<unk> <unk>  is a method for<unk>  small blood vessels in tissue like the nail bed or lip. It uses a light source of linearly polarized light with a wavelength of 550 nanometers, an isosbestic point for hemoglobin, thus<unk>  the erythrocytes as they are flowing through the small blood vessels. The reflected light<unk>  (at a 90° angle) to the emitted light is recorded, thus eliminating direct reflections. The depolarized light forms an image of the microcirculation on a CCD, which can be captured through single frames or on videotape. The image produced is as if the light source is actually placed behind the desired target or transilluminated. It has been validated, even under low hematocrit circumstances.
Orthogonal polarization spectral imaging
Spectral imaging 
Multiple scattering low coherence interferometry
Functional near-infrared spectroscopy
Diffuse optical imaging
Pan–Tompkins algorithm
Sabin–Feldman dye test
Lancaster red-green test