Analysis of temperature responses to diffused ultrasound focal fields produced by a sector-vortex phased array.

The sector-vortex applicator, a disc-shaped ultrasound phased array with a geometric focus having multiple sectors and tracks, can directly synthesize, without scanning, diffuse focal patterns useful for hyperthermia. Temperature distribution patterns resulting from these acoustic fields have been simulated by solving a steady-state bioheat equation numerically for a wide range of blood perfusion rates. These results suggest that the sector-vortex array will be particularly suitable for heating non-superficial small tumours. The temperature distribution pattern changes due to variations in blood perfusion are interpreted based on spatial frequency domain Fourier analysis of temperature responses to different power deposition patterns. The system behaves like a low-pass spatial frequency filter.