Quantitative susceptibility mapping in the human brain at 7T with phase‐cycled balanced SSFP

• Published in: Magnetic resonance in medicine Vol. 94; no. 4; pp. 1469 - 1484
• Main Authors: Acikgoz, Berk Can, Sainz Martinez, Cristina, Mackowiak, Adèle L. C., Plähn, Nils M. J., Safarkhanlo, Yasaman, Peper, Eva S., Radojewski, Piotr, Bonanno, Gabriele, Jorge, João, Bastiaansen, Jessica A. M.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.10.2025
• Subjects: 7 T; Adult; Algorithms; balanced steady‐state free precession; Brain; Brain - diagnostic imaging; Brain mapping; Brain Mapping - methods; bSSFP; Caudate nucleus; Deviation; Feasibility; Female; Globus pallidus; Humans; Image Processing, Computer-Assisted - methods; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Male; Mapping; Phase matching; phase‐cycled bSSFP; Proton density (concentration); Putamen; QSM; quantitative MRI; Susceptibility; Thalamus; quantitative MRI; balanced steady‐state free precession; QSM; 7 T; phase‐cycled bSSFP; bSSFP
• ISSN: 0740-3194; 1522-2594; 1522-2594
• DOI: 10.1002/mrm.30571

Purpose To demonstrate the feasibility of QSM and to show the potential of simultaneous T1$$ {T}_1 $$, T2$$ {T}_2 $$, and proton density (PD) mapping in the human brain at 7T based on phase‐cycled balanced SSFP (bSSFP) MRI. Methods An algorithm was developed to estimate off‐resonance frequency in multi‐compartment scenarios by combining elliptic phase‐cycled bSSFP signal fitting with dictionary matching. Phase‐cycled bSSFP‐based tissue phase and susceptibility maps were compared with multi‐echo gradient‐echo (MEGRE)‐based maps in the brains of eight healthy subjects at 7T. Additionally, T1$$ {T}_1 $$, T2$$ {T}_2 $$, and PD maps were obtained from the same phase‐cycled bSSFP data. To demonstrate the potential of matching scan time with MEGRE, bSSFP profiles were subsampled by 50% and resulting maps compared with the reference data. Results The tissue phase maps obtained from phase‐cycled bSSFP data agreed well with the reference, with a mean absolute deviation of 1.47±0.32$$ 1.47\pm 0.32 $$ Hz in the entire brain of all subjects. The mean absolute deviation of tissue susceptibility was 24±7$$ 24\pm 7 $$ parts‐per‐billion (ppb). Susceptibility in the globus pallidus was overestimated by 67 ppb (p < 0.05), while no significant biases were observed in other regions: 3.2 ppb in putamen, 15.5 ppb in thalamus, and 11.9 ppb in caudate nucleus (all p > 0.05). Quantitative maps showed good contrast between different regions of the brain, aligning well with the literature. Profile subsampling did not significantly (p > 0.05) change the quantitative susceptibility maps. Conclusion The feasibility of phase‐cycled bSSFP for QSM at 7T was demonstrated, with the added benefit of simultaneous T1$$ {T}_1 $$, T2$$ {T}_2 $$, and PD mapping, with a total scan time of ˜20 min.