Numerical simulation of transcranial ultrasound imaging using a two-dimensional phased array

Trans-skull ultrasound imaging of brain structures is a challenging problem because of strong attenuation of the skull and reflections from its boundaries. In addition, because the speed of sound in skull is much higher than in soft tissues, nonuniform thickness and heterogeneous bone structures cause strong refraction and aberration effects. In this work, transcranial ultrasound imaging of a 3D volume was simulated numerically. A linear wave equation in an inhomogeneous medium was modeled using the k-space method. A phased array comprising 10000 identically shaped square elements distributed over 70 x 70 mm2 area was used to generate a quasi-plane 2-cycle pulsed wave at 1 MHz. A spherical 3-mm diameter scatterer was placed 30 mm behind a cranial bone phantom with mass density 1900 kg/m3, sound speed 2500 m/s, and an irregular thickness varying from 5 to 8 mm. First, two reflections from the face and back sides of the phantom were used to determine its thickness. Then, a delay and sum algorithm was applied to the received echo signals to compensate for aberrations. It was shown that the scatterer was only visible when aberration compensation was applied. [Work supported by RSF-14-15-00665.]