128 Element ultrasound array for transcranial imaging

The medical potential of transcranial ultrasound has been severely limited by strong attenuation and scattering by the skull, which has prevented its use through most regions of the bone. We have been investigating methods to image through these areas by applying various encoding approaches at reduced frequency, thus reducing both absorption and scattering while also permitting the propagation of both lateral and shear modes. Based on a simulation study, a 0.75 MHz center frequency was determined to be sufficiently low for transcranial propagation, while still preserving medically-relevant resolution. A 128 element, PZT 1-3 composite configuration was optimized for bandwidth and steering range at a 10 cm focal distance. Preliminary test results of the completed array are presented here. Array performance is assessed using a standardized calibration phantom. B-Mode and C-mode transcranial images are also acquired in polyvinyl alcohol (PVA) brain phantoms after propagation through preserved ex vivo human calvaria. For comparison, identical images are acquired without the calvaria. Overall, the ability to reconstruct features through the skull has been established, and critical information has been obtained for constructing a second-generation array planned for human subject testing.