Time-reversal focusing through the skull : application to High Intensity Focused Ultrasound brain therapy.

Abstract

Bursts of focused ultrasound energy a billion times more intense than diagnostic ultrasound have become available commercially recently for clinical ablation of various biological soft tissues from prostate cancer to uterine fibroids. However, although that the use of High Intensity Focused Ultrasound (HIFU) for brain therapeutic applications was already envisioned in the early 5O’s, the targeting of brain with High Intensity Focused Ultrasound (HIFU) remains today a technological challenge. Due to the large discrepancy between the speed of sound in the bone and in the soft tissues associated with a high absorption of the bone. the ultrasonic wavefront is strongly distorted by the skull bone. resulting in a destruction of the focus. During the last decade, novel adaptive focusing techniques have been developed in order to correct the skull aberrations. The potential of time reversal focusing associated with the development of high power multi-element therapeutic transducers allow now the accurate focusing of high power ultrasound in the brain. Minimally invasive clinical tests on sheep will be presented as well as fully non-invasive tests on monkeys.