Superconducting MRI Magnet With Switchable Secondary Field Control
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Solution Overview
Problem
Conventional MRI systems using superconducting magnets face challenges in rapidly changing the static magnetic field strength, leading to AC loss and high voltage generation, which can cause quench and require lengthy recovery times, especially when shifting between imaging modes or during emergency shutdowns.
Innovation Solution
The implementation of a superconducting magnet configuration with a primary and secondary coil system, where the secondary coil is controlled by external switches to generate a secondary static magnetic field, allowing for instantaneous changes in magnetic field strength without quenching, and featuring non-inductive winding to minimize voltage generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the electric current flowing through the superconducting coil is increased or decreased instantaneously to change the static magnetic field strength, then the static magnetic field strength can be changed rapidly, but AC loss is generated causing heat and risk of quench
Solution Approach 1:
The patent divides the single superconducting coil system into two separate superconducting coils: a first superconducting coil for generating the primary static magnetic field and a second superconducting coil for generating the pre-polarization field. This segmentation allows independent control of each coil, enabling the pre-polarization field to be changed rapidly without causing AC loss in the main imaging coil, thus resolving the contradiction between rapid field change speed and quench risk.
2Speed
If the electric current flowing through the superconducting coil is increased or decreased rapidly, then the static magnetic field strength can be changed quickly, but high voltage is generated due to inductance
Solution Approach 1:
By segmenting the magnetic field generation function into two separate coils, the patent allows the second coil to handle rapid current changes for pre-polarization while the first coil maintains stable current for primary imaging. This separation prevents high voltage generation in the main imaging coil while still achieving rapid field changes when needed.
Solution Approach 2:
The second superconducting coil acts as an intermediary device that handles the rapid current changes and associated high voltage effects, protecting the primary imaging system. This intermediary coil absorbs the electrical stress of rapid switching, allowing the main imaging coil to operate safely and stably.
3Speed
If the superconducting magnet is shifted to quenched state for emergency shutdown, then the magnetic field can be rapidly reduced, but it takes long time and many efforts to return to imageable state
Solution Approach 1:
The patent enables selective shutdown of the second superconducting coil without affecting the first superconducting coil. This segmentation allows emergency shutdown of the pre-polarization field while maintaining the primary static magnetic field for imaging, avoiding the need to quench the entire magnet system and thus eliminating lengthy recovery procedures.
Solution Approach 2:
The patent implements dynamic control capability where the operating state of each superconducting coil can be independently adjusted. This dynamic control allows flexible shutdown scenarios where only necessary components are deactivated, enabling rapid field reduction without permanent system shutdown and facilitating quick recovery by simply reactivating the appropriate coil.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables rapid and controlled changes in static magnetic field strength, reducing AC loss and quench risk, and allows for instantaneous shutdown and recovery without entering a quenched state, enhancing imaging quality and operational efficiency.
Implementation Method 1
a superconducting coil is cooled down to an extremely low temperature by, for example, liquid helium. This static magnetic field magnet generates a static magnetic field by applying an electric current supplied from a static-magnetic-field power supply to the superconducting coil in an excitation mode
Implementation Method 2
a superconducting coil is cooled down to an extremely low temperature by, for example, liquid helium
Implementation Method 3
the static-magnetic-field control switch supplies the secondary superconducting coil with part of the persistent current to generate the secondary static magnetic field by being closed in response to the external control during the persistent current mode
Implementation Method 4
it is necessary to instantaneously increase and decrease the strength of the static magnetic field to be generated by the superconducting coil. However, if the strength of the static magnetic field is increased or decreased instantaneously by increasing or decreasing the electric current flowing through the superconducting coil, at least the following two problems may arise
Data Source
AI summary
In one embodiment, a superconducting magnet includes: at least one primary superconducting coil configured to generate a primary static magnetic field by a persistent current flowing during a persistent current mode; at least one secondary superconducting coil configured to generate a secondary static magnetic field different from the primary static magnetic field in response to external control; and a static-magnetic-field control switch configured to (i) supply the secondary superconducting coil with part of the persistent current to generate the secondary static magnetic field by being closed in response to the external control during the persistent current mode and (ii) stop energization of the secondary superconducting coil and generation of the secondary static magnetic field by being opened in response to the external control during the persistent current mode.