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Quantitative susceptibility mapping in the human brain at 7T with phase-cycled balanced SSFP
Berk Can Acikgoz1,2,3, Cristina Sainz Martinez4,5, Adèle L C Mackowiak1,2,6
1Department of Diagnostic, Interventional and Pediatric Radiology (DIPR), Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland.
Magnetic Resonance in Medicine
|June 3, 2025
Summary
This study demonstrates the feasibility of quantitative susceptibility mapping (QSM) using phase-cycled balanced SSFP (bSSFP) MRI at 7T. The method also enables simultaneous T1, T2, and proton density mapping in under 20 minutes.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Medical Physics
- Neuroimaging
Background:
- Quantitative susceptibility mapping (QSM) is crucial for neuroimaging at high fields like 7T.
- Simultaneous mapping of various tissue properties (T1, T2, PD) is desirable for comprehensive brain analysis.
- Phase-cycled balanced steady-state free precession (bSSFP) offers potential for efficient multi-contrast imaging.
Purpose of the Study:
- To establish the feasibility of QSM using phase-cycled bSSFP MRI at 7 Tesla (7T).
- To showcase the capability of simultaneous T1, T2, and proton density (PD) mapping.
- To evaluate the performance against established multi-echo gradient-echo (MEGRE) methods.
Main Methods:
- Developed an algorithm for off-resonance frequency estimation using elliptic phase-cycled bSSFP signal fitting and dictionary matching.
- Compared phase-cycled bSSFP-derived susceptibility maps with MEGRE-based maps in 8 healthy subjects at 7T.
- Acquired simultaneous T1, T2, and PD maps from the same bSSFP data; subsampled data to assess scan time efficiency.
Main Results:
- Phase-cycled bSSFP yielded tissue phase maps with good agreement to reference data (mean absolute deviation: 1.47 ± 0.32 Hz).
- Mean absolute deviation for tissue susceptibility was 24 ± 7 parts-per-billion (ppb), with minor overestimation in globus pallidus.
- Subsampling data by 50% did not significantly alter quantitative susceptibility maps, indicating potential for faster acquisition.
Conclusions:
- Phase-cycled bSSFP is a feasible technique for QSM at 7T.
- This method allows for simultaneous T1, T2, and PD mapping, enhancing its utility.
- The entire process can be completed within a scan time of approximately 20 minutes.
