Image uniformity improvement for birdcage-like volume coils at 400 MHz using multichannel excitations

We present a new method to deal with MRI non-uniformities caused by electromagnetic wave interference patterns at 300–400 MHz in lossy dielectrics. The non-uniformities are also known as “dielectric resonance” effects, yielding bright and dark spots at higher frequencies. The proposed method consists of applying a series of multiple cos(nϕ) (n = 1, …) circular current distributions on the birdcage legs in independent MRI experiments. The signals obtained during each experiment are then coalesced into a uniform image using appropriate weighting factors. The level of uniformity is improved by the application of additional cos(nϕ)-birdcage-like channels.