Ultrasonic waveguide applicator arrays for interstitial heating: a model study

In this paper we describe an ultrasonic waveguide multiapplicator array for interstitial heating. We first discuss the heat generation term common for this type of applicator and show that the radius of the applicator is the limiting factor in the pattern of heat deposition. We carry out finite element analysis simulations of temperature profiles for three- and four-applicator array, and we test the simulations by measurements in a large volume tissue phantom. With the positive result of this test, we use the simulations to evaluate the size of the heated volume for several applicators (three to six) and for various geometries of their positioning. We do the simulations for a range of the effective thermal conductivity and for two applicator diameters. The volume of the medium with temperatures above 42/spl deg/C was in the 25 to 73 cm/sup 5/ range. This volume increased linearly with the diameter of the boundary at the basal temperature. Power required to produce preselected temperature elevation increased monotonically with the effective thermal conductivity. With the 24 mm between the applicators, the array could elevate the temperature to the required value up to the 0.030 W/cm/K effective thermal conductivity.