Microstrip Butler matrix design and realization for 7 T MRI

Area of Science:

• Electrical Engineering
• Magnetic Resonance Imaging

Background:

• High-field MRI systems (7 Tesla) require advanced radiofrequency (RF) coil arrays for improved image quality.
• Efficient signal distribution and mode control are critical for optimal performance in these systems.

Purpose of the Study:

• To design and realize compact, high-performance 8x8 and 16x16 Butler matrices for 7T MRI.
• To achieve low insertion loss and high amplitude/phase accuracy for pure mode excitation.

Main Methods:

• Utilized microstrip line integration technology (microwave-integrated circuit).
• Employed high permittivity (ε(r) = 11) and thick (h = 3.2 mm) laminate material.
• Incorporated circuit folding, meandering, and shielding structures to optimize size and reduce coupling.

Main Results:

• Achieved insertion losses of 0.73 dB (8x8) and 1.1 dB (16x16).
• Demonstrated high amplitude/phase accuracy with unwanted modes suppressed by 40 dB (8x8) and 35 dB (16x16).
• Successfully implemented and operated matrices in a 7T MRI system for RF mode shimming experiments up to 8 kW RF power.

Conclusions:

• The designed Butler matrices offer a viable solution for advanced 7T MRI systems.
• The chosen design and materials provide an excellent trade-off between board size, insertion loss, and performance.
• These matrices facilitate efficient RF power delivery and mode control for demanding MRI applications.