Abstract

Hyperthermia achieved with an ultrasonic interstitial applicator is discussed. The applicator consists of a G19 hypodermic needle attached via conical velocity transformer to a planar PZT transducer operated in a C.W. mode at 1.03 MHz. Hyperthermia in a tissue phantom did not involve blood perfusion effects and hence heat conduction problem was used to analyze temperature elevation produced by the applicator. Pressure distribution along the axis of the applicator's antenna exhibited standing wave pattern of 2.2 mm spatial periodicity with a modulated amplitude. Approximated solution for temperature elevation was interpreted as leading to a distribution in axial direction independent of the intensity pattern around the antenna. Measurements of temperature distribution done with a miniature thermistor (active diameter of 0.23 mm) confirmed the conclusion. Axial variation of elevated temperature (12 OC at the peak) at various radial distances from the antenna showed no rapid variation characteristic to the observed pressure distribution.

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