Measurement of the refractive index of the gray matter of the cow's brain at wavelengths of 480-1550 nm when exposed to different temperatures.

Abstract

The knowledge of the optical properties of biological tissues in a wide spectral range is highly important for the development of noninvasive diagnostic or treatment procedures. The dispersion coefficient is one of those properties, from which various information about tissue components can be retrieved. This study is focused on the measurements of the refractive index of ex vivo cow brain gray matter samples in the visible/near-infrared (NIR) spectral range at room temperature for characteristic laser wavelengths: 480, 486, 546, 589, 644, 656, 680, 800, 930, 1100, 1300, and 1550 nm. Measurements were performed using the multiwavelength Abbe refractometer. Cow brain gray matter samples of 0.5 mm thick obtained from ex vivo cow brain were investigated. The specific increment of the refractive index depending on the temperature of the samples and the Sellmeier coefficients was calculated. The experimental results allowed us to calculate the cow brain gray matter dispersion with the Cauchy, Conrady, and Cornu equations. It was observed that all those equations provided good data fitting in the spectral range of the measurements, but differences were observed outside these limits. We validated the proposed method using distilled water and the cow brain gray matter ex vivo, and the experimental results were consistent with the reference data.