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The Influence of Radio-Frequency Transmit Field Inhomogeneities on the Accuracy of G-ratio Weighted Imaging

Emmenegger, Tim M. ; David, Gergely ; Ashtarayeh, Mohammad ; Fritz, Francisco J. ; Ellerbrock, Isabel ; Helms, Gunther LU orcid ; Balteau, Evelyne ; Freund, Patrick and Mohammadi, Siawoosh (2021) In Frontiers in Neuroscience 15.
Abstract

G-ratio weighted imaging is a non-invasive, in-vivo MRI-based technique that aims at estimating an aggregated measure of relative myelination of axons across the entire brain white matter. The MR g-ratio and its constituents (axonal and myelin volume fraction) are more specific to the tissue microstructure than conventional MRI metrics targeting either the myelin or axonal compartment. To calculate the MR g-ratio, an MRI-based myelin-mapping technique is combined with an axon-sensitive MR technique (such as diffusion MRI). Correction for radio-frequency transmit (B1+) field inhomogeneities is crucial for myelin mapping techniques such as magnetization transfer saturation. Here we assessed the effect of B1+ correction on g-ratio weighted... (More)

G-ratio weighted imaging is a non-invasive, in-vivo MRI-based technique that aims at estimating an aggregated measure of relative myelination of axons across the entire brain white matter. The MR g-ratio and its constituents (axonal and myelin volume fraction) are more specific to the tissue microstructure than conventional MRI metrics targeting either the myelin or axonal compartment. To calculate the MR g-ratio, an MRI-based myelin-mapping technique is combined with an axon-sensitive MR technique (such as diffusion MRI). Correction for radio-frequency transmit (B1+) field inhomogeneities is crucial for myelin mapping techniques such as magnetization transfer saturation. Here we assessed the effect of B1+ correction on g-ratio weighted imaging. To this end, the B1+ field was measured and the B1+ corrected MR g-ratio was used as the reference in a Bland-Altman analysis. We found a substantial bias (≈-89%) and error (≈37%) relative to the dynamic range of g-ratio values in the white matter if the B1+ correction was not applied. Moreover, we tested the efficiency of a data-driven B1+ correction approach that was applied retrospectively without additional reference measurements. We found that it reduced the bias and error in the MR g-ratio by a factor of three. The data-driven correction is readily available in the open-source hMRI toolbox (www.hmri.info) which is embedded in the statistical parameter mapping (SPM) framework.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
axon volume fraction, B+ correction, diffusion MRI, magnetization transfer saturation, MR g-ratio, multi-parameter mapping, myelin volume fraction, radio-frequency transmit field inhomogeneities
in
Frontiers in Neuroscience
volume
15
article number
674719
publisher
Frontiers Media S. A.
external identifiers
  • pmid:34290579
  • scopus:85110849500
ISSN
1662-4548
DOI
10.3389/fnins.2021.674719
language
English
LU publication?
yes
id
4b43824c-c67f-48d1-8063-ec13bcb4dd5b
date added to LUP
2021-08-20 13:27:35
date last changed
2024-09-07 22:53:16
@article{4b43824c-c67f-48d1-8063-ec13bcb4dd5b,
  abstract     = {{<p>G-ratio weighted imaging is a non-invasive, in-vivo MRI-based technique that aims at estimating an aggregated measure of relative myelination of axons across the entire brain white matter. The MR g-ratio and its constituents (axonal and myelin volume fraction) are more specific to the tissue microstructure than conventional MRI metrics targeting either the myelin or axonal compartment. To calculate the MR g-ratio, an MRI-based myelin-mapping technique is combined with an axon-sensitive MR technique (such as diffusion MRI). Correction for radio-frequency transmit (B1+) field inhomogeneities is crucial for myelin mapping techniques such as magnetization transfer saturation. Here we assessed the effect of B1+ correction on g-ratio weighted imaging. To this end, the B1+ field was measured and the B1+ corrected MR g-ratio was used as the reference in a Bland-Altman analysis. We found a substantial bias (≈-89%) and error (≈37%) relative to the dynamic range of g-ratio values in the white matter if the B1+ correction was not applied. Moreover, we tested the efficiency of a data-driven B1+ correction approach that was applied retrospectively without additional reference measurements. We found that it reduced the bias and error in the MR g-ratio by a factor of three. The data-driven correction is readily available in the open-source hMRI toolbox (www.hmri.info) which is embedded in the statistical parameter mapping (SPM) framework.</p>}},
  author       = {{Emmenegger, Tim M. and David, Gergely and Ashtarayeh, Mohammad and Fritz, Francisco J. and Ellerbrock, Isabel and Helms, Gunther and Balteau, Evelyne and Freund, Patrick and Mohammadi, Siawoosh}},
  issn         = {{1662-4548}},
  keywords     = {{axon volume fraction; B+ correction; diffusion MRI; magnetization transfer saturation; MR g-ratio; multi-parameter mapping; myelin volume fraction; radio-frequency transmit field inhomogeneities}},
  language     = {{eng}},
  publisher    = {{Frontiers Media S. A.}},
  series       = {{Frontiers in Neuroscience}},
  title        = {{The Influence of Radio-Frequency Transmit Field Inhomogeneities on the Accuracy of G-ratio Weighted Imaging}},
  url          = {{http://dx.doi.org/10.3389/fnins.2021.674719}},
  doi          = {{10.3389/fnins.2021.674719}},
  volume       = {{15}},
  year         = {{2021}},
}