Computationally efficient transcranial ultrasonic focusing: taking advantage of the high correlation length of the human skull.

: The phase correction necessary for transcranial ultrasound therapy requires numerical simulation to noninvasively assess the phase shift induced by the skull bone. Ideally the numerical simulations need to be fast enough for clinical implementation in a brain therapy protocol and to provide accurate estimation of the phase shift to optimize the refocusing through the skull. In this paper, we experimentally performed transcranial ultrasound focusing at 900kHz on N=5 human skulls. To reduce the computation time, we propose here to perform the numerical simulation at 450kHz and use the corresponding phase shifts experimentally at 900kHz. We demonstrate that a 450kHz simulation restores 94.2% of the pressure as compared to a simulation performed at 900kHz and 85.0% of the gold standard pressure obtained by an invasive time reversal procedure based on the signal recorded by a hydrophone placed at the target. From a 900kHz simulation to a 450kHz simulation, the grid size is divided by eight and the computation time is divided by ten.