Radial MR Data Trajectory Filtering for Metal Artifact Reduction
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Solution Overview
Problem
Radial collection of MR data is more sensitive to artifacts caused by metal parts compared to Cartesian collection, leading to increased interference in reconstructed MR images.
Innovation Solution
The method involves acquiring MR data along arbitrary radial trajectories and reconstructing the MR image using only data from trajectories with readout directions restricted to a specific solid angle, defined by a partial surface of a sphere, which reduces sensitivity to off-resonance artifacts by minimizing antiparallel readout directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If radial collection of MR data is used, then sensitivity to movement is reduced, but sensitivity to artifacts caused by metal parts increases
Solution Approach 1:
The patent extracts and removes trajectories with readout directions that would cause artifacts from the reconstruction process. Specifically, trajectories whose readout directions fall outside the predetermined solid angle (defined by partial surfaces of a sphere) are excluded from image reconstruction, thereby eliminating the source of metal artifact contamination while preserving beneficial radial trajectories
Solution Approach 2:
The patent applies different quality criteria to different trajectories based on their readout directions. Trajectories within the predetermined solid angle are accepted for reconstruction, while those outside are rejected. This local quality differentiation allows the system to maintain movement robustness while minimizing metal artifact sensitivity on a trajectory-by-trajectory basis
2Measurement precision
If radial collection of MR data is used, then movement sensitivity is improved, but system reliability deteriorates due to gradient delays and off-resonance effects
Solution Approach 1:
The patent changes the parameter of readout direction selection by introducing a predetermined solid angle constraint. This parameter change filters out trajectories susceptible to off-resonance effects and gradient delays while maintaining the movement insensitivity advantage of radial sampling, thereby improving system reliability without sacrificing measurement precision
3Measurement precision
If all radially collected MR data are used for reconstruction, then image quality is improved, but artifact occurrence increases
Solution Approach 1:
The patent extracts only the beneficial subset of radial trajectories for reconstruction by excluding those with readout directions outside the predetermined solid angle. This selective extraction maintains image quality from valid trajectories while removing artifact-causing trajectories, resolving the contradiction between utilizing all data and avoiding artifacts
Data Source
AI summary
For the creation of a magnetic resonance (MR) image of a predetermined volume section of an object of investigation, MR data of the volume section are collected along radial trajectories, and each trajectory is assigned a readout direction in which the MR data are collected along the respective trajectory. The MR image is reconstructed on the basis of the collected MR data. In the reconstruction, only MR data are taken into consideration that were collected along trajectories with a readout direction restricted to the field of a solid angle that is defined by a partial surface of a sphere. The partial surface (A) at most corresponds to 75% of the total surface of the sphere.