Modelling cortical laminae with 7T magnetic resonance imaging

• Main Author: Wähnert, Miriam
• Other Authors: Universität Leipzig, Fakultät für Physik und Geowissenschaften
• Format: Doctoral Thesis
• Language: English
• Published: Universitätsbibliothek Leipzig 2015
• Subjects: Magnetresonanztomographie; Bildverarbeitung; Bildgebung; MRT; Kortex; Gehirn; 7 Tesla; Anatomie; Schichten; Krümmung; Oberflächen; Areale; Brodmann; Myelin; Myeloarchitektur; Cytoarchitektur; Vogt; magnetic resonance imaging; image processing; imaging; MRI; cortex; brain; anatomy; cortical; layer; curvature; surfaces; area; myelin; myeloarchitecture; cytoarchitecture; ddc:610; ddc:530; ddc:570; ddc:538; ddc:571; ddc:611
• Online Access: http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-159094; http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-159094; http://www.qucosa.de/fileadmin/data/qucosa/documents/15909/thesis_pflichtexemplare.pdf; http://www.qucosa.de/fileadmin/data/qucosa/documents/15909/zweiteZusammenfassung_v4.pdf

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.