Broadly speaking, a technique for studying brain activity that involves measuring tiny changes in the scattering or bending and absorption of infrared light. The simplest and most widely used type of optical imaging is endoscopy. As for brain imaging, diffuse optical imaging (DOI) is the most widely used of its type, and is also referred to as near-red optical spectroscopy (NIRS). A laser using near-infrared light, it measures a hemodynamic response associated with neural activity in the brain. Put another way, via optical fiber bundles, it detects changes in blood flow by measuring the light absorption of oxygenated and deoxygenated blood in a a specific part of the brain, while the scattering of light reflects physiological processes such as the swelling of a neuron that occurs when it generates a signal. Optical imaging is a ‘close technical cousin’ of functional magnetic imaging (fMRI). In contrast to optical imaging, fMRI detects blood flow changes through measuring the magnetic signal from deoxygenated blood. Compared to fMRI, DOI has a better temporal, but a poorer spatial, resolution (spatial resolution also being a limitation with EEG even more so than with optical imaging). Optical imaging, however offers a number of advantages over other brain-imaging techniques. To begin with, it is not subject to movement artefacts, a bonus when studying the brain activity of infants and young children. Next, optical imaging uses non-ionizing radiation, which greatly reduces radiation effects in repeated recordings. Furthermore, it can be combined with a range of other imaging techniques. Finally, DOI is relatively cheap, portable and unaffected by electrical interference. For studying brain and other organ morphology, tetrahertz time-domain imaging holds great promise as it can detect information unavailable to other optical imaging techniques.
See Brain (neuro-) imaging, Deoxyhemoglobin (dHB), Electroencephalogram (EEG, Functional magnetic resonance imaging (fMRI), Functional near-red spectroscopy (NIRS), Hemoglobin, Optical tomography, Optical topography, Oxyhemoglobin