Novel quadrature birdcage coil for a vertical B0 field open MRI system

✍ Scribed by Hiroyuki Fujita; William O. Braum; Michael A. Morich

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 535 KB
• Volume: 44
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/1522-2594(200010)44:4<633::aid-mrm18>3.0.co;2-k

✦ Synopsis

A birdcage coil possesses various intrinsic resonant modes. One of the modes produces sinusoidal current distribution around the rung elements of the birdcage and generates a highly uniform B 1 field in the transverse plane. Another mode is the end-ring resonant mode, in which there are no currents in the rungs of the birdcage, leaving the currents flowing in the top and bottom end-rings. Thus, this mode behaves like a "Helmholtz pair," producing a highly uniform B 1 field along the axis of the birdcage. By combining the sinusoidal resonant mode and the end-ring resonant mode at the same frequency, a quadrature birdcage coil for a vertical B 0 field is made possible. In particular, the coil dimension can be chosen such that the two end-ring loops behave as a Helmholtz pair, assuring the optimized B 1 field uniformity around the coil center region. The coil is well suited for a vertical B 0 MRI system, as both B 1 fields are perpendicular to the vertical B 0 field. To mimic a vertical B 0 field orientation, an existing horizontal bore MRI system was used with the RF coil oriented to simulate a "vertical" B 0 field. This is a report of the successful quadrature implementation of this novel birdcage coil.