Quantification of cerebral hemoglobin as a function of oxygenation using near-infrared time-resolved spectroscopy in a piglet model of hypoxia

Near-infrared spectroscopy (NIRS) has been used for mea- surement of cerebral hemoglobin (Hb) concentrations in neonates to study cerebral oxygenation and hemodynamics. We perform mea- surements by portable three-wavelength NIR time-resolved spectros- copy (TRS) in a piglet hypoxia model with various degrees of oxygen- ation to estimate the absorption coefficient (m a) and reduced scattering coefficient (m s) of the head. Measurements of absolute val- ues of m a at three wavelengths enable estimation of Hb concentration and Hb oxygen saturation in the head (SO2). However, there is a problem concerning which background absorption should be used to estimate Hb concentration in the head derived from m a at three wave- lengths because it is different from a simple in vitro model. Therefore, we use two different background absorption values with the assump- tion that background absorption is due only to 85% (by volume) water or that background absorption is equal to absorption of the piglet head with blood exchange transfusion by fluorocarbon (FC), and we compared SO2 measured by TRS with arterial Hb oxygen saturation (SaO2) and sagittal sinus venous Hb oxygen saturation (SvO2) mea- sured by a co-oximeter at several inspired fractional O2(FIO 2 ) concen- trations. We find that SO2 values using the absorption (abs) of the piglet head with blood exchange transfusion (BET) by FC are not sig- nificantly different from SO2 values using the water-only background at FIO2 in the range of 15 to 100%, but that the values using abs of the head with BET by FC are lower than the values using the water-only background at FIO2 in the range of 12 to 4%. The SO2 values calcu- lated from the water-only background are higher than those of SaO2 at FIO2 in the range of 10 to 4%. However, SO2 values using the abs of the head with BET by FC are between those of SaO2 and SvO2 over the whole range of FIO 2 . Therefore, abs of the head with BET by FC is more useful for estimation of the absolute values of oxyHb and deoxyHb of the piglet head. © 2005 Society of Photo-Optical Instrumentation En- gineers. (DOI: 10.1117/1.1899184)