How Imagent™ Works

Imagent™’s working principle is based on the use of near infrared light for probing the cortical surface. The main tissue absorbers in the wavelength region spanning from 700 nm to 900 nm are oxy-hemoglobin (HbO₂) and deoxy-hemoglobin (Hb). On a smaller scale, water, fat and cytochrome oxidase contribute to the partial absorption of the light. The penetration depth of light in tissues is quite significant in this wavelength range. For typical head tissue (skin/scalp, skull and cortical layer), with an absorption coefficient of μa = 0.1 cm^-1 and a scattering coefficient μ_s' = 8 cm^-1, the maximum optical penetration can be estimated to be about 1.5 cm when a detector is placed at 4 cm from the source. The penetration depth can be increased by increasing the distance between the source and the detector, although, eventually, the signal-to-noise ratio of the measurement deteriorates.

Figure 1. Main tissue absorbers in the 600-1100 nm region.

Imagent™ utilizes laser diodes emitting at 690 nm and 830 nm. The light is delivered by fiber optics positioned on the skull. Upon entering the tissue, the near infrared light, albeit weakly absorbed, is highly scattered by the tissue inhomogeneities. A fraction of the light leaves the tissue and it is collected by the collecting fiber that carries it back to the light detectors housed in the unit for data processing.

Figure 2. Multiple scattering of photons in the tissue.

Figure 3. Light penetration in brain tissue using Imagent™.