Novel ¹H/¹⁹F double-tuned coil using an asymmetrical butterfly coil

Fluorine-19 (¹⁹F) magnetic resonance imaging (MRI) is a non-invasive imaging tool for the targeted application of fluorinated agents, such as cell tracking, and for the demonstration of oximetry. However, as the SNR of ¹⁹F is significantly weaker than that of proton (¹H) imaging, the ¹⁹F coil must be combined with ¹H coils for anatomical co-registration and B₀ shimming. This is difficult due to the strong coupling between the coils when they are in proximity, and is problematic since the Larmor frequency of ¹⁹F is 94% that of ¹H, further increasing the potential for coupling between the ¹H and ¹⁹F elements.

Conventional double-tuned coil methods tend to generate loss compared to single-tuned reference coils. The asymmetrical butterfly coil has a split resonance peak, which can cover frequencies of ¹H and ¹⁹F without losses arising from lossy traps or switching circuits. In this study, the use of an asymmetrical butterfly coil was evaluated for ¹H/¹⁹F applications.

To increase quadrature efficiency at both the ¹H and ¹⁹F frequencies, the left and right loops of the butterfly coil were tuned asymmetrically. The coil's tuning and performance were evaluated in simulations and MR measurements, and the results were compared to a dimension-matched single-tuned loop coil.

The split resonance peak of the asymmetrical butterfly coil successfully spanned the ¹⁹F to ¹H frequency. It operated with higher quadrature efficiency at both ¹H and ¹⁹F frequencies and demonstrated superior receive sensitivity and SNR compared to the dimension-matched single-tuned loop coil.

The split resonance peak of the asymmetrical butterfly coil supported both ¹H and ¹⁹F frequencies, delivering a higher SNR than that of the single-tuned loop coil. Since the asymmetrical butterfly coil can cover ¹H and ¹⁹F frequencies without loss and provides higher efficiency than the reference single-tuned coil, it can be effectively utilized for ¹H/¹⁹F MRI applications.