How does NIRS work ?
NIR spectrum light takes advantage of the optical window in which skin, tissue, and bone are mostly transparent to NIR light in the spectrum of 700-900 nm, while haemoglobin (Hb) and deoxygenated-haemoglobin (deoxy-Hb) are stronger absorbers of light. Differences in the absorption spectra of deoxy-Hb and oxy-Hb allow the measurement of relative changes in haemoglobin concentration through the use of light attenuation at multiple wavelengths. Typically the light emitter and detector are placed ipsilaterally on the subjects skull so recorded measurements are due to back-scattered (reflected) light following elliptical pathways. The fNIRS sensor is attached to the subject’s forehead and data can be recorded as he or she engages in specific task.