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

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Chapter 2 Literature Review 23<br />

does not inclu<strong>de</strong> alveus <strong>and</strong> fimbria, <strong>and</strong> the volume is 10% less than the volume<br />

measured on the manual segmentation.<br />

2.1.2 Survey of segmentation algorithms<br />

Earlier <strong>de</strong>velopments in image segmentation are usually solely based on image<br />

features, such as thresholding of image intensity, textual analysis, region grow-<br />

ing etc. Artificial neural network (ANN) has been used by Pérez <strong>de</strong> Alejo et al.<br />

(2003) for hippocampal segmentation, in which an tissue classification is obtained<br />

by an ANN-based vector quantization, <strong>and</strong> subsequently a supervised multi-layer<br />

perceptron on a selected ROI is used to segment the anatomical structure of hip-<br />

pocampus. Methodologies incorporating anatomical templates <strong>and</strong> atlases mo<strong>de</strong>l-<br />

ing the shape <strong>and</strong> appearance of anatomical structures are later <strong>de</strong>veloped to <strong>de</strong>al<br />

with objects such as hippocampus. Apart from the segmentation per se, a meta-<br />

segmentation method using AdaBoost classifiers (Freund <strong>and</strong> Schapire, 1995) has<br />

been <strong>de</strong>veloped by (Wang et al., 2011) to <strong>de</strong>tect <strong>and</strong> correct systematic error in<br />

the segmentation based on the spatial, contextual <strong>and</strong> intensity patterns of the<br />

error.<br />

2.1.2.1 Region growing <strong>and</strong> <strong>de</strong>formable mo<strong>de</strong>ls<br />

Region growing <strong>and</strong> <strong>de</strong>formable mo<strong>de</strong>l methods usually start from a initial set of<br />

seed points, which <strong>de</strong>forms or grows to match the structure to be segmented. In<br />

Ashton et al. (1997), the region starts from a line of seeds along the long axis<br />

of the hippocampus, <strong>and</strong> <strong>de</strong>forms elastically constrained by the surface tension,<br />

<strong>de</strong>viation from expected surface normal <strong>and</strong> the force from surrounding tissues.<br />

Driven by gray level gradient <strong>and</strong> internal forces from surface curvature, an initial<br />

stack of polygons localizing the hippocampus on parallel slices was used by Ghanei<br />

et al. (1998, 2001) <strong>and</strong> Ghanei <strong>and</strong> Soltanian-Za<strong>de</strong>h (2002). The <strong>Segmentation</strong><br />

Automatisée Compétitive <strong>de</strong> l’Hippocampe et <strong>de</strong> l’Amygdale (SACHA) algorithm<br />

<strong>de</strong>veloped by Chupin et al. (2007, 2009) segments simultaneously hippocampus <strong>and</strong>

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