Observation of Guided Acoustic Waves in a Human Skull.

Human skull poses a significant barrier for the propagation of ultrasound waves. Development of methods enabling more efficient ultrasound transmission into and from the brain is therefore critical for the advancement of ultrasound-mediated transcranial imaging or actuation techniques. We report on the first observation of guided acoustic waves in the near field of an ex vivo human skull specimen in the frequency range between 0.2 and 1.5MHz. In contrast to what was previously observed for guided wave propagation in thin rodent skulls, the guided wave observed in a higher-frequency regime corresponds to a quasi-Rayleigh wave, confined mostly to the cortical bone layer. The newly discovered near-field properties of the human skull are expected to facilitate the development of more efficient diagnostic and therapeutic techniques based on transcranial ultrasound.