METHOD IN MAGNETIC RESONANCE IMAGING AND MAGNETIC RESONANCE IMAGING APPARATUS
A method in magnetic resonance imaging according to an exemplary embodiment includes acquiring a first temperature variation amount as a variation amount of a temperature of a gradient coil unit which includes a gradient coil corresponding to an X-axis; a gradient coil corresponding to a Y-axis; and a gradient coil corresponding to a Z-axis; and a first frequency variation amount as a shift amount of a center frequency at which nuclear spin of a subject causes magnetic resonance, the first temperature variation amount and the first frequency variation amount being caused by execution of a first sequence based on a first setting in which a readout gradient magnetic field is applied in a direction of the X-axis by the gradient coil unit; acquiring a second temperature variation amount as the variation amount of the temperature of the gradient coil unit and a second frequency variation amount as the shift amount of the center frequency, the second temperature variation amount and the second frequency variation amount being caused by execution of the first sequence based on a second setting in which the readout gradient magnetic field is applied in a direction of the Y-axis by the gradient coil unit; acquiring a third temperature variation amount as the variation amount of the temperature of the gradient coil unit and a third frequency variation amount as a shift amount of the center frequency, the third temperature variation amount and the third frequency variation amount being caused by execution of the first sequence based on a third setting in which the readout gradient magnetic field is applied in a direction of the Z-axis by the gradient coil unit; and acquiring a fourth temperature variation amount as the variation amount of the temperature of the gradient coil unit caused by execution of a second sequence to be executed after the first sequence, and calculating a value corresponding to the shift amount of the center frequency in the second sequence, based on the first temperature variation amount, the first frequency variation amount, the second temperature variation amount, the second frequency variation amount, the third temperature variation amount, the third frequency variation amount, the fourth temperature variation amount, and a weighting value corresponding to a gradient magnetic field to be applied in the second sequence.
1 . A method in a magnetic resonance imaging, the method comprising:
acquiring a first temperature variation amount as a variation amount of a temperature of a gradient coil unit which includes a gradient coil corresponding to an X-axis; a gradient coil corresponding to a Y-axis; and a gradient coil corresponding to a Z-axis; and a first frequency variation amount as a shift amount of a center frequency at which nuclear spin of a subject causes magnetic resonance, the first temperature variation amount and the first frequency variation amount being caused by execution of a first sequence based on a first setting in which a readout gradient magnetic field is applied in a direction of the X-axis by the gradient coil unit;
acquiring a second temperature variation amount as the variation amount of the temperature of the gradient coil unit and a second frequency variation amount as the shift amount of the center frequency, the second temperature variation amount and the second frequency variation amount being caused by execution of the first sequence based on a second setting in which the readout gradient magnetic field is applied in a direction of the Y-axis by the gradient coil unit;
acquiring a third temperature variation amount as the variation amount of the temperature of the gradient coil unit and a third frequency variation amount as the shift amount of the center frequency, the third temperature variation amount and the third frequency variation amount being caused by execution of the first sequence based on a third setting in which the readout gradient magnetic field is applied in a direction of the Z-axis by the gradient coil unit;
acquiring a fourth temperature variation amount as the variation amount of the temperature of the gradient coil unit caused by execution of a second sequence to be executed after the first sequence; and
calculating a value corresponding to the shift amount of the center frequency in the second sequence, based on the first temperature variation amount, the first frequency variation amount, the second temperature variation amount, the second frequency variation amount, the third temperature variation amount, the third frequency variation amount, the fourth temperature variation amount and a weighting value corresponding to a gradient magnetic field to be applied in the second sequence.
2 . The method according to claim 1 , further comprising setting a center frequency of a radio frequency (RF) pulse in the second sequence based on the calculated value corresponding to the shift amount of the center frequency in the second sequence, the RF pulse being applied to a subject to be imaged.
3 . The method according to claim 2 , wherein the center frequency of the RF pulse in the second sequence is set at least one of timings of between addition counts, between multi-slices and between dynamic scans during execution of the second sequence.
