Magnetic resonance array square coils: Dependence of the frequency and sample conductivity on decoupling

Area of Science:

• Magnetic Resonance Imaging
• Electromagnetics
• Coil Design

Background:

• Radio frequency (RF) coils are essential components in magnetic resonance (MR) systems for signal transmission and reception.
• Designing custom, organ-specific RF coils can be challenging for research projects.
• Array coils, combining multiple surface coils, offer high signal-to-noise ratio (SNR) over a wide field-of-view but require minimized mutual coupling between elements.

Purpose of the Study:

• To investigate the impact of coil tuning frequency and sample conductivity on mutual coupling in RF coil arrays.
• To determine the optimal spacing between coil elements to minimize mutual coupling.
• To propose and evaluate a numerical method for analyzing sample-coil interactions in loaded array configurations.

Main Methods:

• Utilized a numerical full-wave method, specifically the finite-difference time-domain (FDTD) algorithm.
• Simulated mutual coupling between two square loop elements in a loaded array configuration.
• Evaluated the S12 scattering parameter across various coil element positions, frequencies (64, 128, 298 MHz), and sample conductivities (0.6, 1.5, 3 S/m).

Main Results:

• The optimal distance to minimize mutual coupling was found to be between 87%-93% of the loop side length.
• Mutual coupling showed a slight variation (approx. 7%) with changes in frequency and sample conductivity.
• The S12 scattering parameter analysis provided insights into the coil element positioning for optimal performance.

Conclusions:

• Understanding sample-coil interaction models is vital for designing tightly coupled array coils.
• The optimal coil element spacing is a critical parameter for maximizing SNR in MR systems.
• FDTD simulations offer a valuable tool for optimizing RF coil array design and development.