One of the favorite methods to produce a homogeneous
radiofrequency (RF) magnetic field, B1, in MRI is
with a cylindrical birdcage coil. While this coil produces a
very homogeneous field in a cylidrical volume, a coil that is
shaped more like the human body would be more sensitive to the
signal received from the nuclei in the body. We have developed a
method for optimization and implementation of birdcage coils
with elliptical cross-sections and linearly polarized B1
fields (ref). Notable gains in signal-to-noise ratio over those
of cylindrical birdcage coils are achieved. More recently, we
have developed a method for numerically optimizing non-circular
coils with circularly-polarized B1 fields within
cylindrical RF shields and implementing them. Figure 1 is an
experimental B1 map in a non-optimized elliptical
birdcage coil(all capacitors being equal). Figure 2 is an
experimental B1 map in an optimized elliptical
birdcage coil.
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