Skull surface detection algorithm to optimize time reversal focusing through a human skull

Ultrasound has two main medical applications: imaging and therapy. Echographic imaging is particularly suited for soft tissues, such as liver, kidney or fetus. Treatment trials mainly concern liver, prostate, and bladder. In order to develop clinical applications dedicated to the human brain, one has to precisely focus ultrasound through the skull. The human skull induces both phase and amplitude aberrations. It has been shown that time reversal coupled with amplitude compensation is an interesting technique to correct those aberrations. We show here numerically that a more precise focusing can be achieved by compensating the amplitude at the exact location of the skull. To implement this in practice, a skull surface detection algorithm is investigated in order to determine the shape of the skull. It is based on the time of flight of pulsed signals emitted and received by each pair of transducers of an echographic array.