Combining X-nuclei with proton MRI allows accessing valuable cellular and metabolic information.^{1, 2} Due to lower intrinsic sensitivity of non-proton NMR, compared to ¹H, it is important to ensure that the signal-to-noise ratio (SNR) of X-nuclei is as high as possible. Quadrature coils are widely used due to the benefit in SNR.³ In this work, a novel, double-tuned (¹H/²³Na) surface coil using LCC traps^4,5 was designed in which ²³Na was driven in quadrature. The performance of this coil was evaluated and compared with geometrically identical single-tuned butterfly and loop coils.As shown in Figure 1, a double-tuned loop coil on the top of a single-tuned ²³Na butterfly coil was designed and constructed. These two coils were geometrically isolated and LCC traps were added only to the loop in order to achieve dual frequencies and not to lose the sensitivity of the butterfly sodium coil. This allowed quadrature operation at the sodium frequency. A T/R switch including a ²³Na hybrid coupler was built and three reference coils of single-tuned ¹H loop, ²³Na loop and ²³Na butterfly were also prepared for comparison. These probes were tuned and matched to a uniform water phantom containing 44.8 mM NaCl and 4.7 mM NiSO₄, and the loaded/unloaded Q factors were measured on the bench using a double-sniffer loop positioned at ~15 mm from the coil (Figure 2). All the experiments were carried out on a 4T whole-body system corresponding to the Larmor frequency of 168.2 MHz for proton and 44.5 MHz for sodium. Shimming was adjusted using the ¹H coil and the obtained shim values were applied for the sodium measurements. ¹H and ²³Na images were acquired using a 2D and a 3D FLASH sequence, respectively. The imaging parameters for proton/sodium were TR = 150/130 ms, TE = 4.34/2.78 ms, averages = 2/8, 5 mm slice thickness and the acquisition time = 0:38/13:19 minutes. SNR values were measured at the selected regions of interest (ROIs) – large, centre and side (top right in Figure 3) and plotted across the imaging volume (top left in Figure 3). The first and last two slices were discarded for the SNR calculations as these were either too close to the coil or too far. It is known that the loop coil provides high signal intensity around the coil surface but not at the centre while the butterfly coil does the opposite. The SNR profiles (bottom in Figure 3) demonstrate this and also indicate that the proposed concept can compensate for this effect with maintaining comparable SNR to the single-tuned reference coils at the side, centre and overall. It was shown that the images obtained by the quadrature compensated double-tuned RF coil were more uniform in each slice and the SNRs were slightly higher over the selected ROIs compared to these from the reference coils. The loss in the proton side due to the inserted traps was less than 10% (e.g. slice #3: SNR_single = 2901, SNR_double = 2704), which may also be minimised by optimising the LCC traps. The LCC traps may also be included only in the butterfly coil rather than in the loop. We intend to apply this concept to an animal surface coil and/or a human volume array and to carry out further investigation.