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Related Experiment Videos

Resonant trapezoidal gradient generation for use in echo-planar imaging

P R Harvey1, P Mansfield

  • 1Department of Physics, University of Nottingham, United Kingdom.

Magnetic Resonance Imaging
|January 1, 1994
PubMed
Summary
This summary is machine-generated.

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Two passive filter circuits for magnetic resonance imaging gradients were evaluated. Software control allows waveform shaping, enabling efficient trapezoidal gradient modulation for faster imaging.

Area of Science:

  • Medical Imaging
  • Electrical Engineering
  • Physics

Background:

  • Echo-planar imaging (EPI) and echo-volumar imaging (EVI) rely on modulated read gradients.
  • Efficient gradient waveform generation is crucial for optimizing imaging speed and quality.

Purpose of the Study:

  • To compare two passive filter circuit designs for series resonant trapezoidal gradient drive.
  • To evaluate power requirements and performance for high-current applications.
  • To investigate software-controlled waveform shaping capabilities.

Main Methods:

  • Circuit simulations were performed for 7th order passive filters with a 110 microH gradient coil.
  • Evaluated fundamental frequencies ranged from 800 Hz to 2000 Hz.
  • Peak operating currents up to 1000 A were simulated.

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Main Results:

  • The simpler passive filter circuit was not necessarily the most efficient.
  • Software modification of input waveforms enabled control over gradient waveform shape (triangular to trapezoidal).
  • Fast rise trapezoidal waveforms were achieved, independent of amplifier power, with risetimes under 60 microseconds at >320 A.

Conclusions:

  • Passive filter circuits can efficiently generate trapezoidal gradient waveforms for EPI and EVI.
  • Software control offers flexibility in gradient waveform shaping, optimizing performance.
  • The non-dissipative nature of the circuits allows for rapid gradient switching, potentially improving imaging speed and reducing peripheral nerve stimulation.