4 . The method according to claim 1 , further comprising correcting data corresponding to a magnetic resonance signal in a k-space obtained by the second sequence so that an effect of the shift amount is reduced based on the calculated value corresponding to the shift amount of the center frequency in the second sequence.
5 . The method according to claim 1 , further comprising correcting data corresponding to a magnetic resonance signal in a real space obtained by the second sequence so that an effect of the shift amount is reduced based on the calculated value corresponding to the shift amount of the center frequency in the second sequence.
6 . The method according to claim 1 , further comprising setting a center frequency of an RF pulse in the second sequence based on a value obtained by weighting a ratio between the first frequency variation amount and the first temperature variation amount, a ratio between the second frequency variation amount and the second temperature variation amount and a ratio between the third frequency variation amount and the third temperature variation amount by the weighting value, the RF pulse being applied to a subject to be imaged.
7 . The method according to claim 1 , wherein the weighting value includes a first value, a second value and a third value, the first value being a ratio between energy to be consumed by the gradient coil corresponding to the X-axis, the gradient coil corresponding to the Y-axis and the gradient coil corresponding to the Z-axis by executing the second sequence and energy to be consumed by the gradient coil corresponding to the X-axis by executing the second sequence, the second value being a ratio between energy to be consumed by the gradient coil corresponding to the X-axis, the gradient coil corresponding to the Y-axis and the gradient coil corresponding to the Z-axis by executing the second sequence and energy to be consumed by the gradient coil corresponding to the Y-axis by executing the second sequence, the third value being a ratio between energy to be consumed by the gradient coil corresponding to the X-axis, the gradient coil corresponding to the Y-axis and the gradient coil corresponding to the Z-axis by executing the second sequence and energy to be consumed by the gradient coil corresponding to the Z-axis by executing the second sequence.
8 . The method according to claim 1 ,
Wherein each of the first temperature variation amount, the second temperature variation amount, the third temperature variation amount, and the fourth temperature variation amount are acquired at a plurality of predetermined positions on the gradient coil unit, and
wherein the value corresponding to the shift amount of the center frequency in the second sequence is calculated based on a plurality of first temperature variation amounts, the first frequency variation amount, a plurality of second temperature variation amounts, the second frequency variation amount, a plurality of third temperature variation amounts, the third frequency variation amount, a plurality of fourth temperature variation amounts and the weighting value corresponding to the gradient magnetic field to be applied in the second sequence.
9 . The method according to claim 1 , wherein the first sequence is identical or similar to the second sequence.
10 . A method in a magnetic resonance imaging, the method comprising:
acquiring a first temperature variation amount as a variation amount of a temperature of a gradient coil unit which includes a gradient coil corresponding to a first axis and a gradient coil corresponding to a second axis, and acquiring a first frequency variation amount as a shift amount of a center frequency at which nuclear spin of a subject causes magnetic resonance, the first temperature variation amount and the first frequency variation amount being caused by execution of a first sequence based on a first setting in which a readout gradient magnetic field is applied in a direction of the first axis by the gradient coil unit;
acquiring a second temperature variation amount as the variation amount of the temperature of the gradient coil unit and a second frequency variation amount as the shift amount of the center frequency, the second temperature variation amount and the second frequency variation amount being caused by execution of the first sequence based on a second setting in which the readout gradient magnetic field is applied in a direction of the second axis by the gradient coil unit;
acquiring a third temperature variation amount as the variation amount of the temperature of the gradient coil unit caused by execution of a second sequence to be executed after the first sequence; and
calculating a value corresponding to the shift amount of the center frequency in the second sequence, based on the first temperature variation amount, the first frequency variation amount, the second temperature variation amount, the second frequency variation amount, the third temperature variation amount and a weighting value corresponding to a gradient magnetic field to be applied in the second sequence.
