Temperature changes induced in human muscle by radio-frequency H-1 decoupling: measurement with an MR imaging diffusion technique. Work in progress.

To investigate temperature increases in tissues during magnetic resonance (MR) imaging or spectroscopy, the authors measured temperature changes in vitro and in vivo (leg of a volunteer) in a condition simulating hydrogen-1 decoupling in MR spectroscopy. Noninvasive measurements were obtained by using the temperature dependence of the translational diffusion coefficient of water. Temperature was measured at 0.5 T (86 MHz) by using a stimulated-echo sequence that included intense gradient pulses and a procedure reducing sensitivity to bulk tissue motion. Calibration curves of the diffusion coefficient against thermocouple-measured temperature were obtained for a gelatin phantom and bovine muscle. Temperature changes were 5.3 degrees C +/- 0.5 at 2.5 cm from the coil in gelatin and 7.7 degrees C +/- 0.5 at 0.7 cm in bovine muscle. The temperature changed by 4.9 degrees C +/- 1.9 at 2.2 cm from the coil in the calf muscle of a volunteer. The H-1 decoupling protocol can be adapted (modifications in transmission power, duty cycle) to reduce heating effects to below safety recommendations.