#8 Integration of Diffusion Tensor Imaging (Tractography)

Overview

If you wanted to know how the halogen headlights in your automobile worked but only looked at the switch on the dashboard, and ignored all the wiring that goes from the switch to the battery and lights, you’d never understand the system. In a way, that’s how it used to be in the study of the brain before the recent introduction of diffusion tensor imaging (DTI) unveiled the all-important fiber pathways that connected the hundreds of billions of neurons in the brain.

DTI is the new technology that allows neuroscientists to non-invasively probe the long-neglected half of the brain called white matter, with its densely packed collection of intertwining insulated projections of neurons that join all four of the brain’s lobes, allowing them to communicate with each other.

Previously, permanent damage could often occur to white matter during brain surgery, because technologies were not available to give neurosurgeons an accurate roadmap of white matter pathways.

With DTI, however, neuroscientists can locate the orientation of nerve fiber bundles. This allimportant information is now used in surgical planning and prognosis, allowing experts to accurately map the living brain noninvasively. The results are presented in stunning two-and three-dimensional color images, which are available at the time of surgery. The images can be integrated with the three-dimensional localization system to precisely localize pathways with the exact part of the brain viewed by the surgeon.

“White matter comprises almost half of the brain, providing the connectivity and allowing the brain to perform its many mental operations,” says Micheal D. Phillips, M.D., a neuroradiologist at the Imaging Institute at the Cleveland Clinic. “Until we had diffusion tensor imaging, which measures the movement of water in the brain to infer the location of white matter fibers that link brain regions, we had no imaging method to accurately localize connecting pathways. DTI is helping us create the detailed spatial wiring map of the brain.”

Using diffusion tensor technology, for example, doctors can look at the specific pathway that connects brain regions responsible for understanding speech with the brain region responsible for producing speech. Water diffusion in the region of the pathway is greatest parallel to the pathway fibers. Using this knowledge, doctors can map out the pathway called the arcuate fasciculus, which is critical for normal conversational speech. Importantly, knowing the exact position of this pathway would allow a surgeon to avoid injuring the pathway during surgery.

“When it comes to neuroimaging, DTI is the game-changing technology for how we now understand and map the brain,” says Dr. Phillips. “We haven’t seen anything like this since the introduction of MRI in the 1980s.”

Where Are They Now

This technology is providing important information for neuroscientists probing the long neglected portion of the brain known as white matter, with its densely packed collection of intertwining fibers that allows neurons in the lobes of the brain to communicate with each other. Prior to the development of this technique, assessment of these critical areas was impossible in the living brain. This approach, which employs a modified version of magnetic resonance imaging, is being evaluated in a number of clinical applications.

One particularly important area may be its use in preoperative planning prior to invasive neurologic procedures. Since this is the only non-invasive technique that allows in vivo dissection of white matter tracts, it is increasingly used in pre-surgical mapping in tumors located in the areas of the brain that allow us to communicate, perceive, interact, and have movement. A new application of tractography is in the field of sports medicine to analyze muscle fibers for injuries and changes that occur due to different types of exercise. This enhanced imaging is allowing doctors to create tailored training programs for athletes for better recovery and injury prevention. The company behind this device has recently implemented their technology into one of its first locations in 2016 which will provide the hospital and their patients to immediate access to brain pathway imagery. The hopeful impact of this technology is smaller incisions, shorter recovery times for patients and the preservation of both vital brain and spinal cord functions.

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