Acoustic Wave Sparsely-Activated Localization Microscopy (AWSALM): In Vivo Fast Ultrasound Super-Resolution Imaging using Nanodroplets

Current localization-based super-resolution ultrasound imaging requires a low concentration of flowing microbubbles to visualize microvasculature beyond the diffraction limit and acquisition is slow. Nanodroplets offer a promising solution as they can be sparsely activated and deactivated on-demand. In this study, acoustic wave sparsely-activated localization microscopy (AWSALM) using activation and deactivation of nanodroplets, an acoustic counterpart of photo-activated localization microscopy (PALM) which is less dependent on agent concentration and the presence of flow, is demonstrated for super-resolution imaging in deep tissues in vivo. An in vivo super-resolution image of a rabbit kidney is obtained in 1.1 seconds using AWSALM, where micro-vessels with apparent sizes far below the half-wavelength of 220 µm were visualized. This preliminary result demonstrates the feasibility of applying AWSALM for in vivo super-resolution imaging.