An asymmetrical whole-body birdcage RF coil without RF shield for hyperpolarized 129Xe lung MR imaging at 1.5 T

Abstract

Purpose: This study describes the development and testing of an asymmetrical xenon-129 (129Xe) birdcage radiofrequency (RF) coil for 129Xe lung ventilation imaging at 1.5 Tesla, which allows proton (1H) system body coil transmit–receive functionality. Methods: The 129Xe RF coil is a whole-body asymmetrical elliptical birdcage constructed without an outer RF shield to enable 1H imaging. (Formula presented.) field homogeneity and flip angle mapping of the 129Xe birdcage RF coil and 1H system body RF coil with the 129Xe RF coil in situ were evaluated in the MR scanner. The functionality of the 129Xe birdcage RF coil was demonstrated through hyperpolarized 129Xe lung ventilation imaging with the birdcage in both transceiver configuration and transmit-only configuration when combined with an 8-channel 129Xe receive-only RF coil array. The functionality of 1H system body coil with the 129Xe RF coil in situ was demonstrated by acquiring coregistered 1H lung anatomical MR images. Results: The asymmetrical birdcage produced a homogeneous (Formula presented.) 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 1H anatomical images from the system body coil along with 129Xe lung images demonstrated concurrent and compatible arrangement of the RF coils. Conclusion: A large asymmetrical birdcage for homogenous (Formula presented.) transmission with high sensitivity reception for 129Xe lung MRI at 1.5 Tesla has been demonstrated. The unshielded asymmetrical birdcage design enables 1H structural lung MR imaging in the same exam.