A method to create an optimum current distribution and homogeneous B1 field for elliptical birdcage coils.
For a birdcage coil with elliptical cross-section, a sinusoidal current pattern does not provide a homogeneous B1 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 B1 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 B1 field was theoretically calculated and experimentally mapped for the optimized elliptical bird-cage coil and a nonoptimized coil. The results demonstrate that by optimizing the current distribution, a very homogeneous B1 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.
Li
S
S
Department of Radiology, Pennsylvania State University College of Medicine, Hershey 17033, USA.
Collins
C M
CM
Dardzinski
B J
BJ
Chin
C L
CL
Smith
M B
MB
D003198:Computer Simulation; D017352:Echo-Planar Imaging / Q000295:instrumentation*; D004867:Equipment Design; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008280:Magnetics; D008962:Models, Theoretical; D019047:Phantoms, Imaging