Efficient Turbo Spin Echo Pulse Sequences for T2-Weighted Imaging and T2 Mapping

Abstract

Magnetic Resonance Imaging techniques such as Turbo Spin Echo (TSE) are routinely used in the clinic for the diagnosis of a variety of pathologies using tissue properties based on T2 relaxation for image contrast. Quantitative estimation of T2 relaxation using T2 maps can be used to further improve the quality of diagnosis in applications including cardiac, abdominal, neurological, and musculoskeletal imaging. A two-dimensional (2D) radial TSE (RADTSE) pulse sequence was previously proposed for T2-weighted imaging and T2 mapping. While RADTSE enables accelerated and accurate estimation of T2, it suffers from reduced slice coverage for breath-held abdominal imaging and black-blood myocardial imaging, leading to a compromise between slice coverage and scan time. Furthermore, the 2D nature of this pulse sequence makes it unsuitable for thin slice isotropic voxel imaging due to hardware limitations and signal to noise ratio (SNR) degradation. This dissertation is aimed at the design and development of novel techniques to improve the utility of RADTSE for clinical applications, providing efficient slice coverage within shorter scan times while maintaining T2 estimation accuracy and an acceptable SNR. A RADTSE pulse sequence with very long echo train lengths and variable refocusing flip angles is proposed to improve the slice coverage of 2D abdominal breath-held imaging. Accurate T2 estimation in the presence of imperfect slice profiles is enabled by introducing a partial volume corrected estimation algorithm. A multi-band excitation technique is presented to improve the slice and SNR efficiency of double inversion RADTSE for cardiac imaging. Finally, a radial stack-of-stars TSE pulse sequence is introduced for three dimensional (3D) isotropic T2-weighted imaging and T2 mapping for neurological and musculoskeletal applications. Performance of the proposed approaches are validated using numerical simulations, phantom experiments, and in vivo clinical data. The proposed techniques provide diagnostic quality T2-weighted images and quantitative T2 maps within clinically acceptable scan times in the aforementioned applications.