Orthogonal polarization spectral imaging

Orthogonal polarization spectral imaging is a method for imaging small blood vessels^[1] 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 imaging the erythrocytes as they are flowing through the small blood vessels. The reflected light orthogonal (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.^[2]

It has been validated, even under low hematocrit circumstances.^[3]

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