Non-invasive in-vivo temperature mapping of ultrasound heating using fluorine-based magnetic resonance imaging agents

The aim of this study was to investigate the feasibility of using fluorine based magnetic resonance to measure accurately hepatic heating from a focused ultrasound transducer in rats. This new method uses the temperature dependence of the difference in fluorine chemical shifts within a single molecule to provide internal compensation for complicating physiological effects. Female Sprague-Dawley rats were exposed to 5 minutes of CW irradiation at 1.37 MHz from a focused transducer. Theoretical calculations based on the monopole source solution to the bio-heat transfer equation gave a volume-averaged temperature rise of 2.1/spl deg/C. Preliminary experiments using protein encapsulated perfluorooctylbromide targeted to the liver gave an empirical rise of 2.0/spl plusmn/0.4/spl deg/C.