MRI quantification of ice gradients in dough during freezing or thawing processes

The general aim of the work was to characterize the ice gradients in a dough stick during freezing and thawing processes in transient thermal conditions using MRI data. Firstly, the MRI signals obtained in steady-state thermal conditions for different MRI sequences were presented and discussed over the range [−15, +30 °C]. From these previous results, a direct relation between the MRI signal and the ice fraction was observed over the range [−10.8 °C, θm] with θm the initial freezing temperature. To validate the MRI method in transient thermal conditions, the ice fraction estimated from the MRI signal was converted into equivalent temperature (assuming thermodynamic equilibrium conditions) and compared with thermocouple temperature evolution during the freezing of a dough stick over the range [−10.8 °C, θm]. Good agreement confirmed that ice fraction could be monitored from MRI signal in transient thermal conditions.