Real-time transcranial phase aberration correction using a ray tracing method

Transcranial focused ultrasound being used for human brain stimulation encounters challenges due to aberration induced by the skull bone. These effects can result in the emergence of multiple focus spots and shifts away from the target location, necessitating the need for compensation. We propose a real-time capable, multi-layer ray tracing approach enabling a clinical single-session procedure without offline planning between therapy sessions. The patient-individual transducer excitation delays are calculated using a ray tracing method considering local speed of sound values and diffraction effects which takes less than one minute on a commercial PC depending on the lateral and axial step size of the searching volume. The transducer is excited with corresponding time-shifted transmit signal patterns. Measurements with transmission through the skull cap and focusing on-axis or with beam steering show defocused acoustic pressure distributions with multiple hot spots at similar peak intensity in the XY plot at focal depth. Applying of the computed delay values leads to a reduction of the additional hot spots and an intensity gain in the focus.