MRI Eddy Current Distortion Correction via Marker Sequence
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Diffusion-weighted echo planar imaging (DW-EPI) in MRI is prone to image distortion due to eddy current fields, which affects the accuracy of diffusion-weighted images and apparent diffusion coefficient (ADC) calculations when images with different diffusion directions and weights are combined without correction.
Innovation Solution
A method involving a combined sequence of marker and DW-EPI sequences to acquire images, where marker images with zero and non-zero b values are used to calculate stretching and displacement coefficients for correcting image distortions, allowing for precise alignment and correction of DW-EPI images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If DW-EPI sequence is used to acquire diffusion-weighted images with different diffusion directions and weights, then the imaging speed is very high, but image distortion is easily introduced due to eddy current fields
Solution Approach 1:
The patent applies a marker sequence before the DW-EPI sequence to pre-acquire distortion information. The marker sequence is used to calculate distortion coefficients that will be applied to correct the DW-EPI images, performing the correction preparation in advance before the actual diffusion-weighted imaging is completed.
Solution Approach 2:
The patent introduces a marker sequence as an intermediary element between the gradient pulse and the DW-EPI sequence. This marker sequence acts as a mediator that captures the distortion characteristics caused by eddy currents, allowing the distortion to be quantified and corrected without affecting the main imaging process.
2Ease of manufacture
If multiple single images with different diffusion directions and weights are acquired without correction, then the imaging process is simple, but the distortion degrees and types are not identical causing blurs in DWI and errors in ADC calculations
Solution Approach 1:
The marker sequence is acquired before the DW-EPI sequence to pre-calculate distortion coefficients for each diffusion direction and weight combination. This preliminary acquisition of distortion information allows subsequent correction to be applied systematically to all images, ensuring consistent distortion correction across different diffusion parameters.
Solution Approach 2:
The patent calculates distortion coefficients as parameters that vary with diffusion direction and weight (b value). By determining these coefficients as functions of the diffusion parameters, the system can adaptively correct each image according to its specific distortion characteristics, maintaining measurement precision across all diffusion-weighted images.
3Object-affected harmful factors
If pre-enhancement of gradient coils and gradient pulses using self-shielding is applied, then the eddy current field is reduced, but cannot completely eliminate the influence of eddy current field
Solution Approach 1:
The patent converts the harmful eddy current field into a measurable and correctable parameter. Instead of trying to completely eliminate the eddy current field through gradient coil design, the system measures its effect through the marker sequence and uses the measured distortion coefficients to correct the images, turning the harmful distortion into a quantifiable parameter that can be compensated.
Solution Approach 2:
The marker sequence serves as an intermediary that quantifies the eddy current field's effect. By introducing this intermediate measurement mechanism, the system can characterize the harmful field's impact and apply corrections based on the measured distortion, achieving better precision than direct suppression alone.
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
Effectively corrects image distortions caused by eddy currents, improving the quality of diffusion-weighted images and ADC calculations by aligning and correcting distorted images relative to reference images, thereby enhancing the accuracy and clarity of MRI results.
Implementation Method 1
The diffusion gradient of the DW-EPI sequence will introduce an eddy current field into the imaging space, and the additional magnetic field of eddy current field causes image distortion.
Implementation Method 2
Self-shielding coils include a main coil and a shielding coil, wherein the direction of the magnetic field generated by the shielding coil during imaging is opposite to that of the main coil
Data Source
AI summary
In a method for an apparatus correcting image distortion in diffusion-weighted echo-planar magnetic resonance imaging, a marker sequence is applied before a diffusion-weighted echo planar imaging sequence, to form a combined sequence. The combined sequence is used to obtain marked images with different preset b values and different preset diffusion directions. The diffusion-weighted echo planar imaging sequence is used to obtain diffusion-weighted echo planar images with the same b values and diffusion directions as the marked images. A stretching coefficient and a displacement coefficient are calculated for each image data column of the diffusion-weighted echo planar image. The stretching coefficient and displacement coefficient are used to correct the diffusion-weighted echo planar images.