Variable Phase Coding for MRI Metal Artifact Reduction
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Solution Overview
Problem
Conventional MRI methods, such as SEMAC for metal artifact correction in TSE sequences, significantly increase measurement time due to linearly increasing phase coding steps, making clinical protocols impractical.
Innovation Solution
A method that adjusts the number of phase coding steps along one direction based on the value of the first phase coding gradient, allowing for reduced phase coding steps and thus shorter measurement times, while maintaining effective suppression of metal artifacts by optimizing phase coding gradients and their moments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of SEMAC phase coding steps is increased to suppress metal artifacts, then the quality of metal artifact suppression is improved, but the measurement time increases linearly
Solution Approach 1:
The patent applies dynamics by making the number of phase coding steps variable rather than fixed. The system dynamically adjusts the number of SEMAC phase coding steps based on the actual metal artifact severity and slice position, allowing optimal balance between artifact suppression quality and measurement time for each specific imaging scenario
Solution Approach 2:
The patent implements local quality by applying different numbers of phase coding steps to different slices or regions based on their specific needs._slices closer to metal implants use more phase coding steps for better artifact suppression, while slices farther away use fewer steps, thereby optimizing the overall measurement time while maintaining necessary artifact suppression quality where needed
2Loss of information
If the number of phase coding steps along the second direction is kept constant at 256, then the coverage of k-space is complete, but the measurement time becomes excessively long
Solution Approach 1:
The patent applies partial action by acquiring only the necessary portion of k-space rather than the complete 256 phase coding steps. The system determines the optimal number of phase coding steps based on the actual slice position and metal artifact characteristics, acquiring sufficient information for diagnostic quality while avoiding unnecessary measurements that would extend scan time
Solution Approach 2:
The patent implements parameter changes by making the number of phase coding steps a variable parameter rather than a fixed constant. The system adjusts this parameter based on slice position, metal implant location, and desired artifact suppression quality, thereby optimizing the balance between information coverage and measurement time
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 measurement time without substantial information loss, particularly by prioritizing k-space lines closer to the slice of interest, and allows for efficient MR data acquisition even in the presence of magnetic field inhomogeneities.
Implementation Method 1
Switch a slice selection gradient along a first direction or, respectively, slice selection direction which is orthogonal to the slice
Implementation Method 2
Radiate an RF excitation pulse for selective excitation of the slice while the slice selection gradient is being switched, such that only the spins of the slice are excited
Implementation Method 3
Switch a first phase coding gradient along the first direction. The switching of this first phase coding gradient can also be designated as a SEMAC coding... Switch a second phase coding gradient along a second direction which is orthogonal to the first direction
Implementation Method 4
Switch a readout gradient along a third direction which is orthogonal to the first direction and second direction. Read out the MR data while the readout gradient is being switched
Data Source
AI summary
In a method and a magnetic resonance system to acquire MR data of a slice of a volume segment within an examination subject, a slice selection gradient is activated along a first direction that is orthogonal to the slice. An RF excitation pulse is radiated for selective excitation of the slice, a first phase coding gradient is activated along the first direction, and a second phase coding gradient is activated along a second direction. The second direction is orthogonal to the first direction. A readout gradient is activated along a third direction that is orthogonal to the first direction and the second direction. MR data are acquired while the readout gradient is activated. A number of phase coding steps for the second phase coding gradient is determined depending on the first phase coding gradient.