Docteur de l'université Automatic Segmentation and Shape Analysis ...

20 Chapter 2 Literature Review
Figure 2.2: AAL labeling overlayed on collins27. From left to right: axial,
coronal, sagittal section.
effect of averaging, the blurred boundary in these atlases represents the probability
of structural labeling at a given coordinate in the normalized space. A single
subject template collins27 from MNI with more structural details was created by
repeated acquisitions of the same young male subject for 27 times, which were
then normalized to the same space of MNI305 to produce an average image. The
automated anatomical labeling (AAL, Tzourio-Mazoyer et al., 2002, see Figure 2.2)
has been developed on the MNI single subject image, identifying 45 anatomical
volumes of interest in each hemisphere. In the definition by AAL, the hippocampal
region was defined on the sagittal views as the gray matter under the inferior horn
of the lateral ventricle. The dentate gyrus, the uncus, and the hippocampus proper
are included. The posterior boundary is limited by the parahippocampal ramus
of the collateral fissure.
Besides the standard labelings of AAL, the Internet Brain Segmentation Reposi-
tory (IBSR) 1 also provides the segmented data of 18 subjects, which are labeled by
trained experts into 43 individual regions including subcortical structures such as
caudate, hippocampus, pallindum, putamen, thalamus, amygdala, etc. The hip-
pocampal segmentations in IBSR are to be used as atlases in the preparation of this
thesis. The segmentations are manually traced using intensity contour line with
manual editing (Makris et al., 2004). The hippocampus-amygdala border is traced
in the sagittal view by drawing a sulci line in the middle of the inferior ventricle.
1 Available at http://www.cma.mgh.harvard.edu/ibsr/.