Miniaturized Fluorescence Microscopes

The observations of neural circuitry in freely moving animals like mice or rats require a wearable fluorescence microscope attached to imaging cannulas chronically implanted in the animal’s brain. In the middle of the visible spectrum, the scattering  and absorption through the brain tissue limits imaging to about 150 µm. The imaging limited to those depths from the brain surface can be performed without insertion of all-glass relay lenses. At larger brain depths, it is absolutely necessary to use relay lens systems that may consist of homogeneous or gradient-index lenses that bring the image into focus of the microscope objective and effectively reduce the optical path through the brain tissue.