Gradient power source apparatus for magnetic resonance imaging system
AssigneeKabushiki Kaisha Toshiba
InventorFumikazu Takahashi
Life of this patent
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Abstract
A capacitor is connected in parallel with a gradient coil to form a parallel resonance circuit with the gradient coil. A gradient coil current is reversed utilizing parallel resonance of the gradient coil and the capacitor. The gradient coil current is detected by a shunt resistor connected in series to a power source. A voltage across the shunt resistor is compared with a reference voltage to control a power-source voltage, thereby controlling a gradient-coil current waveform. This arrangement allows imaging sequences to be performed in a short time without involving gradient field waveform distortion and increasing power consumption. A gradient power source apparatus suited for ultra high-speed MRI apparatus is provided.
Claims18
A gradient power source apparatus for use with gradient coil means used in magnetic resonance imaging apparatus to cause said gradient coil means to produce a gradient magnetic field, comprising:
- capacitor means, connected in parallel with said gradient coil means, for forming a resonance circuit with said gradient coil means;
- switching devices connected together to form a bridge circuit which is connected between a power supply terminal and said gradient coil means, said bridge circuit having two nodes, said capacitor means and said gradient coil means connected between the same two nodes of said bridge circuit;
- and
- control means for controlling said switching devices to thereby control a current supplied to said gradient coil means, said control means including means for bringing said resonance circuit to resonance to thereby reverse a current flowing through said gradient coil means.
A gradient magnetic field generating apparatus for use in a magnetic resonance imaging apparatus, comprising:
- variable-output power source means having a terminal;
- coil means for generating a gradient magnetic field when supplied with a current from said power source means;
- capacitor means, connected in parallel with said coil means, for forming a resonance circuit with said coil means
- switching devices, connected between said resonance circuit and said power source means to form a bridge circuit which is connected between the terminal of said variable-output power source means and said coil means, said bridge circuit having two nodes, said capacitor means and said coil means connected between the same two nodes of said bridge circuit, for controlling charging/discharging of said capacitor means and a current flowing through said coil means including its direction, said switching devices charging an electric charge of a first polarity in said capacitor means bringing said resonance circuit to resonance to thereby cause a discharging current of said capacitor means to flow through said coil means in a first direction, causing a current from said power source means to flow through said coil means in said first direction following said discharging current from said capacitor means, charging an electric charge of a second polarity in said capacitor means, bringing said resonance circuit to resonance to thereby cause a discharging current of said capacitor means to flow through said capacitor means in a second direction, and causing a current from said power source means to flow through said coil means in said second direction, thereby causing said coil means to generate a rectangular gradient magnetic field;
- and
- control means for detecting a current flowing through said coil means and varying an output of said power source means so that a detected current equals a predetermined value.
Dependencies are inferred from the claim text.