Imaging Device Locates Veins for Injection

The utilization of a charge-coupled device (CCD) camera combined with the power of the digital computer and state-of-the-art image processing algorithms can now be applied to medical imaging problems.

This new medical device is set to go on trial in a U.S. hospital. By highlighting subcutaneous veins, it will help hospital staff locate a suitable vein for a drip or injection. It utilizes a diffused source of near-infrared light and a CCD infrared camera to project an enhanced image of the vein back onto the patient's skin.

The device is designed to prevent the discomfort and delay of failed attempts to penetrate veins for injections and blood tests. "To stick a vein properly you need to get it in exactly the right place. If you hit it off-center, it just rolls out of the way,” observed Dr. Herbert Zeman, a biomedical engineer at the University of Tennessee (Memphis, TN, USA). The prototype device, called a vein contrast enhancer (VCE), uses a near-infrared camera to capture a real-time video image of the patient's veins, a personal computer (PC) to enhance the contrast of the image, and a desktop video projector to display it in real time on the skin. An array of near-infrared light-emitting diodes (LEDs) surrounding the camera's lens highlights the skin at a wavelength of 740 nm. This wavelength is quickly absorbed by blood, but is dispersed by the surrounding tissue.

"Fat and tissue look light, veins and blood look dark,” said Dr. Zeman. The camera's image is transmitted to a PC running imaging software that maps the image onto a bright green background. The PC then transmits this image to a projector that beams it onto the skin. The complex part is making sure the image of the veins is projected in precisely the correct place. To do this wrong, the system becomes useless. The solution to this problem is a device called a "hot mirror,” which is transparent to visible light but reflects infrared wavelengths.

To use the system, the camera and video projector are positioned at 90o to each other facing the mirror, which is positioned at 45o to both of them. After calibration, this ensures that a vein always appears within 0.06 mm of its correct position, according to Dr. Zeman. The VCE can locate veins up to 8 mm below the surface of the skin. Green light is used as the backdrop because it is not seen by the infrared camera. Dr. Zeman has now miniaturized the system to fit in a package the size of a shoebox, making it portable enough to be placed on an intravenous drip stand. Three prototypes will start clinical trials at a hospital in Tennessee later this year.

"From the patient's standpoint, anything that makes the placement of the intravenous drip easier is great,” said Dr. Dennis Ernst, director of the Center for Phlebotomy Education in Ramsey (IN, USA). He believes that patients, particularly children, will enjoy the mysterious green image of the vasculature on their arms. That is a bonus, he said, because usually the small veins and baby fat of young children mean that more than half the attempts to find a vein are unsuccessful.


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