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Magn Reson Med. 2018 Apr;79(4):2332-2345. doi: 10.1002/mrm.26832. Epub 2017 Jul 16.

Assessing the validity of the approximation of diffusion-weighted-MRI signals from crossing fascicles by sums of signals from single fascicles.

Author information

1
ICTEAM Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
2
Computational Radiology Laboratory, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA.

Abstract

PURPOSE:

To assess the validity of the superposition approximation for crossing fascicles, i.e., the assumption that the total diffusion-weighted MRI signal is the sum of the signals arising from each fascicle independently, even when the fascicles intermingle in a voxel.

METHODS:

Monte Carlo simulations were used to study the impact of the approximation on the diffusion-weighted MRI signal and to assess whether this approximate model allows microstructural features of interwoven fascicles to be accurately estimated, despite signal differences.

RESULTS:

Small normalized signal differences were observed, typically 10-3-10-2. The use of the approximation had little impact on the estimation of the crossing angle, the axonal density index, and the radius index in clinically realistic scenarios wherein the acquisition noise was the predominant source of errors. In the absence of noise, large systematic errors due to the superposition approximation only persisted for the radius index, mainly driven by a low sensitivity of diffusion-weighted MRI signals to small radii in general.

CONCLUSION:

The use of the superposition approximation rather than a model of interwoven fascicles does not adversely impact the estimation of microstructural features of interwoven fascicles in most current clinical settings. Magn Reson Med 79:2332-2345, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

KEYWORDS:

Monte Carlo simulations; crossing fascicles; diffusion-weighted MRI; superposition approximation; tissue microstructure

PMID:
28714064
PMCID:
PMC5770244
[Available on 2019-04-01]
DOI:
10.1002/mrm.26832

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