A concentric-loops coil enhancing RF coil B₁ efficiency and reducing imaging noise compared to traditional single-loop coil

We proposed a simple approach to optimize a concentric-loops RF coil, consisting of an inner primary coil as the driving coil and an outer secondary coil as a passive resonator. By adjusting the tuning capacitor in the secondary loop to raise its self-resonance frequency to be slightly above the operating Larmor frequency, we enabled the preferred operation condition (additive mode), where both secondary and primary loops contributed to the largely enhanced RF coil transmit and receive magnetic fields (B₁) within the area enclosed by the primary loop as compared to a single-loop secondary coil. Compared to a single secondary loop coil as control, electromagnetic (EM) simulations and phantom MRS/MRI at 10.5 Tesla (T) ¹⁷O (60.6 MHz), 7 T ³¹P (120.7 MHz), and 1.5 T ¹H (63.8 MHz) operating frequencies show that the concentric-loops coil (8 cm diameter for the secondary loop coil) provides 1.2 to 1.4-fold higher B₁ and coil detection sensitivity in the near-coil region (0–3 cm). In the far region, it offers slightly enhanced B₁ and coil sensitivity, which becomes similar to the control coil at 9 cm away from the coil plane. Additionally, the concentric-loops coil reduces imaging noise by 15–30 %, collectively, resulting in an ∼1.7-fold signal-to-noise ratio (SNR) gain at the near-coil region. The concentric-loops coil with the presented optimization strategy provides an effective and simple coil design with largely improved imaging SNR compared to a conventional single-loop coil for a broad range of MRS/MRI applications across different field strengths.