Ultrasonic stars for time-reversal focusing using induced cavitation bubbles

Ultrasound waves can be focused by multichannel arrays through heterogeneous media using a time-reversal focusing method. In this method, it is required that a reference signal be either sent by a small active source embedded in the medium or backscattered by a strong scatterer acting as a passive source. The potential of this method in ultrasonic medical imaging has been already envisioned for aberration corrections. However, in many practical situations it is not possible to insert an active source in the medium or to rely on the presence of a unique strong scatterer in order to generate the reference signal. Analogous to the field of adaptive optics in astronomy, we propose here to create artificial ultrasonic stars in the body. The trick consists of first creating a bubble inside the medium using a section of the ultrasonic array. Due to cavitation, the bubble generates a spherical wave that propagates through a heterogeneous medium to the ultrasound array. The time-reversal method is then applied to the ultrasonic wave received by the array. This technique is experimentally validated for aberrations corrections in tissue mimicking phantoms.