OSCILLATE: A low‐rank approach for accelerated magnetic resonance elastography

Abstract

Purpose: MR elastography (MRE) is a technique to characterize brain mechanical properties in vivo. Due to the need to capture tissue deformation in multiple directions over time, MRE is an inherently long acquisition, which limits achievable resolution and use in challenging populations. The purpose of this work is to develop a method for accelerating MRE acquisition by using low-rank image reconstruction to exploit inherent spatiotemporal correlations in MRE data. Theory and Methods:The proposed MRE sampling and reconstruction method, OSCILLATE (Observing Spatiotemporal Correlations for Imaging with Low-rank Leveraged Acceleration in Turbo Elastography), involves alternating which k-space points are sampled between each repetition by a reduction factor, R OSC. Using a predetermined temporal basis from a low-resolution navigator in a joint low-rank image reconstruction, all images can be accurately reconstructed from a reduced amount of k-space data. Results: Decomposition of MRE displacement data demonstrated that, on average, 96.1% of all energy from an MRE dataset is captured at rank L = 12 (reduced from a full rank of 24). Retrospectively undersampling data with R OSC = 2 and reconstructing at low-rank (L = 12) yields highly accurate stiffness maps with voxel-wise error of 5.8% ± 0.7%. Prospectively undersampled data at R OSC = 2 were successfully reconstructed without loss of material property map fidelity, with average global stiffness error of 1.0% ± 0.7% compared to fully sampled data.Conclusions: OSCILLATE produces whole-brain MRE data at 2 mm isotropic resolution in 1 min 48 s.

Correlated noise in brain magnetic resonance elastography

“…Noise suppression techniques should be considered for MRE, however, traditional approaches to limit physiological noise in MRI may not necessarily translate for MRE 48 . Cardiac gating has been implemented in diffusion encoding to trigger motion encoding away from cardiac cycle peaks, such that data is only collected during diastole 24 .…”

“…Error is reduced at higher OSS-SNR levels MRE. 48 Cardiac gating has been implemented in diffusion encoding to trigger motion encoding away from cardiac cycle peaks, such that data is only collected during diastole. 24 However, the beat-to-beat variability of the cardiac cycle may interfere with the typical MRE actuation scheme that uses continuous or near-continuous application of harmonic motion.…”

Hippocampal subfield viscoelasticity in amnestic mild cognitive impairment evaluated with MR elastography

“…Each participant underwent an MRI session on a Siemens 3 T Prisma, which included two structural scans: a 0.9 mm 3 T 1 -weighted magnetization prepared rapid gradient echo (MPRAGE) and a 0.4x0.4x2.0 mm 3 T 2 -weighted turbo spin echo (TSE) scan aligned to the hippocampus; and a high-resolution MRE scan using a 3D multiband, multishot spiral MRE sequence with 1.25 mm isotropic resolution ( Johnson et al, 2016a , McIlvain et al, 2022a ), which included the following imaging parameters: repetition time/echo time (TR/TE) = 3360/70 ms, 192x192 matrix size, 240 mm × 240 mm field-of-view (FOV), 96 axial slices, with a total scan time of 10 min and 45 s. We used a commercial Resoundant pneumatic actuator (Resoundant, Rochester, MN) to generate shear waves in the brain via vibrations at 50 Hz, with the resulting displacement fields captured by the MRE sequence. A magnetic field inhomogeneity map was separately collected and use to correct distortion during image reconstruction to improve the quality of the displacement information ( McIlvain et al, 2022b , Sutton et al, 2003 ).…”

Mechanical Property Based Brain Age Prediction using Convolutional Neural Networks

“…All MRE data was collected using a pneumatic actuator pillow system (Resoundant, Rochester, MN) using 50 Hz vibration. Each MRE scan had a corresponding field map of the same resolution and brain coverage, which was used during image reconstruction to minimize geometric distortion (McIlvain et al, 2022).…”

“…All imaging data included a whole-brain, high-resolution T1-weighted magnetization-prepared rapid acquisition gradient echo (MPRAGE) with 0.9 mm 3 isotropic resolution and a highresolution MRE scan. MRE data acquisitions were taken using either the 3D multislab, multishot spiral sequence (Johnson et al, 2014) or the 3D multiband, multishot spiral sequence McIlvain, Cerjanic, et al, 2022), with resolutions ranging from 1.25 mm to 2 mm isotropic and whole-brain coverage. Images were downsampled to 2 mm resolution prior to analysis.…”