A non-invasive opticalimaging method involving the quantification of chromophore concentration, whichis resolved from the measurement of changes in near-infrared (NIR) lightattenuation (a chromophore being a chemical group that can absorb light at a specific frequency to give a molecule color to a molecule. Biologicaltissue is relatively transparent to light in the near-infrared part of thespectrum. Therefore several centimeters of tissue can be illuminated, throughthe scalp and skull. As the chromophore hemoglobin has differential absorptionspectra in oxygenated and deoxygenated form, near-infrared absorptionspectroscopy methods can provide maps of regional cortical oxygenation, whichcan be used to assess localised brain activation. In practice, this involves the placement of sources (whichemit near-infrared light) and detectors on the head, the measurement of the changes in the amount of the diffuselight reaching the detector, and therefore the measure of changes in cerebralhemoglobin concentration from the portion of the detected light, which willhave sampled the brain.
See Chromophores, Hemoglobin, Cytochrome c oxidase (CCO), Functional magnetic resonance imaging (fMRI), Optical imaging