Revealing the Unseen
New imaging helps surgeons navigate complex brain fibers
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| A regular brain scan shows a cavernoma, or blood vessel malformation, in the patient’s brain. |
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| This image, made using tractography techniques, shows white-matter tracts that have never before been visible. |
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| Using a combined image, the neurosurgeon can see important tracts located near the cavernoma that need to be avoided during surgery. |
From the outside, the brain looks like a gray lump of tissue, covered with ridges and bumps. But inside, a complex network of thread-like white fibers carries signals back and forth between areas of the brain and the spinal cord. Each fiber is crucial to a particular aspect of how the mind communicates with the body.
Until recently, neurosurgeons couldn’t see these fibers — called white-matter tracts. Invisible to the naked eye and impossible to see on normal brain scans, they are easily damaged during brain operations to remove tumors or treat severe epilepsy. The result can be permanent damage to the senses, movement or cognitive ability.
“In the past, we’ve never been able to see the direct connections from one part of the brain to another, or from one part of the brain to the spinal cord,” says Suresh Mukherji, M.D., who directs the Division of Neuroradiology. “Now we can see those connections by looking at the sub-cellular level to see how water molecules move in brain tissue.” Mukherji is a professor of radiology, of otorhinolaryngology and of radiation oncology.
The Health System is one of the first medical centers to offer image-guided surgery using a new white-matter imaging technique called tractography. Brain-imaging specialists like Mukherji work closely with U-M neurosurgeons, who perform thousands of brain and spine operations each year, and with neurologists who diagnose and treat brain and nerve disorders.
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Oren Sagher consults the new MRI imagery in the operating room |
Oren Sagher, M.D., an associate professor of neurosurgery and of anesthesiology, says this teamwork makes it possible for him to operate with the best possible information about each patient’s brain. “Thoroughly imaging the brain is one of the keys to successful brain surgery,” Sagher says. “We have to be able to see all the structures we’re going after and all the structures in our way that need to be avoided.”
Tractography uses powerful magnetic resonance imaging (MRI) scanners that create images of the patient’s brain one thin slice at a time. Then, ultra-fast computers equipped with special software compile all the slices into a three-dimensional image of the brain. Lastly, the neuroimaging team uses special techniques to see how water molecules are oriented and move inside every area of the virtual 3-D brain. The end result is a series of spectacular images that show the entire network of white-matter tracts with their individual nerve fibers.
These images become a roadmap for surgeons like Sagher, especially when they’re superimposed on other images that show the specific areas of “gray matter” where epileptic seizures begin or where tumors lurk.
This cross-registration fuses information about two areas of the brain: areas the surgeon needs to remove or destroy to treat the patient’s condition and areas the surgeon needs to avoid to preserve a patient’s vision, for instance, or her ability to move her right arm.
Mukherji, Sagher and their colleagues predict that tractography will change brain surgery and the way we see the brain’s function forever, just like the first CT and MRI scans changed the diagnosis and treatment of many brain disorders. The team is pursuing research to improve the technique and show how it can best be used — and how it helps spare patients from unintended consequences.
“Instead of imaging the brain, we’re essentially imaging the mind,” says Mukherji. “We’re able to image how a person’s thoughts and brain impulses travel, and this is just the beginning.”
—Kara Gavin
For an expanded version of the story:
www.med.umich.edu/opm/newspage/2007/hmepilepsy.htm
