SEMAC MR Imaging Reducing Metal Artifacts and Scan Time
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Solution Overview
Problem
Current MR imaging techniques for suppressing metal artifacts, such as SEMAC, require prolonged scanning times due to the need for multiple phase encoding steps, which is not feasible in clinical settings, especially for T2-weighted TSE protocols with long repetition times.
Innovation Solution
The method involves fully sampling MR data in a central reference region of k-space and undersampling outside this region, combining the fully sampled data to create a reference dataset for efficient image reconstruction using GRAPPA or CS/SENSE techniques, reducing the number of reference lines needed for image acquisition and reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SEMAC technique is used to suppress metal artifacts, then metal artifact suppression is improved, but scanning time increases significantly
Solution Approach 1:
The patent segments k-space into a central reference region and peripheral regions. Full sampling is performed only in the central reference region, while peripheral regions are undersampled. This segmentation allows the use of parallel imaging techniques (GRAPPA or SENSE) to reconstruct the undersampled regions from the fully sampled reference region, thereby reducing the number of phase encoding steps and scanning time while maintaining metal artifact suppression capability.
2Manufacturing precision
If the number of SEMAC steps is increased to resolve metal artifacts, then image quality is improved, but measurement time increases linearly
Solution Approach 1:
The patent applies different sampling strategies to different regions of k-space. The central reference region is fully sampled to ensure accurate metal artifact correction, while the peripheral regions are undersampled and reconstructed using parallel imaging. This local differentiation of quality requirements allows reduction of total sampling steps while maintaining sufficient image quality for diagnostic purposes.
3Reliability
If T2-weighted TSE protocol with long TR is used, then image contrast is improved, but total measurement time increases significantly
Solution Approach 1:
The patent dynamically adjusts the sampling strategy based on the specific requirements of T2-weighted imaging with long TR. By combining the inherent contrast benefits of long TR sequences with dynamic k-space sampling (full sampling in central region, undersampling in peripheral regions) and parallel imaging reconstruction, the protocol achieves both high image contrast and reduced total 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 significantly accelerates MR image acquisition while maintaining effective metal artifact suppression, reducing scanning time and improving efficiency by utilizing symmetries and analogies in the MR data, thus providing high-quality images with reduced measurement time.
Implementation Method 1
Magnetic resonance imaging provides very good soft-tissue contrast
Implementation Method 2
The use of spin echoes recovers much of the signal loss
Implementation Method 3
by phase encoding and a Fourier transform in the slice-selection direction
Implementation Method 4
metal-induced artifacts, such as distortion, signal voids and pile-up artifacts, often render MR images unusable for diagnostic purposes. These metal artifacts exist both in in-plane and through-slice direction, resulting from static field inhomogeneities near metal implants due to the susceptibility difference between tissues and metal
Implementation Method 5
the range of frequencies around metallic implants typically exceed the excitation pulse bandwidth, such that is impossible to correct distortion and avoid signal loss without increasing the amount of data acquired
Data Source
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AI summary
A method for suppressing metal artifacts in MR images of slices of a patient containing a metallic implant using a Slice Encoding for Metal Artifact Correction (SEMAC) sequence is provided. Therein, MR data of each slice is fully sampled in k-space in a reference region, which is located in a center of k-space in phase-encoding direction and a central section in slice-selection direction, and wherein the MR-data of each slice outside the reference region is undersampled in k-space. The fully sampled MR data from the reference regions of each slice is combined to generate a reference data set for reconstructing an MR image of each slice.