Ultra-high-field dual-frequency litz-foil RF coils for multi-nuclear preclinical MRI and its application to water transport and metabolism in mouse fetal organs

Multi-nuclear MRI enables observation of metabolic and physiological processes that are complementary to conventional proton imaging but often suffers from inherently low sensitivity, justifying the need for efficient dual-frequency RF coil designs for ultra-high-fields (UHF). We present the design and optimization of dual-frequency H/X RF coil modules suitable for a wide range of sizes and fields and show results for a coil with 36-mm inner diameter at 15.2 T for small-animal imaging. The module combines orthogonal linear “litz-foil” coils employing insulated crossovers that enforce a more optimal current distribution and improve B₁ efficiency and homogeneity. Optimization was performed through an iterative combination of detailed circuit modeling and full-wave 3D electromagnetic simulations. The multi-nuclear low-frequency coil is tunable from ¹⁴N to ²³Na via plug-in capacitors and can reach ³¹P at reduced efficiency, while the high-frequency coil operates efficiently from ¹H to ¹⁹F. Simulations predict high B₁ efficiency and homogeneity, good channel isolation, and minimal parasitic modes. Experimental measurements confirm these predictions and demonstrate high-quality ¹H and ²H imaging in vivo at 15.2 T Deuterium MRI following administration of D₂O reveals water transport across mouse placentas and into fetal organs with unprecedented spatial and time-dependence detail. These results illustrate the advantages of orthogonal litz-foil RF architectures and demonstrate the value of combined circuit-plus-EM optimization for broadband multi-nuclear MRI at ultra-high field.