Switching device to linearly conduct a current between a gradient amplifier and a gradient coil assembly of an MRI system
First Claim
1. A magnetic resonance imaging (MRI) system performing an MRI scan in accordance with a pulse sequence, the pulse sequence including at least a first pulse, the system comprising:
- a gradient coil assembly generating a gradient magnetic field during the MRI scan;
an amplifier driving the gradient coil assembly such that the gradient coil assembly generates the gradient magnetic field in accordance with the pulse sequence; and
a switch assembly providing a conductive path between the amplifier and the gradient coil assembly, the switch assembly comprising;
a first switching device having a conductive state during a first portion of the first pulse of the pulse sequence, the first portion dependent only on the magnitude of a current applied to the gradient coil assembly by the driving amplifier; and
a second switching device coupled in parallel with the first switching device, the second switching device having a conductive state during a second portion of the first pulse of the pulse sequence during which the current from the amplifier to the gradient coil assembly is below a non-zero threshold value, wherein the conductive path is provided between the amplifier and the gradient coil assembly during substantially the entire duration of the first pulse.
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Abstract
A switching circuit configured to substantially linearly conduct current between a source and a load includes a switching device and a steering circuit. The switching device has a conductive state in which a first portion of the current flows between the source and the load, the conductive state being dependent on the magnitude of the current. The steering circuit has a conductive state in which a second portion of the current flows, such that substantially the entire current is conducted between the source and the load. The switching circuit is particularly suited for use in a magnetic resonance imaging system to conduct gradient current between the gradient amplifiers and the gradient coils.
46 Citations
18 Claims
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1. A magnetic resonance imaging (MRI) system performing an MRI scan in accordance with a pulse sequence, the pulse sequence including at least a first pulse, the system comprising:
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a gradient coil assembly generating a gradient magnetic field during the MRI scan;
an amplifier driving the gradient coil assembly such that the gradient coil assembly generates the gradient magnetic field in accordance with the pulse sequence; and
a switch assembly providing a conductive path between the amplifier and the gradient coil assembly, the switch assembly comprising;
a first switching device having a conductive state during a first portion of the first pulse of the pulse sequence, the first portion dependent only on the magnitude of a current applied to the gradient coil assembly by the driving amplifier; and
a second switching device coupled in parallel with the first switching device, the second switching device having a conductive state during a second portion of the first pulse of the pulse sequence during which the current from the amplifier to the gradient coil assembly is below a non-zero threshold value, wherein the conductive path is provided between the amplifier and the gradient coil assembly during substantially the entire duration of the first pulse. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A magnetic resonance imaging (MRI) system acquiring MRI data, the system comprising:
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a processor controlling acquisition of the MRI data in accordance with a program stored in a memory, the program including an imaging protocol having a sequence of gradient pulses and a sequence of detection pulses;
a gradient amplifier driving the gradient coil assembly in accordance with the sequence of gradient pulses;
an MRI scanner performing an MRI scan, in accordance with the stored imaging protocol, the MRI scanner comprising a magnet, a gradient coil assembly, and an RF coil assembly, the gradient coil assembly generating a gradient magnetic field in accordance with the sequence of pulses;
a switch assembly coupled between the gradient amplifier and the gradient coil assembly providing a conductive path therebetween, the switch assembly comprising;
a first switching device having a conductive state during a first portion of the first pulse of the pulse sequence, the first portion dependent only on the magnitude of a current applied to the gradient coil assembly by the driving amplifier; and
a second switching device coupled in parallel with the first switching device, the second switching device having a conductive state during a second portion of the first pulse of the pulse sequence during which the current from the amplifier to the gradient coil assembly is below a non-zero threshold value, wherein the conductive path is provided between the amplifier and the gradient coil assembly during substantially the entire duration of the first pulse; and
an RF detector coupled to the RF coil to detect MRI data resulting from the MRI scan in accordance with the sequence of detection pulses. - View Dependent Claims (10, 11, 12, 13)
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14. A method for performing a magnetic resonance imaging (MRI) scan with an MRI system including a gradient coil assembly, the MRI scan being performed in accordance with a pulse sequence, the method comprising:
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receiving a pulse sequence;
generating a current to drive the gradient coil assembly in accordance with the pulse sequence, the current comprising a plurality of current pulses;
conducting the current to the gradient coil assembly through a switch assembly, the switch assembly comprising a first switching device and a second switching device coupled in parallel with the first switching device;
placing the first switching device in a conductive state during a first portion of a first current pulse, the conductive state of the first switching device dependent only on the magnitude of the current applied to the gradient coil assembly during the first current pulse by a driving amplifier; and
placing the second witching device in a conductive state during a second portion of the first current pulse, such that the current is conducted to the gradient coil assembly during substantially the entire duration of the first current pulse wherein placing the second switching device in the conductive state occurs when the absolute value of the magnitude of the current applied to the gradient coil assembly is below a non-zero threshold value. - View Dependent Claims (15, 16, 17, 18)
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Specification