Geometry-Based Field Prediction for MRI Phase Artifact Removal
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Solution Overview
Problem
Existing magnetic resonance imaging (MRI) techniques face challenges in handling rapid phase aliasing due to changes in background magnetic fields caused by air/tissue interfaces, particularly in brain regions, leading to loss of local phase information.
Innovation Solution
A method that estimates magnetic susceptibility values based on the geometry of scanned objects using an iterative process, dividing voxels into regions and assigning revised susceptibility values to generate a susceptibility image or map, which helps in removing phase aliasing effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a strong high pass filter is used to remove rapid phase aliasing near air/tissue interfaces, then phase aliasing is removed, but important local phase information is lost
Solution Approach 1:
The image space is divided into multiple subspaces based on dominant field directions. Each subspace is processed independently with a tailored high pass filter that preserves local phase information while removing aliasing artifacts specific to that region's field orientation.
Solution Approach 2:
Different high pass filtering strategies are applied to different spatial regions according to their local field characteristics. The filtering strength and direction are adapted locally rather than applying a uniform filter across the entire image, preserving local phase information while removing aliasing.
2Reliability
If phase unwrapping and polynomial fitting are used to remove background fields, then low spatial frequency field variations are removed, but the process is complex and may alter local phase information
Solution Approach 1:
The processing is segmented into direction-specific subspaces, each handled independently. This breaks down the complex global polynomial fitting problem into simpler local filtering operations that are computationally more efficient and easier to implement.
Solution Approach 2:
The mechanical process of phase unwrapping followed by polynomial fitting is replaced with a direct high pass filtering approach in the spatial domain, operating on complex image data without requiring phase unwrapping. This substitution simplifies the processing pipeline while achieving similar background field removal.
3Reliability
If slice by slice polynomial fitting with different order polynomials is used, then phase aliasing is removed in each slice, but the process is time-consuming and computationally intensive
Solution Approach 1:
A universal high pass filtering approach is applied across all slices and directions using a consistent algorithmic framework. This multi-functional approach handles different field orientations and slice configurations with a single unified method, improving processing efficiency while maintaining effectiveness.
Solution Approach 2:
Instead of performing exhaustive polynomial fitting with variable order polynomials across all slices, the method applies a standardized high pass filter that provides sufficient aliasing removal with reduced computational overhead, accepting a slight approximation for significant speed improvement.
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 removes geometry-dependent phase from MRI data, preserving local phase information and improving the accuracy of susceptibility mapping, particularly in brain imaging, with potential applications in disease diagnosis and tissue characterization.
Implementation Method 1
changes in the background magnetic field caused by the presence of air/tissue interfaces... arising from local susceptibility differences
Implementation Method 2
rapid phase aliasing resulting from changes in the background magnetic field... rapid unwanted field variations particularly near the mastoid, frontal, ethmoid and sphenoid sinuses
Data Source
AI summary
The present invention provides a method of handling rapid phase aliasing in magnetic resonance images arising from local magnetic susceptibility differences. The methods of the present invention can be used to estimate the field effects within an object arising from the interfaces of regions having differences in magnetic susceptibilities, and to subtract out the resulting phase from the original or source phase data prior to any further phase processing. The methods of the present invention also include a process of accurately determining the susceptibility values of multiple voxel regions based on the geometry of such regions.


