Accelerated Quantitative Magnetization Transfer (qMT) Imaging

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Quantitative magnetization transfer (qMT) is an advanced magnetic resonance imaging (MRI) technique with enhanced specificity to myelin. The acquisition of many images with unique magnetization transfer (MT) saturation results in a signal response curve known as the z-spectrum. The two-pool tissue model, which describes properties of nuclei with free and restricted motion, can be fit to the z-spectrum to provide details of macromolecular tissue content (including myelin) beyond what can be seen from conventional single saturation approaches (e.g. MT ratio). Widespread use of qMT has been hindered by long acquisition times inherent to z-spectrum-based imaging techniques including qMT and chemical exchange saturation transfer (CEST). This thesis uses sparseSENSE, a combined parallel imaging and compressed sensing technique, to accelerate MT-weighted images. In this thesis, sparsifying reconstruction algorithms are shown to enable high-quality image reconstruction from 4D qMT datasets, retrospectively under-sampled by factors of up to 32. MT-weighted images demonstrate exceptional image quality at high acceleration factors, which is shown to translate well to accelerated z-spectra. However, qMT parametric maps produced from accelerated z-spectra are shown to be sensitive to acceleration artifacts and can only be accelerated by a factor of 4 with minimal loss of image quality. Nonetheless, this acceleration can yield a significant acquisition time savings when applied to prospectively under-sampled data. In addition, time savings created by acceleration can be used to increase spatial resolution or collect more MT-weighted images, enabling even higher acceleration factors. Long acquisition times have often been cited as a limitation of the qMT method. This work has addressed that limitation, making qMT protocols more feasible for in vivo research studies, particularly in youth and patient populations.
MRI, qMT, Compressed Sensing, Magnetization Transfer
Mclean, M. A. (2018). Accelerated Quantitative Magnetization Transfer (qMT) Imaging (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/33223