Shining Light on Detection

HealSpring 2008
Volume 2
Issue 1

New optical imaging techniques may help find cancers that aren't otherwise obvious

Perhaps nowhere is this technology more needed than with the detection of pancreatic cancer, which has one of the worst survival rates of any malignancy. Outcomes are poor largely because the cancer can grow silently in the pancreas until symptoms develop, usually at an advanced stage. There is no screening technique, like the blood test for prostate-specific antigen given routinely to older men.

Recently, a team of scientists described a technique that might eventually allow doctors to look at a segment of the intestine adjacent to the pancreas and see — in a sense — faint wisps of cancer. The research is part of a rapidly growing field of investigation: sensing or imaging tumors with light (optical imaging). While experiments encompass various approaches and strategies, the goal is the same: to enable doctors to easily probe tissue itself and find the footprints of cancer.

Radiology has always existed at the nexus of physics and medicine. Most radiological techniques today, however, still rely on the use of X-rays, sound waves and other approaches that can capture abnormal patterns that may indicate tumors but don’t examine cancerous tissue itself (which is what a biopsy does). Optical imaging would provide a direct view and one that is, ideally, easier to obtain.

But a computer might be the one looking. For example, in a recent study of pancreatic cancer detection, published in the journal Clinical Cancer Research, researchers from Northwestern University examined differences in the way cancerous and non-cancerous tissue reflect light. The behavior of light can reveal much about a surface; you see colors on this page because some wavelengths of visible light are absorbed and some bounce back to your eyes.

Applying a similar concept, the Northwestern scientists compared the reflected “signatures” — patterns made by wavelengths of light from the visible spectrum and beyond, which bounce off the tissue. Using sophisticated sensing technology and software to distinguish normal from malignant tissue, the research team examined tissue samples taken from the area of intestine next to the pancreas (19 of the samples came from cancer patients and 32 from people without cancer). The light patterns detected tumors that were present 95 percent of the time.

“You’re trying to gain more information than the doctor can see,” says Irving Bigio, PhD, of Boston University’s Department of Biomedical Engineering, who wrote an editorial that accompanies the research.

If this technique pans out, doctors might one day be able to pick up traces of tumors even before visible changes appear in the body. For example, Vadim Backman, PhD, and colleagues at Northwestern are also conducting experiments to see whether such light-scattering signatures in rectal tissue could predict the presence of colon cancer. The technique might someday also detect normal tissue at risk of becoming cancerous, possibly leading doctors to more closely tailor screening methods to individuals.

Optical detection may pinpoint other types of cancer in different ways. Researchers from Georgetown University Medical Center are experimenting with a way to perform real-time breast biopsies at a patient’s bedside. They are making use of the same idea — comparing patterns of reflected and absorbed light — but using a different approach. In a recent paper in the Journal of Biomedical Optics, the scientists described a special microscope that reflects near-infrared light off a sample of breast tissue. A normal microscope shines light through tissue, which means the sample must be preserved and sliced like lunchmeat before being studied piece by piece.

Optical imaging would provide a direct view, and one that is, ideally, easier to obtain.

This experimental light-reflecting micro­scope can examine an entire needle biopsy within minutes. In the journal, the researchers report that they were able to successfully tell the difference between cancerous and non-cancerous tissue in all the breast biopsies they studied, although greater detail could not be discerned.

Lead researcher Priscilla Furth, MD, of Lombardi Comprehensive Cancer Center at Georgetown, predicts that eventually optical detection of cancer will reach routine clinical practice, if radiology’s past is any indication of its future. When she began medical school in the 1970s, she pointed out, ultrasound images looked to the untrained eye almost like a snowy TV screen. “Now,” she said, “we can visualize babies.”