Experimental Uses of Magnetic Resonance Imaging–Guided Focused Ultrasound Surgery

Ultrasound is a pressure wave with a frequency above the audible range of a human ear(18-20 kHz); it is generated by a mechanical motion that induces the molecules in amedium to oscillate around their rest positions. Due to the bonding between themolecules, the disturbance is transmitted to neighboring molecules. The motion causescompressions and rarefactions of the medium and thus a pressure wave travels with themechanical disturbance (Figs. 1 and 2).