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

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22 Chapter 2 Literature Review<br />

• the inferior medial bor<strong>de</strong>r;<br />

• <strong>and</strong> the use of arbitrary lines.<br />

One of the most wi<strong>de</strong>ly adopted protocol (15% of the studies reviewed by Geuze<br />

et al., 2004) was <strong>de</strong>veloped by Watson et al. (1992), with high inter-rater reliability<br />

reported (di Sclafani et al., 1998; Du et al., 2001). It <strong>de</strong>fines the hippocampus com-<br />

prising the hippocampus proper, subicular complex, <strong>de</strong>ntate gyrus, <strong>and</strong> including<br />

the white matter structures of alveus <strong>and</strong> fimbria. According to this protocol, the<br />

hippocampus is traced on the coronal plane. The head of hippocampus is sepa-<br />

rated from amygdala by the inferior horn of the lateral ventricle (mainly CSF),<br />

which extends to the <strong>de</strong>ep part of the uncus forming the uncal recess. If the<br />

inferior horn is not visible in the image, the following three alternatives may be<br />

used to outline the hippocampus-amygdala boundary: the alveus, an arbitrary<br />

line from the inferior horn of lateral ventricle to the sulcus at the inferior margin<br />

of the semilunar gyrus, or from straight horizontal line connecting the plane of the<br />

inferior horn of the lateral ventricle with the surface of the uncus. The posterior<br />

bor<strong>de</strong>r is <strong>de</strong>fined by the section with the crus of fornix separating the hippocampus<br />

from the fimbria. The inferior bor<strong>de</strong>r is drawn to inclu<strong>de</strong> the subicular complex<br />

<strong>and</strong> uncal cleft, separating from the parahippocampal gyrus by the angle between<br />

the most medial extent of subiculum <strong>and</strong> parahippocampal gyrus. This protocol<br />

is estimated to inclu<strong>de</strong> 90-95% of the total volume of hippocampal formation.<br />

The protocol set forth by Watson et al. (1992) has been used to validate the au-<br />

tomatic segmentations provi<strong>de</strong>d by Alzheimer’s Disease Neuroimaging Initiative<br />

(ADNI) 2 . The automatic segmentation uses the high-dimensional brain mapping<br />

tool SNT (Surgical Navigation Technologies), which is commercially available from<br />

Medtronic Surgical Navigation Technologies (Louisville, Colorado, USA). The val-<br />

idation was been performed on the normal aging, MCI <strong>and</strong> AD subjects (Hsu et al.,<br />

2002). The hippocampal volumes from ADNI used in the preparation of this thesis<br />

are segmented using the SNT tool, with corrections by qualified reviewers. Com-<br />

pared to the manual segmentation protocol, the automated SNT segmentation<br />

2 Available at www.loni.ucla.edu/ADNI. For a <strong>de</strong>scription of the data provi<strong>de</strong>d by ADNI,<br />

see §3.4.2.1.

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