AeroCoil: Pneumatically Controlled Dual-Tunable RF Coil for Proton (¹H) and Deuterium (²H)

In specific MRI applications, RF coils must operate at multiple resonance frequencies to support multinuclear imaging and spectroscopy. Designing such coils that can either resonate at or switch between multiple frequencies presents considerable technical challenges. Traditional multituned coils typically suffer from strong electromagnetic (EM) coupling due to limited physical space and the interaction between multiple resonating structures. Frequency-switchable coils offer an alternative by adjusting circuit capacitance or inductance to tune for different nuclei, typically relying on PIN diodes or similar electronic switches. However, these designs require frequency-sensitive bias circuitry, dedicated drivers, and long DC control lines, all of which are prone to RF interference within the MRI environment. Furthermore, PIN diodes introduce inherent RF leakage and nonlinearities that can significantly degrade image quality. This study introduces a pneumatically actuated frequency-switchable RF coil, termed AeroCoil, that enables resonance switching without electrical biasing. The AeroCoil design utilizes air pressure to mechanically adjust capacitance, enabling transitions between the ¹H and ²H Larmor frequencies at 9.4 T. This pneumatic mechanism eliminates the need for local electrical components near the imaging volume, thereby reducing RF noise, eliminating EM interference, and simplifying the coil's circuit architecture. The AeroCoil's performance was benchmarked against single-tuned coils, representing optimal performance at each frequency, and a PIN diode-based switchable coil. Bench measurements evaluated return losses and quality factors, whereas MRI experiments assessed SNR and image artifacts. The AeroCoil retained 88.2%-91.9% of the SNR compared with a single-tuned ¹H coil, whereas the PIN diode-based ¹H coil achieved only 68.3%-75%. At the ²H frequency, AeroCoil performance was further emphasized, retaining 71.7%-74.6% SNR, whereas the PIN diode-based design dropped sharply to 27.1%-28.8%.