Optical imaging is the gold standard of non-invasive biological imaging. Moreover, optical stimulation techniques are rapidly expanding. For example, optogenetics has proven to be a powerful method for neural stimulation.
However, two serious challenges need to be addressed for optical interrogation to be effective for deep-tissue imaging and stimulation. First is targeted delivery of light deep into the brain tissue (at least a few millimeters) and second is non-invasive beam steering in the tissue.
Current methods of light delivery and beam steering require inserting optical fibers, waveguides, or active light sources, which would cause a significant tissue displacement and damage to the vasculature. In this project, we take a radical approach to use ultrasonic waves to define and steer the trajectory of light in the brain for non-invasive targeted optogenetic stimulation and imaging of local neuron clusters.
We are applying this technique to selectively stimulate different basal ganglia nuclei to come up with new therapeutics for Parkinson's disease.
In addition to optical stimulation brain, we are applying this novel acousto-optic technique for imaging through turbid media.
(a) A local refractive index contrast is generated in the tissue by US pressure waves; (b) a collimated beam of light is expanded as a result of scattering in the tissue; (c) light is guided in the high refractive index region, contrasting the effect of the scattering. Pictures from experiments showing: (d) laser beam focused by ultrasound in a minimally scattering media; (e) intensity attenuation of laser beam passing through a scattering sample; (f) laser beam focused by ultrasound in a scattering tissue, competing with the diffusive effect of scattering. (g) Microscope is immersed in scattering medium to demonstrate the relaying effect of acousto-optic relay lens; (h) when the transducer is OFF, the image is out of focus and the background illumination caused by scattering is evident; (i) when the transducer is driven at 50V, the target object is clearly resolved.