We have built a low cost vein viewer, such a medical device detects veins under the skin using infrared (IR) light and projects them in real time onto the skin. This allows the early recognition and thus treatment of vascular disease. Building such a device - which is usually very expensive - was particularly challenging as the manufacturer has not published any plans.
We succeeded in visualizing the veins under the skin using a cheap webcam, a laptop, a ring of IR-LEDs, an IR filter and two polarizers. In order to detect IR radiation, we had to remove the IR blocking filter of the camera. We chose a perpendicular arrangement of camera and projector and we separated IR-radiation and projector light using a beam splitter. This worked in principle, however, the quality of the projection of these images onto the skin was still disappointing.
We improved this by dramatically changing the experimental setup. We removed the beam splitter and the polarizers and placed the camera directly next to the objective of the projector. Furthermore, we replaced the webcam with a monochrome USB camera, which is more sensitive in the near-IR. We placed an IR filter in front of the camera and a green filter in front of the projector objective to ensure that the camera does not see the projected image. By finding suitable settings of the image processing software we were able to realize a good real time projection of the veins directly onto the skin.
