A generalized strategy for designing ¹⁹F/¹H dual-frequency MRI coil for small animal imaging at 4.7 Tesla

Purpose: To propose and test a universal strategy for building ¹⁹F/¹H dual-frequency RF coil that permits multiple coil geometries. Materials and Methods: The feasibility to design ¹⁹F/¹H dual-frequency RF coil based on coupled resonator model was investigated. A series capacitive matching network enables robust impedance matching for both harmonic oscillating modes of the coupled resonator. Two typical designs of ¹⁹F/¹H volume coils (birdcage and saddle) at 4.7T were implemented and evaluated with electrical bench test and in vivo ¹⁹F/¹H dual-nuclei imaging. Results: For various combinations of internal resistances of the sample coil and secondary resonator, numerical solutions for the tunable capacitors to optimize impedance matching were obtained using a root-seeking program. Identical and homogeneous B1 field distribution at ¹⁹F and ¹H frequencies were observed in bench test and phantom image. Finally, in vivo mouse imaging confirmed the sensitivity and homogeneity of the ¹⁹F/¹H dual-frequency coil design. Conclusion: A generalized strategy for designing ¹⁹F/¹H dual-frequency coils based on the coupled resonator approach was developed and validated. A unique feature of this design is that it preserves the B1 field homogeneity of the RF coil at both resonant frequencies. Thus it minimizes the susceptibility effect on image co-registration.