Functional near-infrared imaging

fNIR stands for functional near-infrared imaging. fNIR is a spectroscopic neuro-imaging method for measuring the level of neuronal activity in the brain. The method is based on neuro-vascular coupling, that is, the relationship between metabolic activity and oxygen level (oxygenated hemoglobin) in feeding blood vessels.

There are three types of fNIR:

• CW – continuous wave – In this method, infrared light shines at the same intensity level during the measurement period. The detected signal is lower intensity static signal (dc valued)

• FD – frequency domain – In this method, input signal is modulated sinusoid at some frequency and detected output signal has changes in amplitude and phase.

• TR – time resolved – In time resolve spectroscopy, a very short pulse is introduced to measured and the pulse length is usually on the order of picoseconds. The detected signal is usually a longer signal and has a decay time.

• fNIR device was first invented by Dr. Britton Chance of the University of Pennsylvania. Current cwFNIR devices have improved with the advent of electronics.[1] At the Optical Brain Imaging Lab of Drexel University, in collaboration with Penn, battery operated, wireless cwfNIR devices have been developed.[2]