Graded-field microscopy with white light.

We present a general imaging technique called graded-field microscopy for obtaining phase-gradient contrast in biological tissue slices. The technique is based on introducing partial beam blocks in the illumination and detection apertures of a standard white-light widefield transillumination microscope. Depending on the relative aperture sizes, one block produces phase-gradient contrast while the other reduces brightfield background, allowing a full operating range between brightfield and darkfield contrast. We demonstrate graded-field imaging of neurons in a rat brain slice.