Fast neuroimaging techniques in MRI [electronic resource]

Magnetic Resonance Imaging (MRI) is a non-invasive modality for neuroimaging that has been widely applied into various clinical and scientific studies. In many applications, one particular challenge for MRI is the scanning speed and efficiency. Three major novel fast neuroimaging techniques are presented in this work, including high-resolution 3D diffusion imaging (3D-SNAILS), an iterative reconstruction algorithm for high accelerating parallel imaging (PRUNO), and motion insensitive 3D non-contrast perfusion imaging (3D-PCASL-PROMO). 3D DWI and DTI provide attractive features such as isotropic resolution, high SNR and good tractography. However, 3D volumetric DWI/DTI scans suffer from long scan time and severe motion artifacts. In this project, a steady-state multi-shot pulse sequence is demonstrated to perform fast high resolution 3D diffusion imaging, in which 3D self-navigated interleaved rotating spirals (3D-SNAILS) are used as readout trajectories. This acquisition scheme has low sensitivity to motion induced phase errors and the inherent navigators can be utilized to further reduce motion artifacts. In vivo human/animal results have shown that this technique can be used to perform 3D high resolution DTI studies, particularly for animals with smaller brains. GRAPPA has been a successful k-space data-driven reconstruction algorithm for parallel imaging during the last decade. However, the performance of GRAPPA drops significantly as the accelerating factor increases. A novel iterative method termed parallel reconstruction using null operations (PRUNO) is developed in this project. In this approach, both data calibration and image reconstruction are formulated into generalized linear system equations based on intrinsic small k-space nulling kernels. And a conjugate-gradient (CG) method is proposed to solve the reconstruction equation feasibly. With more accurate problem formulation and higher calibration efficiency, PRUNO produces much better image quality than GRAPPA, especially under high accelerating factors. Pulsed continuous arterial spin labeling (PCASL) is a novel technique for 3D whole-brain perfusion imaging. However, a whole brain clinical PCASL protocol takes long imaging time due to multiple image acquisitions and averages. A real-time motion correction algorithm is thus desired for such a protocol. Prospective motion correction (PROMO) is a navigator based module, which can be easily inserted into various MR pulse sequences for real-time 3D motion estimation and correction. PROMO is successfully integrated into PCASL in this project. Our preliminary results show that the new pulse sequence is much more robust against patient motions and PROMO navigators have almost no negative influence to the imaging sequence. In addition, brief abstracts of two other fast imaging projects are also demonstrated in this dissertation, including a fast T2* imaging pulse sequence called iESGRE, and 7T diffusion imaging of rats using SNAILS.

Keywords: Electrical Engineering
Advisor: Moseley Michael E. (Michael Eugene)
Pauly John (John M.) primary advisor. Thesis advisor
Zaharchuk Greg advisor. Thesis advisor