11 . A magnetic resonance imaging apparatus comprising:
a static field magnet configured to generate a static magnetic field within a bore in which a subject to be imaged is located;
a gradient coil unit including a gradient coil corresponding to an X-axis, a gradient coil corresponding to a Y-axis, and a gradient coil corresponding to a Z-axis; and
a processing circuitry configured to:
acquire a first temperature variation amount as a variation amount of the temperature of the gradient coil unit and a first frequency variation amount as a shift amount of a center frequency at which nuclear spin of the subject causes magnetic resonance, the first temperature variation amount and the first frequency variation amount being caused by execution of a first sequence based on a first setting in which a readout gradient magnetic field is applied in a direction of the X-axis by the gradient coil unit;
acquire a second temperature variation amount as the variation amount of the temperature of the gradient coil unit and a second frequency variation amount as the shift amount of the center frequency, the second temperature variation amount and the second frequency variation amount being caused by execution of the first sequence based on a second setting in which the readout gradient magnetic field is applied in a direction of the Y-axis by the gradient coil unit;
acquire a third temperature variation amount as the variation amount of the temperature of the gradient coil unit and a third frequency variation amount as the shift amount of the center frequency, the third temperature variation amount and the third frequency variation amount being caused by execution of the first sequence based on a third setting in which the readout gradient magnetic field is applied in a direction of the Z-axis by the gradient coil unit;
acquire a fourth temperature variation amount as the variation amount of the temperature of the gradient coil unit caused by execution of a second sequence to be executed after the first sequence; and
calculate a value corresponding to the shift amount of the center frequency in the second sequence, based on the first temperature variation amount, the first frequency variation amount, the second temperature variation amount, the second frequency variation amount, the third temperature variation amount, the third frequency variation amount, the fourth temperature variation amount and a weighting value corresponding to a gradient magnetic field to be applied in the second sequence.
12 . The magnetic resonance imaging apparatus according to claim 11 , wherein the processing circuitry is configured to set a center frequency of an RF pulse in the second sequence based on the value corresponding to the shift amount of the center frequency in the second sequence, the RF pulse being applied to the subject.
13 . The magnetic resonance imaging apparatus according to claim 12 , wherein the processing circuitry is configured to set the center frequency of the RF pulse in the second sequence at at least one of timings of between addition counts, between multi-slices, and between dynamic scans during execution of the second sequence.
14 . The magnetic resonance imaging apparatus according to claim 11 , wherein the processing circuitry is configured to correct data corresponding to a magnetic resonance signal in a k-space obtained by the second sequence so that an effect of the shift amount is reduced based on the value corresponding to the shift amount of the center frequency in the second sequence.
15 . The magnetic resonance imaging apparatus according to claim 11 , wherein the processing circuitry is configured to correct data corresponding to a magnetic resonance signal in a real space obtained by the second sequence so that an effect of the shift amount is reduced based on the value corresponding to the shift amount of the center frequency in the second sequence.
16 . The magnetic resonance imaging apparatus according to claim 11 , wherein the processing circuitry is configured to set a center frequency of an RF pulse in the second sequence based on a value obtained by weighting a ratio between the first frequency variation amount and the first temperature variation amount, a ratio between the second frequency variation amount and the second temperature variation amount and a ratio between the third frequency variation amount and the third temperature variation amount by the weighting value, the RF pulse being applied to a subject to be imaged.
17 . The magnetic resonance imaging apparatus according to claim 11 , wherein the weighting value includes a first value, a second value and a third value, the first value being a ratio between energy to be consumed by the gradient coil corresponding to the X-axis, the gradient coil corresponding to the Y-axis and the gradient coil corresponding to the Z-axis by executing the second sequence and energy to be consumed by the gradient coil corresponding to the X-axis by executing the second sequence, the second value being a ratio between energy to be consumed by the gradient coil corresponding to the X-axis, the gradient coil corresponding to the Y-axis and the gradient coil corresponding to the Z-axis by executing the second sequence and energy to be consumed by the gradient coil corresponding to the Y-axis by executing the second sequence, the third value being a ratio between energy to be consumed by the gradient coil corresponding to the X-axis, the gradient coil corresponding to the Y-axis and the gradient coil corresponding to the Z-axis by executing the second sequence and energy to be consumed by the gradient coil corresponding to the Z-axis by executing the second sequence.