Energizing and discharging a superconducting magnet of an MRI system

Abstract

A magnetic resonance imaging (MRI) system includes a superconducting magnet assembly with a superconducting field coil for generating a stationary uniform main magnetic field. A gradient system includes a gradient coil for generating gradient magnetic fields and a gradient amplifier which is connectable to the gradient coil for driving the gradient coil. A switch assembly is adapted for galvanically coupling the superconducting field coil to the gradient amplifier. In this way, it is possible for energizing and discharging a superconducting magnet of an MRI system in an easy and cost-efficient way.

Claims

1. A magnetic resonance imaging (MRI) system comprising: a superconducting magnet assembly with a superconducting field coil for generating a stationary uniform main magnetic field due to an electrical DC current, a gradient system including a gradient coil for generating gradient magnetic fields and a gradient amplifier which is connectable to the gradient coil for driving the gradient coil, a quench assembly to switch-off the superconducting field coil a switch assembly which is adapted for galvanically coupling the superconducting field coil to the gradient coil and a switch control configured to control the switch assembly to galvanically couple the superconducting field coil to the gradient coil so as to discharge the superconducting field coil resistively over the gradient coil to the threshold value of the electrical DC current strength and activate the quench assembly when the electrical DC current strength falls below the threshold value.

2. The MRI system of claim 1, wherein the switch assembly is adapted for galvanically coupling the superconducting field coil simultaneously to the gradient amplifier and to the gradient coil and the switch controller is also adapted to control the gradient amplifier so as to active the gradient amplifier to operate in reverse mode during discharge of the superconducting field coil over the gradient amplifier and/or the gradient coil.

3. The MRI system claim 1, wherein the switch assembly is adapted for galvanically decoupling the superconducting field coil for a persistent mode of the superconducting field coil.

4. The MRI system of claim 1, wherein the switch assembly is adapted for galvanically coupling the superconducting field coil to the gradient amplifier alone.

5. The MRI system of claim 1, wherein the superconducting field coil, the gradient coil and the gradient amplifier each have a first connector and a second connector for galvanic connections to the superconducting field coil, the gradient coil and the gradient amplifier, respectively, the first connector of the gradient amplifier is connected to the first connector of the gradient coil via a first electrical line (L1) and the second connector of the gradient amplifier is connected to the second connector of the gradient coil via a second electrical line (L2), the first connector of the superconducting field coil is connected to the first electrical line (L1) via a third electrical line (L3) and the second connector of the superconducting field coil is connected to the second electrical line (L2) via a fourth electrical line (L4), and the third electrical line (L3) comprises a first switch (S1) of the switch assembly (30) for opening and closing the third electrical line (L3), and the fourth electrical line (L4) comprises a second switch (S2) of the switch assembly (30) for opening and closing the fourth electrical line (L4).

6. The MRI system of claim 1, further comprising: a diode array which is adapted for parallel circuit to the third electrical line (L3 and/or the fourth electrical line (L4), and a fourth switch (S4) of the switch assembly for connecting or disconnecting the diode array to the fourth electrical line (L4).

7. The MRI system of claim 6, wherein the first electrical line (L1) and/or the second electrical line (L2) comprises a third switch (S3) of the switch assembly for opening and closing the second electrical line (L2).

8. The MRI system of claim 1 further comprising: a plurality of gradient systems each including a gradient coil for generating gradient magnetic fields and a gradient amplifier which is connectable to the gradient coil for driving the gradient coil, and a switch assembly which is adapted for galvanically coupling the superconducting field coil to each of the plurality of gradient amplifiers and to each of the plurality of gradient coils.

9. The MRI system of claim 1, wherein the plurality of gradient coils and the plurality of gradient amplifiers each have a first connector and a second connector for galvanic connections to the superconducting field coil, the plurality of gradient coils and the plurality of gradient amplifiers, respectively, the first connector of a second gradient amplifier is connected to the first connector of a second gradient coil via a fifth electrical line (L5) and the second connector of the second gradient amplifier is connected to the second connector of the second gradient coil via a sixth electrical line (L6), the third electrical line (L3) is connected with the fifth electrical line (L5) via a seventh electrical line (L7) and the fourth electrical line (L4) is connected with the sixth electrical line (L6) via an eighth electrical line (L8), and the fifth electrical line (L5) comprises a fifth switch (S5) of the switch assembly (30) for opening and closing the fifth electrical line (L5), and the seventh electrical line (L7) comprises a sixth switch (S6) of the switch assembly (30) for opening and closing the seventh electrical line (L7), and the eighth electrical line (L8) comprises a seventh switch (S7) of the switch assembly for opening and closing the eighth electrical line (L8).

