Advance Health

Near Infrared Technology

The principle used in identifying intracranial haematomas with NIRS is that extravascular blood absorbs NIR light more than intravascular blood since there is a greater (usually 10-fold greater) concentration of hemoglobin in the acute haematoma than in the brain tissue where blood is contained within vessels. Therefore, the absorbance of NIR light is greater (and therefore the reflected light less) on the side of the brain containing a haematoma, than on the uninjured side.

With specified wavelength ranges, optical light source(s) or emitter(s) and photodetector are placed at a distance, which allows proper NIRS absorption measurements in a desired volume of tissue.

The NIRS probe is placed successively in the left and right frontal, temporal, parietal, and occipital areas of the head and the absorbance of light at selected wavelengths is recorded.

Frontal: Left/Right forehead, above the frontal sinus
Temporal: In the Left/Right temporal fossa
Parietal: Above the Left/Right ear, midway between the ear and the midline of the skull
Occipital: Behind the Left/Right ear, midway between the ear and the occipital protuberance

The difference in optical density (ΔOD) in the different areas is calculated from the following formula:

where IN = the intensity of reflected light on the normal side, IH = the intensity of reflected light on the haematoma side.

Photo Gallery