Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Patent
1993-11-10
1996-01-02
Arana, Louis M.
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
324322, G01V 300
Patent
active
054811929
ABSTRACT:
A magnetic resonance apparatus includes a magnet system (1) for generating a steady magnetic field in a measuring space (35), a gradient coil system (3) for generating gradient fields in the measuring space, and a power supply source (7) for the gradient coils (3) which comprises at least one gradient signal generator (9) and a number of gradient amplifiers (11), each of which is connected between an output of the gradient signal generator and at least one of the gradient coils. In order to cancel annoying noise caused by the gradient coils (3), the apparatus also includes a noise cancellation device which includes the following elements:
a) a first filter device (39) having a number of inputs which corresponds to the number of gradient amplifiers (11), each of the inputs being connected to an output of the gradient signal generator (9), and also includes a corresponding number of outputs, the first filter device having transfer functions, all of which correspond approximately to the transfer function of one of the chains extending from the gradient signal generator (9), via one of the gradient amplifiers (11), the gradient coil (coils) (3) connected to this gradient amplifier, and air, to a region (40, 42) which is referred to as a region of silence and in which the sound of the gradient coils (3) is to be cancelled; b) an adder circuit (51), having inputs which are connected to outputs of the first filter device (39) and an output (63) which is connected to an input of a sound reproducing device which comprises at least one sound reproducer (57) arranged in or near the region of silence (40); and
c) a signal delay device (41) for inducing a predetermined time difference between the signal transfer from the gradient signal generator (9) to the gradient coils (3) on the one hand and the signal transfer from the gradient signal generator to the first filter device (39) on the other hand.
REFERENCES:
patent: 4677677 (1987-06-01), Eriksson
patent: 4954781 (1990-09-01), Hirata
"Reduction of Sound Levels with Antinoise in MR Imaging" Goldman et al, Radiology, vol. 173, No. 2, Nov. 1, 1989 pp. 549-550.
Ham Cornelis L. G.
Mehlkopf Antoon F.
Arana Louis M.
Slobod Jack D.
U.S. Philips Corporation
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