10. The MRI system of claim 1, wherein the threshold value is in the range between 15-30% of the superconducting field coil's nominal electrical DC current strength.

11. The MRI system of claim 1, wherein the threshold value is in the range of 22-27% of the superconducting field coil's nominal electrical DC current strength.

12. A method for operating a magnetic resonance imaging (MRI) system, the MRI system including a superconducting magnet assembly with a superconducting field coil for generating a stationary uniform main magnetic field due to an electrical DC current, a gradient system including a gradient coil for generating gradient magnetic fields, generating gradient magnetic fields and a quench assembly to switch-off the superconducting field coil, gradient coil for generating gradient magnetic fields and a quench assembly to switch-off the superconducting field coil, wherein the method comprises: galvanically couple the superconducting field coil to the gradient coil so as to discharge the superconducting field coil resistively over the gradient coil to a threshold value of the electrical DC current strength and active the quench assembly when the electrical DC current strength falls below the threshold value.

13. The method of claim 12, wherein the method comprises the method step of galvanically coupling the superconducting field coil simultaneously to the gradient amplifier and to the gradient coil for discharging the superconducting field coil.

14. The method of claim 12, wherein the method comprises the method step of galvanically coupling the superconducting field coil to the gradient amplifier by connecting the diode array and opening the fourth electrical line (L4) for discharging the uperconducting field coil.

15. A non-transitory computer-readable medium, comprising instructions stored thereon, that when executed on a processor or on a controller in a magnet control unit, induce a MRI system comprising a superconducting magnet assembly with a superconducting field coil for generating a stationary uniform main magnetic field, and a gradient system including a gradient coil for generating gradient magnetic fields and a gradient amplifier which is connectable to the gradient coil for driving the gradient coil to perform a method according to claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. Such an embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention.

(2) In the drawings:

(3) FIG. 1 schematically depicts a circuit of a magnetic resonance imaging (MRI) system according to a preferred embodiment of the invention, including a superconducting magnet assembly, a gradient system and a switch assembly;

(4) FIG. 2 schematically depicts a circuit of a magnetic resonance imaging (MRI) system according to a preferred embodiment of the invention, including a superconducting magnet assembly, a gradient system, a switch assembly and a diode array; and

(5) FIG. 3 schematically depicts a circuit of a magnetic resonance imaging (MRI) system according to a preferred embodiment of the invention, including a superconducting magnet assembly, a plurality of gradient systems and a switch assembly.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) FIG. 1 schematically depicts a circuit of an MRI system according to a preferred embodiment of the invention, including a superconducting magnet assembly 10, a gradient system 20 and a switch assembly 30. The superconducting field coil 12, the gradient coil 22 and the gradient amplifier 24 each have a first connector 121, 221, 241 and a second connector 122, 222, 242 for galvanic connections to the superconducting field coil 12, the gradient coil 22 and the gradient amplifier 24, respectively.

(7) The first connector 241 of the gradient amplifier 24 is connected to the first connector 221 of the gradient coil 22 via a first electrical line L1 and the second connector 242 of the gradient amplifier 24 is connected to the second connector 222 of the gradient coil 22 via a second electrical line L2.

(8) The first connector 121 of the superconducting field coil 12 is connected to the first electrical line L1 via a third electrical line L3 and the second connector 122 of the superconducting field coil 12 is connected to the second electrical line L2 via a fourth electrical line L4.

(9) The third electrical line L3 comprises a first switch S1 of the switch assembly 30 for opening and closing the third electrical line L3, and the fourth electrical line L4 comprises a second switch S2 of the switch assembly 30 for opening and closing the fourth electrical line L4.

(10) The second electrical line L2 comprises a third switch S3 for connecting or disconnecting the gradient coil 22.

(11) For energizing the superconducting field coil 12, the third switch S3 is opened, the first switch S1 and the second switch S2 are closed. The superconducting field coil 12 is connected to the gradient amplifier 24 that delivers the power to the superconducting field coil 12. The gradient coil 22 is disconnected.

