Multiband Multishot MRE for High-Resolution Brain Imaging
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Solution Overview
Problem
Current magnetic resonance elastography (MRE) techniques face challenges in balancing scan time, signal-to-noise ratio (SNR), and distortions from field inhomogeneity, particularly in achieving high-resolution viscoelastic maps of brain tissue for neurodegenerative condition assessment and intracranial tumor analysis.
Innovation Solution
The implementation of a multiband, multishot MRE method using a novel sequence with multiband RF excitation and 3D encoding of distributed slabs with multishot spirals, enabling optimal SNR efficiency, reduced distortions, and parallel imaging acceleration both in-plane and through-plane, while correcting nonlinear motion-induced phase errors using a k-blipped spiral-in 3D navigator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If traditional single-band, single-shot MRE sequences are used, then the imaging coverage is limited, but the scan time is extended and spatial resolution is reduced
Solution Approach 1:
The imaging volume is divided into multiple non-contiguous slabs that can be excited and imaged simultaneously using multiband RF pulses. Each slab is further segmented into multiple slices that are encoded in the third dimension using kz gradient blips, enabling parallel acquisition of multiple spatial locations within a single shot
Solution Approach 2:
The patent extends traditional 2D slice encoding into 3D by introducing kz gradient blips that encode the slab dimension. This creates a 3D k-space sampling pattern where multiple slabs are encoded along the kz dimension, allowing simultaneous imaging of multiple non-adjacent slices in three dimensions without extending scan time
2Measurement precision
If higher spatial resolution is achieved through more slices, then the signal-to-noise ratio decreases and scan time increases
Solution Approach 1:
The multiband RF excitation pulses continuously excite multiple slabs simultaneously, and the multishot spiral readout continuously samples k-space for all excited slices throughout the echo train. This continuous acquisition of signal from multiple slices maintains high SNR while achieving high spatial resolution through parallel imaging
Solution Approach 2:
The imaging volume is divided into multiple non-contiguous slabs that can be excited and imaged simultaneously using multiband RF pulses. Each slab is further segmented into multiple slices that are encoded in the third dimension using kz gradient blips, enabling parallel acquisition of multiple spatial locations within a single shot
3Reliability
If longer scan time is used to improve SNR, then field inhomogeneity distortions increase
Solution Approach 1:
The patent uses periodic refocusing pulses within the echo train to maintain signal coherence and reduce sensitivity to field inhomogeneities. The periodic application of refocusing pulses compensates for phase accumulation due to field variations, reducing distortions while maintaining high SNR through efficient signal utilization
Solution Approach 2:
The patent replaces traditional mechanical gradient switching with spiral-based k-space trajectories that are inherently more robust to field inhomogeneities. The spiral readout pattern and associated gradient waveforms are designed to minimize sensitivity to B0 variations, reducing geometric distortions and signal loss in regions with field inhomogeneity
4Measurement precision
If multiband, multishot sequences with 3D encoding are implemented, then scan time and computational complexity increase
Solution Approach 1:
The patent applies preliminary motion correction using navigator echoes acquired before the main imaging data. These navigators measure bulk motion and physiological movements, which are then used to correct the phase errors in the multishot spiral data. This preliminary correction simplifies the reconstruction process by separating motion correction from the complex 3D k-space sampling reconstruction
Solution Approach 2:
The patent introduces navigator echoes as an intermediary measurement that captures motion information separately from the main imaging data. These navigators serve as a mediator between the complex multishot spiral acquisition and the final image reconstruction, providing motion correction data that simplifies the overall reconstruction process and reduces 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 allows for the rapid acquisition of high-resolution, high-SNR brain MRE displacement data, overcoming the limitations of previous methods by achieving whole-brain imaging coverage at 2×2×2 mm3 resolution in 3 minutes with improved image quality and reduced artifacts, enhancing the clinical adoption and resolution of MRE methods.
Implementation Method 1
applying a first multiband radio frequency (RF) excitation pulse to a sample
Implementation Method 2
applying first and second motion encoding gradients
Implementation Method 3
applying first and second motion encoding gradients and a multiband RF refocusing pulse
Data Source
AI summary
A method and system provides an acquisition scheme for generating magnetic resonance elastography displacement data with whole-sample coverage, high spatial resolution, and adequate SNR in a short scan time. The method and system can acquire in-plane and through-plane k-space shots over a volume of a sample divided into a plurality of slabs that each include a plurality of non-adjacent slices to obtain three dimensional multiband, multishot data, can apply multiband radio frequency refocusing pulses to the sample, can acquire navigators before readout, and can correct for non-linear motion errors.