MRI Static Field Homogeneity Adjustment via Low-Current Dynamic Control
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Solution Overview
Problem
The existing methods for adjusting static magnetic fields in MRI systems are time-consuming and costly due to errors caused by magnetization of magnetic shims, human error, and environmental magnetic fields, requiring multiple repetitions of the adjustment process and significant consumption of liquid helium during demagnetization.
Innovation Solution
An MRI apparatus with a superconducting coil, a correction magnetic field generating unit, a measurement unit, an excitation power source, and a calculation control unit that selectively supplies rated or low current values to the coil, allowing for repeated adjustments of the magnetic field without complete demagnetization, thereby reducing inhomogeneity and helium consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the passive shim method is used to correct static magnetic field inhomogeneity, then magnetic field homogeneity is improved, but adjustment time and operational complexity increase due to multiple repetitions required
Solution Approach 1:
The patent changes the operational parameter of the superconducting magnet from a static high-field state to a dynamic low-field state during adjustment. By reducing the magnetic field strength to a low level, the magnetization of magnetic shims is minimized, allowing accurate field measurement and correction without the interference of strong magnetization effects. This parameter change enables single-pass or reduced-pass adjustment, resolving the time loss contradiction.
Solution Approach 2:
The patent introduces dynamic control of the magnetic field strength, allowing the system to transition between high-field operational mode and low-field adjustment mode. This dynamic capability enables the operator to switch field strengths based on the adjustment phase, eliminating the need for complete demagnetization cycles and reducing the number of repetitions required for achieving homogeneous magnetic field.
2Manufacturing precision
If complete demagnetization is performed between adjustments, then magnetic shim magnetization errors are corrected, but liquid helium consumption increases
Solution Approach 1:
Instead of performing complete demagnetization between adjustments, the patent applies partial action by reducing the magnetic field to a low level. This partial field reduction is sufficient to minimize magnetic shim magnetization and enable accurate measurement and correction, but does not require the energy-intensive complete demagnetization process. This partial action significantly reduces liquid helium consumption while still achieving the necessary correction precision.
Solution Approach 2:
The patent converts the potentially harmful effect of magnetic shim magnetization into a beneficial measurement condition. By operating at low magnetic field strength during adjustment, the magnetization becomes negligible, allowing direct measurement of the magnetic field distribution without complex demagnetization procedures. This converts what would be a source of error requiring expensive correction into a useful low-interference measurement state.
3Manufacturing precision
If multiple repetitions of adjustment process are performed, then magnetic field homogeneity is improved, but operational cost and time consumption increase
Solution Approach 1:
The patent performs preliminary action by reducing the magnetic field to a low level before conducting the measurement and adjustment process. This preliminary field reduction prepares the system in an optimal state for measurement, minimizing magnetic shim magnetization effects in advance. By preparing the system in this low-field state beforehand, the subsequent adjustment process can be completed in fewer repetitions, improving overall productivity and system readiness speed.
4Measurement precision
If high magnetic field strength is maintained during adjustment, then measurement accuracy is improved, but magnetic shim magnetization errors increase
Solution Approach 1:
The patent employs dynamic control of magnetic field strength, switching between high-field and low-field states based on the measurement and adjustment phase. During the measurement phase, the field is reduced to low strength to minimize magnetic shim magnetization effects, ensuring accurate measurement. During the operational phase, the field is restored to high strength for optimal imaging performance. This dynamic switching resolves the contradiction between measurement accuracy and magnetic field homogeneity.
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 reduces the time and cost associated with magnetic field adjustment by allowing more frequent corrections within a shorter timeframe and minimizing helium usage, leading to faster system readiness and lower operational costs.
Implementation Method 1
a static magnetic field generating device that includes a superconducting coil and generates a static magnetic field in an imaging space
Implementation Method 2
a correction magnetic field generating unit that generates a correction magnetic field to reduce inhomogeneity of a static magnetic field distribution
Data Source
AI summary
Static magnetic field inhomogeneity is reduced by measuring inhomogeneity of a static magnetic field distribution in an imaging space, evaluating a distribution of a correction magnetic field that should be generated by a correction magnetic field generating unit disposed in the vicinity of the imaging space based on the measured static magnetic field distribution, reducing the electric current value of the superconducting coil to a predetermined (greater than zero) low current value smaller than a rated current value, notifying an operator to set a correction magnetic field of the correction magnetic field generating unit to the correction magnetic field evaluated by calculation in a state where an electric current at the low current value is flowing in the superconducting coil and a low static magnetic field B_low is being generated, and repeating the above operations.