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Bias field correction of MPRAGE by an external reference - The poor man's MP2RAGE

Olsson, Hampus LU ; Andersen, Mads LU and Helms, Gunther LU orcid (2021)
Abstract
Purpose:
To implement and evaluate a sequential approach to obtain semi-quantitative T1-weighted MPRAGE images, unbiased by B1 inhomogeneities at 7T.
Methods:
In the reference gradient echo used for normalization of the MPRAGE image, flip
angle (αGE) and acquisition voxel size (Vref) was varied to optimize tissue contrast and acquisition time (Tacq). The finalized protocol was implemented at three different resolutions and the reproducibility was evaluated. Maps of T1 were derived based on the normalized MPRAGE through forward signal modelling.
Results:
A good compromise between tissue contrast and SNR was reached at αGE=3°.... (More)
Purpose:
To implement and evaluate a sequential approach to obtain semi-quantitative T1-weighted MPRAGE images, unbiased by B1 inhomogeneities at 7T.
Methods:
In the reference gradient echo used for normalization of the MPRAGE image, flip
angle (αGE) and acquisition voxel size (Vref) was varied to optimize tissue contrast and acquisition time (Tacq). The finalized protocol was implemented at three different resolutions and the reproducibility was evaluated. Maps of T1 were derived based on the normalized MPRAGE through forward signal modelling.
Results:
A good compromise between tissue contrast and SNR was reached at αGE=3°. A
reduction of the reference GE Tacq by a factor of 4, at the cost of negligible bias, was obtained by increasing Vref with a factor of 8 relative the MPRAGE resolution. The coefficient-ofvariation in segmented WM was 9±5% after normalization, compared to 24±12% before. The T1 maps showed no obvious bias and had reasonable values with regard to literature, especially after optional B1 correction through separate flip angle mapping.
Conclusion:
A non-interleaved acquisition for normalization of MPRAGE offers a simple
alternative to MP2RAGE to obtain semi-quantitative purely T1-weighted images. These
images can be converted to T1 maps analogously to the established MP2RAGE approach. Scan time can be reduced by increasing Vref which has a miniscule effect on image quality. (Less)
Please use this url to cite or link to this publication:
author
; and
organization
publishing date
type
Working paper/Preprint
publication status
published
subject
pages
23 pages
publisher
arXiv.org
project
Multiparametric mapping of the brain at 7T using gradient echoes
language
English
LU publication?
yes
id
ddc9d137-be8a-42f2-9743-d771c234c6c0
alternative location
https://arxiv.org/abs/2104.14020
date added to LUP
2021-04-30 09:17:16
date last changed
2022-03-16 14:00:56
@misc{ddc9d137-be8a-42f2-9743-d771c234c6c0,
  abstract     = {{Purpose: <br/>To implement and evaluate a sequential approach to obtain semi-quantitative T<sub>1</sub>-weighted MPRAGE images, unbiased by B<sub>1</sub> inhomogeneities at 7T.<br/>Methods: <br/>In the reference gradient echo used for normalization of the MPRAGE image, flip<br/>angle (α<sub>GE</sub>) and acquisition voxel size (<i>V</i><sub>ref</sub>) was varied to optimize tissue contrast and acquisition time (<i>Tacq</i>). The finalized protocol was implemented at three different resolutions and the reproducibility was evaluated. Maps of T<sub>1</sub> were derived based on the normalized MPRAGE through forward signal modelling.<br/>Results: <br/>A good compromise between tissue contrast and SNR was reached at α<sub>GE</sub>=3°. A<br/>reduction of the reference GE <i>T</i><sub>acq</sub> by a factor of 4, at the cost of negligible bias, was obtained by increasing <i>V</i><sub>ref</sub> with a factor of 8 relative the MPRAGE resolution. The coefficient-ofvariation in segmented WM was 9±5% after normalization, compared to 24±12% before. The T<sub>1</sub> maps showed no obvious bias and had reasonable values with regard to literature, especially after optional B<sub>1</sub> correction through separate flip angle mapping.<br/>Conclusion: <br/>A non-interleaved acquisition for normalization of MPRAGE offers a simple<br/>alternative to MP2RAGE to obtain semi-quantitative purely T<sub>1</sub>-weighted images. These<br/>images can be converted to T<sub>1</sub> maps analogously to the established MP2RAGE approach. Scan time can be reduced by increasing V<sub>ref</sub> which has a miniscule effect on image quality.}},
  author       = {{Olsson, Hampus and Andersen, Mads and Helms, Gunther}},
  language     = {{eng}},
  month        = {{04}},
  note         = {{Preprint}},
  publisher    = {{arXiv.org}},
  title        = {{Bias field correction of MPRAGE by an external reference - The poor man's MP2RAGE}},
  url          = {{https://lup.lub.lu.se/search/files/115180970/2104.14020.pdf}},
  year         = {{2021}},
}