• About
  • Policies
  • What is open access
  • Library
  • Contact
Advanced search
      View Item 
      •   BUIR Home
      • Scholarly Publications
      • National Magnetic Resonance Research Center (UMRAM)
      • View Item
      •   BUIR Home
      • Scholarly Publications
      • National Magnetic Resonance Research Center (UMRAM)
      • View Item
      JavaScript is disabled for your browser. Some features of this site may not work without it.

      Nonlinear droop compensation for current waveforms in MRI gradient systems

      Thumbnail
      View / Download
      5.0 Mb
      Author(s)
      Babaloo, Reza
      Atalar, Ergin
      Date
      2022-03-28
      Source Title
      Magnetic Resonance in Medicine
      Print ISSN
      0740-3194
      Publisher
      John Wiley and Sons Inc
      Volume
      88
      Issue
      2
      Pages
      973 - 985
      Language
      English
      Type
      Article
      Item Usage Stats
      5
      views
      1
      downloads
      Abstract
      Purpose: 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.
      Keywords
      Droop compensation
      Gradient array
      High-switching gradient power amplifier
      MRI gradient system characterization
      Nonlinear feedforward controller
      State-space averaging
      Permalink
      http://hdl.handle.net/11693/111971
      Published Version (Please cite this version)
      https://dx.doi.org/10.1002/mrm.29246
      Collections
      • Department of Electrical and Electronics Engineering 4011
      • National Magnetic Resonance Research Center (UMRAM) 301
      Show full item record

      Browse

      All of BUIRCommunities & CollectionsTitlesAuthorsAdvisorsBy Issue DateKeywordsTypeDepartmentsCoursesThis CollectionTitlesAuthorsAdvisorsBy Issue DateKeywordsTypeDepartmentsCourses

      My Account

      Login

      Statistics

      View Usage StatisticsView Google Analytics Statistics

      Bilkent University

      If you have trouble accessing this page and need to request an alternate format, contact the site administrator. Phone: (312) 290 2976
      © Bilkent University - Library IT

      Contact Us | Send Feedback | Off-Campus Access | Admin | Privacy