Ultrasound applicators for interstitial thermal coagulation

Direct-coupled (DC) and catheter-cooled (CC) ultrasound applicator configur ations were evaluated for high-temperature ultrasound interstitial thermal therapy (USITT) using computer simulations, acoustic beam measurements, and in vivo temperature measurements. The DC devices consist of 2.2-mm diamete r tubular ultrasound transducers encapsulated within a thin biocompatible p lastic coating, which can be inserted directly into the tissue. The CC devi ces incorporate 1.5-mm diameter tubular transducers, which are inserted wit hin 2.2- to 2.4-mm diameter plastic implant catheters and require an integr ated water-cooling schema, Simulated transient temperature profiles and cum ulative thermal dose distributions indicate that each of these applicator c onfigurations can produce target temperatures greater than 50 degrees C and corresponding thermal doses greater than 300 to 600 equivalent minutes at 43 degrees C (EM43 degrees C) within 5 min at a radial depth of 1 to 1.5 cm in moderately perfused tissues. Theoretical investigations of air-cooling implemented within DC applicators demonstrated a significant enhancement of thermal penetration compared with non-cooled DC applicators, thus approach ing performance attainable with CC devices. Temperature distributions achie ved with DC and CC applicators in vivo were in agreement with theoretical c alculations and further demonstrate that the devices are practical, suffici ent power output levels can be obtained, and the angular heating profiles c an be shaped or directed to protect non-targeted critical normal tissues. T his preliminary study demonstrates that these interstitial ultrasound appli cators have potential to provide controlled thermal coagulation and necrosi s of small target regions and deserve further investigation and development for possible implementation in the treatment of benign and cancerous lesio ns in sites such as prostate, liver, and brain.