"Night vision" NIR camera enables observation of real-time lymphatic flow

May 1, 2009

HOUSTON, TX, USA--Lymphatic vessels are too small to carry sufficient amounts of contrast agent for magnetic-resonance or X-ray imaging. And nuclear techniques don't allow observation of fluid movement. The new Center for Molecular Imaging at The University of Texas Health Science Center at Houston has a solution: near-infrared "night vision" technology. The approach promises to facilitate early detection of edema before symptoms materialize.

HOUSTON, TX, USA--Much is known about the blood system. But Eva Sevick, Ph.D., who leads the 20-person research team in the Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases (IMM) at the University of Texas Health Science Center at Houston, says that until recently, comparatively little was known about the lymphatic system. Unlike blood, lymphatic fluid is clear, which makes it hard to see. Also, lymphatic vessels are so small that they cannot carry sufficient amounts of contrast agent needed for magnetic resonance imaging or X-ray imaging. And nuclear techniques don't allow observation of fluid movementbecause they take too long to acquire an image.

Sevick's solution involves injecting tiny amounts of fluorescent dye below the skin where the lymphatic system can sweep it up. Then with the aid of a small laser and a near infrared (NIR) night-vision camera, Sevick's team is able to observe the dye move through the lymph system below the surface of the skin. This is possible because the night vision camera can acquire images in less than one second, and recognized very small amounts of light.

This movie, captured with the researchers' setup, shows lymph flow in the upper arm of a volunteer subject. The movie runs at about three times normal speed. "The bright streaks are the lymphatic vessels, and the bright moving spots are packets of lymph that are being propelled through the system," explains John C. Rasmussen, Ph.D., an engineering scientist at the Health Science Center.

"No one had ever watched this before," said Caroline Fife, M.D., clinical associate professor of medicine at The University of Texas Medical School at Houston and director of clinical research for the Memorial Hermann - TMC Wound and Lymphedema Center. "This was like Christopher Columbus discovering America. Until now, we've never had a good way to study the lymph system. It felt like being a doctor before antibiotics."

The lymphatic system is of particular interest to cancer specialists because malignant cells will often end up in lymphatic filters. "Lymph nodes filter out bacteria and tumor cells," said Fife, noting that the lymphatic system processes six liters of fluid every day.

Much like plumbing when it backs up, lymphatic drainage problems can cause fluid retention or swelling, which results in a condition called lymphedema. About one in 200 are born with lymphedema, according to the Lymphatic Research Foundation (LRF); however, most in the United States acquire it as result of surgery, infection or trauma that interferes with the lymphatic system. About 30 percent of breast cancer survivors develop lymphedema, the LRF states.

While there is no cure, lymphedema symptoms can sometimes be treated with massage and compression bandaging.

"The Center for Molecular Imaging is poised to develop and translate molecular imaging agents, instruments and computer algorithms for improving patient care in a variety of diseases," Sevick said. "With our optical technologies, we could image disease before the onset of symptoms. We also investigate the impact of breast cancer therapy on lymphatic function in order to evaluate how long-term treatments impact quality of life for cancer survivors."

Sevick is working to translate her bench discoveries into patient care. With the approval of the U. S. Food & Drug Administration, the researchers in her lab have begun patient trials using this medical imaging technique, which could aid in the diagnosis and treatment of many diseases including those of the lymphatic system.

In one trial, Sevick's team is recruiting 18 subjects for a clinical study to determine the effect of an automated massage device on lymphatic flow in persons with lymphedema of either one arm or one leg. In a second study, her research team is evaluating the effect of genetic makeup in persons with hereditary lymphedema and acquired lymphedema.

For more information see the paper Driving fast-spiking cells induces gamma rhythm and controls sensory responses in Nature. And, see more about Dr. Sevickat the Brown Foundation Institute website. More information is also available by dialing 713-500-3561.

Posted by Barbara G. Goode, [email protected], for BioOptics World.