An orthogonal shim coil for 3T brain imaging

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering
• Physics

Background:

• Achieving optimal magnetic field homogeneity is crucial for high-resolution Magnetic Resonance Imaging (MRI).
• Existing shimming techniques can sometimes interfere with radiofrequency (RF) coils, impacting signal-to-noise ratio (SNR).
• Minimizing interference between shim coils and RF coils is essential for advanced MRI applications.

Purpose of the Study:

• To design and implement an orthogonal shim array to improve magnetic field homogeneity.
• To minimize interference between shim coils and neighboring RF coils.
• To evaluate the performance of the orthogonal shim array in enhancing MRI quality.

Main Methods:

• Designed an orthogonal shim array with coil planes perpendicular to adjacent RF coils.
• Evaluated shim coil performance using realistic off-resonance maps of the human brain via simulations.
• Developed a 7-channel orthogonal shim array and utilized an open-source current driver for shim currents.

Main Results:

• The 7-channel orthogonal shim array demonstrated a 30% improvement in magnetic field homogeneity during slice-optimized shimming.
• The implemented array showed comparable performance to the scanner's 2nd order spherical harmonic shimming.
• The orthogonal shim array caused only marginal signal-to-noise ratio (SNR) loss to an integrated 32-channel RF-shim array.

Conclusions:

• Orthogonal shim coils effectively enhance magnetic field homogeneity in MRI.
• This approach maintains high image SNR, addressing a key limitation of conventional methods.
• The developed orthogonal shim array offers a promising solution for improved MRI performance.