(12) For discharging the superconducting field coil 12 with the gradient coil 22, the first switch S1, the second switch S2 and the third switch S3 is closed. The gradient amplifier 24 remains connected in parallel with the gradient coil 22, wherein the current through the gradient amplifier 24 is zero.

(13) For discharging the last amount of current, the gradient coil 22 is disconnected by opening the third switch S3. The current runs through the gradient amplifier 24.

(14) FIG. 2 schematically depicts a circuit of an MRI system according to a preferred embodiment of the invention, including a superconducting magnet assembly 10, a gradient system 20, a switch assembly 30 and a diode array 40.

(15) The diode array 40 is in parallel circuit to the fourth electrical line L4 and a fourth switch S4 of the switch assembly 30 to connect or disconnect the diode array 40 to the fourth electrical line L4.

(16) The diode array is activated if the second switch S2 is opened and the fourth switch S4 is closed, so that the fourth electrical line L4 is opened and the current runs through the diode array 40. The diode array 40 may be connected only during discharging at low current values. The diode array 40 also may be adapted to be connected during the entire discharging. In that case the diode array 40 is adapted for higher currents which requires for example an additional cooling provision of the diode array 40.

(17) FIG. 3 schematically depicts a circuit of an MRI system according to a preferred embodiment of the invention, including a superconducting magnet assembly 10, a plurality of gradient systems 20A, 20B and a switch assembly 30.

(18) The plurality of gradient coils 22A, 22B and the plurality of gradient amplifiers 24A, 24B each have a first connector 221A, 221B, 241A, 241B and a second connector 222A, 222B, 242A, 242B for galvanic connections to the superconducting field coil 12, the plurality of gradient coils 22A, 22B and the plurality of gradient amplifiers 24A, 24B, respectively.

(19) The first connector 241B of a second gradient amplifier 24B is connected to the first connector 221B of a second gradient coil 22B via a fifth electrical line L5 and the second connector 242B of the second gradient amplifier 24B is connected to the second connector 222B of the second gradient coil 22B via a sixth electrical line L6.

(20) The third electrical line L3 is connected with the fifth electrical line L5 via a seventh electrical line L7 and the fourth electrical line L4 is connected with the sixth electrical line L6 via an eighth electrical line L8.

(21) The fifth electrical line L5 comprises a fifth switch S5 of the switch assembly 30 for opening and closing the fifth electrical line L5 and the seventh electrical line L7 comprises a sixth switch S6 of the switch assembly 30 for opening and closing the seventh electrical line L7, and the eighth electrical line L8 comprises a seventh switch S7 of the switch assembly 30 for opening and closing the eighth electrical line L8.

(22) The two gradient amplifiers 24A, 24B supply a sufficient current for the superconducting field coil 12 and the two gradient coils 22A, 22B are adapted for discharging the magnet. If the current is low enough during discharging one gradient coil 22B may be disconnected, so that one gradient coil 22A remains connected to increase the discharge voltage.

(23) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. Further, for the sake of clearness, not all elements in the drawings may have been supplied with reference signs.

REFERENCE SYMBOL LIST

(24) superconducting magnet assembly 10

(25) superconducting field coil 12

(26) first connector 121

(27) second connector 122

(28) gradient system 20

(29) first gradient system 20A

(30) second gradient system 20B

(31) gradient coil 22

(32) first gradient coil 22A

(33) second gradient coil 22B

(34) first connector 221

(35) first connector 221A

(36) first connector 221B

(37) second connector 222

(38) second connector 222A

(39) second connector 222B

(40) gradient amplifier 24

(41) first gradient amplifier 24A

(42) second gradient amplifier 24B

(43) first connector 241

(44) first connector 241A

(45) first connector 241B

(46) second connector 242

(47) second connector 242A

(48) second connector 242B

(49) switch assembly 30

(50) first switch S1

(51) second switch S2

(52) third switch S3

(53) fourth switch S4

(54) fifth switch S5

(55) sixth switch S6

(56) seventh switch S7

(57) first electrical line L1

(58) second electrical line L2

(59) third electrical line L3

(60) fourth electrical line L4

(61) fifth electrical line L5

(62) sixth electrical line L6

(63) seventh electrical line L7

(64) eight electrical line L8

(65) diode array 40