Polefaceless Permanent Magnet Assembly for MRI
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Solution Overview
Problem
In MRI systems, the presence of pole pieces interferes with the magnetic field generated by permanent magnets, requiring larger and more costly magnets to achieve an acceptable magnetic field strength, increasing complexity and cost due to bulkiness and heaviness.
Innovation Solution
A permanent magnet assembly with a stepped second surface and a hollow ring section that forms a pocket, allowing for adjustable shimming with metal shims, which optimizes the magnetic field strength and uniformity without the need for pole pieces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pole pieces are used to shape the magnetic field and eliminate eddy currents, then the magnetic field uniformity is improved, but the magnitude of the magnetic field reaching the imaging volume decreases, requiring larger and more expensive permanent magnets
Solution Approach 1:
The invention removes the pole pieces from the magnetic field path between the permanent magnets and the imaging volume. By extracting this interfering component, the magnetic field generated by the permanent magnets reaches the imaging volume directly without being blocked or distorted by pole pieces, thereby maintaining field magnitude while achieving uniformity through alternative means (shimming).
Solution Approach 2:
The invention introduces shims as intermediary elements placed between the permanent magnets and the imaging volume. These shims act as mediators to shape and uniform the magnetic field without blocking its passage, replacing the function of pole pieces while allowing the magnetic field to reach the imaging volume with sufficient magnitude.
2Manufacturing precision
If pole pieces are used to shape the magnetic field, then the magnetic field distribution is improved, but the complexity and cost of the imaging system increases due to larger magnet requirements
Solution Approach 1:
The invention extracts the pole pieces from the system, simplifying the overall structure. By removing this component, the system becomes less complex with fewer parts to manufacture, assemble, and maintain, while the magnetic field distribution is achieved through the simpler shim-based approach.
Solution Approach 2:
The invention replaces expensive, complex pole pieces with simpler, cheaper shims that can be easily adjusted or replaced. These shims are less costly than pole pieces and permanent magnet material, providing an economical solution for achieving proper magnetic field distribution.
3Power
If larger permanent magnets are used to compensate for pole piece interference, then the magnetic field strength in the imaging volume is maintained, but the weight and bulkiness of the system increases
Solution Approach 1:
The invention removes the pole pieces that were causing magnetic field interference, eliminating the need to compensate with larger permanent magnets. This extraction allows the use of smaller, lighter permanent magnets while maintaining sufficient magnetic field strength in the imaging volume.
Solution Approach 2:
The shims act as intermediaries that enhance the effectiveness of the permanent magnets by optimizing magnetic field distribution. This allows smaller permanent magnets to achieve the same effective field strength in the imaging volume that would otherwise require larger magnets when pole pieces are present.
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
The design enhances magnetic field strength and uniformity within the imaging volume, reducing the need for larger magnets and simplifying manufacturing while maintaining cost-effectiveness.
Implementation Method 1
permanent magnet body having a first surface and a stepped second surface which is adapted to face an imaging volume of the imaging apparatus
Implementation Method 2
at least one layer of a soft magnetic material and a permanent magnet body
Data Source
AI summary
A permanent magnet assembly for an imaging apparatus having a permanent magnet body having a first surface and a stepped second surface which is adapted to face an imaging volume of the imaging apparatus, wherein the stepped second surface contains at least four steps.