Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Reexamination Certificate
2006-02-14
2006-02-14
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
C324S318000
Reexamination Certificate
active
06998949
ABSTRACT:
The invention relates to a magnetic resonance imaging (MRI) system (1) comprising an examination volume (11), a main magnet system (17) for generating a magnetic field (B0) in the examination volume, and a gradient magnet system (25) for generating altering gradients of the magnetic field in the examination volume. The gradient magnet system is accommodated in a housing (31) having a main wall (33) facing the examination volume and a substantially conical wall (35) facing away from the examination volume. The main wall and the conical wall enclose a substantially angular tip portion (47) of the housing. In order to limit the level of the acoustic vibrations in and around the MRI system (1) caused by mechanical vibrations of the angular tip portion (47), the MRI system comprises a plurality of acoustic resonators (55) which each comprise an elongate resonance volume (57) with an open end (59) and a closed end (61) and a length (L) between the open end and the closed end. The open ends of the resonators are arranged near the angular tip portion, and the length of the resonators is substantially equal to 0,25 k*(, wherein k=1, 3, 5, 7, . . . , and wherein (is the wavelength of an acoustic wave caused by mechanical vibrations of the angular tip portion. The resonators have the acoustic property of neutralizing acoustic waves having said wavelength (. Preferably, the length of the resonators is tuned to at least one of the wavelengths corresponding to the mechanical resonance frequencies of the vibrating angular tip portion, as the acoustic waves originating from the vibrations at these resonance frequencies constitute a main portion of the overall acoustic level of the MRI system.
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Ham Cornelis Leonardus Gerardus
Harvey Paul Royston
La Grange Martijn Roger
Limpens Patrick Willem Paul
Roozen Nicolaas Bernardus
Donovan Lincoln
Lundin Thomas M.
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