In vivo high-resolution magnetic resonance imaging
Abstract/Contents
- Abstract
- Magnetic resonance imaging is a powerful, non-invasive modality that provides excellent soft-tissue contrast, but it suffers from a relatively low signal-to-noise ratio and is inherently prone to artifacts. Although technological progress over the last few decades has dramatically enhanced the resolution and quality of magnetic resonance images, specific clinical challenges highlight the need for further improvements. First, patients with peripheral arterial disease are at high risk for developing skin ulcers, which are often detected at a late stage, when amputation is the only treatment option. High-resolution imaging might detect changes in skin early enough to enable alternative treatments. Second, higher-resolution larynx imaging is highly desirable for the exact assessment of cartilage invasion, which is a critical step in cancer staging and in the selection of the appropriate treatment. High-resolution skin and larynx magnetic resonance imaging poses specific engineering challenges. The resolution of magnetic resonance images is first hampered by insufficient signal-to-noise ratio. Dedicated surface coils and/or higher field strengths overcome this limitation. Receive-only and transmit/receive 1-inch-diameter coils are shown to be suitable for skin imaging at 1.5 T, 3 T, and 7 T, and a dedicated three-channel array for larynx imaging provides a dramatic increase in resolution over the conventionally used 8-channel neurovascular array. The next engineering challenge involves eliminating artifacts from high-resolution images. Chemical shift artifacts are a concern in skin imaging, especially at higher field strengths, because the hypodermis is a fat layer. A multi-echo sequence is introduced that separates fat and water and provides good signal-to-noise ratio for all skin layers. Motion artifacts affect both skin and larynx images. In skin, where motion is usually rigid-body, navigator-based motion correction proves effective, and navigators can be integrated into the multi-echo sequence that separates fat and water. In larynx, where motion is complex, a new real-time algorithm combining a reacquisition strategy with navigator-based motion correction accounts for the different types of motion. One additional concern with skin imaging at higher field strengths is the increase in the spin-lattice relaxation time T1, which compromises the signal-to-noise ratio. Robust T1 mapping requires the use of a 4-parameter model. A novel nonlinear Least-Squares algorithm reduces the complex minimization problem to a straightforward 1D search, making the fitting procedure much faster. T1 mapping performed in skin at 1.5 T, 3 T, and 7 T shows that the increase in T1 slightly attenuates the benefits of higher field strengths but does not offset them.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2010 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Barral, Joelle |
|---|---|
| Associated with | Stanford University, Department of Electrical Engineering |
| Primary advisor | Nishimura, Dwight George |
| Primary advisor | Pauly, John (John M.) |
| Thesis advisor | Nishimura, Dwight George |
| Thesis advisor | Pauly, John (John M.) |
| Thesis advisor | Damrose, Edward J |
| Thesis advisor | Conolly, Steven |
| Advisor | Damrose, Edward J |
| Advisor | Conolly, Steven |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Joëlle Karine Barral. |
|---|---|
| Note | Submitted to the Department of Electrical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2010. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2010 by Joelle Barral
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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