Ronnie Wirestam
Professor
Reducing bias in dual flip angle T1-mapping in human brain at 7T
Författare
Summary, in Swedish
Purpose: To address the systematic bias in whole-brain dual flip angle (DFA) T1-mapping at
7T by optimizing the flip angle pair and carefully selecting RF pulse shape and duration.
Theory and Methods: Spoiled gradient echoes can be used to estimate whole-brain maps of
T1. This can be accomplished by using only two acquisitions with different flip angles, i.e., a
DFA-based approach. Although DFA-based T1-mapping is seemingly straightforward to
implement, it is sensitive to bias caused by incomplete spoiling and incidental magnetization
transfer (MT) effects. Further bias is introduced by the increased B0 and B1
+ inhomogeneities at 7T. Experiments were performed to determine the optimal flip angle pair and appropriate
RF pulse shape and duration. Obtained T1 estimates were validated using inversion recovery
prepared EPI and compared to literature values. A multi-echo readout was used to increase
SNR, enabling quantification of R2* and susceptibility, χ.
Results: Incomplete spoiling was observed above a local flip angle of approximately 20°. An
asymmetric gauss-filtered sinc pulse with a constant duration of 700 μs showed a sufficiently
flat frequency response profile to avoid incomplete excitation in areas with high B0 offsets. A
pulse duration of 700 μs minimized effects from incidental MT.
Conclusion: When performing DFA-based T1-mapping one should (i) limit the higher flip
angle to avoid incomplete spoiling, (ii) use a RF pulse shape insensitive to B0
inhomogeneities and (iii) apply a constant RF pulse duration, balanced to minimize incidental
MT.
7T by optimizing the flip angle pair and carefully selecting RF pulse shape and duration.
Theory and Methods: Spoiled gradient echoes can be used to estimate whole-brain maps of
T1. This can be accomplished by using only two acquisitions with different flip angles, i.e., a
DFA-based approach. Although DFA-based T1-mapping is seemingly straightforward to
implement, it is sensitive to bias caused by incomplete spoiling and incidental magnetization
transfer (MT) effects. Further bias is introduced by the increased B0 and B1
+ inhomogeneities at 7T. Experiments were performed to determine the optimal flip angle pair and appropriate
RF pulse shape and duration. Obtained T1 estimates were validated using inversion recovery
prepared EPI and compared to literature values. A multi-echo readout was used to increase
SNR, enabling quantification of R2* and susceptibility, χ.
Results: Incomplete spoiling was observed above a local flip angle of approximately 20°. An
asymmetric gauss-filtered sinc pulse with a constant duration of 700 μs showed a sufficiently
flat frequency response profile to avoid incomplete excitation in areas with high B0 offsets. A
pulse duration of 700 μs minimized effects from incidental MT.
Conclusion: When performing DFA-based T1-mapping one should (i) limit the higher flip
angle to avoid incomplete spoiling, (ii) use a RF pulse shape insensitive to B0
inhomogeneities and (iii) apply a constant RF pulse duration, balanced to minimize incidental
MT.
Avdelning/ar
- MR Physics
Publiceringsår
2020-09
Språk
Engelska
Sidor
1347-1358
Publikation/Tidskrift/Serie
Magnetic Resonance in Medicine
Volym
84
Issue
3
Fulltext
Dokumenttyp
Artikel i tidskrift
Förlag
John Wiley & Sons Inc.
Ämne
- Medical Image Processing
- Neurology
- Other Physics Topics
Nyckelord
- T1
- 7T
- Longitudinal relaxation time
- human brain
- 7T
- dual flip angle
- human brain
- longitudinal relaxation
- spoiled gradient echo
- T1
Aktiv
Published
Projekt
- Gradient echo-based quantitative MRI of human brain at 7T
- Effects of Relaxation and Magnetization Transfer in VFA Experiments
- Multiparametric mapping of the brain at 7T using gradient echoes
- Automated data pipeline for clinical quantitative 7T MRI
Forskningsgrupp
- MR Physics
ISBN/ISSN/Övrigt
- ISSN: 1522-2594