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@PHDTHESIS{Menzel:750948,
author = {Menzel, Miriam},
othercontributors = {Michielsen, Kristel Francine and Weßel, Stefan and Amunts,
Katrin},
title = {{F}inite-difference time-domain simulations assisting to
reconstruct the brain's nerve fiber architecture by 3{D}
polarized light imaging},
volume = {188},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH, Zentralbibliothek, Verlag},
reportid = {RWTH-2018-230974},
isbn = {978-3-95806-368-6},
series = {Schriften des Forschungszentrums Jülich, Reihe
Schlüsseltechnologien},
pages = {ix, 296 S.},
year = {2018},
note = {Druckausgabe: 2018. - Onlineausgabe: 2018. - Auch
veröffentlicht auf dem Publikationsserver der RWTH Aachen
University. - Ausgezeichnet mit der Borchers-Plakette.;
Dissertation, RWTH Aachen University, 2018},
abstract = {The neuroimaging technique Three-dimensional Polarized
Light Imaging (3D-PLI) reconstructs the brain’s nerve
fiber architecture by transmitting polarized light through
histological brain sections and measuring their
birefringence. Measurements have shown that the
polarization-independent transmitted light intensity
(transmittance) depends on the out-of-plane inclination
angle of the nerve fibers. Furthermore, the optical
anisotropy that causes the birefringence leads to
polarization-dependent attenuation of light (diattenuation),
which might provide additional information about the
underlying fiber configuration. In this thesis, analytical
considerations, supplementary measurements, and numerical
simulations were performed to study the transmittance and
diattenuation effects in more detail, and to develop ideas
how the effects can assist the nerve fiber reconstruction
with 3D-PLI. The propagation of the polarized light wave
through the brain tissue was modeled by Finite-Difference
Time-Domain (FDTD) simulations. Following a bottom-up
approach, the simplest possible model was identified that
describes the observed transmittance and diattenuation
effects. The experimental studies in this work have shown
that the transmittance significantly decreases with
increasing inclination angle of the fibers (by more than 50
$\%).$ The FDTD simulations could model this effect and show
that the decrease in transmittance is mainly caused by
polarization-independent light scattering in combination
with the limited numerical aperture of the imaging system.
Moreover, the simulations revealed that the transmittance
does not depend on the crossing angle between horizontal
fibers. Combining the simulation results with experimental
data, it could be demonstrated that the transmittance can be
used to distinguish between horizontal crossing and vertical
fibers, which is not possible in standard 3D-PLI
measurements. To study the diattenuation of brain tissue, a
measurement protocol has been developed that allows to
measure the diattenuation even with a low signal-to-noise
ratio: Diattenuation Imaging (DI). The experimental studies
in this work revealed that the diattenuation of brain tissue
is relatively small (less than 10 $\%)$ and that it has
practically no impact on the measured 3D-PLI signal. More
importantly, it was demonstrated that there exist two
different types of diattenuation that are specific to
certain fiber configurations: in some brain regions, the
transmitted light intensity becomes maximal when the light
is polarized parallel to the nerve fibers (D+), in other
brain regions, it becomes minimal (D−). The FDTD
simulations could successfully model the diattenuation and
show that diattenuation of type D− is caused by
anisotropic scattering of light which decreases with
increasing time after tissue embedding, while diattenuation
of type D+ can be caused both by anisotropic scattering and
by anisotropic absorption (dichroism). In addition, the
simulations confirmed that steep fibers only show
diattenuation of type D+ and that the diattenuation also
depends on the tissue composition. This makes Diattenuation
Imaging a promising imaging technique that reveals different
types of fibrous structures which cannot be distinguished
with current imaging techniques.},
cin = {137620 / 130000},
ddc = {530},
cid = {$I:(DE-82)137620_20140620$ / $I:(DE-82)130000_20140620$},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
doi = {10.18154/RWTH-2018-230974},
url = {https://publications.rwth-aachen.de/record/750948},
}
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