fNIRS Explorer

Functional Near-Infrared Spectroscopy Mechanism & Physics Simulator

Anatomical Model

NIRS Emitter (690nm + 830nm)
NIRS Detector
Blood Vessel Flow (O₂Hb & HHb)
Scalp
Skull
CSF
Brain Tissue
Optode System Wavelengths
690 nm (HHb Target) + 830 nm (O₂Hb Target)
Simultaneous emission allows multi-hemoglobin state sorting.
Laser Optic Core
Continuous Pulsed Acquisition
Acquiring

Oxyhemoglobin (O₂Hb)

Highly oxygenated blood entering the tissue. In near-infrared spectroscopy, 830 nm light is primarily absorbed by O₂Hb because of its specific chemical properties and oxygenated state.

Oxygen
Level
Active State
Rises rapidly during activation

Deoxyhemoglobin (HHb)

Deoxygenated blood returning through capillary networks. 690 nm light exhibits higher optical absorption for HHb, making it the primary target wavelength for detecting oxygen depletion.

Oxygen
Level
Active State
Drops slightly as oxygen flushes in

fNIRS Signal Display

Concentration Changes (ΔO₂Hb, ΔHHb, Δ[HbT]) over time

Resting
ΔO₂Hb
0.0
μM * mm
ΔHHb
0.0
μM * mm
Δ[HbT]
0.0
Total Blood Vol

Optical Absorption Spectrum

Extinction coefficient of O₂Hb and HHb across NIR window

Note the crossover point (isosbestic point) at approximately 800 nm, where extinction coefficients for both oxygenation states are equal.

Interactive Science Guide

Step 1

Neurovascular Coupling

Clicking "Trigger Neural Activation" stimulates neurons. This triggers localized oxygen consumption and triggers a rapid increase of regional cerebral blood flow.

Step 2

The Near-Infrared Window

Living tissues are transparent to NIR light (650-900nm), allowing photons to penetrate scalp, skull, and CSF, reaching up to 1-2cm into cerebral cortex.

Step 3

Modified Beer-Lambert Law

Because light scatters in a banana-shaped path, the modified Beer-Lambert Law calculates relative concentration changes of O₂Hb and HHb based on optical density changes.