Near Infrared Spectroscopy for Functional Assessment and Rehabilitation Engineering in Muscle and Brain

Near infrared spectroscopy (NIRS) is a novel technique that employs diffuse light to non-invasively monitor tissue haemodynamics and oxidative metabolism. NIRS employs optical radiation in the range 600-1000 nm where light attenuation by tissue constituents (water, lipid, oxyhaemoglobin and deoxy-haemoglobin) is relatively low and accounts for penetration through several centimetres of tissue. The difference in the absorption spectra of oxyand deoxyhaemoglobin (O2Hb, HHb) allows the separate measurements of the concentration of these two species, and the derivation of physiologically relevant parameters like blood oxygen saturation, SO2 = O2Hb/(HHb+O2Hb). NIRS provides high temporal resolution and relatively low spatial resolution without having the high costs and poor mobility of fMRI and of PET. In the muscle NIRS can help in studying mechanisms related to normal physiology under exercise, but also to pathology caused by myopathies and/or peripheral circulation diseases. In the brain NIRS systems have been developed and tested to provide spatial maps of hemodynamic changes of frontal, temporal, parietal, and visual cortical areas upon different stimuli both in normal and pathologic subjects (e.g. stroke, epilepsy, traumatic brain injury, brain haemorrhage). Thanks to the non-invasiveness of optical radiation, NIRS is most suited for long term monitoring and repetitive measurements.