Multi-Channel Near Infrared Spectroscopy for Characterisation of Cortical Perfusion

Near-infrared spectroscopy (NIRS) allows the cortical concentrations of oxy- and deoxygenated haemoglobin to be determined in a non-invasive fashion. Therefore modern multi-channel systems provide an alternative to functional magnetic resonance imaging for assessing task-related cortical patterns of activation. Moreover, here too bolus administration of exogenous contrast media facilitates the measurement of perfusion-related parameters. Sampling rates of up to 10 Hz provide a temporal accuracy that is difficult to achieve by the use of tomographic imaging modalities. In the present study time-to-peak (TTP) maps were acquired by multi-channel near-infrared spectroscopy after bolus administration of indocyanine green in 10 healthy controls and 10 patients suffering from unilateral severe stenosis or occlusion of the middle cerebral artery. In 9 of these patients TTP was increased on the affected hemisphere. Mean difference in TTP between affected and unaffected hemisphere was 0.44s (p < 0.05) as compared to a mean lateral difference of 0.12 s found in the controls. A linear correlation of 0.61 between TTP values determined by NIRS and dynamic susceptibility MRI in one patient was found to be statistically significant (p < 0.001). Furthermore, a statistically significant correlation between reciprocal post-stenotic flow velocity, as determined by transcranial duplex sonography, and NIRS-TTP in the core distribution of the middle cerebral artery could be established (r = 0.81, p = 0.042). The results of our study suggest that multi-channel near-infrared spectroscopy is sensitive to changes in cortical perfusion as found, e.g., in stenosis or occlusion of cerebral arteries. This technique might therefore provide clinical benefit in monitoring patients suffering from cerebrovascular disease.