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

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Chapter 2 Literature Review 25<br />

intensities (Patenau<strong>de</strong> et al., 2011; the implementation is available from FMRIB<br />

Software Library, Smith et al., 2004; Woolrich et al., 2009)<br />

The state-of-the-art segmentation method publicly available in the FreeSurfer<br />

package (Dale et al., 1999; Fischl et al., 1999) labels 37 areas for the whole brain,<br />

including 18 subcortical structures. Based on the nonstationary anisotropic MRF<br />

mo<strong>de</strong>ling of the segmentation, it uses the spatial information from a template<br />

in the Talairach space, <strong>and</strong> a nonlinear transform to account for the inter-subject<br />

anatomical variability (Fischl et al., 2002). Forward mo<strong>de</strong>ls of the imaging process<br />

are embed<strong>de</strong>d in the segmentation method to achieve the sequence in<strong>de</strong>pen<strong>de</strong>nce<br />

(Fischl et al., 2004).<br />

2.1.2.3 Atlas based methods<br />

Atlas based segmentation methods are wi<strong>de</strong>ly employed in medical image analysis.<br />

Using manually <strong>de</strong>lineated atlas as gold st<strong>and</strong>ard, this method transform the label<br />

map of the atlas to the query image by the registration algorithms from the atlas<br />

to the query. Registration methods such as elastic (Miller et al., 1993; Iosifescu<br />

et al., 1997; Christensen <strong>and</strong> Johnson, 2001), fluid (Haller et al., 1996, 1997; Hogan<br />

et al., 2000; Crum et al., 2001), <strong>and</strong> optical flow based registration (Baillard et al.,<br />

2001; Dawant et al., 1999; Hartmann et al., 1999) have been involved in matching<br />

the image with the atlas. In ANIMAL framework (Collins et al., 1995; Collins<br />

<strong>and</strong> Evans, 1997), the subject image is used as the source, <strong>and</strong> the atlas as the<br />

target in the non-rigid registration, <strong>and</strong> the mapping of the labels is achieved by<br />

the inverse transformation recovered by ANIMAL. Based on an initial FreeSurfer<br />

labeling, the method by Khan et al. (2008) uses the Large Deformation Diffeomor-<br />

phic Metric Mapping (LDDMM, Beg et al., 2005) to search for optimal nonlinear<br />

transform between the image <strong>and</strong> the atlas. Appearance mo<strong>de</strong>l based methods<br />

have been proposed to gui<strong>de</strong> the <strong>de</strong>formation (Duchesne et al., 2002; Klemencic<br />

et al., 2004). Besi<strong>de</strong>s the atlas of segmented individual, probabilistic atlases are<br />

also used in segmentation, providing the spatial priors such as in the Bayesian

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