3D shear wave generation in soft tissues using the time reversal kaleidoscopes

The time reversal kaleidoscope provides elegant possibilities for both temporal and spatial concentration of acoustic energy in a wide frequency band. Using such ultrasound focused beams, it is possible to generate mechanical sources radiating low frequency shear waves inside tissues. Shear waves are of great interest to investigate tissue viscoelastic properties. In most techniques relying on this concept, generation and imaging of shear waves are realized with a single ultrasonic probe, limiting the capabilities concerning the generation of the shear source. Here we propose a system able to generate and image shear waves in a full 3D volume with any kind of polarization. The focused beam is generated by the time reversal kaleidoscope. By combining the concepts of time reversal mirrors and chaotic reverberating cavities, the time reversal kaleidoscope is able to focus ultrasound beams in a large 3D volume with only some tens of transducers and presents equivalent performances than conventional 2D matrices made of thousands of transducers. The kaleidoscope is triggered by an ultrafast imaging system able to image the resulting shear waves. In vitro results in tissue mimicking phantoms are presented. Chaotic cavities of different geometries are tested and compared. [Work supported in part by NIH grant.]