Understanding the Brain: The Neurobiology of

Everday Life

Diffusion Tensor Imaging Use in Stroke Patients to Predict Motor Outcome

For the Neurobiology of Everyday Life Coursera MOOC, I would like to share some research on my Masters project in Biomedical Engineering

and how this coures helped me understand the biological processes behind what I study.

Diffusion Tensor Imaging

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Non-DiffusionWeighted

Diffusion-WeightedMany Directions

Diffusion Tensor forEvery Voxel

Diffusion Weighted Imaging is a Magnetic Resonance Imaging technique that allows one to look at the diffusion of water in the brain.

The process consists of taking 1 or 2 “non-diffusion weighted images” to which one compares many “diffusion-weighted images”. This allows the computation of a “diffusion matrix”, which characterizes the direction of and magnitude of water diffusion in different parts of the brain.

Neurons

Beaulieu, C. 2002

Myelinated Axon

Brain TissueFree Diffusion Strongest

in Direction of Axon

Healthy Neurons

Why do we care about water diffusion in the brain ?

Water diffusion strength and direction is determined by the orientation of axons and degree of myelination !

By looking at diffusion of water in the brain, we can obtain information about the integrity of axons and neurons

Myelinated Axon

Brain TissueFree Diffusion Strongest

in Direction of Axon

Beaulieu, C. 2002

Damaged Neurons

When axons are damaged, for example, by stroke, degradation of internal structures makes water diffusion in the direction of the axon decrease

Also, because the myelin sheet and axonal membrane will eventually degrade, diffusion perpendicular to the axon will increase

Neurons

Stroke

Neuroscience, 2nd Ed., Purves, D. 2001

The artery that is most commonly affected by stroke is the middle cerebral artery which vascularizes the white matter tracts of the corticospinal tract as well as the basal ganglia, which are critical to movement of the upper and lower limbs !

My Project

Clinical Neuroanatomy & Neuroscience, 6th Ed., FitzGerald, MJ et al., 2012

I share with you an aspect of my Masters thesis: to look at how the integrity of axons change in response to ischemic stroke by looking at the diffusion of water in the axons.

By looking at the severity of the damage at early time points through “Diffusion Tensor Imaging”, we hope to be able to predict by how much a person can recover upper or lower limb strength months after stroke onset.

Parts of Nervous System Involved

Cellular Structures (Axonal Membrane, Myelin)

Axons

Cortical Spinal Tract

Here, the cellular components of the neurons in the cortical spinal tract are impaired by ischemic stroke, resulting in a decrease in motor strength, and dexterity of the upper and lower limbs

Objectives of the Study

The Neurobiology of Everyday Life has helped me understand my Masters project in several ways.

My undergraduate background was in physics and engineering, so the technological aspects of Magnetic Resonance Imaging and Diffusion Tensor Imaging are more familiar to me. I am therefore less proficient in the neurobiology of motor output and neuronal damage.

This course has helped me to bridge the gap between physics, engineering and neuroscience. I now understand better the biological origin of the signals we are measuring in MRI in our patient database and how to relate them to future motor outcome.

Above all, this course allows me to broaden my perspectives on how brain imaging techniques (such as MRI and DTI) can be used to study other pathologies by knowing their biological mechanisms and properties

References Internship

THANK YOU !

References Internship

Beaulieu, C. (2002). The basis of anisotropic water diffusion in the nervous system - a technical review. NMR in Biomedicine, 15(7-8), 435–55. doi:10.1002/nbm.782

Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001.

M. J. T. FitzGerald MD PhD DSC MRIA, Gregory Gruener MD MBA. Clinical Neuroanatomy and Neuroscience. 6th edition. Saunders; 2012