Robust Fat and Fluid Suppression in MR Imaging: Technical Developments and Advanced Clinical Applications

Fat and fluid suppression methods are widely used in MR imaging to improve the lesion conspicuity, reduce the artifacts, increase quantification accuracy etc. However, these methods often suffer from either low signal to noise ratio (SNR), incomplete fat suppression or long scan times in some challenging clinical applications, such as MR Neurography, abdominal imaging, whole-body imaging and diffusion-weighted imaging. The research in this thesis aims to improve and develop MR sequences and reconstruction methods for robust fat and fluid suppression in several advanced clinical applications. The first topic of this thesis focuses on improving fat suppression. A frequency offset corrected inversion (FOCI) pulse based short tau inversion recovery (STIR) sequence was developed to improve the fat suppression in brachial plexus imaging, where large B1 and B0 inhomogeneities are often encountered. However, similar to the conventional STIR, it suffers from low SNR. Then, a multi-echo Dixon based variable flip angle TSE sequence was implemented for robust fat suppression with improved SNR and blood suppression, increasing the visualization of brachial plexus. The multi-echo Dixon method was later extended to single shot TSE (SShTSE) sequence to improve the fat suppression in breathhold abdominal imaging, where the commonly used fat suppression method (SPAIR) suffers from incomplete fat suppression due to the large B0 inhomogeneities. The second topic was simultaneous fat and fluid suppression. A dual-echo 3D TSE sequence combined with multi-echo Dixon was developed to generate simultaneous fat and fluid suppressed images of the cervical spines in a single acquisition. It can also simultaneously generate the standard T2-weighted image, fluid suppressed image and myelogram, significantly reducing the total scan time compared to the current clinical protocols. Then a fast whole-body MR imaging (7 min) sequence was developed for metastatic cancer detection by combining the simultaneous fat and fluid suppression method with the SShTSE acquisition. The images generated from the proposed sequence showed good lesion conspicuity without EPI-associated geometric distortions. Finally, the multi-echo Dixon was implemented with the TSE-based diffusion-weighted imaging sequence, to generate distortion-fee diffusion images with improved fat suppression and lesion conspicuity in areas with large B0 inhomogeneities, such as cervical spinal cord.