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Radiofrequency bias correction of magnetization prepared rapid gradient echo MRI at 7.0 Tesla using an external reference in a sequential protocol

Olsson, Hampus LU ; Novén, Mikael LU ; Lätt, Jimmy LU ; Wirestam, Ronnie LU orcid and Helms, Gunther LU orcid (2021) In Tomography : a journal for imaging research 7(3). p.434-451
Abstract
At field strengths of 7 T and above, T1-weighted imaging of human brain suffers increasingly from radiofrequency (RF) B1 inhomogeneities. The well-known MP2RAGE (magnetization prepared two rapid acquisition gradient echoes) sequence provides a solution but may not be readily available for all MR systems. Here, we describe the implementation and evaluation of a sequential protocol to obtain normalized magnetization prepared rapid gradient echo (MPRAGE) images at 0.7,
0.8, or 0.9-mm isotropic spatial resolution. Optimization focused on the reference gradient-recalled echo (GRE) that was used for normalization of the MPRAGE. A good compromise between white-gray matter contrast and the signal-to-noise ratio (SNR) was reached at a flip... (More)
At field strengths of 7 T and above, T1-weighted imaging of human brain suffers increasingly from radiofrequency (RF) B1 inhomogeneities. The well-known MP2RAGE (magnetization prepared two rapid acquisition gradient echoes) sequence provides a solution but may not be readily available for all MR systems. Here, we describe the implementation and evaluation of a sequential protocol to obtain normalized magnetization prepared rapid gradient echo (MPRAGE) images at 0.7,
0.8, or 0.9-mm isotropic spatial resolution. Optimization focused on the reference gradient-recalled echo (GRE) that was used for normalization of the MPRAGE. A good compromise between white-gray matter contrast and the signal-to-noise ratio (SNR) was reached at a flip angle of 3° and total scan time was reduced by increasing the reference voxel size by a factor of 8 relative to the MPRAGE resolution. The average intra-subject coefficient-of-variation (CV) in segmented white matter (WM) was 7.9 ±3.3% after normalization, compared to 20 ±8.4% before. The corresponding inter-subject average CV in WM as 7.6 ±7.6% and 13 ±7.8%. Maps of T1 derived from forward signal modelling showed no obvious bias after correction by a separately acquired flip angle map. To conclude, 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 the reference voxel size which has only a miniscule effect on image quality. (Less)
Please use this url to cite or link to this publication:
author
; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Bias correction, Intensity correction, MPRAGE, MP2RAGE, B1, 7T, Ultra-high field, Longitudinal relaxation, T1, T1-mapping
in
Tomography : a journal for imaging research
volume
7
issue
3
pages
434 - 451
publisher
Grapho Publications LLC
external identifiers
  • scopus:85115292423
ISSN
2379-1381
project
Gradient echo-based quantitative MRI of human brain at 7T
Automated data pipeline for clinical quantitative 7T MRI
Multiparametric mapping of the brain at 7T using gradient echoes
language
English
LU publication?
yes
id
eede6974-9cfb-400c-8b3f-521257ad2b8a
alternative location
https://www.mdpi.com/2379-139X/7/3/38/htm
date added to LUP
2021-09-13 11:59:27
date last changed
2023-10-11 00:52:39
@article{eede6974-9cfb-400c-8b3f-521257ad2b8a,
  abstract     = {{At field strengths of 7 T and above, T1-weighted imaging of human brain suffers increasingly from radiofrequency (RF) B1 inhomogeneities. The well-known MP2RAGE (magnetization prepared two rapid acquisition gradient echoes) sequence provides a solution but may not be readily available for all MR systems. Here, we describe the implementation and evaluation of a sequential protocol to obtain normalized magnetization prepared rapid gradient echo (MPRAGE) images at 0.7,<br/>0.8, or 0.9-mm isotropic spatial resolution. Optimization focused on the reference gradient-recalled echo (GRE) that was used for normalization of the MPRAGE. A good compromise between white-gray matter contrast and the signal-to-noise ratio (SNR) was reached at a flip angle of 3° and total scan time was reduced by increasing the reference voxel size by a factor of 8 relative to the MPRAGE resolution. The average intra-subject coefficient-of-variation (CV) in segmented white matter (WM) was 7.9 ±3.3% after normalization, compared to 20 ±8.4% before. The corresponding inter-subject average CV in WM as 7.6 ±7.6% and 13 ±7.8%. Maps of T1 derived from forward signal modelling showed no obvious bias after correction by a separately acquired flip angle map. To conclude, 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 the reference voxel size which has only a miniscule effect on image quality.}},
  author       = {{Olsson, Hampus and Novén, Mikael and Lätt, Jimmy and Wirestam, Ronnie and Helms, Gunther}},
  issn         = {{2379-1381}},
  keywords     = {{Bias correction; Intensity correction; MPRAGE; MP2RAGE; B1; 7T; Ultra-high field; Longitudinal relaxation; T1; T1-mapping}},
  language     = {{eng}},
  number       = {{3}},
  pages        = {{434--451}},
  publisher    = {{Grapho Publications LLC}},
  series       = {{Tomography : a journal for imaging research}},
  title        = {{Radiofrequency bias correction of magnetization prepared rapid gradient echo MRI at 7.0 Tesla using an external reference in a sequential protocol}},
  url          = {{https://lup.lub.lu.se/search/files/102355637/21_Olsson_tomography_07_00038.pdf}},
  volume       = {{7}},
  year         = {{2021}},
}