Diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging
<p>Diffusion-weighted (DW) magnetic resonance imaging is an important neuroimaging technique that has successful applications in diagnosis of ischemic stroke and methods based on diffusion tensor imaging (DTI). Tensor measures have been used for detecting changes in tissue microstructure and f...
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| Format: | Thesis |
| Language: | English |
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2012
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| _version_ | 1826285725406986240 |
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| author | Frost, S |
| author2 | Jezzard, P |
| author_facet | Jezzard, P Frost, S |
| author_sort | Frost, S |
| collection | OXFORD |
| description | <p>Diffusion-weighted (DW) magnetic resonance imaging is an important neuroimaging technique that has successful applications in diagnosis of ischemic stroke and methods based on diffusion tensor imaging (DTI). Tensor measures have been used for detecting changes in tissue microstructure and for non-invasively tracing white matter connections <em>in vivo</em>. The most common image acquistion strategy is to use a DW single-shot echo-planar imaging (ss-EPI) pulse sequence, which is attractive due to its robustness to motion artefacts and high imaging speed. However, this sequence has limited achievable spatial resolution and suffers from geometric distortion and blurring artefacts.</p> <p>Readout-segmented echo-planar imaging (rs-EPI) is a DW sequence that is capable of acquiring high-resolution images by segmenting the acquisition of k- space into multiple shots. The fast, short readouts reduce distortion and blurring and the problem of artefacts due to motion-induced phase changes between shots can be overcome with navigator techniques.</p> <p>The rs-EPI sequence has two main shortcomings. (i) The method is slow to produce image volumes, which is limiting for clinical scans due to patient welfare and prevents us from acquiring very many directions in DTI. (ii) The sequence (like other diffusion techniques) is far from the optimum repetition time (TR) for acquiring data with the highest possible signal-to-noise ratio (SNR) in a given time. The work in this thesis seeks to address both of these important issues using a range of approaches.</p> <p>In Chapter 4 a partial Fourier extension is presented, which addresses point (i) by reducing the number of readout segments acquired and estimating the missing data. This allows reductions in scan time by approximately 40% and the reliability of the images is demonstrated in comparisons with the original images.</p> <p>The application of a simultaneous multi-slice scheme to rs-EPI, to address points (i) and (ii), is described in Chapter 5. Using the slice-accelerated rs-EPI sequence, tractography data were compared to ss-EPI data and high-resolution trace-weighted data were acquired in clinically relevant scan times.</p> <p>Finally, a 3D multi-slab extension that addresses point (i) is presented in Chapter 6. A 3D sequence could also allow higher resolution in the slice direction than 2D multi-slice methods, which are limited by the difficulties in exciting thin, accurate slices. A 3D version of rs-EPI was simulated and implemented and a k-space acquisition synchronised to the cardiac cycle showed substantial improvements in image artefacts compared to a conventional k-space acquisition.</p> |
| first_indexed | 2024-03-07T01:33:08Z |
| format | Thesis |
| id | oxford-uuid:94421cdc-6bcb-49c2-b9d9-64e016b875f8 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T01:33:08Z |
| publishDate | 2012 |
| record_format | dspace |
| spelling | oxford-uuid:94421cdc-6bcb-49c2-b9d9-64e016b875f82022-03-26T23:38:09ZDiffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imagingThesishttp://purl.org/coar/resource_type/c_db06uuid:94421cdc-6bcb-49c2-b9d9-64e016b875f8Diffusion tensor imagingBrain--Magnetic resonance imagingDiffusion magnetic resonance imagingMagnetic resonance imagingEnglishORA Deposit2012Frost, SJezzard, PMiller, K<p>Diffusion-weighted (DW) magnetic resonance imaging is an important neuroimaging technique that has successful applications in diagnosis of ischemic stroke and methods based on diffusion tensor imaging (DTI). Tensor measures have been used for detecting changes in tissue microstructure and for non-invasively tracing white matter connections <em>in vivo</em>. The most common image acquistion strategy is to use a DW single-shot echo-planar imaging (ss-EPI) pulse sequence, which is attractive due to its robustness to motion artefacts and high imaging speed. However, this sequence has limited achievable spatial resolution and suffers from geometric distortion and blurring artefacts.</p> <p>Readout-segmented echo-planar imaging (rs-EPI) is a DW sequence that is capable of acquiring high-resolution images by segmenting the acquisition of k- space into multiple shots. The fast, short readouts reduce distortion and blurring and the problem of artefacts due to motion-induced phase changes between shots can be overcome with navigator techniques.</p> <p>The rs-EPI sequence has two main shortcomings. (i) The method is slow to produce image volumes, which is limiting for clinical scans due to patient welfare and prevents us from acquiring very many directions in DTI. (ii) The sequence (like other diffusion techniques) is far from the optimum repetition time (TR) for acquiring data with the highest possible signal-to-noise ratio (SNR) in a given time. The work in this thesis seeks to address both of these important issues using a range of approaches.</p> <p>In Chapter 4 a partial Fourier extension is presented, which addresses point (i) by reducing the number of readout segments acquired and estimating the missing data. This allows reductions in scan time by approximately 40% and the reliability of the images is demonstrated in comparisons with the original images.</p> <p>The application of a simultaneous multi-slice scheme to rs-EPI, to address points (i) and (ii), is described in Chapter 5. Using the slice-accelerated rs-EPI sequence, tractography data were compared to ss-EPI data and high-resolution trace-weighted data were acquired in clinically relevant scan times.</p> <p>Finally, a 3D multi-slab extension that addresses point (i) is presented in Chapter 6. A 3D sequence could also allow higher resolution in the slice direction than 2D multi-slice methods, which are limited by the difficulties in exciting thin, accurate slices. A 3D version of rs-EPI was simulated and implemented and a k-space acquisition synchronised to the cardiac cycle showed substantial improvements in image artefacts compared to a conventional k-space acquisition.</p> |
| spellingShingle | Diffusion tensor imaging Brain--Magnetic resonance imaging Diffusion magnetic resonance imaging Magnetic resonance imaging Frost, S Diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging |
| title | Diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging |
| title_full | Diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging |
| title_fullStr | Diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging |
| title_full_unstemmed | Diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging |
| title_short | Diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging |
| title_sort | diffusion weighted magnetic resonance imaging with readout segmented echo planar imaging |
| topic | Diffusion tensor imaging Brain--Magnetic resonance imaging Diffusion magnetic resonance imaging Magnetic resonance imaging |
| work_keys_str_mv | AT frosts diffusionweightedmagneticresonanceimagingwithreadoutsegmentedechoplanarimaging |