: Quantification of the Underlying Calibration as a Function of Temperature

Motivation: CEST-based pH mapping relies on a strongly temperature-dependent calibration, yielding the parameter kc characterizing the exchange rate. Previously, this calibration has only been performed at T=37°C, thus impeding quantitative pH mapping at different temperatures. Goal(s): Enabling more reliable, i.e. temperature-corrected, quantitative CEST-based pH mapping. Approach: We quantified the temperature dependency of kc(T) for amide, amine and guanidino protons at B0=9.4T using creatine and protamine model solutions at various pH and temperatures. Results: For all proton species, the measured kc(T) showed exponential temperature dependencies with doubling of kc(T) for distinct temperature increases (ΔT=Tdouble) of around 4−11°C. Interestingly, each proton species exhibited a characteristic Tdouble. Impact: These findings enable CEST-based pH mapping at any desired temperature, which, previously, has only been possible at T=37°C. Prospectively, quantitative pH mapping will now also be possible in anatomical regions, e.g. human lower leg, where temperatures may deviate from T=37°C.