Quantitative MR temperature monitoring of high-intensity focused ultrasound therapy

A new quantitative method has been developed for real-time mapping of tempe rature changes induced by high intensity focused ultrasound (HIFU), It is b ased on the temperature dependence of the T-1 relaxation time and the equil ibrium magnetization, To calibrate the temperature measurement, the functio nal relationship between T-1 and temperature was examined in different samp les of porcine muscle and fatty tissue. The method was validated by a compa rison of calculated temperature maps with fiber-optic measurements in heate d muscle tissue. The experiment showed that the accuracy of the MR method f or temperature measurements is better than 1 degrees C, Since the acquisiti on time of the employed MR sequence Lakes only 3 s per slice and the calcul ation of the temperature map can be performed within seconds, the imaging t echnique works nearly in real-time. The temperature measurement could be re alized during HIFU showing no disturbances by ultrasound sonication. In com parison to other MR approaches, the advantages of the introduced method lie in a sufficient accuracy and time resolution combined with a reasonable ro bustness against motion as well as the feasibility for temperature monitori ng in fatty tissues. (C) 1999 Elsevier Science Inc.