Magnetic resonance imaging apparatus and gradient magnetic field power supply

1. A magnetic resonance imaging apparatus, comprising:

a gradient magnetic field power supply configured to supply power to a gradient coil, the gradient magnetic field power supply including

a plurality of switching circuits, each of which includes a plurality of switching elements, and is configured to output a predetermined pulse voltage by performing a switching operation of each of the switching elements; and

processing circuitry configured to switch an operation mode between a first mode and a second mode in accordance with an intensity of a voltage to be output to the gradient coil, the first mode causing switching circuits of a first number to perform the switching operation of each of the switching elements among the plurality of switching circuits, and the second mode causing switching circuits of a second number smaller than the first number to perform the switching operation of each of the switching elements among the plurality of switching circuits,

wherein the processing circuitry is further configured to switch the operation mode based on at least one of a duty ratio of the pulse voltage that is output from an operating switching circuit and a slew rate of a gradient magnetic field generated by the gradient coil.

2. The magnetic resonance imaging apparatus according to claim 1 , wherein the processing circuitry is further configured to switch the operation mode to the second mode when a duty ratio of the pulse voltage that is output from an operating switching circuit becomes less than a first threshold in a state where the switching circuits operate in the first mode, and switches the operation mode to the first mode when the duty ratio of the pulse voltage that is output from the operating switching circuit becomes equal to or greater than a second threshold in a state where the switching circuits operate in the second mode.

3. The magnetic resonance imaging apparatus according to claim 1 , wherein

the gradient magnetic field power supply is further configured to output the voltage to the gradient coil based on an input signal that indicates a waveform of a gradient magnetic field generated by the gradient coil, and

the processing circuitry is further configured to:

calculate a differential value of the input signal; and

operate the switching circuits in the first mode when the differential value is equal to or greater than a predetermined threshold, and operate the switching circuits in the second mode when the differential value is less than the predetermined threshold, to switch the operation mode.

4. The magnetic resonance imaging apparatus according to claim 1 , wherein the processing circuitry is further configured to operate the switching circuits in the first mode when a slew rate of a gradient magnetic field generated by the gradient coil is equal to or greater than a predetermined threshold, and operate the switching circuits in the second mode when the slew rate is less than the predetermined threshold, to switch the operation mode.

5. The magnetic resonance imaging apparatus according to claim 4 , further comprising:

controlling circuitry configured to control imaging, wherein

the controlling circuitry is configured to determine in which of the first mode and the second mode the switching circuits are to be operated, based on the slew rate of the gradient magnetic field, and to transmit a switching signal indicating a result of the determination to the gradient magnetic field power supply, and

the processing circuitry is further configured to switch the operation mode in accordance with the switching signal.

6. The magnetic resonance imaging apparatus according to claim 4 , further comprising:

controlling circuitry configured to control imaging, wherein

the controlling circuitry is configured to transmit information indicating the slew rate to the gradient magnetic field power supply, and

the processing circuitry is further configured to determine in which of the first mode and the second mode the switching circuits are to be operated, based on the information indicating the slew rate, and to switch the operation mode in accordance with a result of the determination.

7. The magnetic resonance imaging apparatus according to claim 1 , wherein the gradient magnetic field power supply further includes compensating circuitry configured to feed back an output signal that is output from each of the switching circuits,

the processing circuitry is further configured to:

calculate a difference between an input signal indicating a waveform of a gradient magnetic field generated by the gradient coil and a feedback signal transmitted from the compensating circuitry;

convert, with proportionating circuitry, an error signal obtained as the difference with a predetermined proportional gain;

convert, with integrating circuitry, the error signal with a predetermined integral gain; and

add the signal that is output from the proportionating circuitry to the signal that is output from the integrating circuitry, and output a resultant signal as a control signal, and

each of the switching circuits is further configured to output the pulse voltage in accordance with the control signal,

wherein the processing circuitry is further configured to switch the proportional gain and the integral gain when switching the operation mode.

8. The magnetic resonance imaging apparatus according to claim 1 , wherein each of the switching circuits is a full bridge circuit.

