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Magn Reson Med. 2019 Feb;81(2):1399-1411. doi: 10.1002/mrm.27483. Epub 2018 Sep 28.

Weak-harmonic regularization for quantitative susceptibility mapping.

Author information

1
Department of Electrical Engineering, Pontificia Universidad Catolica de Chile, Santiago, Chile.
2
Biomedical Imaging Center, Pontificia Universidad Catolica de Chile, Santiago, Chile.
3
Martinos Center for Biomedical Imaging, Harvard Medical School, Boston, Massachusetts.
4
Department of Neurology, Medical University of Graz, Graz, Austria.
5
Wellcome Centre for Human Neuroimaging, UCL Institute of Neurology, University College London, London, United Kingdom.

Abstract

PURPOSE:

Background-field removal is a crucial preprocessing step for quantitative susceptibility mapping (QSM). Remnants from this step often contaminate the estimated local field, which in turn leads to erroneous tissue-susceptibility reconstructions. The present work aimed to mitigate this undesirable behavior with the development of a new approach that simultaneously decouples background contributions and local susceptibility sources on QSM inversion.

METHODS:

Input phase data for QSM can be seen as a composite scalar field of local effects and residual background components. We developed a new weak-harmonic regularizer to constrain the latter and to separate the 2 components. The resulting optimization problem was solved with the alternating directions of multipliers method framework to achieve fast convergence. In addition, for convenience, a new alternating directions of multipliers method-based preconditioned nonlinear projection onto dipole fields solver was developed to enable initializations with wrapped-phase distributions. Weak-harmonic QSM, with and without nonlinear projection onto dipole fields preconditioning, was compared with the original (alternating directions of multipliers method-based) total variation QSM algorithm in phantom and in vivo experiments.

RESULTS:

Weak-harmonic QSM returned improved reconstructions regardless of the method used for background-field removal, although the proposed nonlinear projection onto dipole fields method often obtained better results. Streaking and shadowing artifacts were substantially suppressed, and residual background components were effectively removed.

CONCLUSION:

Weak-harmonic QSM with field preconditioning is a robust dipole inversion technique and has the potential to be extended as a single-step formulation for initialization with uncombined multi-echo data.

KEYWORDS:

alternating direction method of multipliers (ADMM); augmented lagrangian; background field removal; nonlinear inversion; total variation

PMID:
30265767
DOI:
10.1002/mrm.27483

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