A method to create an optimum current distribution and homogeneous B-1 field for elliptical birdcage coils

For a birdcage coil with elliptical cross-section, a sinusoidal current pattern does not provide a homogeneous B-1 field, A simple theory was developed to create an optimized current distribution for elliptical birdcage coils, This optimized current pattern can create a perfectly homogeneous B-1 field inside any elliptical shape, To verify the theory, a 16-element high-pass elliptical birdcage coil was built inside a circular RF shield, The current was optimized by using the inductance characteristics of the coil components to calculate the end-ring capacitances. The B-1 field was theoretically calculated and experimentally mapped for the optimized elliptical birdcage coil and a nonoptimized coil, The results demonstrate that by optimizing the current distribution, a very homogeneous B-1 field is produced, This method can be directly applied in design and construction of elliptical birdcage coils for imaging of the naturally occurring elliptical cross-sectional geometries in the human body.