Focused-ultrasound phased array (transcranial)

The hardware and physics of concentrating ultrasound to a millimetre focus deep in the brain through the intact skull. Hemispheric phased arrays with hundreds to thousands of independently-driven elements electronically steer and focus the beam, and — critically — apply per-element phase corrections (typically derived from a CT scan of the individual skull) to compensate for the aberration, attenuation, and mode conversion the bone introduces.

Clinically, MR-guided focused ultrasound already delivers thermal ablation for essential tremor and Parkinsonian tremor, with real-time MR thermometry closing the loop. The same aberration-corrected steering underlies transcranial low-intensity neuromodulation and microbubble-mediated blood-brain-barrier opening; open challenges include skull heating, standing waves, and reaching superficial or off-axis targets.