Deep laser microscopy using optical clearing by ultrasound-induced gas bubbles

Although laser scanning microscopy is a pivotal imaging tool in biomedical research, optical scattering from tissue limits the depth of the imaging. To overcome this limitation, we propose a scheme called ultrasound-induced optical clearing microscopy, which makes use of temporary, localized optical clearing based on ultrasound-induced gas bubbles. In this method, bubbles are generated by high-intensity pulsed ultrasound at a desired depth and subsequently maintained by low-intensity continuous ultrasound during imaging. As a result, optical scattering and unwanted changes in the propagation direction of the incident photons are minimized in the bubble cloud, and thus the laser can be tightly focused at a deeper imaging plane. Through phantom and ex vivo experiments, we demonstrate that ultrasound-induced optical clearing microscopy is capable of increasing the imaging depth by a factor of six or more, while the resolution is similar to that of conventional laser scanning microscopy.