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Related Concept Videos

Magnetic Damping01:17

Magnetic Damping

Eddy currents can produce significant drag on motion, called magnetic damping. For instance, when a metallic pendulum bob swings between the poles of a strong magnet, significant drag acts on the bob as it enters and leaves the field, quickly damping the motion.
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Dynamic Equilibrium

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Related Experiment Video

Updated: Jun 3, 2026

Real-Time DC-dynamic Biasing Method for Switching Time Improvement in Severely Underdamped Fringing-field Electrostatic MEMS Actuators
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Real-Time DC-dynamic Biasing Method for Switching Time Improvement in Severely Underdamped Fringing-field Electrostatic MEMS Actuators

Published on: August 15, 2014

Dynamic B0 shimming at 7 T.

Saikat Sengupta1, E Brian Welch, Yansong Zhao

  • 1Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN 37235, USA. saikat.sengupta@vanderbilt.edu

Magnetic Resonance Imaging
|March 15, 2011
PubMed
Summary
This summary is machine-generated.

Dynamic slice-wise shimming significantly enhances B0 field homogeneity in MRI scans compared to static global shimming. This technique reduces image distortions and signal loss, improving overall image quality in both phantom and human studies.

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Biomedical Engineering
  • Physics

Background:

  • B0 field inhomogeneity is a major challenge in high-field MRI, leading to image distortions and signal dropout.
  • Static global shimming provides a single correction, which is often insufficient for complex B0 variations across slices.
  • Dynamic slice-wise shimming offers a promising solution by adapting shim currents per slice for improved field homogeneity.

Purpose of the Study:

  • Evaluate slice-wise, field-map-based, second-order dynamic shimming against static global shimming at 7 Tesla.
  • Characterize eddy currents induced by second and third-order shim switching.
  • Compare global and dynamic shimming across different shim orders to assess benefits of higher orders and dynamic updates.

Main Methods:

  • Implemented an external hardware module for dynamic, slice-optimized shim value updates during multislice acquisition.
  • Acquired high-bandwidth gradient echo and low-bandwidth echo planar imaging data on phantoms and human subjects.
  • Measured eddy currents via step response phase changes and analyzed shim performance across various orders and hybrid approaches.

Main Results:

  • Dynamic shimming substantially improved B0 homogeneity over static global shimming in phantoms and humans, reducing artifacts.
  • Second and third-order shims generated significant B0 and eddy fields with multi-exponential time constants.
  • Increasing shim order improved homogeneity, with dynamic shimming outperforming global methods; hybrid approaches showed intermediate results.

Conclusions:

  • Slice-wise dynamic shimming is superior to static global shimming for improving B0 homogeneity and image quality in 7T MRI.
  • Eddy current characterization is crucial for understanding and mitigating artifacts from higher-order shim switching.
  • Further optimization of dynamic and hybrid shimming strategies can enhance MRI performance at high fields.