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Magnetic field shimming by Fourier analysis
L Brateman1, T T Bowman, S Dønstrup
1Radiology Department, College of Medicine, University of Florida, Gainesville 32610.
Magnetic Resonance in Medicine
|April 1, 1988
Summary
Magnetic field homogeneity was significantly improved using passive and electronic shims. This enhancement benefits in vivo spectroscopy by enabling clearer data acquisition for larger samples.
Area of Science:
- Physics
- Magnetic Resonance Imaging
Background:
- Achieving high magnetic field homogeneity is crucial for advanced Magnetic Resonance Imaging (MRI) and spectroscopy.
- The Oxford 85/310HR magnet requires optimization for demanding applications like in vivo spectroscopy.
Purpose of the Study:
- To optimize the magnetic field homogeneity of an Oxford 85/310HR magnet.
- To improve field uniformity for enhanced in vivo spectroscopy applications.
Main Methods:
- Utilized passive shims (steel pieces) and room-temperature electronic shims for magnetic field correction.
- Employed Fourier analysis of circular field plot data to assess and minimize field inhomogeneities.
- Developed and presented techniques for magnetic field measurement, data analysis, and correction.
Main Results:
- Achieved excellent magnetic field homogeneity over a 10-cm diameter sphere with a peak-to-peak variation of 3.2 ppm, surpassing the manufacturer's 5 ppm specification.
- Reduced the half-height linewidth to 0.14 ppm in a 10 cm water sphere after fine-tuning shimming.
- Demonstrated a substantial improvement in field homogeneity compared to the original state.
Conclusions:
- The optimized magnetic field is highly homogeneous, suitable for acquiring improved spectra from centimeter-sized samples.
- Enhanced field homogeneity significantly improves the utility of the magnet for its intended purpose of in vivo spectroscopy.
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