Folded four-ring double-tuned birdcage coil design

In this work, we designed a double-tuned ¹H/²³Na four-ring birdcage coil with a modification that entailed folding the outer end-rings by 90 degrees to overcome the available space limitation. And ²³Na SNR of the folded four-ring birdcage coil reached more than 93% of that obtained with the single-tuned birdcage coil. One benefit of folded four-ring birdcage coil compared to conventional four-ring birdcage coil is that there is no space restriction. This helps to build double-tuned coils that have a smaller diameter, leading to higher filling factors.