Cold Head Motion Compensation in Superconducting MR Magnets
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Solution Overview
Problem
Magnetic resonance (MR) imaging systems face challenges in maintaining signal quality due to periodic B0 modulations caused by the repetitive motion of a cold head in superconductive magnets, leading to temperature increases and disrupted cooling processes.
Innovation Solution
A method involving sensor measurements to identify periodic spatial field components, synchronizing these components with auxiliary parameters, and applying compensation signals to mitigate the effects of the cold head's motion, allowing continuous operation and improved signal acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the cold head is operated continuously to cool the main magnet coils, then the temperature stability is improved, but periodic B0 modulations occur due to the repetitive motion of the cold head displacer
Solution Approach 1:
The patent measures the periodic B0 modulations caused by cold head motion and applies compensation signals that are specifically designed to counteract these modulations. The harmful vibrations and field modulations are converted into a correctable signal pattern, allowing the cold head to operate continuously while maintaining signal quality.
Solution Approach 2:
The system continuously monitors the B0 field modulations using sensor means and feeds this information back to the control means, which then adjusts the compensation signals in real-time. This closed-loop feedback mechanism ensures that the cold head motion-induced modulations are actively compensated, maintaining both temperature stability and signal quality.
2Object-affected harmful factors
If the cold head displacer is shut down to eliminate field modulation, then the signal quality is improved, but the temperature increases and cooling process is disrupted
Solution Approach 1:
Instead of shutting down the cold head, the system measures the B0 modulations caused by its operation and applies compensation signals to counteract the harmful effects. This converts the previously harmful field modulations into a manageable parameter, allowing continuous cooling while maintaining signal quality for various MR imaging sequences.
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 approach enhances MR imaging system performance by reducing the impact of periodic B0 modulations, maintaining stable temperatures, and enabling continuous cooling, thus improving image quality and reducing the need for additional components.
Implementation Method 1
The superconducting coils are directly cooled from a cold head, e.g. via copper strands
Implementation Method 2
main windings of the main magnet are cooled to superconductivity by the cold head
Implementation Method 3
The cold head is provided to re-condense evaporated helium within the inner vessel
Implementation Method 4
The cryogen is typically provided as liquid having a low boiling temperature, e.g. a boiling temperature of about 4.2 K in case of helium, which already evaporates when small amounts of heat enter
Implementation Method 5
The cold head displacer moves up and down, thereby inducing vibrations into the cryogenic vessel. This displacement results in a field modulation with a repetition time
Data Source
AI summary
The present invention provides a method for compensation of periodic B0 modulations from a periodic motion of a cold head (212) of a main magnet (114) of a magnetic resonance (MR) imaging system (110), whereby main windings (200) of the main magnet (114) are cooled to superconductivity by the cold head (212), which exerts a repetitive motion, the method comprising the steps of measuring a periodic occurrence of spatial field components of the B-field based on a motion of the cold head (212) as a function of time, performing a sensor measurement of a periodic, auxiliary parameter of the MR imaging system (110), which is not the periodic occurrence of spatial field components, synchronizing the periodic occurrence of spatial field components of the B-field with the measured periodic, auxiliary parameter of the MR imaging system (110), and triggering based on the measured periodic sensor measurement of the MR imaging system (110) a periodic application of compensation signals to compensate the periodic occurrence of spatial field components of the B-field based on a motion of the cold head (212). Furthermore, the present invention provides a MR imaging system (110) for providing an image representation of a region of interest (142) of a subject of interest (120) positioned in an examination space (116) of the MR imaging system (110), wherein the MR imaging system (110) is adapted to perform the above method.