DETERMINATION OF LASER-INDUCED TEMPERATURE DISTRIBUTIONS USING ECHO-SHIFTED TURBOFLASH

An echo-shifted TurboFLASH sequence implemented on a clinical whole bo dy MR scanner was used to determine thermal changes in tissue, With th is snapshot-like data acquisition, temperature-related phase shifts we re measured with a temporal resolution of 1.3 s. For different types o f tissue (postmortem porcine brain, liver, and muscle) the temperature coefficients of the proton chemical shift were recorded during unifor m heating of the specimen in a water bath, The specific temperature-de pendent frequency shifts appeared similar to the proton chemical shift of free water (-0.01 ppm/degrees C), With this method, laser-induced ablation in postmortem porcine brain was monitored by temperature mapp ing, Comparison of the induced temperature profiles measured with NiCr Ni-thermocouples with the MR calculated profiles demonstrated excellen t temperature sensitivity and accuracy for this method of MR thermomet ry, with a maximum deviation of the determined temperatures of only -1 .8 degrees C. This investigation was designed as a feasibility study f or this rapid version of the phase mapping method, and no in vivo stud ies were performed.