Measurement of changes in tissue temperature using MR imaging.

The spin-lattice relaxation time T1 of tissue has been measured as a function of temperature using a magnetic resonance imager. Both in vitro and in vivo tissues have been heated within the imager using radiofrequency power applied to either implanted electrodes or capacitive plates. The temperature distribution was monitored with implanted thermocouples and T1 was found to have a linear dependence with temperature with a slope of 5-10 ms/degrees C. The uncertainty in T1 corresponds to a temperature resolution of 1-2 degrees C, which combined with a spatial resolution of 4-5 mm and scan time of 1 min suggests the method should be valuable for noninvasive temperature mapping in clinical hyperthermia.