B0 Field Map Fat Artifact Correction
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Solution Overview
Problem
Current B0 field mapping methods face challenges in accurately measuring magnetic resonance data due to chemical shifts between fat and water, leading to ambiguities and artifacts, especially in multi-echo methods where phase wraps occur, and no effective correction method exists to remove sudden fat regions from B0 field maps.
Innovation Solution
A method that segments the B0 field map using a segmentation criterion to identify clusters of neighboring picture elements, applying smoothness and compactness criteria to determine if a cluster contains a majority of protons bonded to fat, and correcting these clusters by adjusting Larmor frequency values to account for chemical shifts, thereby optimizing the smoothness and compactness of the B0 field map.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-echo methods are used to measure B0 field map, then measurement precision is improved, but chemical shift artifacts between fat and water cause ambiguities and errors in the B0 map calculation
Solution Approach 1:
The patent segments the B0 field map into multiple clusters based on Larmor frequency values. By dividing the image into contiguous clusters with similar frequency characteristics, the method can identify and correct regions affected by chemical shifts between fat and water, resolving phase wrap ambiguities while maintaining measurement precision
Solution Approach 2:
The patent introduces an intermediary correction step that uses cluster-based classification to mediate between the raw multi-echo measurements and the final B0 map. This intermediary process identifies fat-containing clusters and applies frequency offset corrections, eliminating chemical shift artifacts while preserving the high precision of multi-echo methods
2Measurement precision
If echo time difference is increased to improve sensitivity for detecting small Larmor frequency deviations, then measurement sensitivity is improved, but phase wraps occur more frequently leading to ambiguities
Solution Approach 1:
The patent implements a feedback mechanism where the B0 field map is iteratively refined. After initial clustering and correction, the method evaluates the results and applies additional corrections where needed, using the detected phase wrap patterns to guide further refinement and eliminate ambiguities
Solution Approach 2:
The patent changes the parameter representation by working with Larmor frequency values and their deviations from nominal frequencies. By clustering based on these frequency parameters and applying frequency offset corrections, the method can handle large phase wraps while maintaining sensitivity to small frequency deviations
3Ease of operation
If automated correction method is implemented to remove chemical shift artifacts, then ease of operation is improved, but device complexity increases due to additional processing steps
Solution Approach 1:
The patent implements a self-service automated system that performs cluster identification, fat region detection, and frequency correction without user intervention. The algorithm autonomously processes the B0 field map, applies corrections based on detected chemical shift patterns, and outputs the corrected map, eliminating the need for manual artifact removal
Solution Approach 2:
The patent merges multiple processing functions into a unified automated workflow. Cluster-based segmentation, chemical shift detection, frequency offset correction, and map refinement are combined into a single integrated process that operates automatically, managing complexity through functional integration rather than separate manual steps
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 allows for a reliable, fast, and automated correction of artifacts caused by chemical shifts in B0 field maps recorded with multi-echo methods, improving the accuracy and quality of magnetic resonance imaging by distinguishing between water and fat regions without user interaction.
Implementation Method 1
deviations from a nominal Larmor frequency for protons bonded into water (a variable describing this deviation is usually referred to below as the Larmor frequency value) for protons bonded into fat and water that are not in phase, especially using a multi-echo method
Implementation Method 2
Magnetic resonance imaging and its fundamentals are widely known. An object to be examined is introduced into a basic magnetic field with a relatively high field strength, known as the B0 field. In order to be able to acquire magnetic resonance data, in a slice of a subject for example, the nuclear spins of this slice are excited and the decay of this excitation is evaluated as a signal
Implementation Method 3
By operation of a gradient coil arrangement, gradient fields can be created, while radio-frequency excitation pulses, which are frequently referred to as radio-frequency pulses, are being radiated by a radio-frequency coil arrangement
Data Source
AI summary
In a method for correction of a B0 field map measured with a magnetic resonance device, that describes deviations from a nominal field strength in the homogeneity area of the magnetic resonance device by deviations from a nominal frequency for protons bonded to water, the deviations being represented as Larmor frequency values for different picture elements shifted by chemical shifts, the B0 field map is recorded with spins of the fat and water protons not in phase. The B0 field map is segmented by evaluating the differences of the Larmor frequency values of adjacent picture elements of the B0 field map in at least two contiguous clusters. For each cluster, a decision is made on the basis of a smoothness criterion and a compactness criterion as to whether a cluster containing a majority of protons bonded into fat is involved. Clusters identified as containing a majority of protons bonded into fat are corrected by lowering the Larmor frequency values by the difference between the nominal frequency for protons bonded into water and the corresponding nominal frequency for protons bonded to fat.