It looks like a ghoulish Halloween trick. Yet the device, which projects a creepy green video image of a patient�s veins onto their skin, is about to go on trial in a US hospital. The idea is that it will help staff to pinpoint a suitable vein for an injection or a drip.
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An array of near-infrared LEDs surrounding the camera�s lens illuminates the skin at a wavelength of 740 nanometres. This wavelength is strongly absorbed by blood, but is scattered by the surrounding tissue. �Fat and tissue look light, veins and blood look dark,� says Zeman.

The image from the camera is fed to a PC running imaging software that maps the image onto a bright green background in real time and boosts the contrast between the veins and surrounding tissue. The PC then feeds this image to a projector that beams it onto the skin.