500‐element ultrasound phased array system for noninvasive focal surgery of the brain: A preliminary rabbit study with ex vivo human skulls

TLDR

The study aimed to test a prototype MRI‑compatible focused ultrasound phased array for trans‑skull brain tissue ablation. The prototype hemispherical 500‑element array (700–800 kHz) sonicated rabbit thigh muscle and brain with an ex vivo human skull between array and tissue, while temperature rise was monitored by MRI thermometry and lesions were confirmed by T2/T1‑weighted imaging and histology; the device was later re‑oriented for clinical use and validated in phantom experiments. Sharp temperature rises up to 55 °C and focal lesions were produced in both thigh muscle and brain, with lesion size increasing with peak temperature, demonstrating that ultrasound‑induced lesions can be created in vivo through a human skull under MRI guidance with this large‑scale phased array.

Abstract

The aim of this study was to test a prototype MRI-compatible focused ultrasound phased array system for trans-skull brain tissue ablation. Rabbit thigh muscle and brain were sonicated with a prototype, hemispherical 500-element ultrasound phased array operating at frequencies of 700-800 kHz. An ex vivo human skull sample was placed between the array and the animal tissue. The temperature elevation during 20-30-sec sonications was monitored using MRI thermometry. The induced focal lesions were observed in T2 and contrast-enhanced T1-weighted fast spin echo images. Whole brain histology evaluation was performed after the sonications. The results showed that sharp temperature elevations can be produced both in the thigh muscle and in the brain. High-power sonications (600-1080 W) produced peak temperatures up to 55 degrees C and focal lesions that were consistent with thermal tissue damage. The lesion size was found to increase with increasing peak temperature. The device was then modified to operate in the orientation that will be used in the clinic and successfully tested in phantom experiments. As a conclusion, this study demonstrates that it is possible to create ultrasound-induced lesions in vivo through a human skull under MRI guidance with this large-scale phased array.