Refractive index of adipose tissue and lipid droplet measured in wide spectral and temperature ranges

This study presents refractive index measurements of human and porcine adipose tissues and lipid droplet content in the visible and near-infrared. The coefficients of the Sellmeier formula were calculated for approximation of tissue dispersion. For the first time, to the best of our knowledge, the phase transition temperatures and temperature increments dn/dT of adipose tissue were quantified for a wide wavelength range from 480 to 1550 nm and from room temperature up to 50°C. For human abdominal adipose tissue, the refractive index increment averaged across all wavelengths is dn/dT=−(3.54±0.15)×10−4°C−1, for porcine tissue dn/dT=−7.92(0.74)×10−4°C−1, and for porcine lipid droplet dn/dT=−6.01(0.29)×10−4°C−1. Data available in literature for refractive indices of adipose tissues measured by different techniques are summarized and compared with the received data.