SEMAC MR Imaging Near Metal Using Overlapping Slabs and Gradient Reduction
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Solution Overview
Problem
Current MR imaging techniques face challenges in effectively imaging soft tissue near metal implants due to susceptibility issues, resulting in artifacts such as signal pile-up, signal voids, and geometric distortions, particularly the ripple-artefact caused by suboptimal transitions between adjacent image slices or slabs.
Innovation Solution
The method involves adjusting the slice-selection profile by overlapping adjacent slices or slabs by at least 10% to 50% in the slice-selection direction, reducing the strength of the slice-selection magnetic field gradient while maintaining a wide RF bandwidth, and applying undersampling in the phase-encoding direction, combined with sparsity constraints for stable image reconstruction using parallel imaging techniques like SENSE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MR imaging sequences are used near metal implants, then the imaging process is simple and fast, but susceptibility artifacts (signal pile-up, signal voids, geometric distortions) severely degrade image quality
Solution Approach 1:
The imaging volume is divided into multiple overlapping slabs instead of imaging the entire volume at once. Each slab is imaged separately with optimized parameters, and the final image is reconstructed by combining the overlapping slab images. This segmentation approach reduces the impact of susceptibility artifacts within each slab while maintaining coverage of the entire region of interest.
Solution Approach 2:
Different imaging parameters are applied to different regions of the image. Specifically, the slice-selection bandwidth is reduced and slice thickness is increased in regions affected by metal implants, while other regions use standard parameters. This local optimization improves image quality near metal without unnecessarily increasing scan time for the entire volume.
2Reliability
If multispectral imaging techniques like SEMAC or MAVRIC are used to counter susceptibility issues, then image quality near metal improves, but scan duration increases significantly
Solution Approach 1:
Instead of applying full multispectral imaging techniques (SEMAC/MAVRIC) to the entire imaging volume, the invention applies optimized slice parameters only to specific slabs that contain or are near metal implants. Other slabs are imaged with standard parameters, thus achieving improved image quality near metal while minimizing the increase in scan duration.
Solution Approach 2:
The invention introduces slab selection as an additional dimension beyond traditional slice selection. By organizing the imaging volume into multiple overlapping slabs along the frequency-encoding direction, the method creates a new dimension for parameter optimization, allowing susceptibility artifact reduction without proportionally increasing scan time.
3Measurement precision
If slice thickness is reduced to improve resolution, then spatial resolution improves, but ripple-artefacts increase due to suboptimal transitions between adjacent slices
Solution Approach 1:
Adjacent slabs are made to overlap by at least 10-20% of the slice thickness. This overlap ensures that regions between slices are covered by multiple slabs, eliminating gaps and reducing ripple artifacts. The final image is reconstructed by merging the overlapping slab images, which smooths out transitions and reduces artifacts while maintaining spatial resolution.
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 ripple-artefacts, enabling more reliable evaluation of soft tissue near metal implants and reducing scan time by stabilizing parallel image reconstruction, allowing for diagnostic imaging closer to metal implants than conventional methods.
Implementation Method 1
a main magnet coil for generating a uniform steady magnetic field within an examination volume
Implementation Method 2
a number of gradient coils for generating switched magnetic field gradients in different spatial directions within the examination volume
Implementation Method 3
at least one RF coil for generating RF pulses within the examination volume and/or for receiving MR signals from a body of a patient positioned in the examination volume
Data Source
AI summary
The invention relates to a method of MR imaging near metal parts using SEMAC. It is an object of the invention to provide an improved MR imaging technique that is sufficiently fast and robust against susceptibility effects. The invention proposes to apply a weaker slice-selection magnetic field gradient (Gslice) for reduction of ripple-artefacts near metal parts or to apply undersampling in the slice-selection direction of the SEMAC sequence or to apply both these aspects. According to one aspect of the invention, a sparsity constraint is used to make the reconstruction of the undersampled MR images more stable. Moreover, the invention relates to a MR device (1) and to a computer program to be run on a MR device (1).