Nonlinear droop compensation for current waveforms in MRI gradient systems

buir.contributor.authorBabaloo, Reza
buir.contributor.authorAtalar, Ergin
buir.contributor.orcidBabaloo, Reza|0000-0002-2604-6491
buir.contributor.orcidAtalar, Ergin|0000-0002-6874-6103
dc.citation.epage985en_US
dc.citation.issueNumber2en_US
dc.citation.spage973en_US
dc.citation.volumeNumber88en_US
dc.contributor.authorBabaloo, Reza
dc.contributor.authorAtalar, Ergin
dc.date.accessioned2023-02-28T17:21:40Z
dc.date.available2023-02-28T17:21:40Z
dc.date.issued2022-03-28
dc.departmentDepartment of Electrical and Electronics Engineeringen_US
dc.departmentNational Magnetic Resonance Research Center (UMRAM)en_US
dc.description.abstractPurpose: Providing accurate gradient currents is challenging due to the gradient chain nonlinearities, arising from gradient power amplifiers and power supply stages. This work introduces a new characterization approach that takes the amplifier and power supply into account, resulting in a nonlinear model that compensates for the current droop. Methods: The gradient power amplifier and power supply stage were characterized by a modified state-space averaging technique. The resulting nonlinear model was inverted and used in feedforward to control the gradient coil current. A custom-built two-channel z-gradient coil was driven by high-switching (1 MHz), low-cost amplifiers (<$200) using linear and nonlinear controllers. High-resolution (<80 ps) pulse-width-modulation signals were used to drive the amplifiers. MRI experiments were performed to validate the nonlinear controller's effectiveness. Results: The simulation results validated the functionality of the state-space averaging method in characterizing the gradient system. The performance of linear and nonlinear controllers in generating a trapezoidal current waveform was compared in simulations and experiments. The integral errors between the desired waveform and waveforms generated by linear and nonlinear controllers were 1.9% and 0.13%, respectively, confirming the capability of the nonlinear controller to compensate for the current droop. Phantom images validated the nonlinear controller's ability to correct droop-induced distortions. Conclusion: Benchtop measurements and MRI experiments demonstrated that the proposed nonlinear characterization and digitally implemented feedforward controller could drive gradient coils with droop-free current waveforms (without a feedback loop). In experiments, the nonlinear controller outperformed the linear controller by a 14-fold reduction in the integral error of a test waveform.en_US
dc.identifier.doi10.1002/mrm.29246en_US
dc.identifier.issn0740-3194
dc.identifier.urihttp://hdl.handle.net/11693/111971
dc.language.isoEnglishen_US
dc.publisherJohn Wiley and Sons Incen_US
dc.relation.isversionofhttps://dx.doi.org/10.1002/mrm.29246en_US
dc.source.titleMagnetic Resonance in Medicineen_US
dc.subjectDroop compensationen_US
dc.subjectGradient arrayen_US
dc.subjectHigh-switching gradient power amplifieren_US
dc.subjectMRI gradient system characterizationen_US
dc.subjectNonlinear feedforward controlleren_US
dc.subjectState-space averagingen_US
dc.titleNonlinear droop compensation for current waveforms in MRI gradient systemsen_US
dc.typeArticleen_US

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