An asymmetrical whole-body birdcage RF coil without RF shield for hyperpolarized Xe lung MR imaging at 1.5 T.

PURPOSE

This study describes the development and testing of an asymmetrical xenon-129 ( Xe) birdcage radiofrequency (RF) coil for Xe lung ventilation imaging at 1.5 Tesla, which allows proton ( H) system body coil transmit-receive functionality.

METHODS

The Xe RF coil is a whole-body asymmetrical elliptical birdcage constructed without an outer RF shield to enable H imaging. field homogeneity and flip angle mapping of the Xe birdcage RF coil and H system body RF coil with the Xe RF coil in situ were evaluated in the MR scanner. The functionality of the Xe birdcage RF coil was demonstrated through hyperpolarized Xe lung ventilation imaging with the birdcage in both transceiver configuration and transmit-only configuration when combined with an 8-channel Xe receive-only RF coil array. The functionality of H system body coil with the Xe RF coil in situ was demonstrated by acquiring coregistered H lung anatomical MR images.

RESULTS

The asymmetrical birdcage produced a homogeneous field (±10%) in agreement with electromagnetic simulations. Simulations indicated an optimal detuning configuration with 4 diodes. The obtained g-factor of 1.4 for acceleration factor of R = 2 indicates optimal array configuration. Coregistered H anatomical images from the system body coil along with Xe lung images demonstrated concurrent and compatible arrangement of the RF coils.

CONCLUSION

A large asymmetrical birdcage for homogenous transmission with high sensitivity reception for Xe lung MRI at 1.5 Tesla has been demonstrated. The unshielded asymmetrical birdcage design enables H structural lung MR imaging in the same exam.