Non-invasive temperature imaging of muscles with magnetic resonance imaging using spin-echo sequences

The application of spin-echo magnetic resonance imaging sequences on non-in vasive temperature imaging for temperature mapping of human limbs is invest igated. In an in vitro experiment performed on a meat sample, the equilibri um magnetisation P and the spin-lattice relaxation time T-1 are calculated from the values for the repetition time TR and the signal intensities obtai ned by a spin-echo sequence at different tissue temperatures as measured by a fibre-optic probe. T-1 is linearly correlated to the tissue temperature, and P is linearly correlated to the reciprocal value of the absolute tempe rature. Both effects, taken together, lead to a non-linear dependency of th e signal intensity on temperature. Therefore a TR leading to maximum temper ature dependency of the signal intensity is calculated and used in the furt her experiments. In the in vivo experiments, the lower legs of two voluntee rs are cooled from outside. Images are acquired with a spin-echo sequence ( 1.5 T, TR = 1200ms, TE = 10ms). A rise in signal intensity in the muscle wi th falling skin temperature is observed, particularly in more peripheral mu scle layers. This study shows that spin-echo sequences can be used to monit or temperature changes and temperature differences in living muscle tissue.