A multi-element ultrasonic hyperthermia applicator with independent element control.

Acoustic field patterns from a planar multi-element ultrasonic applicator were determined experimentally and compared with theory. Measurements were obtained from square arrays of 4 and 16 elements. The acoustic fields produced by various configurations of individual square elements (3.6 cm X 3.6 cm) driven at 1 MHz were measured in water. Transverse and axial scans paths were used to characterize the acoustic beam for different aperture sizes and individual element excitations. Unequal power excitation of adjacent elements produced multiple peaked acoustic intensity patterns. While a simple theoretical model was not able to account for all the experimentally determined transverse and axial field patterns, a model including mechanical damping improved the agreement between theory and experiment. However, less ripple in the axial pattern was measured than predicted by either theoretical model. The ability of the applicator to generate acoustic field patterns suitable for local tissue heating was demonstrated by an experimental study in dog thigh muscle.