| Autor: |
Fujita H; USA Instruments, Inc., Aurora, Ohio 44202, USA. hfujita@usainstruments.com, Braum WO, Morich MA |
| Jazyk: |
angličtina |
| Zdroj: |
Magnetic resonance in medicine [Magn Reson Med] 2000 Oct; Vol. 44 (4), pp. 633-40. |
| DOI: |
10.1002/1522-2594(200010)44:4<633::aid-mrm18>3.0.co;2-k |
| Abstrakt: |
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. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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