Human brain quantitative susceptibility mapping at 5 T: A prospective multicenter traveling-subject study with...

Quantitative susceptibility mapping (QSM) quantifies tissue magnetic susceptibility from gradient-echo phase data and is increasingly used to assess brain iron content. Although QSM has been validated from 1.5 T to 9.4 T, its multicenter performance at 5 T has not been evaluated. Six healthy volunteers (3 men, 3 women; mean age 29 ± 4 years) underwent brain QSM as a traveling-subject cohort across six 5 T MRI systems at different institutions, with a 3 T system as the clinical reference. Three-dimensional multi-echo gradient-echo data were acquired using standardized protocols, and QSM maps were reconstructed with a uniform pipeline. Nine bilateral regions of interest were measured using combined automated and manual segmentation. The 5 T scan-rescan assessment showed high repeatability, with ICCs ranged from 0.93 to 0.99. Inter-scanner reproducibility at 5 T was high for large deep gray matter structures (within-subject standard deviation < 5 ppb for pallidum, putamen, and caudate), comparable to multicenter data at 3 T and 7 T. Cross-field agreement between 3 T and 5 T was good/excellent agreement for putamen, thalamus, pallidum, substantia nigra, and white matter, but moderate cross-field ICC or wide LoA for brainstem, caudate, dentate nucleus, and red nucleus. The established susceptibility hierarchy was preserved at 5 T, and values were consistent with normative data across field strengths. An apparent trend of decreasing QSM values at higher field was observed across pooled studies, which should be interpreted as protocol/literature dependent rather than intrinsic field effects. These findings provide the first multicenter benchmark for brain QSM at 5 T.