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A method to create an optimum current distribution and homogeneous B 1 field for elliptical birdcage coils
Author(s) -
Li Shizhe,
Collins Christopher M.,
Dardzinski Bernard J.,
Chin ChihLiang,
Smith Michael B.
Publication year - 1997
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910370420
Subject(s) - electromagnetic coil , homogeneous , physics , current (fluid) , nuclear magnetic resonance , field (mathematics) , inductance , optics , materials science , acoustics , voltage , mathematics , quantum mechanics , pure mathematics , thermodynamics
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 endring 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.