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Dynamic shim updating (DSU) for multislice signal acquisition
Robin A de Graaf1, Peter B Brown, Scott McIntyre
1Magnetic Resonance Center, Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA. robin.degraaf@yale.edu
Magnetic Resonance in Medicine
|February 21, 2003
Summary
Dynamic shim updating (DSU) enhances magnetic field homogeneity in MRI by adjusting shims for each slice. This technique improves uniformity across extended volumes, especially for off-center slices.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Biophysics
- Medical Physics
Background:
- Achieving optimal magnetic field homogeneity is crucial for high-quality MRI.
- Traditional methods struggle with homogeneity over extended volumes in multislice acquisitions.
Purpose of the Study:
- To describe the practical implementation of dynamic shim updating (DSU) using all first- and second-order shims.
- To investigate temporal effects of shim current switching and implement compensation.
- To evaluate DSU's performance in improving magnetic field homogeneity.
Main Methods:
- DSU implementation with hardware and software requirements detailed.
- Investigation of temporal effects of shim current switching.
- Development and implementation of a Z(2)-to-Z(0) compensation unit.
- Determination of optimal shim settings using a multislice phase-mapping sequence.
- In vivo evaluation on rat brain using phase maps and spectroscopic images.
Main Results:
- DSU successfully improved magnetic field homogeneity across all spatial slices.
- The effect was more pronounced on slices further from the magnet isocenter.
- DSU ensured highly uniform magnetic field homogeneity over an extended volume.
- Temporal Z(0) variations following Z(2) shim current changes were counteracted.
Conclusions:
- DSU is a practical technique for achieving optimal magnetic field homogeneity in multislice MRI.
- The implemented Z(2)-to-Z(0) compensation effectively manages temporal variations.
- DSU significantly enhances overall magnetic field uniformity, improving image quality in extended regions.
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