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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

At field strengths of 7 T and above, T(1)-weighted imaging of human brain suffers increasingly from radiofrequency (RF) B(1) 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...

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Autores principales: Olsson, Hampus, Novén, Mikael, Lätt, Jimmy, Wirestam, Ronnie, Helms, Gunther
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8482199/
https://www.ncbi.nlm.nih.gov/pubmed/34564300
http://dx.doi.org/10.3390/tomography7030038
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author Olsson, Hampus
Novén, Mikael
Lätt, Jimmy
Wirestam, Ronnie
Helms, Gunther
author_facet Olsson, Hampus
Novén, Mikael
Lätt, Jimmy
Wirestam, Ronnie
Helms, Gunther
author_sort Olsson, Hampus
collection PubMed
description At field strengths of 7 T and above, T(1)-weighted imaging of human brain suffers increasingly from radiofrequency (RF) B(1) 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 was 7.6 ± 7.6% and 13 ± 7.8%. Maps of T(1) 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 T(1)-weighted images. These images can be converted to T(1) 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.
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spelling pubmed-84821992021-10-01 Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External Reference in a Sequential Protocol Olsson, Hampus Novén, Mikael Lätt, Jimmy Wirestam, Ronnie Helms, Gunther Tomography Article At field strengths of 7 T and above, T(1)-weighted imaging of human brain suffers increasingly from radiofrequency (RF) B(1) 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 was 7.6 ± 7.6% and 13 ± 7.8%. Maps of T(1) 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 T(1)-weighted images. These images can be converted to T(1) 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. MDPI 2021-09-13 /pmc/articles/PMC8482199/ /pubmed/34564300 http://dx.doi.org/10.3390/tomography7030038 Text en © 2021 by the authors. https://creativecommons.org/licenses/by/4.0/Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Olsson, Hampus
Novén, Mikael
Lätt, Jimmy
Wirestam, Ronnie
Helms, Gunther
Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External Reference in a Sequential Protocol
title Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External Reference in a Sequential Protocol
title_full Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External Reference in a Sequential Protocol
title_fullStr Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External Reference in a Sequential Protocol
title_full_unstemmed Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External Reference in a Sequential Protocol
title_short Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External Reference in a Sequential Protocol
title_sort radiofrequency bias correction of magnetization prepared rapid gradient echo mri at 7.0 tesla using an external reference in a sequential protocol
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8482199/
https://www.ncbi.nlm.nih.gov/pubmed/34564300
http://dx.doi.org/10.3390/tomography7030038
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