This device is surely to be welcomed by doctors and patients alike. New Scientist provides all the working details:
“To stick a vein properly you need to get it in exactly the right place,” says the device’s inventor, Herbert Zeman, a biomedical engineer at the University of Tennessee in Memphis. “If you hit it off-centre, it just rolls out of the way.”
Zeman will demonstrate the device this week at the Frontiers in Optics conference in Rochester, New York. The prototype of the system, which he calls a vein contrast enhancer (VCE), uses a near-infrared camera to capture a real-time video image of the patient’s veins, a PC to enhance the contrast of the image and a desktop video projector to display it on the skin in real time (see graphic).
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.
The tricky part is making sure the image of the veins is projected in exactly the right place. Get this wrong, and the system becomes worse than useless. The key is device called a “hot mirror”, which is transparent to visible light but reflects infrared (hot) wavelengths.
The video projector and camera are set at 90 degrees to each other facing the mirror, which is set at 45 degrees to both of them. After calibration, this ensures that a vein always appears within 0.06 millimetres of its correct position, Zeman says.