Adaptive K-space Sampling for Metal Artifact Correction
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Solution Overview
Problem
The existing SEMAC method for metal artifact correction in MRI increases measurement time significantly and affects image quality due to the need for additional encoding steps, which linearly increases with the number of SEMAC steps required.
Innovation Solution
A method that adapts the k-space sampling based on the extent of magnetic field distortion, using a density function to optimize the distribution and number of k-space lines, allowing for fewer samples in areas of low distortion and more in areas of high distortion, thereby improving image quality without excessive increase in measurement time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SEMAC encoding with multiple encoding steps is used to suppress metal artifacts, then image quality is improved, but measurement time increases linearly with the number of encoding steps
Solution Approach 1:
The patent applies local quality by adapting the k-space sampling density to the local extent of magnetic field distortion. Areas with high distortion (near metal artifacts) receive denser sampling, while areas with low distortion receive sparser sampling. This is implemented through a distortion-dependent sampling density function that modulates the number of k-space lines acquired in different regions, thereby reducing overall measurement time while maintaining image quality where needed.
Solution Approach 2:
The patent changes the parameter of k-space sampling density based on the extent of magnetic field distortion. By varying the sampling density as a function of distortion extent, the system optimizes the balance between artifact suppression and measurement time. The sampling density is increased in regions with higher distortion and decreased in regions with lower distortion, resolving the contradiction between image quality and measurement time.
2Productivity
If the number of k-space lines is reduced to decrease measurement time, then measurement efficiency is improved, but image quality deteriorates due to insufficient sampling in high distortion areas
Solution Approach 1:
The patent ensures that high distortion areas receive adequate sampling density while low distortion areas use reduced sampling. The sampling density is locally adapted based on the extent of magnetic field distortion, so that image quality is maintained in critical regions while measurement efficiency is improved overall by reducing unnecessary sampling in low-distortion regions.
Solution Approach 2:
The patent applies partial action by acquiring only the necessary number of k-space lines in each region. Instead of uniformly acquiring maximum k-space lines throughout, the system acquires a variable number of lines based on local distortion characteristics, avoiding excessive sampling in low-distortion areas while ensuring sufficient sampling in high-distortion areas.
3Loss of time
If uniform k-space sampling is used across the entire volume, then measurement time is minimized, but image quality deteriorates in areas with high magnetic field distortion
Solution Approach 1:
The patent replaces uniform sampling with non-uniform, distortion-dependent sampling. The sampling density is locally adapted based on the extent of magnetic field distortion in each region, ensuring that high distortion areas receive adequate sampling for quality imaging while low distortion areas use reduced sampling to minimize measurement time.
Solution Approach 2:
The patent changes the sampling parameter (number of k-space lines) as a function of magnetic field distortion extent. This creates a variable sampling scheme where the sampling density is increased in regions with higher distortion and decreased in regions with lower distortion, resolving the contradiction between minimizing measurement time and maintaining image quality in high distortion areas.
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 reduces the number of k-space lines needed in areas of low distortion while ensuring sufficient sampling in areas of high distortion, optimizing image quality and measurement efficiency.
Implementation Method 1
An extent of magnetic field distortion within the volume section is ascertained
Implementation Method 2
An RF excitation pulse is radiated for the selective excitation of a slice in the volume section while the first gradient is switched
Implementation Method 3
A first phase-encoding gradient is switched along a second direction. A second phase-encoding gradient or SEMAC encoding gradient is switched along the first direction
Data Source
AI summary
Acquisition of MR data with a compressed sensing technique in a volume section includes ascertaining an extent of magnetic field distortion within the volume section. A first gradient along a first direction is switched. An RF excitation pulse is radiated for selective excitation of a slice in the volume section while the first gradient is switched. The MR data is acquired in a volume of the volume section that is composed of the slice, a partial volume above the slice, and a partial volume below the slice by executing the following multiple times: switching a first phase-encoding gradient along a second direction; switching a second phase-encoding gradient along the first direction; and reading out the MR data in a k-space line while a readout gradient is switched along a readout direction. A set of k-space lines to be read out for the volume is determined in dependence on the extent.