Pi NoIR Camera V2

Obtaining access to blood vessels can be difficult. Near-infrared light might be a option since subsurface blood vessels can be visualized in high contrast due to less absorption and scattering in tissue compared to visible light. Instead of using a camera with ingaas detectors, we use a near-infrared sensitivity inexpensive silicon-based detectors. Human vision is limited to the visible spectral range that is defined by the luminous efficiency functions to range between wavelengths of 370 nm and 750 nm. In contrast Si-based sensor cameras have sensitivities extending to about 1100 nm. Blood vessels that are used for bloodtests are typically located up to a few millimeters below the skin surface. The main chromophores in epidermis, dermis and subcutaneous adipose tissue are melanin, hemoglobin, proteins and water. In the visible part of the spectrum melanin and hemoglobin are highly absorptive, counteracting deep tissue penetration. In the NIR part of the spectrum, there is much less absorption by melanin and hemoglobin. However above 900 nm absorption of water is increasing, again preventing deep tissue penetration. It is important that the light generated by the LED is safe for the eye during normal use. Since NIR light is not visible, and therefore a blinking reflex is absent, this also includes longer exposure times. The light generated by the LED is absorbed and can heat the skin.