The parathyroid glands – four small organs the size of grains of rice located at the back of the throat – glow with a natural fluorescence in the near infrared region of the spectrum.

This unique fluorescent signature was discovered by a team of biomedical engineers and endocrine surgeons at Vanderbilt University, who have used it as the basis of a simple and reliable optical detector that can positively identify the parathyroid glands during endocrine surgery.

The report of the discovery of parathyroid fluorescence and the design of the optical detector was published in the June issue of the Journal of Biomedical Optics.

Damage to these tiny organs can have deleterious, life-long effects on patients’ health because they produce a hormone that controls critical calcium concentrations in bones, intestines and kidneys. However, the parathyroid glands are very difficult to identify with the naked eye. Not only are they small, but their location also varies widely from person to person and it takes a microscope to reliably tell the difference between parathyroid tissue and the thyroid and lymph tissue that surrounds it.

In 2004, more than 80,000 endocrine surgeries were performed in the United States and this number is projected to grow to more than 100,000 by 2020. Today, when a surgeon cuts into a patient’s neck to remove a diseased thyroid, somewhere between 8 to 19 percent of the time the patient’s parathyroid glands are also damaged or removed.

Parathyroid glow is surprisingly strong

“We have discovered that the parathyroid glands are two to 10 times more fluorescent in the near infrared than any other tissues found in the neck,” said Professor of Biomedical Engineering Anita Mahadevan-Jansen, who directed the study. “We have taken measurements with more than 50 patients now and we have found this effect 100 percent of the time, even when the tissue is diseased. That is amazing. You almost never get 100 percent results in biological studies.”

The fluorescence is so strong that it doesn’t take expensive or sophisticated instruments to detect. The Vanderbilt researchers have assembled a detector from off-the-shelf hardware. It consists of a low-powered infrared laser connected to an optical fiber probe. As the fiber connected to the laser illuminates the tissue with invisible near infrared light, other fibers in the probe are connected to a detector that measures the strength of the fluorescence that the laser excites. The university has applied for an international patent that covers this application.

“I was certainly impressed with how accurate this method seems to be,” said John Phay, an endocrine surgeon at the Ohio State University Medical Center, who collaborated in the study when he was at Vanderbilt. “The ability to detect the parathyroids would be a big help: The major problem in parathyroid surgery is finding them and it is very hard to avoid them in thyroid cancer surgery when you need to clear out lymph nodes.”

Using the first generation of the device was “a bit burdensome, because you have to dim the lights,” Phay commented. This will not be a problem with the next version, because it will include a filter that will block out visible light. According to the surgeon, the system will be the most useful with the planned addition of a camera that displays the fluorescence of all the tissues in the throat on a single display.