Focusing ultrasonic vortices across the human skull by acoustic holograms

Abstract

Acoustic vortices can be applied to trap and guide drug delivery carriers, microbubbles, or small objects. However, when focusing acoustic waves through aberration layers such as the human skull at ultrasonic frequencies results in strong phase aberrations, preventing the generation of sharp acoustic vortices. In this work, we demonstrate that phase-conjugated acoustic holograms can encode time-reversed fields simultaneously allowing the compensation of the aberrations of the skull and the generation of a focused vortex inside an ex-vivo human skull. An acoustic hologram is designed by time-reversal methods using CT images of an ex-vivo human skull. The lens is 3D printed using stereolithographic techniques, coupled to a 100-mm aperture, 140-mm focal and 500-kHz focused ultrasound transducer. The field is measured with and without the skull bone in a water tank. Measurements agree with simulations in both, water and including the skull bones. The acoustic hologram generates a focused vortex at an arbitrary focal position inside the skull by encode time-reversed fields containing phase dislocations with great accuracy using very simple and compact ultrasonic systems. On the one hand, acoustic holograms allow one to compensate the aberrations of the skull, and, on the other hand, they simultaneously tune the phase of the wavefront to generate a focused vortex by introducing a rotational phase profile. This results in a personalized single-element system that can focus a vortex inside the human skull. This work paves the way to designing low-cost particle-trapping systems, clot manipulation, torque exertion in the brain, and acoustic-radiation-force-based biomedical applications, opening a path to exploring the biological response of tissues to therapeutic ultrasonic vortex beams.

@inproceedings{Jimenez2021ISTUvortex,
 author = {Noé Jiménez and Sergio Jiménez-Gambín and José María Benlloch and Francisco Camarena},
 booktitle = {ISTU 2021: 20th International Symposium for Therapeutic Ultrasound. Gyeongju, Korea. 6 - 9 June},
 editor = {Conference proceedings},
 isbn = {ISBN: 978-84-87985-30-4},
 month = {6},
 organization = {International Society for Therapeutic Ultrasound},
 publisher = {European Focused Ultrasound Charitable Society},
 series = {Poster},
 title = {Focusing ultrasonic vortices across the human skull by acoustic holograms},
 year = {2021}
}