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Measuring motion-induced B0 -fluctuations in the brain using field probes

2016

Purpose: Fluctuations of the background magnetic field (B0)due to body and breathing motion can lead to significant artifactsin brain imaging at ultrahigh field. Corrections based onreal-time sensing using external field probes show greatpotential. This study evaluates different aspects of field interpolationfrom these probes into the brain which is implicit insuch methods. Measurements and simulations were performedto quantify how well B0-fluctuations in the brain due tobody and breathing motion are reflected in external field probemeasurements.Methods: Field probe measurements were compared withscanner acquired B0-maps from experiments with breathingand shoulder movements. A realistic simulation of B0-fluctuationscaused by breathing was performed, and used for testingdifferent sets of field probe positions.Results: The B0-fluctuations were well reflected in the fieldprobe measurements in the shoulder experiments, while thebreathing experiments showed only moderate correspondence.The simulations showed the importance of the probepositions, and that performing full 3rd order corrections basedon 16 field probes is not recommended.Conclusion: Methods for quantitative assessment of the fieldinterpolation problem were developed and demonstrated. Fieldcorrections based on external field measurements show greatpotential, although potential pitfalls were identified.