Fig 1.

A, Schematic representation of the temperature-dependency of the water proton resonance frequency chemical shift. A water hydrogen bonding scenario for water molecules in two milieu of differing temperatures is depicted. Increasing temperatures drive the water hydrogen bonding equilibrium towards greater free water proportions through disruption of hydrogen bonds. Electronic currents (“e-”) about the hydrogen proton shield it from the main magnetic flux, but will vary in strength between strongly (left) and weakly (right) bound water pools. The greater shielding of free water hydrogens (right) yields lower precessional frequencies, governed by the gyromagnetic ratio of hydrogen, ∼42MHz/T. B, Within the hydrogen PRF spectrum, higher temperatures translate the water resonance upfield (i.e. towards lower chemical shifts), reducing the chemical shift difference between water and a non-temperature dependent reference such as the methyl resonance of NAA, producing a linear correlation coefficient (C) of ∼−0.01 ppm/C. As shown, the relationship between hydrogen bonding equilibrium, PRF, and temperature remains linear across even supraphysiologic temperature ranges as demonstrated in an aqueous cytosolic phantom during real time fiberoptic temperature monitoring. Adapted from Dehkharghani et al.⁷⁶