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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

1
Department of Medical Radiation Physics, Clinical Sciences Lund, Lund University, 221 85 Lund, Sweden
2
Department of Linguistics and Phonetics, Lund University, 221 00 Lund, Sweden
3
Center for Medical Imaging and Physiology, Skåne University Hospital, 221 00 Lund, Sweden
*
Author to whom correspondence should be addressed.
Academic Editor: Bradford A. Moffat
Tomography 2021, 7(3), 434-451; https://doi.org/10.3390/tomography7030038
Received: 15 July 2021 / Revised: 27 August 2021 / Accepted: 9 September 2021 / Published: 13 September 2021
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 was 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. View Full-Text
Keywords: bias correction; intensity correction; MPRAGE; MP2RAGE; B1; 7T; ultra-high field; longitudinal relaxation; T1; T1-mapping bias correction; intensity correction; MPRAGE; MP2RAGE; B1; 7T; ultra-high field; longitudinal relaxation; T1; T1-mapping
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Figure 1

  • Externally hosted supplementary file 1
    Link: https://openneuro.org/datasets/ds003769
    Description: Single-subject dataset used for the experiment (not including the inter-subject variability experiment).
MDPI and ACS Style

Olsson, H.; Novén, M.; Lätt, J.; Wirestam, R.; Helms, G. Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External Reference in a Sequential Protocol. Tomography 2021, 7, 434-451. https://doi.org/10.3390/tomography7030038

AMA Style

Olsson H, Novén M, Lätt J, Wirestam R, Helms G. Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External Reference in a Sequential Protocol. Tomography. 2021; 7(3):434-451. https://doi.org/10.3390/tomography7030038

Chicago/Turabian Style

Olsson, Hampus, Mikael Novén, Jimmy Lätt, Ronnie Wirestam, and Gunther Helms. 2021. "Radiofrequency Bias Correction of Magnetization Prepared Rapid Gradient Echo MRI at 7.0 Tesla Using an External Reference in a Sequential Protocol" Tomography 7, no. 3: 434-451. https://doi.org/10.3390/tomography7030038

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