A new imaging technology can be used to help surgeons take out as much brain tumor as possible while keeping surrounding healthy tissue intact, an important technological advance that could improve survival time for brain cancer patients, a U.S. study said Wednesday.
The technology, called quantitative optical coherence tomography (OCT), can do this by providing surgeons with a color- coded map of a patient's brain showing which areas are and are not cancer, according to the study published in the U.S. journal Science Translational Medicine.
"As a neurosurgeon, I'm in agony when I'm taking out a tumor. If I take out too little, the cancer could come back; too much, and the patient can be permanently disabled," said Alfredo Quinones-Hinojosa, a professor of neurosurgery, neuroscience and oncology at the Johns Hopkins University School of Medicine and the clinical leader of the research team. "We think optical coherence tomography has strong potential for helping surgeons know exactly where to cut."
First developed in the early 1990s for imaging the retina, OCT operates on the same echolocation principle used by bats and ultrasound scanners, but it uses light rather than sound waves, yielding a higher-resolution image than ultrasound does.
For the past decade, research groups around the globe, including a group at Johns Hopkins led by Xingde Li, a professor of biomedical engineering, has been working to further develop and apply the technology to other organs beyond the relatively transparent eye.
Li's research first built on the idea that cancers tend to be relatively dense, which affects how they scatter and reflect lightwaves, but eventually they found a second special property of brain cancer cells -- that they lack the so-called myelin sheaths that coat healthy brain cells -- had a greater effect on the OCT readings than did density.
Based on the characteristic OCT "signature" of brain cancer, the team devised a computer algorithm to process OCT data and, nearly instantaneously, generate a color-coded map with cancer in red and healthy tissue in green.
"We envision that the OCT would be aimed at the area being operated on, and the surgeon could look at a screen to get a continuously updated picture of where the cancer is -- and isn't," Li said.
When they used OCT to look at brain tissue from 32 patients with cancer and five noncancerous brain tissue samples, they found that the imaging technique improved the diagnosis of cancerous versus noncancerous tissues, compared to a surgeon's evaluation.
The team also used OCT to develop color-coded maps of human brain tumors implanted in five mice, and surgically removed the tumor tissue -- and not any healthy tissue -- with the maps' guidance.
So far, the need to identify cancer tissues readily and intraoperatively has led to the development of different surgical adjuncts such as magnetic resonance imaging (MRI) and ultrasound.
But ultrasound has a much lower resolution than OCT, and MRI scanners designed to be wheeled over a patient on the operating table cost 3 million to 5 million dollars each, require an extra hour of operating room time to obtain a single image and do not provide continuous, real-time intraoperative guidance, Li said.
By comparison, the team anticipated that the cost of an OCT- based system would be only about 5 percent of that of a MRI scanner. Additionally, OCT is capable of imaging tissues in three dimensions in real time and in a noncontact way, which will minimize infection risks for intraoperative use.
The team planned to begin clinical trials in patients this summer.
