Afzali, M, Aja-Fernández, S and Jones, DK (2020) Direction-averaged diffusion-weighted MRI signal using different axisymmetric B-tensor encoding schemes. Magnetic Resonance in Medicine, 84 (3). pp. 1579-1591. ISSN 0740-3194
Abstract
Purpose
It has been shown, theoretically and in vivo, that using the Stejskal-Tanner pulsed-gradient, or linear tensor encoding (LTE), and in tissue exhibiting a “stick-like” diffusion geometry, the direction-averaged diffusion-weighted MRI signal at high b-values (7000 < b < 10000 s∕mm2) follows a power-law, decaying as 1∕√b. It has also been shown, theoretically, that for planar tensor encoding (PTE), the direction-averaged diffusion-weighted MRI signal decays as 1/b. We aimed to confirm this theoretical prediction in vivo. We then considered the direction-averaged signal for arbitrary b-tensor shapes and different tissue substrates to look for other conditions under which a power-law exists.
Methods
We considered the signal decay for high b-values for encoding geometries ranging from 2-dimensional PTE, through isotropic or spherical tensor encoding to LTE. When a power-law behavior was suggested, this was tested using in silico simulations and, when appropriate, in vivo using ultra-strong (300 mT/m) gradients.
Results
Our in vivo results confirmed the predicted 1/b power law for PTE. Moreover, our analysis showed that using an axisymmetric b-tensor a power-law only exists under very specific conditions: (a) “stick-like” tissue geometry and purely LTE or purely PTE waveforms; and (b) "pancake-like" tissue geometry and a purely LTE waveform.
Conclusions
A complete analysis of the power-law dependencies of the diffusion-weighted signal at high b-values has been performed. Only three specific forms of encoding result in a power-law dependency, pure linear and pure PTE when the tissue geometry is “stick-like” and pure LTE when the tissue geometry is "pancake-like". The different exponents of these encodings could be used to provide independent validation of the presence of different tissue geometries in vivo.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2020 The Authors. This is an open access article under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0) (https://creativecommons.org/licenses/by/4.0/) |
Keywords: | B-tensor encoding; diffusion-weighted MRI; direction-averaged diffusion signal; high b-value; power-law |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Medicine and Health (Leeds) > School of Medicine (Leeds) > Leeds Institute of Cardiovascular and Metabolic Medicine (LICAMM) > Biomedical Imaging Science Dept (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 10 Jun 2022 13:54 |
Last Modified: | 10 Jun 2022 13:54 |
Status: | Published |
Publisher: | Wiley |
Identification Number: | 10.1002/mrm.28191 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:187654 |