Directional interstitial ultrasound applicators for thermal coagulation of tissue

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Abstract
Direct-coupled and catheter-cooled interstitial ultrasound applicators have been evaluated for thermal necrosis of small, localized tumors. Emphasis of the design criteria has been on directionality of power deposition and the corresponding tissue heating. Ultrasound applicators have been fabricated using piezoceramic tubes operating at approximately 7 MHz. The applicators have full 360 degree(s) active acoustic zones, or are sectored to provide different angular heating patterns. The applicators were characterized through acoustic power output measurements, beam profile distributions in water, thermal distribution measurements in an in vitro perfused kidney model, and in vivo thermal dosimetry in porcine thigh muscle. Bench tests demonstrated that high power output levels could be sustained in both the direct-coupled and catheter-cooled devices without degradation of the ultrasound transducer. The angular power depositions obtained in water were closely correlated to the resultant temperature distributions measured both in the in vitro kidney and in vivo experiments, thus demonstrating the ability to shape the beam profiles for controlled, directional ablation of tissue.

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