Near Infrared Spectroscopy (NIRS)

Near Infrared spectroscopy imaging

Near Infrared spectroscopy (NIRS) is a non-invasive modality for imaging brain function. The technique goes by several other related names such as Near infrared imaging (NIRI), Diffuse optical imaging (DOI) and Optical Topography(OT). NIRS works by exploiting the ability of NIR light to penetrate biological tissues and still be detectable upon remission. Based on this, light is shone onto the scalp by high peak laser diodes tunnelled to the head via fibre optic cables. Within the tissues, photons are scattered, and may take lengthy and irregular paths. The means that highly sensitive light detectors are required to monitor the attenuation in light levels. Ultimately assuming a constant scattering of photons across the cortical surface, the loss of light levels between emitters and detectors are a proportion of the amount of light absorption within the tissue. The primary light absorbers (chromophores) in biological tissue are oxygenated haemoglobin (HbO2) and deoxygenated haemoglobin (HHb). Multichannel NIRS devices like the one illustrated (ETG-4000, Hitachi Medical Corporation, Japan) are capable of monitoring the changes in cortical haemodynamics at several cortical locations simultaneously. The amount of brain activation is inferred from the patterns of haemodynamic change, given that neuronal discharge is tightly coupled to cerebral blood flow.

For further information, please contact Dan Leff at d.leff@imperial.ac.uk