Detecting quench in a magnetic resonance examination system
The present invention relates to a magnetic resonance examination system ( 10 ) and to a method of operating such a magnetic resonance examination system ( 10 ). In particular the present invention relates to a magnetic resonance examination system ( 10 ) comprising a superconducting main magnet ( 20 ) surrounding an examination region ( 18 ) and generating a main magnetic field in the examination region ( 18 ), and further comprising a magnetic field gradient system ( 30 ) selectively causing alternating gradient magnetic fields in the examination region ( 18 ), said magnetic field gradient system ( 30 ) being coupled to the main magnet ( 20 ). In order to provide a technique to reliably detect a quench of the superconducting main magnet ( 20 ) of such a magnetic resonance examination system ( 10 ) a detecting device ( 91 ) is suggested for detecting an emerging quench of the main magnet ( 20 ), said detecting device ( 91 ) being adapted to operate in different modes depending on the mode of operation of the magnetic resonance examination system (e.g. ramp-up, ramp-down or continuous operation).
1. A magnetic resonance examination system, comprising
a superconducting main magnet surrounding an examination region and generating a main magnetic field in the examination region, and
a magnetic field gradient system selectively causing alternating gradient magnetic fields in the examination region, said magnetic field gradient system being coupled to the main magnet,
wherein the magnetic resonance examination system comprises a detecting device for detecting an emerging quench of the main magnet, said detecting device being adapted to operate in different modes depending on the mode of operation of the magnetic resonance examination system,
wherein
the detecting device is adapted to operate in a first operating mode during ramp-up and ramp-down of the main magnet, in which mode the detecting device compares a first measurement signal with a first threshold, and
the detecting device is adapted to operate in a second operating mode during continuous operation of the main magnet, in which mode the detecting device compares a second measurement signal with a second threshold.
2. The system as claimed in claim 1 , wherein the first measurement signal is a bridge voltage over the resistance of an electrical bridge circuit coupled to the coils of the main magnet.
3. The system as claimed in claim 2 , wherein the electrical bridge divides the coils of the main magnet into two symmetric coil sections.
4. The system as claimed in claim 1 , wherein the second measurement signal is the total voltage over the main magnet.
5. The system as claimed in claim 4 , wherein the main magnet is adapted in a way that the magnetic field gradient system do not cause substantial induced voltages in the main magnet during continuous operation of the main magnet.
6. The system as claimed in claim 1 , wherein the detecting device comprises a switching means for switching the detecting device between the first operating mode and the second operating mode, said switching means being adapted to receive signals indicating the mode of operation of the magnetic resonance examination system.
7. The system as claimed in claim 1 , wherein the detecting device is adapted to control a protecting means to protect the main magnet in case of a quench.
8. A method of operating a magnetic resonance examination system, said system comprising a superconducting main magnet surrounding an examination region and generating a main magnetic field in the examination region, and further comprising a magnetic field gradient system selectively causing alternating gradient magnetic fields in the examination region, said magnetic field gradient system being coupled to the main magnet, wherein the method comprises the step of detecting an emerging quench of the main magnet, said detecting being carried out in different modes depending on the mode of operation of the magnetic resonance examination system,
wherein
in a first operating mode during ramp-up and ramp-down of the main magnet, the detection is performed by comparing a first measurement signal with a first threshold, and
in a second operating mode during continuous operation of the main magnet, the detection is performed by comparing a second measurement signal with a second threshold.
9. The method as claimed in claim 8 , wherein the main magnet is divided into symmetrical sections by an electrical bridge and the first measurement signal is based on a measured voltage over the bridge and the second measurement signal is based on a measured voltage over the main magnet.
10. A non-transitory computer-readable medium carrying software for controlling to detect an emerging quench of the main magnet of a magnetic resonance examination system by performing the steps of:
in a first operating mode during ramp-up and ramp-down of the main magnet, receiving a first measurement signal and comparing the first measurement signal with a first threshold, and
in a second operating mode during continuous operation of the main magnet, receiving a second measurement signal and comparing the second measurement signal with a second threshold.
11. The non-transitory computer readable medium as claimed in claim 10 , wherein the main magnet is divided into symmetrical sections by an electrical bridge and the first measurement signal is based on a measured voltage over the bridge and the second measurement signal is based on a measured voltage over the main magnet.