Radiofrequency-transparent local B₀ shimming coils using float traps

Static field (B₀) inhomogeneities present a major challenge in high-field MRI. Multicoil shimming using independent, local, direct-current (DC) shim coils has emerged as a powerful and flexible technique to address this issue. However, many-turn DC coils can lead to significant mutual coupling with radiofrequency (RF) coils, causing transmit field (B₁ ⁺) distortions and signal-to-noise ratio degradation.

We introduce an innovative RF-transparent DC coil that performs B₀ shimming while minimizing RF performance impact. The design incorporates float traps to maintain high RF impedance, allowing flexible placement relative to the RF coil without compromising signal-to-noise ratio or affecting B₁ ⁺. We fabricated square-shaped DC coils with float traps for 3T MRI and compared them with conventional DC coils. To demonstrate high ΔB₀/Amp efficiency, we conducted a B₀ shimming experiment around a metal hip implant.

Bench tests and MRI experimental results demonstrated that the RF-transparent DC coil effectively minimized RF interference, preserved signal-to-noise ratio, and maintained B₁ ⁺, even when placed near the RF receive coil. Additionally, the DC coil significantly improved B₀ homogeneity near metal implants and substantially reduced image distortion.

The RF-transparent DC coil offers a flexible, effective solution for managing B₀ inhomogeneities, paving the way for integrating multiturn DC coils in clinical MRI settings without extensive hardware modifications.