Novel Optical Imaging Methods with Refractive Index Modulating Dyes

Near-infrared (NIR) optical imaging techniques offer a significant advantage due to being non-radiological and offering functional imaging capabilities. However, a key issue remains to be the strong scattering of NIR optical photons in tissue, thus reducing sensitivity and image resolution. recently it was howed that refractive index matching food dyes like Tartrazine can diffuse deep into tissue creating optical transparency. The process involves simply rubbing the dye onto the skin surface. Tartrazine, which is a yellow food dye strongly absorbs around 428nm causing the increase in refractive index of the surrounding water molecules in the adjacent wavelength band 600-900nm range.  This effect can be described by Kramers-Kronig relationship. Thus by matching the water refractive index in 600-900nm range to be closer to that of fats and proteins in the tissue, the dye reduces the overall light scattering which is caused by refractive index variations within the components in the tissue. We will examine the benefits of this refractive index modulation in improvements for NIR refractance imaging. We will also explore the diffusion gradient of these dyes within tissue when applied on skin surface. Physics models, system designs and benefits of refractive index modulation of tissue will be presented.