The principle used in identifying intracranial hematomas 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 hematoma 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 hematoma, 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.

LEFT SIDE		RIGHT SIDE

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 hematoma side.
 

The Infrascanner is not available for sale in the United States and is limited by federal law to investigational use.