Magnetic resonance imaging (MRI) is a powerful and flexible medical imaging modality that can provide excellent morphological and functional information non-invasively. However, MRI is inherently signal-limited. There is a trade-off between the various desired goals of high signal-to-noise ratio (SNR), high contrast-to-noise ratio (CNR), broad spatial field-of-view (FOV), fine spatial resolution, and short scan tune. This dissertation presents efficient acquisition methods for MRI based on a particular concentric rings data sampling trajectory, which can achieve a more flexible trade-off between the many imaging objectives.
The concentric rings non-Cartesian readout trajectory samples data on a polar grid in spatial frequency k-space with a set of concentric circles. The unique circular sampling property of concentric rings enables a reduction in scan time compared to conventional Cartesian encoding while maintaining a high degree of robustness to imperfections that limit the application of other non-Cartesian trajectories.
A detailed account of concentric rings implementation procedures is presented to support both three-dimensional spatial and one-dimensional spectral encoding. Simultaneous encoding of spatial and spectral dimensions is possible for the concentric rings by using an efficient retracing design that takes advantage of its circular symmetry. Trade-offs between spatial/spectral encoding are discussed and important properties are analyzed.
Off-resonance effects pose a major limitation to the application of non-Cartesian trajectories for MRI. Since the concentric rings retracing design can efficiently encode spatial/spectral information, off-resonance effects due to field inhomogeneity and chemical shift can be characterized and accounted for. Experimental results from in vivo fat/water imaging of the knee, head, larynx, and calf show that uniform and reliable fat/water separation can be achieved with the concentric rings. The concentric rings are also applied to the general case of MR spectroscopic imaging.
In addition to enabling efficient spatial/spectral encoding, the concentric rings trajectory can be used for efficient magnetization-prepared imaging. Concentric rings are inherently centric-ordered, provide smooth weighting in k-space, and enable shorter scan times—all of which are vital to magnetization-prepared imaging. Experimental results from in vivo volumetric brain imaging demonstrate that the concentric rings can achieve higher SNR and CNR within a shorter scan duration than conventional Cartesian-encoding methods.
In all of these imaging scenarios and for different anatomical regions, the concentric rings prove to be a robust readout trajectory that enables flexible trade-offs. The concentric rings are easy to implement and can be used to enhance a wide variety of clinical MRI applications.
|Advisor:||Nishimura, Dwight G.|
|School Location:||United States -- California|
|Source:||DAI-B 70/10, Dissertation Abstracts International|
|Subjects:||Biomedical engineering, Electrical engineering|
|Keywords:||Concentric rings, K-space trajectory, Magnetization|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be