Numerical simulations on active shielding methods comparison and wrapped angle optimization for gradient coil design...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Electromagnetism
• Coil Design

Background:

• Gradient coil current switching in MRI induces eddy currents.
• Eddy currents generate secondary magnetic fields detrimental to image quality.
• Active shielding strategies aim to minimize these effects.

Purpose of the Study:

• To compare two active shielding methods for gradient coils: minimizing cryostat surface magnetic fields versus minimizing imaging region secondary magnetic fields.
• To quantitatively assess stray field and eddy current performance under stringent constraints.
• To optimize a wrapped-edge gradient coil design for enhanced stray field control.

Main Methods:

• Numerical simulations were performed to compare two distinct active shielding strategies.
• Constraints included ultra-low maximum stray field intensity (2 G) and extreme secondary field shielding ratio (0.000001).
• Optimization of a wrapped-edge gradient coil design was conducted.

Main Results:

• The secondary magnetic field control strategy yielded coils with superior overall performance.
• Minimizing magnetic fields on the cryostat surface is preferable for achieving ultra-low eddy currents and strict stray field control at the cryostat's edge.
• Optimized wrapping angles for the x and z coils in the wrapped-edge design were determined to be 40° and 90°, respectively.

Conclusions:

• The choice of active shielding strategy in gradient coil design depends on specific performance requirements.
• For applications demanding minimal eddy currents and precise stray field management, minimizing magnetic fields is the recommended approach.
• The wrapped-edge design offers an effective method for controlling stray fields in MRI gradient coils.