The Investigation and Development of High Angular Resolution Diffusion Imaging: The Evaluation of Diffusion Weighting and Improvement of Sampling Efficiency
Date Issued
2009
Date
2009
Author(s)
Cho, Kuan-Hung
Abstract
In past decade, the diffusion MRI has become an important approach to predict complex neural fiber connectivity between different brain regions in neuroscience and clinical fields. Comparing with conventional diffusion MRI techniques, high angular resolution diffusion imaging (HARDI) techniques provide the capability of resolving complex neural fiber architectures, such as intravoxel fiber crossing of white matter tracts. However, so far the HARDI techniques have not been extensively used in clinical application due to excessive scan time and the lack of the knowledge on such techniques for clinicians. Therefore, the main object of this dissertation is to facilitate the application of HARDI for clinicians.irst, we evaluated the q-related accuracy and angular resolution of estimating the complex fiber orientations for HARDI via phantom experiments. By illustrating the relationship between the inherent property of HARDI and the sequence parameters, we could help the psychologists or clinicians to understand how to get a better HARDI result or to set the parameters according to their demands. In our results, a more accurate estimation of fiber orientations was obtained when a higher SNR or lower q value was achieved. The angular resolution was also highly correspondent with the q value, i.e. a higher q value yielded a better angular resolution. It is a trade-off between the accuracy and the angular resolution to optimize the q value.Second, a hemi-spherical encoding scheme was proposed based on the spherically symmetric property of diffusion signals. With correcting for the cross-term, we can get accurate fiber orientation estimate and halve the scan time of HARDI simultaneously. Our results showed an obvious estimation error when using a hemi-spherical encoding scheme without correcting for the cross-term in comparison with the cross-term-free results. This estimation error could be reduced after correcting for the cross-term. Conclusively, the application in clinical and psychological filed would benefit from our studies, which provide the optimization strategy of HARDI and halve the total scan time.
Subjects
high angular resolution diffusion imaging
q-ball imaging
angular resolution
accuracy
hemi-spherical encoding scheme
cross-term correction
Type
thesis
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