Degenerate mode birdcage volume coil for sensitivity-encoded imaging.

A volume birdcage coil for accelerated image encoding with parallel acquisition methods such as SENSE is demonstrated. The coil is degenerately tuned with both the standard homogeneous mode and the first gradient mode of the birdcage coil resonant at the Larmor frequency. Conventional and antisymmetric coupling structures allow imaging from each of these modes simultaneously. The coil for SENSE-type reconstruction with acceleration factors of up to 2-fold is demonstrated. The spatial distribution of the added noise from the SENSE reconstruction (g-factor map) due to geometrical arrangement of the two-channel system is estimated. The spatially averaged g-factors were found to be 1.21, 1.36, and 1.55 for 1.3, 1.6, and 2-fold accelerations, respectively. The system was demonstrated in vivo using accelerated and nonaccelerated anatomical brain images at 1.5 T. The maximal 2-fold acceleration in this dual-mode degenerate birdcage coil offers the potential to extend SENSE-type image reconstruction methods to applications demanding uniform whole brain coverage.