Absolute measurements of ultrasonic pressure by using high magnetic fields

A hydrophone is introduced that exploits the emf signal generated in a cond uctor when sonicated in the presence of a uniform static magnetic field. Th e method uses a small metal coil or metal membrane as a hydrophone receiver . Acoustic signals at 748 kHz are introduced in 1.5T and 4.7T fields and re corded both through direct electrical contact with the hydrophone and via R F pick-up coils, allowing wireless placement of the hydrophone. Linear resp onse is confirmed over four orders of magnitude in the pressure amplitude. Waveforms determined from the detected voltage are shown to be in excellent agreement with those obtained using a calibrated polyvinylidene difluoride film, and absolute values correlate within 20%, The methods are conceptual ly suitable for use in the presence of the high and uniform field of commer cial MR scanners. The hydrophone may appear particularly useful as a qualit y assurance device in therapeutic and diagnostic acoustic techniques that u se MRI.