Simultaneous Time-Interleaved Multislice MRI Acquisition
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Solution Overview
Problem
Current volumetric MRI techniques, such as 3D-GRE and 3D-MPRAGE, face challenges in reducing scan time, improving patient comfort, and minimizing motion sensitivity, while also dealing with slab boundary artifacts and reduced parallel imaging capabilities due to long echo times and inversion times.
Innovation Solution
The implementation of simultaneous time-interleaved multislice (STIMS) acquisition methods, where multiple slices are excited and encoded at different echo times within a single repetition time, exploiting unused time for additional encoding, and using comb-shaped slice groups to avoid artifacts and preserve aliasing voxel separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional 3D-GRE or 3D-MPRAGE sequences are used with long echo times or inversion times, then tissue contrast and phase contrast are improved, but scan time is significantly increased
Solution Approach 1:
The imaging volume is divided into multiple non-contiguous slice groups that are acquired in an interleaved manner. Each slice group is assigned to a different echo time or inversion time, allowing simultaneous acquisition of multiple slices at different contrast parameters within a single TR period. This segmentation enables parallel encoding of multiple slices without requiring sequential acquisition, thereby reducing total scan time while maintaining optimal contrast for each tissue type.
Solution Approach 2:
The patent introduces time-interleaving as an additional dimension for slice encoding. Instead of acquiring slices sequentially in time, multiple slice groups are encoded simultaneously in the slice direction using different echo times or inversion times. This dimensional approach to slice encoding allows the system to exploit unused time periods (such as inversion time in MPRAGE) for additional encoding, achieving substantial scan time reduction while preserving tissue contrast.
2Productivity
If the field-of-view is divided into multiple contiguous slabs for efficient 3D-GRE, then scan time is reduced, but slab boundary artifacts are introduced and parallel imaging capabilities are reduced
Solution Approach 1:
Instead of using contiguous slabs that create symmetric boundary artifacts, the patent employs non-contiguous, asymmetric slice groupings. Each slice group is strategically selected to avoid adjacent slices, creating an asymmetric pattern that eliminates the formation of slab boundary artifacts. This asymmetric segmentation allows multiple slice groups to be acquired simultaneously without the harmful interference that occurs when contiguous slabs are excited and encoded separately.
Solution Approach 2:
The patent extracts and removes the problematic slab boundary regions by selecting non-contiguous slices for each group. By taking out the adjacent slice relationships that cause boundary artifacts, the method eliminates the source of the harmful effects while maintaining efficient parallel encoding of multiple slice groups within the same TR period.
3Productivity
If contiguous slabs are used for multi-slab acquisition, then encoding efficiency is improved, but aliasing voxels become closer reducing parallel imaging capabilities
Solution Approach 1:
The imaging volume is segmented into multiple non-contiguous slice groups, where each group contains slices that are separated by at least one slice gap. This segmentation strategy maintains encoding efficiency by allowing parallel acquisition of multiple slice groups while ensuring that aliased voxels from different groups remain sufficiently separated in the image domain, thereby preserving parallel imaging capabilities and reducing aliasing artifacts.
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 scan time, eliminates slab boundary artifacts, and enables high-quality parallel imaging, achieving substantial acceleration and improved spatial resolution, as demonstrated by an 8/5-fold reduction in total imaging time and further acceleration with parallel imaging techniques.
Implementation Method 1
Volumetric magnetic resonance imaging ('MRI') involves exciting and encoding magnetic spins in a three-dimensional field-of-view
Implementation Method 2
3D gradient-echo ('3D-GRE') and the 3D magnetization prepared rapid gradient-echo ('3D-MPRAGE') pulse sequences
Implementation Method 3
3D-MPRAGE is based on a rapid 3D-GRE pulse sequence with a magnetization preparation module to provide excellent image contrast between gray matter and white matter
Data Source
AI summary
Methods for reducing scan time in magnetic resonance imaging (“MRI”), particularly when imaging three-dimensional image volumes, using a simultaneous time-interleaved multislice (“STIMS”) acquisition are described. The unused time in each repetition time (“TR”) period is exploited to provide an additional reduction in encoding time for a three-dimensional acquisition (e.g., a 3D whole brain coverage). Groups of spatially interleaved slices are excited in a single TR, with the excitation and acquisition of the groups of slices being interleaved in time.