Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Medical Biophysics

Supervisor

Baron, Corey A.

2nd Supervisor

Khan, Ali.

Co-Supervisor

Abstract

Diffusion Magnetic Resonance Imaging (dMRI) is a non-invasive technique that examines the microscopic organization of brain tissues by measuring the random motion of water molecules. Advances like b-tensor encoding have enhanced the ability to distinguish between isotropic and anisotropic diffusion, providing deeper insights into complex tissue structures. This study evaluates the impact of echo time (TE) on dMRI parameters in white matter (WM), cortical gray matter (GM), and deep gray matter (DGM). Using multiple TE values and integrating free water elimination (FWE), we identified significant tissue-specific sensitivities to TE, particularly in kurtosis metrics within DGM. While WM exhibited minimal sensitivity to TE, cortical GM and DGM showed notable variations, reflecting their intricate microstructural properties. These results emphasize the importance of standardized imaging protocols to ensure consistency and reproducibility across institutions. Additionally, TE-sensitive metrics hold potential as biomarkers for diagnosing and monitoring neurological conditions that affect GM and DGM, such as Alzheimer’s disease and stroke. Future studies should aim to disentangle the effects of TE and diffusion time to deepen our understanding and apply these findings to clinical settings.

Keywords: Diffusion Magnetic Resonance Imaging, B-tensor Encoding, Microstructure, Echo Time.

Summary for Lay Audience

The brain is a highly organized network of tissues that allows us to think, feel, and move. Scientists can study its structure and health by tracking how water moves within the brain using a technique called diffusion MRI (dMRI). This water movement changes based on the size, shape, and arrangement of brain cells, offering valuable insights into brain function.

This study examined how a specific scanning setting, called echo time (TE), influences what we see in dMRI images. Researchers focused on different types of brain tissue, including white matter, which helps send signals, and gray matter, which processes information. The results showed that deeper regions, such as the thalamus and hippocampus, were particularly affected by changes in TE, likely due to their complex cellular makeup. These findings are important for improving brain imaging accuracy and ensuring that scans are consistent across hospitals and research facilities.

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