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

Chapter 1 Introduction 9
synaptic efficacy after rhythmic stimulation and persists after a long period of
time. It is now thought to be the mechanism underlying the memory process
(Lynch, 2004).
In Alzheimer’s disease, hippocampus and entorhinal cortex are affected at an early
stage. Amyloid deposit is present in CA1 and subiculum in Braak stage B (Braak
and Braak, 1991). Deficits in LTP and memory have been found following injection
of Aβ in region of hippocampus and the aggregation of amyloid (Stéphan et al.,
2001; Walsh and Selkoe, 2004) The tau pathology first develops in the transen-
torhinal region (Braak stage I), and soon spread to hippocampus (Braak stage
II). As result of the damage caused by the tangles, the hippocampal formation
experiences significant loss of neurons, especially in the CA1 and subiculum, as
the severity of disease progresses.
1.1.3 MRI in AD studies
The advancement in modern imaging technologies provides an approach to the
internal structures and functioning in the studies of the anatomy, physiology and
pathology. A variety of modalities have been developed, and become important
tool in clinical diagnosis. The computational and algorithmic development facili-
tating the signal processing, quantitative analysis, and visualization also prove to
be valuable in the biomedical studies.
Various forms of structural and functional imaging modalities have been employed
in the AD studies and diagnosis (Villemagne et al., 2005; Ebmeier et al., 2005; Vi-
tali et al., 2008; Tartaglia et al., 2011; Barkhof et al., 2011). Among the structural
imaging methods, although CT is widely used in clinical practice, patients are
screened by CT mainly to exclude other dementia of treatable causes such as tu-
mor and haematoma. Structural MRI is the more common choice due to its higher
resolution and better contrast in soft tissues. The structural MRI based atrophy
measures are established as valid marker for AD.