Functional near-infrared spectroscopy
Functional near-infrared spectroscopy (fNIRS) also known as Optical Topography, is a non-invasive quantitative functional neuroimaging modality. Light in the near-infrared range of the electromagnetic spectrum transmits through the soft tissue and bone of the head and can determine the hemoglobin concentrations within the brain. By evaluating variations in the light intensity diffusely mirrored back to the surface of the head, it is feasible to examine changes in hemoglobin concentrations arising from brain activation.1
It was originally described in 1977 by Jöbsis et al. as a technique where the average hemoglobin-oxyhemoglobin equilibrium could be recorded in a continuous fashion and changes in tissue blood volume were quantified. And these properties enabled its application as a monitoring tool of cerebral and myocardial oxygenation.2
In the central nervous system, neuronal activity increases location-specific brain-tissue oxygen demand, and due to neurovascular coupling, there is a reflexive increase in cerebral blood flow to provide compensation. fNIRS can capture the alterations in oxygenated hemoglobin and deoxygenated hemoglobin as a surrogate measure of changes in brain activity and provide functional information.2
fNIRS has several potential advantages including real-time monitoring, portability, it does not require the patient to remain in a confined monitoring environment, or maintain head fixation, there is a relatively low cost as well as maintaining an excellent safety profile for its non-invasive approach.3
Its limitations include difficulty in assessing deep brain structures, relatively poor spatial resolution, and susceptibility to artefacts.
fNIRS is established as a monitoring tool for stroke recovery, including upper/ lower limb neurological recovery, motor learning, cortical function recovery.3 fNIRS is being investigated for its potential application in the development of brain-computer interfaces (BCI), where brain activity signals are used to electronically control external devices.4
- 1. R.J. Cooper, D.A. Boas, Functional Near-Infrared Spectroscopy, Editor(s): Arthur W. Toga, Brain Mapping, Academic Press, 2015, Pages 143-148, ISBN 9780123973160, https://doi.org/10.1016/B978-0-12-397025-1.00016-6. (http://www.sciencedirect.com/science/article/pii/B9780123970251000166)
- 2. Jöbsis FF. Noninvasive, infrared monitoring of cerebral and myocardial oxygen sufficiency and circulatory parameters. Science. 1977 Dec 23;198(4323):1264-7. doi: 10.1126/science.929199. PMID: 929199.
- 3. Masahito Mihara M.D., Ichiro Miyai M.D., "Review of functional near-infrared spectroscopy in neurorehabilitation," Neurophoton. 3(3) 031414 (12 July 2016) https://doi.org/10.1117/1.NPh.3.3.031414
- 4. Yang Muyue, Yang Zhen, Yuan Tifei, Feng Wuwei, Wang Pu. A Systemic Review of Functional Near-Infrared Spectroscopy for Stroke: Current Application and Future Directions. Frontiers in Neurology. 2019;10:58 https://www.frontiersin.org/article/10.3389/fneur.2019.00058 DOI 10.3389/fneur.2019.00058