Concentric coil arrays for parallel MRI.

A new type of coil array is proposed that consists of concentrically placed coil elements, each of which is characterized by symmetrically arranged lobes that have alternating current directions. Symmetries in the coil elements' conductor paths allow for the minimization of mutual inductance and noise correlations. In addition, the concentric arrangement of the coil elements provides spatial encoding capabilities in multiple directions, which is valuable when arrays are used with parallel MRI. Simulations are presented that describe the signal-to-noise ratio (SNR) properties of individual concentric array elements, and a four-element prototype concentric array is constructed. This prototype array is compared experimentally with three alternative four-element array designs. The overall SNR of the concentric array is comparable to the SNR of the competing arrays. Reconstruction of twofold undersampled data using the concentric array yields an average g-factor of less than 1.3 in all directions parallel to the plane of the array. There is some degradation in performance when threefold undersampled data are reconstructed, but the array still shows substantial directional invariance compared to alternative designs. Both fully-sampled and undersampled cardiac images acquired using the concentric array are shown. These results suggest that concentric structures can be useful tools for designing specialized coil arrays for parallel MRI.