High-resolution ultrasonic brain imaging: Noninvasive adaptive focusing based on twin arrays

Abstract

Ultrasonic imaging systems assume a constant acoustic velocity in human tissues in the beamforming process. However, in the case of brain imaging, strong skull aberrations induce a displacement of the focal stain, a spreading in the main lobe, and an increase in the sidelobes level. This limits considerably ultrasonic brain imaging applications. It has been shown that a very accurate focusing could be achieved through a human skull by using an inverse filter technique. This method, based on a set of acoustic sensors located inside the brain, demonstrated invasively that it was possible to achieve high-resolution brain imaging. A noninvasive ultrasonic method is presented. It is based on two arrays located on each side of the head. Each array focuses on the other one to deduce the aberrations induced by the skull bone. Once the effect of the skull bone in front of each array is extracted, the wavefronts are corrected and emitted. This noninvasive technique restores the position of the focal stain and lowers the secondary lobe level up to 15 dB compared to a cylindrical focusing.