The feasibility of using electrically focused ultrasound arrays to induce deep hyperthermia via body cavities

The results of a simulation study and subsequent experimental verification on the feasibility of using electrically focused arrays for intracavitary ultrasound hyperthermia are presented. The relative acoustic pressure fields from these cylindrical phased arrays were calculated for different dimensions and acoustic parameters to determine relevant design criteria. A thermal model based on the bioheat transfer equation was used to compute the resulting steady-state temperature distributions in tissue for various array configurations. This study has shown that cylindrical arrays of a practical size (75 mm long, 15 mm OD), resonating at 0.5 MHz with individual elements that are 1.5-mm wide, can preferentially heat regions that are between 20 and 50 mm from the surface of the array. In addition, it was shown that the temperature distribution can be further controlled by varying the focal position within the target volume, producing heated regions up to 40 mm wide. If practical constraints (i.e. number of amplifiers available or minimum element size attainable) become a limiting factor, arrays with wider elements would also be functional, but with certain restrictions applied to their flexible heating patterns. Thus, these electrically focused ultrasound arrays appear to offer a significant improvement over the existing intracavitary hyperthermia methods by producing a deeper and more controlled energy deposition.