Development and Optimization of Hardware for Delta

electro-magnet and a 1.5T superconducting system are systematicallyidentified and mitigated.Methods: The effects of nonideal fabrication of the field-shifting magnet are taken into consideration through carefulmeasurement during winding and improved accuracy in thedesign of the associated active shield. The shielding perform-ance of the resultant electromagnet is compared against apreviously built system in which the shield design was basedon an ideal primary coil model. Hardware and softwareapproaches implemented to eliminate residual image artifactsare presented in detail.Results: The eddy currents produced by the newly con-structed dreMR system are shown to have a significantlysmaller “long-time-constant” component, consistent with thehypothesis that less energy is deposited into the cryostat ofthe MR system.Conclusion: With active compensation, the dreMR imagingsystem is capable of 0.22T field shifts within a clinical 1.5T MRIwith no significant residual eddy-current fields. Magn ResonMed 000:000–000, 2013.

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