A CLINICAL, NONINVASIVE, MR-IMAGING MONITORED ULTRASOUND SURGERY METHOD

A noninvasive method of tissue ablation that is guided and monitored w ith magnetic resonance (MR) imaging has been developed. The method use s sharply focused ultrasound transducers of different focal lengths to induce a localized temperature elevation during a short exposure (1-2 0 seconds). A hydraulic, computer-controlled positioning device moves the transducer in an MR imager. The positioner is built into a standar d cradle in the imager. The system includes cavitation detection and p ower monitoring circuitry for patient safety. The target volume is out lined with cross-sectional MR images obtained immediately before sonic ation. By means of the software, the focus is moved to ablate the volu me defined with the images. The temperature elevation during the expos ure is monitored by means of the proton resonance frequency shift with fast gradient-echo sequences, and the necrosed volume is demonstrated with T2-weighted fast spin-echo images. This method has been extensiv ely tested in in vivo animal experiments and is now undergoing clinica l trial.