To fully understand how the brain works, it is necessary to relate the
brain’s function to its anatomy. Cortical anatomy is subject-specific. It is character-
ized by the thickness and number of intracortical layers, which differ from one cortical
area to the next. Each cortical area fulfills a certain function. With magnetic res-
onance imaging (MRI) it is possible to study structure and function in-vivo within
the same subject. The resolution of ultra-high field MRI at 7T allows to resolve
intracortical anatomy. This opens the possibility to relate cortical function of a sub-
ject to its corresponding individual structural area, which is one of the main goals of
neuroimaging.
To parcellate the cortex based on its intracortical structure in-vivo, firstly, im-
ages have to be quantitative and homogeneous so that they can be processed fully-
automatically. Moreover, the resolution has to be high enough to resolve intracortical
layers. Therefore, the in-vivo MR images acquired for this work are quantitative T1
maps at 0.5 mm isotropic resolution.
Secondly, computational tools are needed to analyze the cortex observer-independ-
ently. The most recent tools designed for this task are presented in this thesis. They
comprise the segmentation of the cortex, and the construction of a novel equi-volume
coordinate system of cortical depth. The equi-volume model is not restricted to in-
vivo data, but is used on ultra-high resolution post-mortem data from MRI as well.
It could also be used on 3D volumes reconstructed from 2D histological stains.
An equi-volume coordinate system yields firstly intracortical surfaces that follow
anatomical layers all along the cortex, even within areas that are severely folded
where previous models fail. MR intensities can be mapped onto these equi-volume
surfaces to identify the location and size of some structural areas. Surfaces com-
puted with previous coordinate systems are shown to cross into different anatomical
layers, and therefore also show artefactual patterns. Secondly, with the coordinate
system one can compute cortical traverses perpendicularly to the intracortical sur-
faces. Sampling intensities along equi-volume traverses results in cortical profiles that
reflect an anatomical layer pattern, which is specific to every structural area. It is
shown that profiles constructed with previous coordinate systems of cortical depth
disguise the anatomical layer pattern or even show a wrong pattern. In contrast to
equi-volume profiles these profiles from previous models are not suited to analyze the
cortex observer-independently, and hence can not be used for automatic delineations
of cortical areas.
Equi-volume profiles from four different structural areas are presented. These pro-
files show area-specific shapes that are to a certain degree preserved across subjects.
Finally, the profiles are used to classify primary areas observer-independently.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa.de:bsz:15-qucosa-159094 |
| Date | 28 January 2015 |
| Creators | Wähnert, Miriam |
| Contributors | Universität Leipzig, Fakultät für Physik und Geowissenschaften, Professor Robert Turner, Professor Robert Turner, Professor David W. Shattuck |
| Publisher | Universitätsbibliothek Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis |
| Format | application/pdf, application/pdf, application/zip |
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