Advances in Myelin Water Imaging and Stack-of-Spirals MRI: Image Reconstruction and Parameter Estimation

Myelin content plays a critical role in healthy brain function. Myelin water imaging is a quantitative MRI technique that aims to image the myelin content in the brain. Characterizing and quantifying the exchange dynamics in myelin could lead to better understanding of the role of myelin loss in several neurological disorders. This dissertation introduces a method to estimate myelin water exchange in white matter, using MRI experiment design. We optimized the acquisition parameters of a set of phase-cycled bSSFP acquisitions using a cost function based on the Cramer-Rao bound, and obtained low coefficients of variation for estimating myelin water exchange in white matter.

Validating the obtained myelin water exchange maps in vivo is a challenging problem. This dissertation also explores the design and use of an aqueous urea system to validate our proposed bSSFP acquisitions for estimating exchange. To potentially translate our proposed acquisitions to clinically feasible settings, undersampling is an important consideration to bring down scan time. This dissertation studies an undersampling scheme based on stack-of-spirals MRI. We developed an efficient implementation for the 3D NUFFT-based forward model for stack-of-spirals MRI, in the presence of off-resonance effects.

Co Chairs: Dr. Jeffrey A. Fessler and Dr. Jon-Fredrik Nielsen