Ronnie Wirestam
Professor
Radiofrequency bias correction of magnetization prepared rapid gradient echo MRI at 7.0 Tesla using an external reference in a sequential protocol
Författare
Summary, in English
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.
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.
Avdelning/ar
- Medicinsk strålningsfysik, Lund
- MR Physics
- LAMiNATE (Language Acquisition, Multilingualism, and Teaching)
- Allmän språkvetenskap
Publiceringsår
2021
Språk
Engelska
Sidor
434-451
Publikation/Tidskrift/Serie
Tomography : a journal for imaging research
Volym
7
Issue
3
Fulltext
- Available as PDF - 11 MB
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Dokumenttyp
Artikel i tidskrift
Förlag
Grapho Publications LLC
Ämne
- Radiology, Nuclear Medicine and Medical Imaging
- Other Physics Topics
Nyckelord
- Bias correction
- Intensity correction
- MPRAGE
- MP2RAGE
- B1
- 7T
- Ultra-high field
- Longitudinal relaxation
- T1
- T1-mapping
Status
Published
Projekt
- 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
Forskningsgrupp
- MR Physics
- LAMiNATE (Language Acquisition, Multilingualism, and Teaching)
ISBN/ISSN/Övrigt
- ISSN: 2379-1381