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. At the Optical Brain Imaging Lab of Drexel University, in collaboration with Penn, battery operated, wireless cwfNIR devices have been developed.