Design, construction, and use of a tapered-spiral, quadrature ¹H/²³Na double-tuned coil for in ovo MRI at 7 T

Background: In ovo MR presents a promising and viable alternative to traditional in vivo small animal experiments. Sodium MRI complements proton MRI by providing potential access to tissue cellular metabolism. Despite its abundance, sodium MRI is challenged by lower MR sensitivity and faster relaxation times compared to proton MRI. Ensuring a high signal-to-noise ratio and effective B₀ shimming is essential. Double-tuned coils combining ²³Na and ¹H are frequently employed to achieve structural imaging and efficient shim adjustment.

Purpose: This study introduces a novel, highly optimized, double-tuned coil design, specifically for MR scans of chick embryos.

Methods: A tapered-spiral, double-tuned coil was designed and constructed following careful consideration of design parameters. The performance of the coil was rigorously assessed through bench tests, and final validation was conducted on a 7 T MRI scanner using a chick embryo.

Results: Bench tests demonstrated that the return losses for both ¹H and ²³Na coils were better than - 30 dB, and isolation factors were better than - 21 dB, indicating that the double-tuned coil was well-set, with negligible coupling between channels. MR images of chick embryos, obtained using the coil, validated the feasibility of utilizing the design concept for in ovo applications.

Conclusions: The innovative design of the proposed double-tuned coil, characterized by its unique arrangement, offers improved performance. This design has the potential to significantly enhance the quality of in ovo ¹H and ²³Na measurements.