Tuesday, August 19, 2008

Lighting Up Tumors

Surgical imaging system turns cancer tissue neon.

By Katherine Bourzac

Inside view: A real-time surgical imaging system (top) displays live video of a surgical area overlaid with images of hidden features such as cancer cells, blood vessels, and lymph nodes. An image produced by the new system (bottom) shows a pig’s hind leg after injection of a contrast agent. Near-infrared light is displayed in bright green and highlights lymph nodes in the pig’s leg.

Many cancer patients leave surgery still harboring dangerous tumor cells, while others suffer painful aftereffects because a surgeon has removed too much healthy tissue or nicked a nerve. A new imaging system that highlights cancerous tissue in lurid colors should help surgeons remove every last trace of cancer without harming the surrounding tissue. The system, currently in early clinical trials, uses a new class of contrast agents that emit near-infrared light and can attach to virtually any kind of tissue, cancerous or a healthy--showing surgeons just where to cut.

"During surgery, we cannot see small collections of tumor cells we know are being left behind," says John Frangioni, a physician at Beth Israel Deaconess Medical Center in Boston. Frangioni, also an associate professor of medicine and radiology at Harvard Medical School, will present details of his new imaging system and imaging agents at the annual meeting of the American Chemical Society in Philadelphia today.

The imager, which is being licensed by GE Healthcare, augments a normal video feed with near-infrared imagery to show the location of targeted contrast agents--microscopic particles made up mostly of fluorescent proteins administered to the patient before surgery. During a surgical procedure, a boom carrying one visible-light camera and two for different bands of the near-infrared spectrum is suspended above the patient, sending live video and infrared footage to a computer that displays a combined picture on a screen next to the operating table.

The imager is designed to work with any contrast agent that emits near-infrared light, no matter what type of tissues it binds to. Its boom carries a light-emitting diode that illuminates the surgical area with near-infrared light, causing the fluorescent proteins within the contrast agents to also emit near-infrared light. The core proteins may be coupled to any of a large range of targeting molecules that bind to cells within particular tissue types--for example, antibodies that bind to the proteins on the surface of breast cancer cells.

Since near-infrared light is invisible to the naked eye, the imaging system converts it into bright neon colors laid over a visible-light image. By using multiple imaging agents that bind to different tissues and emit different wavelengths of light, a surgeon can see different types of tissue at the same time: blood vessels can be colored bright blue, while tumor cells are shown in bright green.