NIR light absorption differs between oxygenated and de-oxygenated haemoglobin

Evidence

Near infra-red (NIR) light (wavelengths 650–1000 nm) is relatively transparent to human tissues. The absorption spectra of oxygenated and de-oxygenated haemoglobin (HbO and HbR respectively) for NIR light differ in that HbO maximally absorbs light of longer wavelength (900–1000 nm) whereas HbR maximally absorbs light of shorter wavelength. These differential absorption spectra make it possible to separate out changes in the concentration of HbO and HbR. — Dijk, Pim van, Physiology, Psychoacoustics and…, 4273

Categorization

• DEFINE: The optical-physiological mechanism underpinning fNIRS that the reader needs for understanding.