A noninvasive method for focused ultrasound surgery through the human skull

Abstract

A technique for focusing ultrasound through the skull bone is described and verified. The approach is based on a layered wave-vector-frequency domain model, which simulates ultrasound propagation through the skull bone using input from CT scans of the head. The algorithm calculates the driving phase of each element in a transducer array in order to maximize the signal at the intended focus. This approach is tested on ten ex vivo human skulls using a 500-element hemispherical array operated at 0.74 MHz. 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 of the skull. In each trial the phase correction algorithm successfully restored the focus inside the skull in a location within 1 mm from the intended focal point. Focusing at high powers (>800-W electrical input) is demonstrated using a brain phantom placed inside a skull. The results demonstrate the feasibility of using the method for completely noninvasive ultrasound brain surgery and therapy.