Experimental validation of 3D finite differences simulations of ultrasonic wave propagation through the skull

Abstract

High Intensity Focused Ultrasound could provide a non invasive way
for burning tumor located deep inside the brain. However, the skull
induces strong aberrations both in phase and amplitude resulting in a
spreading of the focus. Thus a efficient noninvasive therapy would
require an adaptive focusing taking into account the acoustical
properties of the skull. 3-D simulations based on high-resolution CT
images of a human skull have been successfully performed with a 3D
finite differences code, developed in our laboratory. From the skull
porosity, directly extracted from the CT images, we reconstructed
acoustic speed, density and absorption maps and performed the
computation. Computed wavefronts are in good agreement with experimental
wavefronts acquired through the same part of the skull. It shows that it
is possible to model the acoustical properties of a human skull from CT
images. Moreover, experimental focusing can be achieved by applying time
reversal combined with amplitude compensation. Again the measured
focusing pattern obtained from either experimental or computed wavefront
are very close. It demonstrates the feasibility of non invasive focusing
through the skull by simply using CT images