Depolarization signatures of multiply scattered light (Conference Presentation)

Reconstruction of an OCT tomogram assumes that the signal originates from singly backscattered light. Light that has been multiply scattered only reduces image contrast and resolution. It has been demonstrated that multiple scattering impacts the OCT signal, especially in case of relatively large spherical particles with a size exceeding the wavelength used for OCT. Here, we investigate the association of multiple scattering with depolarization, as measured with polarization sensitive OCT, to verify if it can explain the depolarization previously observed in lipid-rich atherosclerotic plaques imaged with intravascular polarimetry. Atheromatous plaques consist primarily of macrophage cells that have ingested substantial amounts of lipids, stored as intracellular lipid droplets that increase in size as the plaque progresses. Excessive concentration of cholesterol leads to the nucleation of small cholesterol crystals. The strong birefringence and random orientation of these crystalline particles may contribute to the observed depolarization. However, detection of light multiply scattered by spherical particles may better explain the observed strong depolarization. Using the extended Huygens Fresnel principle we estimate the ratio between the contribution of singly and multiply scattered light to the OCT signal of aqueous microsphere suspensions, and compare it to the experimentally observed depolarization signal. Understanding the mechanism of depolarization seen in liquid-rich plaques may offer insight into the size and concentration of the lipid particles, which would be diagnostically relevant.