Abstract:
During the past few years there has been an interest in using magnetic resonance imaging (MRI) to guide focused ultrasound beams during noninvasive surgery. MRI offers good soft tissue contrast, allowing the beam to be accurately aimed. Temperature sensitive MRI sequences can be used during low power test pulses to visualize the temperature elevation in the focal zone at temperature levels that do not cause tissue damage. This allows the beam to be aimed, eliminating all potential image or ultrasound propagation distortions. It may even be possible to calibrate the MRI signal to give the temperature elevation and use it as a feedback to modify the power output to assure adequate thermal exposure during every therapy sonication. Finally, MRI allows tissue changes induced by the sonication to be detected. This may be useful after the treatment to establish the boundaries of the thermal damage and is also very useful when experiments are conducted. All of these aspects of MRI guided ultrasound surgery have been investigated using in vivo experiments and the results will be reviewed here. The future technical developments and potential clinical applications will be discussed. [Work supported by NIH and General Electric Medical Systems.]