Acoustic pressure wave generation within an MR imaging system: potential medical applications

The static magnetic field of a magnetic resonance (MR) imaging system was used as a component of an electromagnetic transducer for generating acoustic pressure waves. To permit limited focusing, the transducer was constructed from a conductive thin plate shaped like a section of a sphere. The plate was placed within the static field of the MR unit (B0 = 1.5 T), and current pulses with a rise time of 73 nsec and amplitude of 1.0 kA were applied to it. Hydrophonic recording demonstrated a shock wave with a peak pressure of 4.8 MPa at the approximated focal point. MR guidance of lithotripsy would be particularly useful to limit undesirable soft-tissue damage. It is also suggested that the integration of an acoustic pressure wave generator with MR imaging and control provides a novel technology for the treatment of solid soft-tissue tumors.