Functional near-infrared spectroscopy (fNIRS) is
a non-invasive continuous brain imaging tool
utilizing a light emitting source and a light receiver
to measure oxyhemoglobin (HbO2) and
deoxyhemoglobin (HbR) concentration changes.
fNIRS signals have been used as indicators of
cerebral hemodynamics and functional connectivity.
Neuronal activity is known to be associated with
changes in the local cerebral blood flow and
local cerebral blood volume in the arteries.
Additionally, concurrent variations in venous
HbO2 and HbR concentrations occur.
These changes are referred to
as cerebral hemodynamics.
The light absorption by water and lipids in the brain
channel at wavelengths of 600–900 nm is negligible.
In contrast, HbO2 and HbR are the two substances
that absorb most of the light at these wavelengths.
Thus, fNIRS employs at least two wavelengths of
600–900 nm, which experience
very low levels of absorption in tissues,
allowing deeper penetration into brain tissue.
The performance improvement is attributable
to joint optimization of system-level architecture,
circuits, and signaling schemes for the implementation.
Such as, high-SNR fNIRS system
with high signal-to-noise ratio (SNR) receivers,
a modulation scheme,
and a multi-input-multi-output- (MIMO-)
based data extraction algorithm.
The multi-channel receivers are implemented
in a single IC to decrease system size for portability.
INTEGRATED CIRCUITS (IC)
IC contains high-SNR receivers and
power & pattern controllable transmitters
SMALL OPTICAL ELEMENTS
Eliminate optical fibers for portability.
The shape of emitting light
from LASER is more collimated than LED.
The spectral density of LASER is more accurate
MULTI-INPUT MULTI-OUTPUT (MIMO)
By using modulation scheme,
NIRSIT can monitor multi-channel of brain information in continuously.
DIFFUSE OPTICAL TOMOGRAPHY (DOT)
DOT estimates spatial distribution of absorption
characteristics of brain in 3D structure
with fine spatial resolution.