Enhanced quantitative susceptibility mapping (QSM) using real-time field control.

PURPOSE: To assess the potential of a real-time field-control (FC) system for mitigating effects of spatiotemporal field fluctuations in quantitative susceptibility mapping (QSM) at 7 T.

METHODS: Magnitude, phase, and QSM images of phantoms and healthy volunteers were acquired under standard conditions and under induced field perturbation (FP) (phantoms: periodic water-bottle displacement; volunteers: deep breathing and forearm movement) with and without FC, which continuously detects and minimizes magnetic-field variations.

RESULTS: Field control successfully eliminated FP-induced impairment of phantom image quality and deviations from a linear susceptibility increase for increasing gadolinium concentration in a Gd dilution series (y = 320x - 0.60, R2  = 0.93 for the scan with FP and FC versus y = 259x - 0.54, R2  = 0.78 for the scan with FP and no FC (slope literature value: 326 ppm L/mol)). Similarly, in volunteers, FC allowed a recovery of a FP-induced loss of identifiable brain structures and reduced the relative change of mean susceptibilities and standard deviations (93 ± 53% to 34 ± 46%) in all regions of interests with respect to the reference scan.

CONCLUSIONS: Real-time FC improved the delineation of brain structures and the match of susceptibility values with reference values obtained without FP. Magn Reson Med 79:770-778, 2018. © 2017 International Society for Magnetic Resonance in Medicine.