MRI Metal Artifact Correction via Adaptive SEMAC
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Solution Overview
Problem
Magnetic Resonance Imaging (MRI) systems face challenges in correcting artifacts caused by metallic objects due to distortions in the static magnetic field, which existing techniques like SEMAC struggle to fully address, especially in terms of reducing scan time and optimizing phase encoding steps.
Innovation Solution
The implementation of a magnetic resonance imaging system that modifies pulse sequence data to identify and skip phase encodings encoding volumes outside the field of view, determines a slice SEMAC factor for each slice, and reorders pulse sequence repetitions to reduce unnecessary phase encodings, thereby shortening acquisition time while maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SEMAC technique uses additional phase encoding during acquisition to correct through-plane distortions, then metal artifact correction is improved, but scan time increases
Solution Approach 1:
The patent applies different SEMAC factors to different slices based on their specific needs. Central slices near metal implants receive higher SEMAC factors for better artifact correction, while peripheral slices use lower or zero SEMAC factors. This localized approach optimizes artifact correction where needed while reducing unnecessary phase encoding steps in regions where metal artifacts are less problematic, thereby reducing overall scan time.
Solution Approach 2:
The patent divides the image volume into multiple slices and processes each slice independently with its own optimized SEMAC factor. This segmentation allows the system to apply phase encoding selectively to only those slices that require metal artifact correction, rather than uniformly applying it to all slices, thus reducing the total number of phase encoding steps and scan time.
2Measurement precision
If maximum SEMAC factor is applied to all slices, then artifact correction is improved, but acquisition time increases
Solution Approach 1:
The patent determines an individual SEMAC factor for each slice based on its distance from metal implants and its specific artifact susceptibility. This localized optimization ensures that the maximum SEMAC factor is applied only where necessary for artifact correction, while other slices use reduced factors, improving acquisition efficiency without compromising essential artifact correction.
Solution Approach 2:
The patent dynamically adjusts the SEMAC factor parameter for each slice based on calculated artifact risk. By changing this parameter locally rather than applying a uniform maximum value, the system optimizes the balance between artifact correction quality and acquisition speed, improving overall productivity.
3Loss of time
If phase encoding steps are reduced to shorten scan time, then scan time is reduced, but metal artifact correction quality deteriorates
Solution Approach 1:
The patent ensures that slices with high metal artifact risk (central slices near implants) receive sufficient phase encoding steps with higher SEMAC factors to maintain correction quality, while slices with lower risk (peripheral slices) use fewer phase encoding steps. This localized quality assignment maintains artifact correction quality where needed while reducing scan time overall.
Solution Approach 2:
The patent applies partial phase encoding to slices where full encoding is unnecessary. By determining the minimum required SEMAC factor for each slice based on its artifact risk, the system applies just enough phase encoding to achieve adequate correction without the excessive action of applying maximum encoding to all slices, thus reducing scan time while maintaining acceptable quality.
Data Source
AI summary
The invention provides for a magnetic resonance imaging system. Instructions cause a processor (136) controlling the magnetic resonance imaging system to modify (200) pulse sequence data by omitting at least some of the phase encodings (408) that encode for volumes outside of the field of view. The pulse sequence data specifies the acquisition of a stack (128) of two dimensional slices of a field of view (126). The pulse sequence data further specifies phase encoding in a direction (130) perpendicular to the two dimensional slices. The pulse sequence data specifies a maximum SEMAC factor (400). The maximum SEMAC factor specifies a maximum number of phase encoding steps in the perpendicular direction for each of the two dimensional slices. The instructions further cause the processor to determine (202) a slice SEMAC factor for each of the stack of two dimensional slices. The slice SEMAC factor is determined by counting the phase encoding steps that encode for regions within the field of view. The instructions further cause the processor to modify (204) the pulse sequence data by dividing the stack of two dimensional slices into multiple packages (502, 504). Slices within each of the multiple packages are ordered using an outer linear profile in the perpendicular direction. The stack of two dimensional slices are divided into the multiple packages by grouping slices which have a slice SEMAC factor within a predetermined range. Each of the multiple packages is acquired as a series of pulse sequence repetitions. The instructions further cause the processor to modify (206) the pulse sequence data by reordering the profile order of a package to remove at least some of the phase encodings outside of the field of view.