Model-based multi-parameter mapping

doi:10.1016/j.media.2021.102149

Model-based multi-parameter mapping

2021-10-01

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DOI：10.1016/j.media.2021.102149

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Quantitative MR imaging is increasingly favoured for its richer information content and standardised measures. However, computing quantitative parameter maps, such as those encoding longitudinal relaxation rate (R-1), apparent transverse relaxation rate (R-2*) or magnetisation-transfer saturation (MTsat), involves inverting a highly non-linear function. Many methods for deriving parameter maps assume perfect measurements and do not consider how noise is propagated through the estimation procedure, resulting in needlessly noisy maps. Instead, we propose a probabilistic generative (forward) model of the entire dataset, which is formulated and inverted to jointly recover (log) parameter maps with a well-defined probabilistic interpretation (e.g., maximum likelihood or maximum a posteriori). The second order optimisation we propose for model fitting achieves rapid and stable convergence thanks to a novel approximate Hessian. We demonstrate the utility of our flexible framework in the context of recovering more accurate maps from data acquired using the popular multi-parameter mapping protocol. We also show how to incorporate a joint total variation prior to further decrease the noise in the maps, noting that the probabilistic formulation allows the uncertainty on the recovered parameter maps to be estimated. Our implementation uses a PyTorch backend and benefits from GPU acceleration. It is available at https://github.com/balbasty/nitorch. (C) 2021 The Authors. Published by Elsevier B.V.

Keywords:

BRAIN IRON

MAGNETIZATION-TRANSFER

PARAMETER-ESTIMATION

IMPROVED ACCURACY

STEADY-STATE

MR-IMAGES

T-1

ANGLE

FLASH

OPTIMIZATION

Model-based multi-parameter mapping

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