Temperature dependence of relaxation times in proton components of fatty acids.

We examined the temperature dependence of relaxation times in proton components of fatty acids in various samples in vitro at 11 tesla as a standard calibration data for quantitative temperature imaging of fat. The spin-lattice relaxation time, T(1), of both the methylene (CH(2)) chain and terminal methyl (CH(3)) was linearly related to temperature (r>0.98, P<0.001) in samples of animal fat. The temperature coefficients for the 2 primary proton components differed significantly; in 5 bovine fat samples, the coefficient at 30 °C was 1.79±0.07 (%/°C) for methylene and 2.98±0.38 (%/°C) for methyl. Numerical simulations based on such a difference demonstrated the possibility of considerable error from inconsistent ratios in fatty acid components when calibrating and estimating temperature. The error reached 3.3 °C per 15 °C in temperature elevation when we used a pure CH(2) signal for calibration and observed the signal with 18% of CH(3) to estimate temperature. These findings suggested that separating the fatty acid components would significantly improve accuracy in quantitative thermometry for fat. Use of the T(1) of CH(2) seems promising in terms of reliability and reproducibility in measuring temperature of fat.