Aberration correction in transcranial ultrasonic imaging using CT data and simulation-based focusing algorithms

International audienceThe complex structure of the skull bone, reflected in particular by spatial variations in thickness and density, leads to a heterogeneity of its acoustic properties. This results in a strong attenuation as well as specific phase shifts of the ultrasonic wave during its crossing, leading to a defocusing of the beam. The improvement of the quality of brain ultrasonography requires knowledge of these acoustic heterogeneities to shape the ultrasonic wavefront during the focusing and imaging processes. CT scan realized on a phantom of a human skull associated to a fusion tool available on an ultrafast ultrasound device (Aixplorer, Supersonic Imagine, France) allows the positioning of the phased array in real-time in the CT volume. Then, for a fixed position of the probe, the real geometry of the skull region insonified by the array can be used as input data of the simulation based imaging algorithms. In particular, the Plane Wave Imaging (PWI) and Total Focusing Method (TFM) algorithms exploit a direct model of beam propagation through 3-D complex surfaces in order to simulate and correct the aberrations due to the skull crossing. We illustrate the potential of this technique on several examples of brain echography