Super-resolution cellular ultrasound imaging via localization of nanodroplets

Abstract

Ultrasound localization microscopy (ULM) had made it possible to differentiate microbubble contrast agents that are separated only by a few micrometers and, thus, opening the path for super-resolution imaging. However, due to the innate limits of acoustic waves and microbubble imaging, similar levels of resolution to optical imaging (i.e., submicron resolution) are still very challenging. In this paper, we utilize ULM to achieve cellular imaging by using phase-change perfluorocarbon nanodroplets (PFCnDs) as a contrast agent that were fabricated with spontaneous nucleation method. To identify the point spread function (PSF) of a single nanodroplet, gaussian fit function was applied for reconstruction. Nanodroplets were injected into cells through patch clamping and later captured with two transducers: a single element transducer for focused ultrasound and linear array transducer for imaging. Nonlinear imaging (NLO) was used to maximize the sound to noise ratio (SNR), which enables optimal amplitude. With the PSF of a phase-transitioned nanodroplet known, stochastic activation of multiple nanodroplets within a cell was accumulated to image a full cell morphology. These findings can lead researchers to develop effective ultrasound imaging paradigms that can visualize intracellular level of organs in deep tissue invivo.