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

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningfagfællebedømt

At field strengths of 7 T and above, T1-weighted imaging of human brain suffers increas-ingly 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.

OriginalsprogEngelsk
TidsskriftTomography
Vol/bind7
Udgave nummer3
Sider (fra-til)434-451
Antal sider18
ISSN2379-1381
DOI
StatusUdgivet - 2021
Eksternt udgivetJa

Bibliografisk note

(Ekstern)
Funding Information:
This research was funded by the Swedish Research Council, grant numbers NT-2014-6193 and M-2017-00995. The APC was funded in part by Lund University.

Publisher Copyright:
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.

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