Interstitial ultrasound applicators with internal cooling for controlled high temperature thermal therapy

The use of internally-cooled, direct-coupled interstitial ultrasound applicators as a means of providing controlled and directed high temperature thermal therapy was investigated. Prototype applicators were constructed using tubular ultrasound sources (1.5-2.5 mm OD) with transducers sectored for 90°, 200°, and 360° active acoustic zones. Effective cooling of the transducer surface was accomplished by the internal flow of chilled air or an integrated water mechanism. Thermal performance of the applicators was characterized through high temperature heating trials in-vivo (porcine thigh muscle and liver) and in-vitro (bovine liver) with varied sonication time and power. In general, internal cooling provided greatly enhanced thermal penetration and improved control of directional heating. This demonstrated ability to control and direct the extent of thermal coagulation shows great potential for treatment of localized tumors in sites such as prostate, brain, and liver