MRI Image Correction for Gradient-Induced Static Field Inhomogeneity
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Solution Overview
Problem
Existing MRI technologies face challenges in correcting static magnetic field inhomogeneity caused by gradient magnetic fields, which can lead to image quality deterioration, and existing methods either require real-time control of shim coils, risking eddy current generation, or necessitate limiting imaging conditions and pulse sequences.
Innovation Solution
An MRI apparatus that estimates static magnetic field inhomogeneity using a simple calculation based on the pulse sequence, allowing for image correction without real-time control of shim coils, and enables flexibility in imaging conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If real-time control of shim coil output is implemented to correct static magnetic field inhomogeneity, then image quality is improved, but eddy current generation occurs and device complexity increases
Solution Approach 1:
The patent pre-calculates the time average value of the gradient magnetic field in a predetermined time unit before actual imaging, and pre-determines the corresponding shim coil output. This preliminary action allows the correction magnetic field to be ready in advance, eliminating the need for real-time switching during imaging, thus avoiding eddy current generation while maintaining image quality correction capability
Solution Approach 2:
The patent creates a lookup table that stores the correspondence between time average values of gradient magnetic fields and optimal shim coil outputs. This copying approach allows the system to quickly retrieve pre-calculated correction parameters without real-time computation or switching, avoiding eddy currents while maintaining correction effectiveness
2Manufacturing precision
If shim coil output is switched dynamically to correct static magnetic field inhomogeneity, then image quality is improved, but response time becomes insufficient and reliability decreases
Solution Approach 1:
The patent pre-calculates and stores the optimal shim coil outputs for various gradient magnetic field conditions in a lookup table before actual imaging. During imaging, the system simply retrieves the pre-determined parameters based on the measured gradient field characteristics, eliminating the need for dynamic switching and allowing slow-responding shim coils to still achieve effective correction
3Manufacturing precision
If preliminary measurement is performed to measure error magnetic field for correction, then image quality is improved, but imaging conditions and pulse sequences are limited
Solution Approach 1:
The patent creates a comprehensive lookup table that stores the correspondence between various gradient magnetic field characteristics (including different pulse sequences and imaging conditions) and their optimal correction parameters. This allows the system to handle diverse imaging conditions without requiring preliminary measurements for each specific condition, thus maintaining correction accuracy while preserving imaging flexibility
Solution Approach 2:
The patent measures the actual gradient magnetic field characteristics (amplitude, duration, timing) during the actual imaging process and uses these measured parameters to query the lookup table for the corresponding correction parameters. This approach adapts to different pulse sequences and imaging conditions without requiring preliminary measurements, maintaining both correction accuracy and imaging versatility
4Manufacturing precision
If complex real-time control systems are used to correct static magnetic field inhomogeneity, then image quality is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex real-time control systems with a simple lookup table approach. The lookup table stores pre-calculated correction parameters for various gradient field conditions, allowing the system to achieve accurate correction by simple table lookup and parameter retrieval, thereby significantly reducing device complexity and cost while maintaining correction effectiveness
Solution Approach 2:
The system automatically measures the gradient magnetic field characteristics during imaging, queries the lookup table for corresponding correction parameters, and applies the correction without requiring complex real-time control algorithms or manual intervention. This self-service approach simplifies the control system while maintaining correction accuracy
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 effectively corrects image quality deterioration due to gradient magnetic fields, eliminating secondary errors and enhancing imaging flexibility, particularly in medium-low magnetic field MRI systems with slow shim coil responses.
Implementation Method 1
a correction magnetic field generating unit configured to generate a correction magnetic field for reducing an influence of the static magnetic field inhomogeneity
Implementation Method 2
applies a high frequency magnetic field to a subject placed in a homogeneous static magnetic field to cause a nuclear magnetic resonance phenomenon in nuclei (protons)
Data Source
AI summary
An MRI apparatus capable of correcting a static magnetic field inhomogeneity caused by application of a gradient magnetic field by a simple calculation, and a correction method of the MRI apparatus are provided. An image quality deterioration due to the static magnetic field inhomogeneity caused by application of a gradient magnetic field is estimated by a simple calculation using a shape of a pulse sequence for imaging. An amount of distortion to be generated in the image acquired by executing the pulse sequence is estimated based on the estimated static magnetic field inhomogeneity and the shape of the pulse sequence, and a distortion of a reconstructed image is corrected. Alternatively, an output of a compensation magnetic field canceling the estimated static magnetic field inhomogeneity is calculated, and is superimposed on a compensation current with an active shimming so as to be supplied to a shim coil.