Excitation and acquisition of cranial guided waves using a concave array transducer

Ultrasonic therapeutic transducers that consist of large numbers of unfocused, low power elements have begun to replace single high power elements. This allows the operator to use phased array techniques to change the focal position in the tissue during therapy. In transcranial therapy, this phased array configuration is essential to reduce local heating at the highly attenuating bone. Recently, Dual Mode Ultrasound Arrays (DMUAs) have been developed which leverage existing elements for imaging during therapy. DMUAs have the benefit of both the therapeutic and imaging systems being co-registered. Unfortunately, the highly reflective nature of bone means that DMUAs have not been applied to skull imaging. However the recent near-field observation of lamb waves in cranial bone opens the possibility for DMUAs to be applied to a guided wave scan of the skull. This would allow co-registration of the bone’s ultrasonic properties with the therapeutic axis. In this work, a beamforming scheme for the excitation of guided waves in cranial bone using a transcranial transducer is described and demonstrated. These guided waves are then observed in the far field and are shown to change velocity with skull thickness.