Magnetic resonance imaging apparatus and operating method
View Patent ↗In order to extend the lifetime of a cooler and reduce down periods of an MRI apparatus due to the maintenance, a cooling capacity of the cooler 107 of the superconducting magnet is controlled so that cooling heat absorption almost equivalent to an amount of heat penetrating into the refrigerant vessel 202 of the superconducting magnet is exerted, and pressure in the refrigerant vessel 202 is maintained within an acceptable pressure range. In addition to this, at least either change amount of magnetic field strength or magnetic field homogeneity in an imaging space due to a pressure change in the refrigerant vessel 202 is compensated by the magnetic field adjustment unit.
1. A magnetic resonance imaging apparatus, comprising:
a superconducting magnet that generates a static magnetic field in an imaging space;
a gradient magnetic field coil that applies a gradient magnetic field to the imaging space;
a high-frequency coil that applies a high-frequency magnetic field to the imaging space; and
a control unit that controls operations of the gradient magnetic field coil and the high-frequency coil to execute a predetermined imaging sequence,
wherein the superconducting magnet includes a refrigerant vessel to accommodate a refrigerant and a superconducting coil, a cooler that is connected to the refrigerant vessel and re-condenses refrigerant gas vaporized in the refrigerant vessel, and a detector to detect pressure in the refrigerant vessel,
wherein the cooler includes a cylinder, a displacer disposed in the cylinder, a driving unit that reciprocates the displacer in the cylinder, and a compressor unit that supplies the cylinder with compressed refrigerant gas, and
wherein
the control unit controls a cooling capacity of the cooler of the superconducting magnet by controlling a frequency of reciprocation of the displacer, and
the control unit compares a pressure value detected by the detector with a predetermined set pressure value and continuously performs feedback control that increases the cooling capacity of the cooler if the pressure value is higher than the set pressure value and that reduces the cooling capacity of the cooler if the pressure value is lower than the set pressure value to maintain a thermal equilibrium state at the set pressure value.
2. The magnetic resonance imaging apparatus according to claim 1 , wherein
there are a plurality of types of imaging sequences, and
the control unit estimates a cooling capacity that should be increased for the cooler based on the amount of heat penetrating into the refrigerant vessel by the gradient magnetic field and high-frequency magnetic field when the imaging sequence is executed after the heat amount is calculated for each type amongst the plurality of types of imaging sequences in advance and increases a cooling capacity of the cooler continuously to the estimated cooling capacity.
3. The magnetic resonance imaging apparatus according to claim 1 , further includes a magnetic field adjustment unit that adjusts at least one of magnetic field strength or magnetic field homogeneity, in the imaging space, and
wherein the magnetic field adjustment unit compensates change amounts of magnetic field strength and magnetic field homogeneity in the imaging space due to a pressure change in the refrigerant vessel.
4. The magnetic resonance imaging apparatus according to claim 2 , wherein the control unit performs feedback control that maintains pressure in the refrigerant vessel to predetermined set pressure even in a state where an imaging sequence is not executed.
5. The magnetic resonance imaging apparatus according to claim 1 , wherein the control unit displays information that shows (i) a change over time of a cooling capacity of the cooler along with (ii) changes over time of a standard cooling capacity on an image display device.
6. A magnetic resonance imaging apparatus, comprising:
a superconducting magnet that generates a static magnetic field in an imaging space;
a gradient magnetic field coil that applies a gradient magnetic field to the imaging space;
a high-frequency coil that applies a high-frequency magnetic field to the imaging space; and
a control unit that controls operations of the gradient magnetic field coil and the high-frequency coil to execute a predetermined imaging sequence,
wherein the superconducting magnet includes a refrigerant vessel to accommodate a refrigerant and a superconducting coil, a cooler that is connected to the refrigerant vessel and re-condenses refrigerant gas vaporized in the refrigerant vessel, and a detector to detect pressure in the refrigerant vessel,
wherein the cooler includes a cylinder, a displacer disposed in the cylinder, a driving unit that reciprocates the displacer in the cylinder, and a compressor unit that supplies the cylinder with compressed refrigerant gas,
wherein the control unit controls a cooling capacity of the cooler of the superconducting magnet by controlling a frequency of reciprocation of the displacer, and the control unit compares a pressure value detected by the detector with a predetermined set pressure value and continuously performs feedback control that increases the cooling capacity of the cooler if the pressure value is higher than the set pressure value and that reduces the cooling capacity of the cooler if the pressure value is lower than the set pressure value to maintain a thermal equilibrium state at the set pressure value, and
wherein the control unit controls the frequency of reciprocation of the displacer based on the pressure value detected by the detector, compared to the predetermined set pressure value, including increasing the frequency of reciprocation of the displacer if the pressure value is higher than the set pressure value and reducing the frequency of reciprocation of the displacer if the pressure value is lower than the set pressure value.