Another area showing some promise uses fluorescence to decipher what is going on within tumors. In fluorescence imaging, a laser can be used to excite fluorophores, molecular components that absorb and emit light. Sensors can then capture the amount of fluorescence being emitted.
Explore This IssueApril 2011
“We can correlate that amount of fluorescence with pathology that we obtained at biopsy,” said Gregory Farwell, MD, associate professor of head and neck oncology-skull base surgery at the University of California at Davis. “What’s become apparent in our studies (Arch Otolaryngol Head Neck Surg. 2010;136(2):126-33) and other groups’ studies is that there’s a very nice correlation between the fluorescence of a tissue and its pathologic state.”
The technology can help make diagnosis a simpler process, Dr. Farwell said. “It can allow for essentially a non-invasive biopsy,” he said. “In areas that are suspicious, we can analyze them with a probe and determine the composition of a tissue without a biopsy.”
In India, with the help of a grant from the Bill and Melinda Gates Foundation, the technology is being tested for the rapid assessment of large numbers of people.
“They’re looking at the ability of this technology to do mass screenings and improve health care delivery to patients at risk for head and neck cancer,” Dr. Farwell said.
Dr. Zinn said that potential application in the operating room is driving the development of fluorescence, particularly in robotic surgery, because the technology could easily be integrated into the tools already used.
“Fluorescence has a much higher spatial resolution than the MR or PET,” he said. “And, of course, it has the ability to zoom in to very small areas and detect sub-millimeter disease potentially. Even 50 to 100 tumor cells could be detected if you had the contrast to show that those cells are there. And you would never be able to do that on a PET- or MR-based approach.”
Dr. Zinn added that more probes are needed to maximize the potential of fluorescence imaging. That includes development of “quenched” probes, for which there is no fluorescence until the tracer is activated by a process in the cancer, offering better visibility by effectively lighting up only the disease.
There are clinical trials afoot for these advances in tracers for fluorescence imaging, but the work has been slow going, Dr. Zinn said.
Ultrasound imaging is being refined with the use of tiny gas bubbles, contrast agents developed to enhance the acoustic signature of blood and to better define other structures in the body. In an assessment of thyroid nodules, for example, ultrasound with contrast bubbles determined benign or malignant status with sensitivity and specificity between 83 percent and 94 percent (Thyroid. 2010;20(1):51-57).