Combined 23Na and 13C imaging at 3.0 Tesla using a single-tuned large FOV birdcage coil

Purpose: An unmet need in carbon-13 (C-13)-MRI is a transmit system that provides uniform excitation across a large FOV and can accommodate patients of wide-ranging body habitus. Due to the small difference between the resonant frequencies, sodium-23 (Na-23) coil developments can inform C-13 coil design while being simpler to assess due to the higher naturally abundant Na-23 signal. Here we present a removable Na-23 birdcage, which also allows operation as a C-13 abdominal coil. Methods: We demonstrate a quadrature-driven 4-rung Na-23 birdcage coil of 50 cm in length for both Na-23 and C-13 abdominal imaging. The coil transmit efficiencies and B-1(+) maps were compared to a linearly driven C-13 Helmholtz-based (clamshell) coil. SNR was investigated with Na-23 and C-13 data using an 8-channel C-13 receive array within the Na-23 birdcage. Results: The Na-23 birdcage longitudinal FOV was > 40 cm, whereas the C-13 clamshell was < 32 cm. The transmit efficiency of the birdcage at the Na-23 frequency was 0.65 mu T/sqrt(W), similar to the clamshell for C-13. However, the coefficient of variation of Na-23-B-1(+) was 16%, nearly half that with the C-13 clamshell. The 8-channel C-13 receive array combined with the Na-23 birdcage coil generated a greater than twofold increase in Na-23-SNR from the central abdomen compared with the birdcage alone. Discussion: This Na-23 birdcage coil has a larger FOV and improved B-1(+) uniformity when compared to the widely used clamshell coil design while also providing similar transmit efficiency. The coil has the potential to be used for both Na-23 and C-13 imaging.

Automated summary

The study introduced a quadrature-driven Na-23 birdcage coil for abdominal imaging, which showed improved FOV and B-1(+) uniformity compared to the clamshell coil design. The combination of an 8-channel C-13 receive array with the Na-23 birdcage coil resulted in a significant increase in SNR for Na-23 imaging in the central abdomen.