Ultrasound Phased Arrays for Hyperthermia: New Techniques Based on the Field Conjugation Method

Phased arrays, which can be focused and steered electronicaliy, offer an attractive alternative to the mechanically scanned focused systems currently in use. This could be attributed to the speed and flexibility o f electronic control systems which, while complex, can be implemented remotely from the a pplicator aperture. However, both electrical and mechanical scanning require a very intense focal spot which could increase the risk of unwanted nonthermal effects, e.g., cavitation. Moreover, hot spots proximal to the tumor might occur because of near-field beam overlapping due to scanning. In this paper, a method is proposed to allow scanning at reduced spatial-peak temporal-peak (SPTP) intensity compared to approaches used in conventional scanning techniques. Moreover, the method permits the direct synthesis of the more diffuse heating patterns useful in hyperthermia without the need for mechanical or electrical scanning.