Local Shimming System for MRI Field Homogeneity
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Solution Overview
Problem
Current magnetic resonance imaging systems face challenges in achieving high-order non-uniform magnetic field compensation due to the need for a large number of shim coils, which increases complexity, cost, and time required for sensitivity field map collection, especially at tissue-air interfaces.
Innovation Solution
A local shimming system with asymmetrically distributed multi-channel shim coils and a fast two-dimensional gradient echo sequence for field mapping, optimizing current values to minimize magnetic field offset standard deviation, and using a computer-controlled DC power system to set optimal current combinations for each channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the number of shim coils is increased to achieve high-order non-uniform magnetic field compensation, then the shimming effect is improved, but the system complexity and cost increase
Solution Approach 1:
The patent divides the shim coil system into multiple independent channel units, where each unit contains a shim coil and associated control circuitry. This segmentation allows for modular assembly and simplifies the overall system architecture, enabling high-order shimming without proportionally increasing system complexity.
Solution Approach 2:
The patent implements local shimming by positioning shim coils at specific locations around the magnet bore, with each coil addressing local field inhomogeneities in its vicinity. This localized approach achieves effective magnetic field homogenization without requiring a dense array of coils throughout the entire space.
2Manufacturing precision
If the number of shim coil channels is increased, then the non-uniform magnetic field compensation capability is improved, but the time required for sensitivity field map collection increases
Solution Approach 1:
The patent combines the sensitivity field map collection process with the actual imaging sequence by using the same gradient echo sequence for both purposes. This merging eliminates the need for separate, time-consuming sensitivity measurements for each channel, as the imaging data itself provides the necessary field map information.
Solution Approach 2:
The system uses the imaging sequence itself to generate the field map data needed for shimming optimization. The gradient echo imaging process automatically provides the phase information required to calculate field maps, making the system self-sufficient and eliminating external measurement steps.
3Manufacturing precision
If more power amplifiers are added to support additional shim coil channels, then the shimming capability is improved, but the system cost and complexity increase
Solution Approach 1:
The patent designs a multi-functional power amplifier system where a single amplifier can drive multiple shim coil channels through sequential switching. This universal amplifier serves multiple purposes, providing power to different coil combinations based on the shimming requirements, thereby reducing the total number of amplifiers needed.
Solution Approach 2:
The patent implements dynamic channel switching in the power amplifier system, allowing the same hardware resources to be dynamically allocated to different shim coil channels based on real-time shimming needs. This dynamic reconfiguration enables high-order shimming capability without requiring a static, one-to-one amplifier-to-channel mapping.
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 achieves a better shimming effect with fewer channels, reducing system complexity and cost, while improving image homogeneity and temperature measurement accuracy in magnetic resonance imaging and temperature imaging applications.
Implementation Method 1
the magnet itself is generally capable of providing a relatively homogeneous static magnetic field B0
Implementation Method 2
due to the difference in magnetic susceptibility of the tissue, local magnetic field changes are generated at the interface
Implementation Method 3
a fast two-dimensional gradient echo sequence to collect the field mapping B0
Data Source
AI summary
A shimming system for magnetic resonance imaging is provided, which includes: a multi-channel local shim coil unit configured to be installed on an inspection table of a magnetic resonance imaging system, where the multi-channel local shim coil unit includes a local multi-channel shim coil and a radio frequency receiving coil for receiving magnetic resonance signals, and the radio frequency receiving coil is placed inside the local multi-channel shim coil and separated by a distance from the local multi-channel shim coil; a computer control system configured to install and set software controlled by a DC power and calculate field maps and calculate optimization processes; a DC power system communicatively connected to the computer control system to control a value of current of each channel; and a housing having a semi-cylindrical configuration, where the local multi-channel shim coil is only distributed on a semi-cylindrical surface of the semi-cylindrical configuration of the housing.