Optical determination of fatty change of the graft liver with near-infrared time-resolved spectroscopy.

A novel method for quantifying the fatty change of the graft liver by characterizing the optical property of the tissue was introduced. A wide range of lipid content in the rat liver was obtained by using different feeding regimens, with lipotropic chow (choline/methionine deficient or low chow). The liver was removed and flushed with Krebs-Ringer buffer solution with 3% albumin, and the optical properties of the liver, i.e., absorption and reduced scattering coefficients (mu(a) and mu(s)'), were measured by time-resolved spectroscopy. The fatty liver showed lower mu(a) and higher mu(s)' than the normal liver. Lower mu(a) and lower succinate dehydrogenase activity of the fatty liver suggested that the decrease in mu(a) might indicate a decrease in the mitochondrial content. The value of mu(s)' was positively correlated with the lipid content of the liver, which indicates that fat droplets inside the hepatocyte act as dominant scatterers. To subtract the contribution of the mitochondrial compartment to mu(s)', the ratio of mu(s)' to mu(a) (mu(s)':mu(a)) was useful for the assessment of the lipid content of the liver. These findings were also relevant with prediction of light scattering by the Mie theory. It was concluded that mu(a) and mu(s)' of the graft liver, measured by time-resolved spectroscopy, can be useful parameters for quantifying the fatty change of the graft liver.