Multi-nuclear MRI of an inhaled inert gases such as ³He, ¹²⁹Xe and ¹⁹F alongside anatomical ¹H imaging provides complementary functional and structural information of the lung for quantitative clinical diagnosis^1,2. Fluorinated gases have the advantage of being relatively cheap and do not require an optical-pumping polarizer. Multi-tuned RF coils for ³He-¹²⁹Xe-¹H for lung imaging have been demonstrated previously using passive trap circuits^3,4. The close resonance frequencies of ¹⁹F and ¹H (60.06 MHz and 68.83 MHz at 1.5T) make passive/active traps infeasible. A potential solution is by active switching the RF coil between the two resonances^5-7.In this study we investigate using Micro-electromechanical systems (MEMS) to switch a transmit-receive coil between the ¹H and ¹⁹F Larmor frequencies. The MEMS (GE Healthcare coils, Aurora, OH, USA) have suitable standoff voltage, isolation impedance and switching time for use in the MRI8 and to actively switch between resonances⁹. The RF coil was constructed in-house and the electrical design is described along with the characterization of equivalent series resistance (ESR) of the MEMS and associated noise/loss factor.Two surface-coil loops of dimension 36 cm $$$\times$$$ 24 cm were designed to operate as a quadrature transmit-receive pair specifically sized for lung imaging as shown in Figure 1. Coils were isolated using a capacitive decoupling network¹⁰. The coil topology and matching equation is shown in Figure 1, where $$$Z_m$$$ is the matched input impedance, $$$Z_{coil}$$$ is the coil input impedance and $$${C_{m1}}, {L_{m2}}, {C_{m3}}$$$ and $$${C_{m4}}$$$ are matching elements. An external DC power supply was used to switch the MEMS. The coil is tuned to ¹H and $$${C_{m4}}$$$ is isolated (off) when the MEMS is open, and tuned to ¹⁹F coils when MEMS is closed (short). In a separate experiment, ESR was found by measuring the quality (Q) factor of a resonant loop (15 cm ×15 cm) coil with and without MEMS. A phantom to emulate the human lungs (tissue and air space) was developed for multi-nuclear imaging made up of an outer container filled with 3.6g/ℓ NaCl and 1.96g/ℓ CuSO₄⋅5H₂O solution and an inner container (8 L) filled with perfluoropropane as shown in Figure 2. RF choke inductors (3.9 nH) were introduced at the MEMS control board and 0.7 m away to prevent induced RF currents. ¹⁹F imaging is performed with the following imaging parameters: fast gradient echo sequence, matrix = 32$$$\times$$$32, TR=100, TE=1.6, BW=8.06 kHz, FOV=48 cm, slice thickness=100 mm and 5 averages (scan time of 16 s). Pixel intensity $$$\rho_{x,y}$$$ at each voxel volume ($$$\triangle$$$V) location (x,y) in the slice is given by¹¹, $$\rho_{x,y}=\alpha\triangle{V{B_1^-}_{x,y}}{\omega_{0}}{M_{0}}\sin(2\pi\gamma\tau{B_1^+}_{x,y})$$ where $$$\alpha$$$ is a constant representing system gain, $$$\gamma$$$ is the gyromagnetic ratio, $$$\tau$$$ is the pulse width, $$$M_0$$$ is the longitudinal magnetization and $$${B_1^+}_{x,y}/{B_1^-}_{x,y}$$$ are the transmit and receive sensitivities. The transmitted RF power (peak) was varied linearly from 193 W to 580 W and measured values were fitted to estimate the flip angle, $$$\phi=2\pi\gamma\tau{B_1^+}_{x,y}$$$ with specified power¹². Co-registered ¹H imaging was performed with a gradient echo sequence. The Imaging parameters were: TR=200, TE=20, flip angle= 70 , BW=15.63 kHz, FOV=48 cm, slice thickness=20 mm, matrix = 256$$$\times$$$256 and 1 average. The imaging parameters of the ¹⁹F superimposed fast gradient echo sequence image were: TR=15, TE=1.9, BW=8.06 KHz, FOV=48 cm, slice thickness=100 mm, matrix = 64$$$\times$$$64 and 150 averages.The measured Q factors of the resonant coil are shown in Table 1. The MEMS inherent impedance was 0.41 Ω + 6.6 nH. $$$Z_{coil}$$$ was 21.8-2.3j Ω and 29.6+30.2j Ω at 60.1 MHz and 63.8 MHz respectively. The circuit values used to satisfy matching are $$$C_{m1}=68 pF,L_{m2}=90 nH ,C_{m3}=10 pF,C_{m4}=68 pF$$$. The calculated noise factor¹³ increased from 1.012 to 1.017 when the MEMS ESR was added, assuming capacitors ($$$C_{m1},C_{m3},C_{m4}$$$) and inductor ($$$L_{m2}$$$) have Q factors of 1000 and 100, respectively. The matching and isolation of the coils with MEMS switched on and off are shown in Figure 3. ¹⁹F flip angle measurement (contours) superimposed on a ¹⁹F image for = 387 W is shown in Figure 4(a). The ¹⁹F image superimposed on co-registered ¹H image is shown in Figure 4(b).Although ESR for MEMS is similar to PIN diodes (0.2 Ω⁶), MEMS power consumption is much lower. We have successful demonstrated MEMS are sufficiently robust to switch between multi-nuclear MR imaging of ¹⁹F fluorinated gas and ¹H using routine imaging sequences. Also, using sample loading dominated transmit-receive dual tuned RF coils the increased loss from the introduced MEMS ESR at frequencies > 60 MHz was negligible. Future studies will evaluate the MEMs in this coil design for human lung imaging.