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Abstract

An ultrasonic hyperthermia system capable of producing discrete heating of a volume of deep-seated, normally perfused tissue. An individual transducer is configured and driven so that its compressional mode of vibration is suppressed near the center, with the result that the near field is characterized by the substantial absence of a strong central (on-axis) peak. This is preferably accomplished by driving the transducer at a frequency such that the transverse mode of vibration is responsible for the suppression. The near field transverse intensity distribution is further characterized by an annular satellite peak that surrounds the axis. As one proceeds axially away from the transducer, the satellite peak decreases and a predominant central peak occurs. A plurality of transducers are mounted in an isospherical configuration so that the corresponding plurality of beams are directed toward a central axis of the system. Simultaneous heating of a relatively large cylindrical region is achieved in a system wherein the beams do not actually cross one another, but rather are offset with respect to the central axis. As the beams approach each other, portions of their satellite peaks add to heat the central portion of the cylindrical region while the central peaks heat the outer portion. In the region where the beams converge, the central peaks concentrate the power within the heated cylindrical region.

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