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Morgan Cox lives in a state that is surrounded on three sides by water. An intellectually gifted 9-year-old, she has spent many happy hours floating and bobbing and mastering swimming strokes. So perhaps it’s appropriate that a revolutionary procedure based on the movement of water molecules helped save her life.
When doctors in Florida told Kim Chokanis that her daughter had cancer, the pediatric nurse immediately began researching her options. Morgan had ganglioglioma, an uncommon tumor that occurs in a rare location; in Morgan’s case, the tumor extended from the upper part of her spinal cord into her brainstem. “The doctors here weren’t sure what to do with Morgan,” Kim says. “I called around the country trying to find out the best way to treat her. Doctors from New York and Duke said that Morgan would be in good hands with Dr. [Robert] Sanford.”
Chief of the Neurosurgery division at St. Jude Children’s Research Hospital, Sanford had access to a new MRI technology called diffusion tensor imaging (DTI). Sanford could use DTI to locate with pinpoint accuracy the white matter tracts in Morgan’s brain. The surgeon wanted to remove the tumor without harming these crucial tracts, which govern motor skills. “Using traditional MRI, I would have been guessing as to where the tracts were,” Sanford explains. But in Morgan’s case, we could identify exactly where they were so that I didn’t have to guess.”
DTI gave Sanford the advantage he sought. “If I had damaged the fiber tracts, Morgan could have been paralyzed from the neck down for the rest of her life,” Sanford says.
Still water moves fast
Neurosurgeons often rely on MRI images to help them determine surgical strategies. Traditional MRI images can be likened to the grainy scenes that appear on black-and-white televisions, but the new DTI images flaunt the flamboyant hues of high-definition color TV.
Although MRI can display minute details, it cannot indicate the direction of fibrous tissues. But on a DTI scan, areas in red show pathways that move from left to right; blue areas indicate pathways that go from head to foot; and green portions delineate pathways that travel from front to back. The colorful DTI images are created by measuring the distances that water molecules diffuse, or spread out, in various tissues.
To the casual observer, a pool of water may appear to be still. But the individual water molecules are constantly moving, colliding at high speeds. The water molecules spread out when they knock against each other or with molecules in tissues. The way that water molecules diffuse indicates the properties of the tissues themselves. DTI takes highly technical information about this diffusion and transforms the data into colorful, 3-D images.
Patients like Morgan don’t care about all of these intricate computations—to them, the beauty of DTI lies in its simplicity. “It’s completely painless for the patient,” says Kathleen Helton, MD, of St. Jude Radiological Sciences. “And the process takes about five minutes. They don’t get stuck with a needle; for them, it’s just like having a regular MRI."
White matter tracts are like telephone cables that connect different parts of the brain. But these tracts do more than just control motor function. St. Jude scientists have discovered a correlation between white matter and intelligence in brain tumor survivors. “We found that the less white matter survivors had, the lower their IQ scores were,” says Gene Reddick, PhD, director of the St. Jude Diagnostic Image and Signal Processing Laboratory. Because white matter is so important, neurosurgeons try to avoid damaging it.
A tumor growing in the brain may push white matter tracts aside. To avoid damaging those fibers, neurosurgeons must know exactly which way they have moved. “If you think the tracts have moved to the left and they haven’t, you’re in trouble,” Sanford says. “We can make educated guesses, but they’re just that—guesses. With MRI, we still had to guess which direction the fibers had moved. But the potential for DTI is unlimited. If we can use DTI to identify where all the critical areas are, then surgery can become a lot safer than it has been in the past.”
For more than a year, Sanford and his colleagues at St. Jude have been using DTI on a case-by-case basis to locate displaced white matter tracts before surgery even begins. Now, however, their use of DTI is about to expand dramatically.
DTI is available at St. Jude through the efforts of a small team of scientists in the hospital’s Radiological Sciences department. Biomedical engineers Robert Ogg, PhD, of Diagnostic Imaging, and Nick Phillips, a doctoral student at the University of Tennessee, Memphis, put the technique in place. Then Helton posed clinical questions that might be answered by using DTI.
For several years, Ogg has been using a process called functional MRI (fMRI) to look for disease- or treatment-induced changes in the way the brain works while doing basic activities. Ogg uses fMRI to visualize which parts of the brain are being activated when a child performs specific tasks or undergoes sensory stimulation. St. Jude is the first institution to use fMRI to investigate the learning problems children encounter during cancer treatment. Now Ogg is harnessing DTI’s potential as part of his fMRI studies. “I’m interested in using DTI to assess the integrity of the white matter pathways that interconnect the different parts of the brain that I identify using functional MRI,” Ogg explains. This marriage of technologies may help Ogg and his colleagues make further strides in identifying and addressing cognitive problems related to cancer treatment.
Meanwhile, Helton is creating a study that will use DTI to identify tumor margins and locate white matter tracts before surgeons make their first incisions.
“Surgeons don’t want to take too much tissue,” Helton says. “They don’t want to take normal brain. But they don’t want to leave any tumor behind, either. DTI is a beautiful tool, and it holds a lot of promise for helping to define the exact borders of tumors. It can help you define which white matter tracts are displaced; it can help us determine whether the tumor’s operable; and it can help surgeons plan surgical approaches before they even get to the operating room.”
Helton’s study will be the first in the world to use DTI to plan brain surgeries for children. “In other places, they’re using DTI to look at treatment effects on kids who’ve had medulloblastoma [a brain tumor],” Helton says, “but no one has reported using it to plan surgery on kids.”
Helton is also planning to use DTI to study the brains of children with sickle cell disease. Children with sickle cell disease are 250 times more likely to have strokes than healthy individuals. “I want to use DTI to look at the white matter of children with sickle cell,” Helton says. “This study may actually help us design earlier, more aggressive treatment for kids with sickle cell disease.”
Rainbows on tap
Before Morgan’s operation, Sanford explained how the brilliant colors of the DTI scan would help him excise the tumor and leave the healthy tissue intact. Morgan, her family and their friends immediately began praying that Sanford would be guided by a “rainbow of color.” At that time, they were unaware that the hues of DTI were actually created by the diffusion of water molecules.
“God did provide Dr. Sanford with a rainbow of color to decipher the good tissue from the tumor,” observes Kim. “It was this rainbow from the very source of life—water—that aided Dr. Sanford.”
Today, Morgan Cox has almost completed her radiation treatments and is looking forward to the time when she can return to a life that encompasses carefree dips in the pool. Morgan’s mom says that the experience has led the family to new depths of faith. “God is in control,” she asserts. “He led us to Dr. Sanford, provided an opportunity to be part of this new development and He continues to show us ‘rainbows’ every day.
“After all,” she continues, “you can’t have a rainbow without water.”
Reprinted from Promise magazine, winter 2004.