Brain Tumor Center
To understand the importance of fiber tract mapping and diffusion tensor imaging (DTI), it is important to understand how the brain conducts signals.
The brain is composed of nerve cells called neurons. Neurons in the white matter of the brain have long, extending myelinated nerve fibers called axons. The myelin provides a protective cover for the axons and increases signal transmission speeds. White matter is found mainly in the central and subcortical regions of the brain. About 60% of the brain is white matter.
Grey matter is also composed of neurons, but these neurons do not have long extending axons covered with myelin. About 40% of the brain is gray matter.
The brain transmits electrical signals via the neurons. Each neuron communicates with other neurons that form networks among the cells. Neurons talk to each other through electrical and chemical signals.
The white matter of the brain allows communication to and from the grey matter and to and from other areas of the body. Messages are processed in the grey matter. Signaling goes on constantly with millions of signals to and from the grey matter every single day.
The specialized networks in the white matter are called tracts.
If the white matter of the brain is damaged, the brain can often develop alternative routes that bypass the damaged areas, allowing communication between white and grey matter to be maintained.
Although we know these brain tracts exist, they cannot be identified using conventional imaging techniques like magnetic resonance imaging (MRI) or computerized tomography (CT) scans.
Diffusion-weighted MRI evaluates brain water diffusion to identify potential damage to the nervous system, including the neurons in the brain. Diffusion describes the movement of molecules due to random thermal motion. The motion can be restricted by abnormalities in the brain tissue such as infection, ischemia or tumor. Diffusion that is restricted appears differently than diffusion that is not restricted. The diffusion is measured and assigned a number that represents the intensity of the restriction. If there is an abnormality in the brain tissue causing restriction of the molecules, the signal intensity will be higher. Computer algorithms help to create a three-dimensional model of diffusion magnitude. This information helps the neurosurgeon define the areas of damage.
Diffusion tensor imaging (DTI) is more specific to fiber tracts and is able to follow a nerve fiber from an axon in the white matter along its entire length. In this way, DTI provides information about connections between the various regions of the brain. DTI may also be used to determine whether functional white matter might be involved in a brain tumor. DTI helps to differentiate between malignant and benign tissue. It can also differentiate between tumor, edema or infarction in brain tissue. Each disease process produces a different intensity value. This technology allows the neurosurgeon to determine if a fiber tract is affected by a tumor and develop a surgical plan that is safer for the patient.
A 14 year old girl with general memory and learning impairment. Defect on the right shown with short straight arrows. Normal anatomy on the left shown with curved arrow. Abnormal segment noted with large straight arrow. These are areas of the limbic system, important in learning and memory.