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

BACKGROUND

Fluorine-19 (F) 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 F is significantly weaker than that of proton (H) imaging, the F coil must be combined with H coils for anatomical co-registration and B 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 F is 94% that of H, further increasing the potential for coupling between the H and F elements.

PURPOSE

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 H and F without losses arising from lossy traps or switching circuits. In this study, the use of an asymmetrical butterfly coil was evaluated for H/F applications.

METHODS

To increase quadrature efficiency at both the H and F 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.

RESULTS

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

CONCLUSIONS

The split resonance peak of the asymmetrical butterfly coil supported both H and F 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.