Rotatable Passive Shim Units for MR Field Homogeneity
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Solution Overview
Problem
Current magnetic resonance imaging systems face challenges in maintaining homogeneous magnetic fields, especially when integrated with rotating radiation sources, as passive shimming provides a static solution that is not adaptable to changes in the environment or magnet rotation, leading to increased field inhomogeneities.
Innovation Solution
A medical imaging system with two passive shim units, one static and one rotatable, is used to compensate for magnetic field distortions of varying orders, with the static unit addressing angle-independent distortions and the rotatable unit addressing angle-dependent distortions, ensuring high field homogeneity even during rotations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If passive shimming is used to compensate for magnetic field distortions, then field homogeneity is improved, but the system cannot adapt to changes in environment or magnet rotation
Solution Approach 1:
The shimming system is divided into multiple passive shim units, each responsible for compensating specific types of field distortions (e.g., first-order, second-order, third-order harmonics). This segmentation allows the system to maintain field homogeneity across different rotation angles by distributing compensation functions across multiple specialized units.
Solution Approach 2:
The patent introduces dynamically adjustable passive shim units that can modify their magnetic field compensation characteristics in response to rotation angle changes. This is achieved through mechanical adjustments or reconfigurable shim element arrangements that adapt to the current operational state, bridging the gap between static passive shimming and dynamic requirements.
2Adaptability or versatility
If the magnet rotates about the longitudinal axis or components rotate around the static magnet, then radiation application angle adjustment is enabled, but magnetic field inhomogeneities increase
Solution Approach 1:
Different regions of the magnetic field are compensated by dedicated shim units positioned and configured to address local field distortions. Each shim unit targets specific spatial harmonics and distortion patterns, providing localized field homogenization that remains effective during rotation.
Solution Approach 2:
The patent addresses field homogeneity in the angular dimension by introducing rotation-angle-dependent shimming strategies. Multiple shim units are configured to compensate for distortions at different rotation angles, effectively adding angular dimension compensation to the traditional spatial shimming approach.
3Adaptability or versatility
If active shimming is used to shield against low-order field distortion harmonics, then dynamic adjustment capability is provided, but higher-order inhomogeneities are not sufficiently suppressed
Solution Approach 1:
The system merges active shimming coils with passive shim units to create a hybrid shimming approach. Active coils provide dynamic adjustment for low-order harmonics, while passive shim units with specifically arranged ferromagnetic elements provide stable compensation for higher-order inhomogeneities, combining the advantages of both methods.
Solution Approach 2:
The shimming system uses composite approaches combining energizable coils with ferromagnetic materials arranged in specific patterns. This composite shimming strategy leverages the dynamic properties of active coils and the stable field-shaping properties of passive ferromagnetic structures to achieve comprehensive distortion suppression across all orders.
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 configuration achieves a highly homogeneous magnetic field, enabling high-quality MR imaging by effectively compensating for magnetic field distortions of up to 95%, improving image fidelity and adaptability to different angles and environments.
Implementation Method 1
a magnetic resonance imaging unit having at least one main magnet for generating a magnetic field
Implementation Method 2
For passive shimming, magnetized material is generally arranged at specific points of the MR scanner during the installation of the magnet
Implementation Method 3
The imaging system is embodied from a static part and a part that is rotatable through an angle of rotation
Data Source
AI summary
An imaging system includes a magnetic resonance imaging device and a radiation generator that are mechanically linked to each other such that both surround a patient bore for receiving and positioning the examination subject. The magnetic resonance imaging device has at least one main magnet for generating a magnetic field, and the radiation generator has a radiation source for generating radiation. The imaging system is configured from a static part and a part that is rotatable through an angle of rotation such that at least one rotatable main magnet is rotatable around a static radiation generation unit or a rotatable radiation generation unit is rotatable around at least one static main magnet. The imaging system includes at least two passive shim units, of which at least one static shim unit is stationary and at least one rotatable shim unit is fixedly connected to the rotatable part.