Dynamic time reversal acoustic focusing of ultrasound for biomedical applications

Abstract

Time Reversal Acoustic (TRA) system provides effective focusing in inhomogeneous media that can be used in various biomedical applications including high intensity ultrasound treatment, ultrasound-assisted drug delivery, ultrasonic battery charging of implants, etc. In many cases, the TRA focusing is conducted in tissues with time varied properties and variation in propagating media degrades the TRA focused signal. Dynamic focusing is required to maintain the same acoustic intensity in the focus. We suggest adjustment to the radiated signal in order to maintain the maximal amplitude in the focus using the inverse filtering technique with Tikhonov regularization. The suggested algorithm enables to determine the radiated signal based on the changes in the focused signal received by a beacon. Developed algorithm of TRA refocusing was tested in the experiments with a TRA system with an aluminum reverberator comprising ten piezotransducers with resonance around 1 MHz, DAC control system and a multi-channel binary amplifier. This system was built in Artann Laboratories for investigation of time reversal acoustic focusing for hyperthermia therapy and drug delivery. The dynamic TRA refocusing is shown to be effective even in the case of significant lateral shifts in the media and strong focused signal variation.