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Intraoperative images improve surgical precision

20 Aug 2008

A NIR fluorescence imaging system could offer real-time image guidance during cancer surgery.

Successful cancer surgery relies on removing as much of the tumour as is possible, while avoiding nearby normal tissue. But without a means to directly visualize the tumour margins, there's no clear way for surgeons to determine in real-time whether they have removed all of the diseased tissue.

At the 236th National Meeting of the American Chemical Society, held this week in Philadelphia, PA, researchers from Beth Israel Deaconess Medical Center (Boston, MA) and Georgia State University (Atlanta, GA) reported on an intraoperative imaging system that can highlight cancerous tissue within the body during surgery. Such a facility could also help surgeons avoid damage to nearby critical structures, such as nerves and blood vessels.

The instrument, known as FLARE (fluorescence-assisted resection and exploration), is a dual-channel, near-infrared (NIR) fluorescence imaging system that permits real-time image guidance using exogenous contrast agents. The system, which has no moving parts and uses LEDs for excitation, makes no contact with the patient. It is said to show particular promise for improving surgery for breast, prostate and lung cancer, in which the tumour boundaries can be difficult to track at advanced stages.

"This technique is really the first time that cancer surgeons can see structures that are otherwise invisible, providing true image-guided surgery," said project director John Frangioni, of Beth Israel Deaconess Medical Center. "If we're able to see cancer, we have a chance of curing it."

Targeted glow
The research team has developed several novel NIR fluorophores – including organic indocyanines and hybrid inorganic/organic quantum dots – that target specific structures, such as cancer cells, when injected into patients. These contrast agents fluoresce upon exposure to NIR light – effectively lighting up the cancer cells.

Images of the fluorescing cancer cells are superimposed over standard images of the surgical field on a video monitor. This enables surgeons to see the cancer cells, even in a background crowded by blood and other anatomical structures. The computerized technique also gives physicians the power to control multiple viewing angles and magnification levels through the use of a footswitch.

"The system is pre-calibrated and registered before the surgery," Frangioni explained. "The three channels – colour, NIR 1 and NIR 2 – appear on the screen simultaneously and are co-registered during the surgery. Merging of any combination of images is also performed in real-time."

In preliminary studies, Frangioni and colleagues used the FLARE system to visualize organs and body fluids of mice and to map the lymph nodes of pigs, all in real-time. The researchers have now begun studying human subjects and predict that broader clinical use could occur within five years.

"A human clinical trial for sentinel lymph-node mapping in breast-cancer patients has already started. Two patients consented and the system worked well," Frangioni told medicalphysicsweb. "A second clinical trial will start within a month or so at Brigham and Women's Hospital [Boston, MA] for sentinel lymph-node mapping in lung cancer."

In the future, fluorophores could be developed that highlight nerves and blood vessels in one colour while visualizing cancer cells in another, allowing multiple structures to be viewed simultaneously. "The future of the technology now is really in the chemistry," Frangioni said. "We have to develop agents for specific tumours, nerves or blood vessels we're trying to visualize."

Tami Freeman is editor of medicalphysicsweb.org

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