Potential advantage of higher-order modes of birdcage coil for parallel imaging

The potential advantages of the higher-order resonant modes of a low-pass birdcage coil for parallel imaging are investigated using FDTD simulations in a spherical phantom. Better parallel imaging performance can be achieved in axial planes than in sagittal planes. If more modes are employed, the average g-factor (gmean) and maximum g-factor (gmax) will be improved for a specific acceleration factor (R). G-factor performance at 3 T (gmean = 1.79, gmax = 3.55) and 7 T (gmean = 1.60, gmax = 2.45) can be achieved even with an acceleration factor as high as four when all six order modes of 12-rung low-pass birdcage coil are incorporated for imaging on a mid-axial plane. For a specific number of channels, the optimum combination of corresponding modes can be obtained for different acceleration factors. Based on the g-factor and SNR performance, the total degenerate multi-mode birdcage coil with six order resonant modes has better homogeneous coverage and SENSE performance than the 8-element phased array coil, although requiring fewer channels. In addition, the dielectric effects at high field can improve the parallel imaging performance.