Phase gradient microscopy in thick tissue with oblique back-illumination

Phase contrast techniques, such as differential interference contrast (DIC) microscopy, are widely used to provide morphological images of unstained biological samples. The trans-illumination geometry required for these techniques has restricted their application to thin samples. We introduce oblique back-illumination microscopy (OBM), a method of collecting en face phase gradient images of thick scattering samples, enabling near video-rate in vivo phase imaging with a miniaturized probe suitable for endoscopy.