Magnetic Resonance Coil Assembly Current Control
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Solution Overview
Problem
Designing coil assemblies to generate uniform and smooth magnetic fields over a large volume is challenging, especially when magnetic materials are present, as existing methods struggle to control higher-order derivatives and environmental interference, leading to unstable feedback loops and inefficient compensation.
Innovation Solution
A method using a geometrically fixed coil assembly where current vectors are calculated to produce desired magnetic field components and exclude unwanted derivatives, employing matrix algebra to decompose and control magnetic field distributions, allowing for active compensation of interference fields even in magnetically shielding rooms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If coils are placed close to the measuring device to generate uniform fields over large volume, then the currents needed to create the fields stay reasonably small, but the field profiles necessarily contain second and higher derivatives
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction current values that compensate for higher-order field derivatives before the actual measurement takes place. The system characterizes the coil assembly's field profile in advance, determines the correction currents needed to eliminate unwanted derivatives, and stores this correction data for immediate application during operation. This allows the system to maintain smooth fields over large volumes without requiring excessively small currents during the actual measurement process.
2Device complexity
If coil assembly is designed by mere calculation, then the design process is simplified, but detailed measurement and characterization of room structure and magnetic properties becomes practically impossible due to complexity
Solution Approach 1:
The patent applies segmentation by dividing the coil assembly design into distinct modular components: (1) calculating ideal field profiles without magnetic materials, (2) measuring actual field profiles with magnetic materials present, (3) computing correction currents based on the difference, and (4) applying these corrections during operation. This segmentation allows the system to handle the complexity of characterizing magnetic materials separately from the overall design process, making the total system manageable while maintaining high accuracy through the combination of calculation and measurement approaches.
3Reliability
If feedback principle is used for active compensation, then compensation effectiveness is improved, but coils must be placed inside the magnetically shielding room causing extra delay and unstable feedback loop
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the correction currents needed for compensation before the feedback loop operates. Instead of relying on real-time feedback from coils inside the magnetically shielding room, the system characterizes the interference fields in advance, calculates the appropriate correction currents, and stores this correction data for immediate application. This eliminates the delay and instability issues associated with real-time feedback while maintaining effective compensation through pre-computed correction fields.
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 enables the creation of accurate and desired magnetic fields that effectively compensate for interference over a large volume, maintaining stability and reducing the need for detailed characterization of magnetic materials, thus improving signal quality in MRI and MEG applications.
Implementation Method 1
an assembly of coils (20) arranged in a geometrically fixed configuration... capable of producing a magnetic field with a desired geometric shape around a given origin
Implementation Method 2
measuring the magnetic field distribution around the origin caused by the test current and decomposing the measured magnetic fields into desired and undesired components
Implementation Method 3
the magnetically shielding room (MSR) housing the MEG device
Data Source
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AI summary
The present invention introduces a method, apparatus and computer program for magnetic resonance imaging or magnetoencephalography applications in order to control currents of a coil assembly (20), and thus achieving desired magnetic fields precisely in the measuring volume (21). The approach is an algebraic method where a field vector is generated for the test currents of each coil (20). Vector and matrix algebra is applied and a linear set of equations is formed. Field components and their derivatives up to the desired order can be taken into account. Principal component analysis or independent component analysis can be applied for determination of the dominant external interference components. By checking the condition value for the matrix (33, 45), it is possible to investigate whether a reasonable solution of currents for desired magnetic fields is possible to achieve. Finally, solved currents can be installed into a current supply unit (29) feeding the coils of the assembly (20). The invention can be applied as an active compensation feature for different interference shapes in the MEG application (25), or for the precise creation of the fields and gradients in the MRI application (24).