Reproducibility and use of myelin imaging methods for the study of adolescent brain development
Year: 2017
Type: dissertation
Study design: Observational Study
Abstract: Human brains have few myelinated axons at birth and continue to myelinate along a temporal and regional specific pattern into adulthood.This prolonged growth trajectory not only contributes to adaptability in functional circuitry, but also presents a vulnerability to certain psychiatric and behavioral disorders.MRI is highly sensitive to tissue constituents such as myelin membranes, but standard imaging techniques are typically limited to depicting macrostructure, such as gross white matter volumes and fiber tracts.More recently, quantitative in vivo myelin imaging has improved via developments in tissue modeling, pulse sequence design, and use of ultra high-field scanners.This dissertation examines the reproducibility and application of two recently developed MRI techniques with sensitivity to myelin content in white matter.First, multiexponential modeling of multiple gradient echo T2* decay curves was used to extract an estimate of myelin content, i.e., myelin water fraction (fMW), at two field strengths (3 T and 7 T) using in vivo and simulated data.At 3 T, model parameters were dominated by noise when compared to 7 T; however, artifacts impeded the assessment of in vivo results at 7 T for use in future studies.To further generalize the effects of noise and myelin parameter estimation, the T2*-based myelin water estimate, fMW, was compared to an alternative indicator of myelin content, the macromolecular proton fraction (fMT), using a newly developed magnetization transfer (MT) technique.All data were acquired at 3 T in iv a cohort of healthy adolescents (ages 12.7 -16.8).The fMT was ten times less variable, and thus more reproducible, versus the fMW.For the final study, the MT approach was applied in a longitudinal study of healthy adolescent development.Here, fMT was found to significantly increase in frontal white matter (p=0.003) over an 18 month delta in mid-to late-adolescence.There were no changes greater than 15% for any white matter region; in addition, changes within individuals were relatively small, averaging 2.5% for the frontal region.As myelin imaging techniques are becoming more widely used, these studies are important for understanding the sensitivity and reproducibility of new measures prior to widespread use in clinical and research applications.v ACKNOWLEDGEMENTS I'd like to share my immense thanks to an unbelievable group of family, friends, and colleagues.First, thank you to my thesis co-advisors, John VanMeter and Jeff Duyn for granting me the flexibility to explore new ideas along an often circuitous path.I have truly valued your guidance, perspective, and thoughtful mentorship.To my lab advisor, Peter van Gelderen -thank you for challenging me and being unendingly patient.I am grateful to have learned so much from you.With two thesis labs, comes the benefit of twice the labmates.To CFMI/ADS -thank you for supporting my projects, even when said projects (temporarily) disrupted the scanner.To AMRI -the quadrant has been my home base, and that goes without saying how special everyone in the lab and the surrounding halls of NIH have made this experience.In particular, thank you Catie Chang for listening, teaching, and always smiling.To those far and wide -thank you Dominic Hare and Nikola Stikov for your mentorship and fostering my enthusiasm for collaboration.To those close to home -thank you for making DC the best possible place to study and grow as a scientist.Britt, Caitlin, Lauren, Patrick, and Brian -thank you for your constant support and happiness, at any and all times.To those at home -thank you Teddy, Steph, and Mariam for making Salem Lane such a magical
Author: Erika P. Raven
Language: English
Subfield: Radiology, Nuclear Medicine and Imaging
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2761179180