Effects of cryogenic grinding on soft-tissue optical properties.

Optical properties obtained from spectrophotometer measurements of reflectance and transmittance were determined for both frozen-ground and intact soft tissues. The tissues used in these experiments were calf aorta, rat jejunum, and rabbit sciatic nerve. Tissue specimens from each tissue type were frozen in liquid nitrogen and then ground with a pestle and mortar into a fine powder. A tissue paste formed once the powder returned to room temperature. The tissue paste was then sandwiched between glass slides for spectrophotometer measurements. For comparison, the optical properties of the intact specimens were also measured. Total transmission and diffuse reflection were obtained on a Varian Cary 5E spectrophotometer (400-850 nm). Absorption and reduced scattering coefficients of the tissues were determined with the Inverse Adding Doubling method. Our results suggested that within the 400-nm to 850-nm spectrum, optical properties of the ground tissue approximated intact tissue within limits of experimental error.