A hybrid distributed capacitance birdcage coil for small-animal MR imaging at 14.1 T.

Abstract

Objective: To develop a transceiver radio frequency (RF) coil optimized for high resolution small-animal imaging at 14.1 T, aimed at enhancing signal-to-noise ratio (SNR) performance.

Methods: A hybrid distributed capacitance (HDC) birdcage coil was designed, combining conventional endring lumped capacitors with distributed capacitance along the legs, implemented using double-layer copper-clad substrates. Electromagnetic (EM) simulations were employed to optimize the coil's structural parameters and capacitance values for maximum RF performance. The HDC birdcage coil's performance was evaluated against a conventional bandpass (BP) design through electromagnetic simulations, bench tests, and phantom imaging. In vivo validation was performed using mouse imaging.

Results: EM simulations demonstrated that the HDC design enhances mean $\text{B}_{1}^{+}$ and $\text{B}_{1}^{-}$ field strengths by 11.8% and 11.7%, respectively, relative to the conventional BP design. The HDC design also showed reduced electric field (E-field) value in phantom, with 4.2% lower mean and 11.4% lower maximum E-field value. Bench measurements revealed a superior quality factor (Q factor) for the HDC coil, with a 34.2% higher unloaded Q value compared to the conventional design. Phantom imaging confirmed a 41% SNR improvement with the HDC design. The optimized HDC coil enabled mouse brain imaging at 50 $\mu$m resolution.

Conclusion: The proposed HDC birdcage coil demonstrated superior receiver sensitivity and Q factor compared to conventional designs, yielding significant SNR improvements in 14.1 T imaging.

Significance: The results demonstrated the feasibility of achieving enhanced coil performance through HDC design at ultra-high field strength, providing a promising approach for improving image quality in small-animal MRI applications.