A non-invasive method for focusing ultrasound through the human skull

TLDR

The study describes and verifies a technique for focusing ultrasound through the human skull. The method uses a layered wavevector‑frequency domain model that propagates ultrasound from a hemisphere‑shaped transducer through the skull, with CT‑derived inputs, and computes element driving phases to maximize focus, validated on ten ex vivo human skulls using a 0.74 MHz, 320‑element array and hydrophone measurements. The phase‑correction algorithm restored focus within 1 mm of the target in all trials, demonstrating the feasibility of non‑invasive ultrasound brain surgery and therapy.

Abstract

A technique for focusing ultrasound through the human skull is described and verified. The approach is based on a layered wavevector-frequency domain model, which propagates ultrasound from a hemisphere-shaped transducer through the skull using input from CT scans of the head. The algorithm calculates the driving phase of each transducer element in order to maximize the signal at the intended focus. This approach is tested on ten ex vivo human skulls using a 0.74 MHz, 320-element array. A stereotaxic reference frame is affixed to the skulls in order to provide accurate registration between the CT images and the transducer. The focal quality is assessed with a hydrophone placed inside the skull. In each trial the phase correction algorithm successfully restored the focus inside the skull at a location within 1 mm from the intended focal point. The results demonstrate the feasibility of using the method for completely non-invasive ultrasound brain surgery and therapy.