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

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24 Chapter 2 Literature Review<br />

amygdala structures. It is initialized by the manual <strong>de</strong>finition of a bounding box<br />

ROI <strong>and</strong> the seeds placed by the operator in each of the structures. The region<br />

growing is gui<strong>de</strong>d by the l<strong>and</strong>mark <strong>and</strong> boundary <strong>de</strong>tection based on extensive<br />

use of anatomical priors <strong>and</strong> image features. The <strong>de</strong>formation of the region is<br />

regularized by Markov r<strong>and</strong>om field (MRF), solved using iterative conditional<br />

mo<strong>de</strong>s algorithm (Besag, 1993). With the automatic <strong>de</strong>finition of the seed point,<br />

the fast marching for automated segmentation of the hippocampus (FMASH) by<br />

Bishop et al. (2011) propagates the region along the path with smallest resistance<br />

<strong>de</strong>fined by a potential function of image intensity using the 3D fast marching<br />

method (Sethian, 1996; Deschamps <strong>and</strong> Cohen, 2000).<br />

2.1.2.2 <strong>Shape</strong> <strong>and</strong> appearance based methods<br />

Active shape mo<strong>de</strong>ls (ASM, Cootes et al., 1995) are used in medical image seg-<br />

mentation by fitting a parametric shape mo<strong>de</strong>l to automatically <strong>de</strong>tected image<br />

features or manually <strong>de</strong>fined l<strong>and</strong>marks (Shen et al., 2002). Using shape informa-<br />

tion, the elastic <strong>de</strong>formation of the mo<strong>de</strong>l to match the intensity profile can be<br />

restricted to a prior shape subspace learned from the training set (Kelemen et al.,<br />

1999). Knowledge of relative position <strong>and</strong> distance between anatomical struc-<br />

tures, <strong>and</strong> texture <strong>de</strong>scriptors have also been ad<strong>de</strong>d to the ASM segmentation of<br />

hippocampus (Pitiot et al., 2004). A shape-intensity joint prior mo<strong>de</strong>l for both<br />

hippocampus <strong>and</strong> amygdala (Yang <strong>and</strong> Duncan, 2004) has been <strong>de</strong>veloped with<br />

neighbor constraints <strong>and</strong> the level set formulation of shape (Yang et al., 2004).<br />

The active appearance mo<strong>de</strong>l (AAM, Cootes et al., 2001) is a generative mo<strong>de</strong>l<br />

that accounts for the image intensity <strong>and</strong> texture, i.e. the ‘appearance,’ in addition<br />

to the shape structure of the l<strong>and</strong>marks. Using the image intensity profile along<br />

the normal of the structure boundary, the profile appearance mo<strong>de</strong>l (Babalola<br />

et al., 2007, 2008, 2009) produces the segmentation by matching the mo<strong>de</strong>l to<br />

the image minimizing the square of residual differences. A Bayesian approach for<br />

AAM method mo<strong>de</strong>ls the conditional distribution of intensity given shape, <strong>and</strong><br />

the segmentation is obtained by the MAP estimation of the shape given image

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