NEUROSCIENCE IMAGING
UCAIR is applying a variety of imaging techniques to answer questions concerning brain function and development. For example: What areas of the brain control which physical functions? How do diseases such as Multiple Sclerosis affect brain function? How is the brain "wired"?
Functional Magnetic Resonance Imaging - also see "MRI"
The purpose of fMRI is to determine which areas of the brain are active during specific tasks. The tasks can involve language, memory, vision, motion, imagined movement, speaking, or attention, to name a few. During an fMRI experiment, high-speed magnetic resonance images called "echo planar images" (EPI) are repeatedly acquired of a subjects brain while the subject performs a task such as flexing the fingers of one hand. Since the brain region that controls the hand is now working, the flow of oxygenated blood to that region increases. The increase in oxygenated blood slightly increases the signal in the EPI image.
Because the increase in signal is slight, it is not usually possible to see the change just by looking at one image. Instead, many images are acquired while the hand is held still, and many are acquired while the hand is flexed, and each area of the brain is statistically analyzed to see if the signal in that area was significantly increased when the person flexed their hand. The resulting collection of active regions is called an "activation map."
Activation maps are overlaid on an anatomic image of the brain to show where the signal changed most during the task. The activation maps are often in color, but that is only to distinguish them from the black-and-white anatomic images. The attached image shows fMRI activation for a subject with Multiple Sclerosis flexing their right hand. As expected, the motor strip on the left side was activated during the task (the color key - bottom right - indicates the extent of brain activation).
In conjunction with the newly formed Brain Institute and researchers from many other departments, Dr. Jim Lee is assisting with the acquisition of fMRI data on the new Siemens Trio (3 Tesla) magnet located at the Center for Advanced Medical Technologies (CAMT) in research park. The functional neuroimaging core is now meeting on Thursdays at 3:30.
Diffusion Magnetic Resonance Imaging
Diffusion-based MRI methods address the "wiring" of the brain and allow the physician or scientist to examine, in the conscious patient, how the axons within the white matter of the brain are oriented. The same technique can be applied to experimental animals to determine, as the animal grows, how the brain develops.
The formation of Magnetic Resonance Images relies on signals from hydrogen atoms within an individual's tissues. Since most hydrogen atoms are to be found in water ( H 2 O), a Magnetic Resonance image reflects both the presence of water and how the signals from the hydrogen atoms of that water are affected by the presence of other components of the tissue.
In pure water, the water molecules and the hydrogen atoms within them are in constant motion in all directions, which is to say, the diffusion of the water molecules is random and not limited to any particular direction. In tissues however, which are highly structured, diffusion or movement of water molecules may be limited to particular directions. For example, tissues which are composed of fibers partially constrain water diffusion to the long axis of the fiber. One such tissue is the white matter of the brain which is composed of long, thin extensions of nerve cells, termed axons,
Diffusion Weighted Imaging (DWI) and Diffusion Tensor Imaging (DTI) methods form images based on the direction of water diffusion. The direction of diffusion in turn reflects the orientation of the tissue fibers in which the water is contained. An image of the brain made by DTI thus reveals the direction of the axons composing the white matter. The image below shows a diffusion map overlayed on an anatomical image of the brain. Colors reflect the directions of water diffusion (up, down, right, left and in and out of the screen).
Multiple Sclerosis
Several diffusion imaging techniques with MRI are being improved and will be a great asset in the understanding and diagnosis and prognosis of multiple sclerosis. Dr. EK Jeong is especially involved in this effort.
