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Shielded resistive electromagnets of arbitrary surface geometry using the boundary element method and a minimum
Chad T Harris1, Dustin W Haw, William B Handler
1Department of Physics and Astronomy, Western University, 1151 Richmond Street, London, Ontario N6A 3K7, Canada.
Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|July 16, 2013
Summary
This study presents a new method for actively shielding magnetic resonance imaging (MRI) coils using the boundary element method. The technique effectively minimizes eddy currents and magnetic field interference, even with non-cylindrical coil designs.
Area of Science:
- Medical Physics
- Biomedical Engineering
- Electromagnetism
Background:
- Eddy currents generated by rapidly switched electromagnets in Magnetic Resonance (MR) imaging cause time-varying and spatially varying magnetic fields.
- These magnetic fields necessitate minimization or correction, a challenge amplified by non-cylindrical insert magnets for specialized applications.
- Active magnetic shielding is the conventional method to interrupt coupling between insert coils and the MR system.
Purpose of the Study:
- To introduce a novel method for actively shielding insert gradient and shim coils of arbitrary surface geometry.
- To apply the boundary element method with a minimum energy constraint for designing effective magnetic shields.
- To demonstrate the versatility of the shielding method across different coil and shield geometries.
Main Methods:
- Utilized the boundary element method (BEM) for coil design, incorporating a minimum energy constraint.
- Applied the BEM-based shielding method to x- and z-gradient coils.
- Tested shielding effectiveness for both cylindrical primary gradients with cylindrical shields and cylindrical primary gradients with rectangular box-shaped shields.
Main Results:
- The BEM method produced shields for the cylindrical case that demonstrated agreement with established analytic solutions.
- Rectangular box-shaped shields exhibited excellent shielding performance, despite their geometric dissimilarity to the primary coils.
- The results validate the method's capability to handle diverse surface geometries in magnetic shielding.
Conclusions:
- The presented boundary element method offers a versatile and effective approach for actively shielding gradient and shim coils in MR systems.
- This method successfully addresses the challenge of eddy current mitigation, particularly for non-standard coil geometries.
- The findings support the application of this technique for improving MR imaging quality and enabling specialized insert coil designs.
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