Application of near-infrared time-resolved spectroscopy to rat liver - a preliminary report for surgical application

Abstract

The applicability of near-infrared time-resolved spectroscopy to rat liver surgery was investigated. First, the technical reliability in determining the absorption coefficient (µa) and reduced scattering coefficient (µ´s) of the liver was checked. Next, boundary effects in determining µa and µ´s of the rat liver were examined. Finally, changes in µa and µ´s of rat liver with ischaemia were directly measured by TRS. Our TRS system showed that the µa value held a linear correlation with the ink concentration in a lipid emulsion until µa reached 1.2 cm-1, while the µ´s was fairly independent. The µa values of blood-free rat liver and blood-containing rat liver at 780 nm were observed to be 0.43 cm-1 and 0.67 cm-1 by using the matching method, indicating that TRS is reliable in determining µa and µ´s of the liver. Possible errors in µa and µ´s determination due to the boundary effects of the rat liver were as small as 7%, when the µa value was as high as observed for the liver. The oxygen saturation of haemoglobin (SO2) was changed from 64.9% to 8.0%, and the haemoglobin content (THB) from 189.1 µM to 131.6 µM by ischaemia. µ´s dynamically changed in the range 7.06 cm-1 to 11.36 cm-1. We conclude that time-resolved measurement is applicable in the high-µa region observed in the liver, and can give quantitative estimations of SO2 and THB in the liver.