Subwavelength far - field ultrasound drug - delivery

The theoretical diffraction-limit of resolution for ultrasound imaging has recently been bypassed in-vitro and in-vivo. However, in the context of ultrasound therapy, the precision of therapeutic beams remains bound to the half-wavelength limit. By combining acoustic vaporization of composite droplets and rapid ultrasound monitoring, we demonstrate that ultrasound drug-delivery can be restricted to a subwavelength zone. Moreover, two release zones closer than wavelength/4 can be distinguished both optically and through ultrafast ultrasound localization microscopy. This proof-of-concept let us envision the possibility to treat specific tissue more precisely without compromising on the penetration depth of the ultrasound wave.