Use of a Hybrid Optical Spectrometer for the Measurement of Changes in Oxidized Cytochrome c Oxidase Concentration and Tissue Scattering During Functional Activation

We report the use of a novel dual-channel hybrid near infrared optical spectrometer for the measurement of changes in oxidized cytochrome c oxidase (oxCCO) concentration and optical scattering in 11 healthy volunteers during functional activation induced by an anagram-solving task. A haemodynamic response consistent with functional activation was seen in 9 out of 11 subjects and in 13 of the total 22 channels measured; only these channels were retained for further analysis. In each of these 13 channels the haemodynamic response was accompanied by a statistically significant change in [oxCCO], although the direction of this change was heterogenous with a significant increase seen in eight channels and a significant decrease seen in five channels. There was no significant change in the optical scattering coefficent measured at four wavelengths, and the use of differential pathlength factor (DPF) calculated in real time using measured absorption and scattering showed a high level of agreement with a conventional algorithm. The possible reasons for the heterogeneity of the [oxCCO] response are discussed.