Revisiting Inductively Coupled Wireless Coils in MRI: Mitigating Over-Coupling With Preamplifiers

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Coil Engineering
• Radiofrequency Physics

Background:

• Inductively coupled coils improve local MRI sensitivity.
• Strong coupling typically causes detrimental resonance splitting and impedance mismatch.

Purpose of the Study:

• Investigate the effectiveness of inductively coupled coils under severe coupling conditions.
• Clarify the role of modern receive preamplifiers in mitigating coupling effects.

Main Methods:

• Bench experiments with varying coil sizes and magnetic field strengths (1.5, 3, 7T).
• Evaluation of resonance and impedance under different preamplifier terminations (open-circuit, 50-Ω, low-input-impedance).
• MRI validation at 7T with coupled coils and varied preamplifier decoupling.

Main Results:

• Low-input-impedance preamplifiers maintained inductively coupled coil resonance despite strong coupling.
• Primary coil impedance shifts were acceptable, causing negligible SNR penalty.
• Degraded preamplifier decoupling reduced SNR by 21%-23%.

Conclusions:

• Modern preamplifiers significantly alter coupled-coil behavior.
• Inductively coupled coils can operate close to primary coils without substantial SNR loss.
• Simplified inductively coupled coil design is enabled by modern preamplifiers.