Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Patent
1995-01-27
1997-01-07
Arana, Louis M.
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
324319, 324322, G01H 300, G01H 314
Patent
active
055920870
ABSTRACT:
A magnetic resonance imaging apparatus includes a magnet assembly (10) for generating a temporally constant primary magnetic field through a central bore (14). The central bore is surrounded by a gradient coil assembly (30) including a dielectric former (32) and gradient coils (34, 36, 38) for generating magnetic field gradient pulses across the examination region. A radio frequency coil assembly (50) including a birdcage coil (52) is mounted inside of the gradient coil assembly and surrounding the examination region. A radio frequency shield (60) includes a dielectric sheet (62) having a plurality of first metal foil strips (72) defined on each surface. The metal strips are defined by etching or cutting gaps (70) in a continuous sheet of copper foil, leaving bridges (74) across the gaps adjacent opposite ends of the foil strips. The foil strips on opposite faces of the dielectric sheet are offset by half the width of one strip such that each strip is capacitively coupled to two strips on the opposite surface. The radio frequency coil induces radio or megahertz frequency eddy currents to which the capacitive coupling appears as a short-circuit, allowing the induced radio frequency currents to pass circumferentially around the shield. The gradient coil assembly induces kilohertz frequency eddy currents to which the capacitive couplings appear as open circuits. The kilohertz eddy currents flow longitudinally along a strip, cross a bridge adjacent one end of the strip, and flow back longitudinally along an adjacent strip, and so forth.
REFERENCES:
patent: 4642569 (1987-02-01), Hayes et al.
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patent: 5243286 (1993-09-01), Rzedzian et al.
patent: 5349297 (1994-09-01), DeMeester et al.
patent: 5396173 (1995-03-01), Sakakura et al.
Morich Michael A.
Richard Mark A.
Zou Xueming
Arana Louis M.
Haynes Mack
Picker International Inc.
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