9. A gradient magnetic field power supply supplying power to a gradient coil in a magnetic resonance imaging apparatus, the gradient magnetic field power supply comprising:

a plurality of switching circuits, each of which includes a plurality of switching elements, and is configured to output a predetermined pulse voltage by performing a switching operation of each of the switching elements; and

processing circuitry configured to switch an operation mode between a first mode and a second mode in accordance with an intensity of voltage to be output to the gradient coil, the first mode causing switching circuits of a first number to perform the switching operation of each of the switching elements among the plurality of switching circuits, and the second mode causing switching circuits of a second number smaller than the first number to perform the switching operation of each of the switching elements among the plurality of switching circuits,

wherein the processing circuitry is further configured to switch the operation mode based on at least one of a duty ratio of the pulse voltage that is output from an operating switching circuit and a slew rate of a gradient magnetic field generated by the gradient coil.

10. A magnetic resonance imaging apparatus, comprising:

a gradient magnetic field power supply configured to supply power to a gradient coil, the gradient magnetic field power supply including

a plurality of switching circuits, each of which includes a plurality of switching elements and is configured to output a predetermined pulse voltage by performing a switching operation of each of the switching elements; and

processing circuitry configured to switch an operation mode between a first mode and a second mode in accordance with an intensity of a voltage to be output to the gradient coil, the first mode causing switching circuits of a first number to perforin the switching operation of each of the switching elements among the switching circuits, and the second mode causing switching circuits of a second number smaller than the first number to perform the switching operation of each of the switching elements among the switching circuits,

wherein the processing circuitry is further configured to switch the operation mode to the second mode when a duty ratio of the pulse voltage that is output from an operating switching circuit becomes less than a first threshold in a state where the switching circuits operate in the first mode, and switch the operation mode to the first mode when the duty ratio of the pulse voltage that is output from the operating switching circuit becomes equal to or greater than a second threshold in a state where the switching circuits operate in the second mode.

11. A magnetic resonance imaging apparatus, comprising:

a gradient magnetic field power supply configured to supply power to a gradient coil, the gradient magnetic field power supply including

a plurality of switching circuits, each of which includes a plurality of switching elements and is configured to output a predetermined pulse voltage by performing a switching operation of each of the switching elements; and

processing circuitry configured to switch an operation mode between a first mode and a second mode in accordance with an intensity of a voltage to be output to the gradient coil, the first mode causing switching circuits of a first number to perform the switching operation of each of the switching elements among the switching circuits, and the second mode causing switching circuits of a second number smaller than the first number to perform the switching operation of each of the switching elements among the switching circuits,

wherein the processing circuitry is further configured to operate the switching circuits in the first mode when a slew rate of a gradient magnetic field generated by the gradient coil is equal to or greater than a predetermined threshold, and operate the switching circuits in the second mode when the slew rate is less than the predetermined threshold, to switch the operation mode.

12. A magnetic resonance imaging apparatus, comprising:

a gradient magnetic field power supply configured to supply power to a gradient coil, the gradient magnetic field power supply including

a plurality of switching circuits, each of which includes a plurality of switching elements and is configured to output a predetermined pulse voltage by performing a switching operation of each of the switching elements; and

processing circuitry configured to change a number of switching circuits that perform the switching operation of each of the switching elements among the switching circuits, in accordance with an intensity of a voltage to be output to the gradient coil,

wherein the processing circuitry is further configured to switch an operation mode between a first mode and a second mode in accordance with the intensity of the voltage to be output to the gradient coil, the first mode causing switching circuits of a first number to perform the switching operation of each of the switching elements among the switching circuits, and the second mode causing switching circuits of a second number smaller than the first number to perform the switching operation of each of the switching elements among the switching circuits,

the gradient magnetic field power supply further includes compensating circuitry configured to feed back an output signal that is output from each of the switching circuits,

the processing circuitry is further configured to

calculate a difference between an input signal indicating a waveform of a gradient magnetic field generated by the gradient coil and a feedback signal transmitted from the compensating circuitry;

convert, with proportionating circuitry, an error signal obtained as the difference with a predetermined proportional gain;

convert, with integrating circuitry, the error signal with a predetermined integral gain; and

add the signal that is output from the proportionating circuitry to the signal that is output from the integrating circuitry, and output a resultant signal as a control signal,

each of the switching circuits is further configured to output the pulse voltage in accordance with the control signal, and

the processing circuitry is further configured to switch the proportional gain and the integral gain when switching the operation mode.