1,677 research outputs found
Geometry of Deep Learning for Magnetic Resonance Fingerprinting
Current popular methods for Magnetic Resonance Fingerprint (MRF) recovery are
bottlenecked by the heavy storage and computation requirements of a
dictionary-matching (DM) step due to the growing size and complexity of the
fingerprint dictionaries in multi-parametric quantitative MRI applications. In
this paper we study a deep learning approach to address these shortcomings.
Coupled with a dimensionality reduction first layer, the proposed MRF-Net is
able to reconstruct quantitative maps by saving more than 60 times in memory
and computations required for a DM baseline. Fine-grid manifold enumeration
i.e. the MRF dictionary is only used for training the network and not during
image reconstruction. We show that the MRF-Net provides a piece-wise affine
approximation to the Bloch response manifold projection and that rather than
memorizing the dictionary, the network efficiently clusters this manifold and
learns a set of hierarchical matched-filters for affine regression of the NMR
characteristics in each segment
Deep learning-based parameter mapping for joint relaxation and diffusion tensor MR Fingerprinting
Magnetic Resonance Fingerprinting (MRF) enables the simultaneous
quantification of multiple properties of biological tissues. It relies on a
pseudo-random acquisition and the matching of acquired signal evolutions to a
precomputed dictionary. However, the dictionary is not scalable to
higher-parametric spaces, limiting MRF to the simultaneous mapping of only a
small number of parameters (proton density, T1 and T2 in general). Inspired by
diffusion-weighted SSFP imaging, we present a proof-of-concept of a novel MRF
sequence with embedded diffusion-encoding gradients along all three axes to
efficiently encode orientational diffusion and T1 and T2 relaxation. We take
advantage of a convolutional neural network (CNN) to reconstruct multiple
quantitative maps from this single, highly undersampled acquisition. We bypass
expensive dictionary matching by learning the implicit physical relationships
between the spatiotemporal MRF data and the T1, T2 and diffusion tensor
parameters. The predicted parameter maps and the derived scalar diffusion
metrics agree well with state-of-the-art reference protocols. Orientational
diffusion information is captured as seen from the estimated primary diffusion
directions. In addition to this, the joint acquisition and reconstruction
framework proves capable of preserving tissue abnormalities in multiple
sclerosis lesions
Deep Unrolling for Magnetic Resonance Fingerprinting
Magnetic Resonance Fingerprinting (MRF) has emerged as a promising
quantitative MR imaging approach. Deep learning methods have been proposed for
MRF and demonstrated improved performance over classical compressed sensing
algorithms. However many of these end-to-end models are physics-free, while
consistency of the predictions with respect to the physical forward model is
crucial for reliably solving inverse problems. To address this, recently [1]
proposed a proximal gradient descent framework that directly incorporates the
forward acquisition and Bloch dynamic models within an unrolled learning
mechanism. However, [1] only evaluated the unrolled model on synthetic data
using Cartesian sampling trajectories. In this paper, as a complementary to
[1], we investigate other choices of encoders to build the proximal neural
network, and evaluate the deep unrolling algorithm on real accelerated MRF
scans with non-Cartesian k-space sampling trajectories.Comment: Tech report. arXiv admin note: substantial text overlap with
arXiv:2006.1527
Rapid three-dimensional multiparametric MRI with quantitative transient-state imaging
Novel methods for quantitative, transient-state multiparametric imaging are
increasingly being demonstrated for assessment of disease and treatment
efficacy. Here, we build on these by assessing the most common Non-Cartesian
readout trajectories (2D/3D radials and spirals), demonstrating efficient
anti-aliasing with a k-space view-sharing technique, and proposing novel
methods for parameter inference with neural networks that incorporate the
estimation of proton density. Our results show good agreement with gold
standard and phantom references for all readout trajectories at 1.5T and 3T.
Parameters inferred with the neural network were within 6.58% difference from
the parameters inferred with a high-resolution dictionary. Concordance
correlation coefficients were above 0.92 and the normalized root mean squared
error ranged between 4.2% - 12.7% with respect to gold-standard phantom
references for T1 and T2. In vivo acquisitions demonstrate sub-millimetric
isotropic resolution in under five minutes with reconstruction and inference
times < 7 minutes. Our 3D quantitative transient-state imaging approach could
enable high-resolution multiparametric tissue quantification within clinically
acceptable acquisition and reconstruction times.Comment: 43 pages, 12 Figures, 5 Table
Learning Bloch Simulations for MR Fingerprinting by Invertible Neural Networks
Magnetic resonance fingerprinting (MRF) enables fast and multiparametric MR
imaging. Despite fast acquisition, the state-of-the-art reconstruction of MRF
based on dictionary matching is slow and lacks scalability. To overcome these
limitations, neural network (NN) approaches estimating MR parameters from
fingerprints have been proposed recently. Here, we revisit NN-based MRF
reconstruction to jointly learn the forward process from MR parameters to
fingerprints and the backward process from fingerprints to MR parameters by
leveraging invertible neural networks (INNs). As a proof-of-concept, we perform
various experiments showing the benefit of learning the forward process, i.e.,
the Bloch simulations, for improved MR parameter estimation. The benefit
especially accentuates when MR parameter estimation is difficult due to MR
physical restrictions. Therefore, INNs might be a feasible alternative to the
current solely backward-based NNs for MRF reconstruction.Comment: Accepted at MICCAI MLMIR 202
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