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Novoselova, Maria

University of British Columbia

Myelin is an important biomarker for neurodegenerative diseases such as multiple sclerosis. It is for this reason that there has been a concerted effort to enhance myelin imaging techniques. Two established methods in this pursuit are myelin water imaging (MWI) and inhomogeneous magnetization transfer (ihMT). Combining these approaches has the potential to further elucidate the microenvironment surrounding myelin. In this study, the viability of this joint method is investigated on a 9.4 Tesla magnetic resonance imaging (MRI) scanner, focusing on pulse sequence implementation and optimizations. The method is then applied to a cohort of 17 formalin-fixed rat spinal cord samples, collected at various stages post-injury: six controls, five at 3 weeks post-injury, and six at 8 weeks post-injury, with the aim to gain insight on the myelin degradation process. Specifically, data with various levels of dipolar relaxation (T₁D) filtering was acquired, selecting for protons experiencing predominantly dipolar coupling, such as those within myelin. These datasets were then subjected to fitting within an expanded 4-pool model framework to extract T₁D for myelin and non-myelin semisolids, as an indirect measure of myelin content. It was discovered that the 9.4T scanner’s high field strength rendered the T₂ value of myelin water too short to be resolved under standard imaging conditions, despite advantages in improved resolution and SNR. This led to truncated myelin water peaks within the T₂ distributions, consequently distorting area estimates under these curves. Additionally, it impeded the scanner’s ability to detect the impact of dual saturation pulses on the myelin water compartment, thereby obstructing subsequent analyses such as determining T₁D. This work underscores the importance of considering field strength when pursuing myelin imaging, highlighting the need for exploration at lower field strengths to harness the full diagnostic potential of this method.

Text

2023-10-18

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86183

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/