Abstract: Implant strategies using multiple catheter-cooledinterstitial ultrasound applicator were investigatedfor the ability to conform temperature distributionsand thermal coagulation within a targeted tissue volumefor either hyperthermia or high temperature thermaltherapy in the prostate. Multi- element ultrasoundapplicators were fabricated using cylindricalpiezoceramic transducers sectored to 220 degrees toprovide angular directional heating, and innon-directional configurations. The applicators weredesigned to be inserted into standard 13 or 14 gagebrachytherapy catheters integrated with water-cooling.Measurements of acoustic power output, and beam profiledistributions were obtained in degassed water. Thermallesions were formed in fresh in vitro beef muscle, andin vivo pig thigh muscle. Axial and radial temperaturedistributions were monitored using multi-junctionthermocouple probes. Thermal lesions measuring 4 cmdiameter were produced in vitro within 4 minutes ofheating with 5 W applied electrical power delivered to6 applicators with an angular spacing of 60 degrees. Invivo thermal lesions generated in pig thigh muscleusing only 4 directional applicators were confined to atarget volume of 3 cm diameter by 3 cm long.Temperatures measured in the center of the targetvolume reached 85 degrees Celsius during heating, whiletemperatures outside the target volume remained below45 degrees Celsius. Results from these studiesindicated the ability to control thermal coagulationwithin the targeted tissue while protecting surroundingtissue from thermal damage. !13
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