Multiple sources array controls shear-wave field in soft tissue using time reversal

In most elastography experiments, shear waves are generated using a single source on the surface with a shaker, or in the bulk with radiation pressure of ultrasound. However, emitting controlled shear waves from multiple sources is a good way to improve the signal to-noise-ratio for shear-wave elastography. The experiments are conducted using six shakers with independent driving electronics in gelatin-graphite to mimic the tissue. Based on time reversal, our approach shows the feasibility of controlling shear-wave field in space with multiple focal spots at chosen locations, and in time with a chosen delay between each focusing. Improved by 10 dB compared to the use of a single source, the signal-to-noise ratio demonstrates that time-reversal as an adaptive filter is a good method to deliver maximum energy vibrations toward deep regions. Furthermore, this adaptive approach allows controlled vibrations to be delivered through bone conduction: a shear-wave focal spot is experimentally observed in a soft brain tissue-mimicking phantom using the multiple sources array applied to a skull model.