MRI Cryogen Vessel Pressure Control During Magnet Ramping
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Solution Overview
Problem
Conventional MRI systems with superconducting magnets face issues during ramping due to localized frictional heating, leading to quench events and helium boil-off, which are costly and time-consuming to resolve, and current methods to increase stability, such as enhancing critical current or cooling, add complexity and expense.
Innovation Solution
Reducing pressure in the cryogen vessel during magnet ramping using a vacuum pump to decrease helium temperature, thereby increasing stability and reducing the likelihood of quenching, and returning pressure to normal levels after ramping is complete.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the critical current of the wires is increased to improve stability during ramping, then the stability margin increases, but the cost and complexity of the MRI system increase
Solution Approach 1:
The patent changes the temperature parameter of the cryogen during ramping operations. By reducing the temperature of the liquid helium from its normal operating temperature (around 4.2K) to a lower temperature (around 3.0K or below), the stability margin of the superconducting magnet during ramping is significantly increased without requiring higher critical current wires or additional cooling infrastructure.
2Reliability
If additional cooling measures are implemented to increase stability during ramping, then the stability margin improves, but the device complexity and cost increase
Solution Approach 1:
The patent utilizes temperature as a controllable parameter by implementing a two-stage cooling system. The first stage maintains normal operating temperature, and the second stage provides additional cooling to reach lower temperatures during ramping. This approach increases stability margin without adding complex active cooling measures during normal operation.
3Reliability
If the MRI system undergoes quench events during ramping, then the magnet must be refilled and re-ramped, but this process is expensive and time-consuming
Solution Approach 1:
The patent performs preliminary cooling to lower temperatures before initiating the ramping process. By pre-cooling the liquid helium to around 3.0K or below before ramping, the system creates a larger stability margin that prevents quench events during ramping, thereby avoiding the time-consuming refill and re-ramp cycle.
4Temperature
If conventional cooling methods are used during ramping, then the system operates at normal temperature, but localized frictional heating can still cause quenching
Solution Approach 1:
The patent changes the temperature parameter from normal operating conditions to sub-cooled conditions during ramping. By reducing the liquid helium temperature to around 3.0K or below, the thermal margin against frictional heating is significantly increased, allowing the magnet to withstand the localized heating that occurs during ramping without quenching.
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 method effectively increases the stability of the superconducting magnet during ramping, reducing the risk of quenching and eliminating the need for additional stabilizing measures like higher critical current or improved cooling, thus reducing costs and complexity.
Implementation Method 1
reducing pressure in a cryogen vessel of an MRI system during magnet ramping
Implementation Method 2
decrease helium temperature, thereby increasing stability
Implementation Method 3
the windings of superconducting wire forming the superconducting magnets are cryogenically cooled using a helium vessel to maintain the magnets below a critical temperature
Implementation Method 4
When the MRI system is energized, and in particular when the superconducting magnet is energized, commonly referred to as ramping, the Lorentz force on the conductors increases, causing small movements of the wire that can lead to localized frictional heating
Implementation Method 5
The normal zone will spread through the winding due to the Joule heat and the thermal conduction
Implementation Method 6
The normal zone will spread through the winding due to the Joule heat and the thermal conduction
Implementation Method 7
The quench is accompanied by the rapid boil-off of helium escaping from the cryogen bath in which the magnet windings are immersed
Data Source
AI summary
Systems and methods for operating a magnetic resonance imaging (MRI) during ramping are provided. One method includes reducing pressure in a cryogen vessel of an MRI system during magnet ramping. The method also includes returning pressure in the cryogen vessel to a normal operating pressure level after magnet ramping is complete.