Dynamic Shimming for MRI Magnetic Field Inhomogeneity Correction
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Solution Overview
Problem
Current MRI systems face challenges in efficiently acquiring magnetic field inhomogeneity values, particularly in applications with short measurement times like Diffusion Weighted Imaging, where additional time for distortion correction cannot be ignored, and existing methods rely on pre-obtained magnetic field charts or point spread functions.
Innovation Solution
A method using a dynamic shimming technique with a 3D low-resolution dual-echo gradient echo sequence to calculate magnetic field inhomogeneity values, allowing for direct calculation of pixel offsets for distortion correction without the need for additional measurements, thereby shortening imaging time and increasing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pre-obtained magnetic field charts or point spread functions are used for distortion correction, then distortion correction accuracy is improved, but measurement time increases
Solution Approach 1:
The patent performs magnetic field mapping and distortion correction parameter acquisition in advance during system setup or calibration phases. The pre-obtained magnetic field charts and point spread functions are stored for later use during actual imaging, eliminating the need to perform these measurements during time-critical clinical scans.
Solution Approach 2:
The patent implements adaptive distortion correction that dynamically adjusts correction parameters based on the specific imaging sequence and protocol being used. The system selects appropriate correction methods and parameters from pre-acquired data based on real-time imaging conditions, optimizing both accuracy and speed for different applications.
2Stability of the object's composition
If dynamic shimming method is used to homogenize magnetic field, then magnetic field homogeneity is improved, but imaging time increases
Solution Approach 1:
The patent applies dynamic shimming only in specific regions or to specific frequency bands where field inhomogeneity most impacts image quality, rather than attempting to homogenize the entire magnetic field. This partial application of shimming reduces the time penalty while maintaining sufficient homogeneity for high-quality imaging.
Solution Approach 2:
The patent dynamically adjusts shimming parameters based on the imaging protocol, region of interest, and detected field inhomogeneity levels. By changing shimming strength and duration parameters adaptively rather than applying fixed shimming, the system achieves necessary field homogeneity with minimal time addition.
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 significantly reduces the time required for magnetic resonance imaging by using data from dynamic shimming to calculate magnetic field inhomogeneity values and pixel shifts, enhancing the efficiency of MRI systems, especially in applications like echo planar imaging and Dixon water-fat imaging.
Implementation Method 1
ΔBoriginal=Δφ/(γ·ΔTE), wherein ΔTE is a difference value of echo times of dual echoes of the 3D low-resolution dual-echo gradient echo sequence, Δφ is a phase difference of two gradient echo images
Implementation Method 2
When an atomic nucleus contains a single proton, as is the case with the nuclei of the hydrogen atoms that are present throughout the human body, this proton exhibits spin motion and resembles a small magnet
Implementation Method 3
In order to homogenize an original basic magnetic field of an MRI system into a target magnetic field, a magnetic field compensation amount for the MRI system is provided by a dynamic shimming method
Implementation Method 4
ΔB=ΔBoriginal+ΔBcompensating, wherein ΔB is the magnetic field inhomogeneity value, ΔBoriginal is a difference value between the original magnetic field and the target magnetic field, and ΔBcompensating is the magnetic field compensation amount
Data Source
AI summary
A method for acquiring a basic magnetic field inhomogeneity value of a magnetic resonance imaging (MRI) system includes homogenizing an original basic magnetic field of the MRI system into a target magnetic field, providing a magnetic field compensation amount for the MRI system by a dynamic shimming method. The dynamic shimming method includes performing a 3D low-resolution dual-echo gradient echo sequence, and using a general formula to acquire the magnetic field inhomogeneity value, the general formula being: ΔB=ΔBoriginal+ΔBcompensating, wherein ΔB is the magnetic field inhomogeneity value, ΔBoriginal is a difference value between the original magnetic field and the target magnetic field, and ΔBcompensating is the magnetic field compensation amount. This method for acquiring a magnetic field inhomogeneity value for an MRI system saves considerable time to map the magnetic field again, thereby shortening the magnetic resonance imaging time, and increasing the efficiency of magnetic resonance imaging.