Optical Method Maps Brain Tumor Borders

When surgeons remove brain tumors, they spend a lot of time snipping out tiny pieces of tissue at the borders between the tumors and healthy tissue. Before cutting, they carefully examine the tissue with a microscope to make sure they’re excising only tumor. Cutting out normal tissue could impair a patient’s vision, speech, or memory.

A new handheld probe could someday help surgeons in their decision-making, thanks to a technique that uses light to differentiate cancerous and normal tissue.

Neurosurgeon Alfredo Quiñones-Hinojosa and biomedical engineer Xingde Li of Johns Hopkins University teamed up to adapt a technique called optical coherence tomography (OCT) to the brain. Doctors have previously used OCT to analyze other tissue types, including the retinas of glaucoma patients.

The new version of OCT involves a handheld probe that shines near-infrared light on brain tissue and then analyzes the amount of light reflected back. The researchers found that tumor tissue reflects more light than healthy white brain matter because tumors degrade neurons’ protective coatings. They developed an algorithm that interprets the reflected light from a section of tissue and outputs a color-coded map showing areas of cancerous and normal tissue.

In tests on tissue samples excised from brain surgery patients, the technique correctly spotted healthy tissue between 80 and 100% of the time, depending on tumor type (Sci. Transl. Med. 2015, DOI: 10.1126/scitranslmed.3010611). Without the probe, Quiñones-Hinojosa correctly identified normal tissue only 40 to 50% of the time by eye. “This device is much more accurate in telling if it’s a tumor or not,” he says. “I’m no better than flipping a coin.”

David W. Roberts of Dartmouth College’s Geisel School of Medicine says the study is a strong first step, but more data are needed to show that OCT is a viable surgical tool. For example, he’d like to know how well the method can characterize tissue as it extends out from the obvious tumor center and infiltrates normal tissue, where the tumor is almost impossible to spot by eye. Also, Roberts says, the team needs to test the technique on actual surgical patients.

Quiñones-Hinojosa and Li say they are planning such a study.