MRI phase mapping of temperature distributions induced in food by microwave heating.

A range of temperature-sensitive MRI parameters of water (T2, T1, diffusion coefficient, and chemical shift) were evaluated to map in three dimensions the non-uniform temperature distributions induced by microwave heating in both model and real food systems. Phase mapping was found to be the most robust method, and evaluations of possible experimental errors were based on semi-quantitative studies of homogeneous and heterogeneous systems. The MRI protocol provides complementary phase and magnitude data, which are related to the sample temperature and structural heterogeneity, respectively. Used together, they relate the temperature changes to the differential thermal properties of the various components within a heterogeneous sample. The potential applications of this technique to microwave and other forms of heating is discussed.