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

Chapter 2 Literature Review 29
Wolz et al. (2009) and an EM approach is proposed to optimize the energy function
(Lötjönen et al., 2010).
2.1.3 Evaluation of segmentation
The segmentation algorithms are usually evaluated in terms of their accuracy,
volume,
The accuracy of the segmentation can be measured by the overlap between the
segmentation result and the ground truth. The Dice similarity coefficient (DSC,
Dice, 1945), also known as the Kappa coefficient in some literature, indicates the
percentage of the overlap between two segmentations
DSC = 2|DS ∩ DR|
, (2.1)
|DS| + |DR|
where DS is the segmented region, and DR is the reference region (e.g. manually
segmented by experts, ground truth). Similar to DSC, the Jaccard index is also a
measurement of the overlap, which is defined as
JI = |DS ∩ DR|
. (2.2)
|DS ∪ DR|
If the voxels in the reference DR are regarded as the actual positives, we can define
the sensitivity
and the specificity
sensitivity = |DS ∩ DR|
, (2.3)
|DR|
specificity = |DC S ∩ DC R|
|DC , (2.4)
R|
where D C R corresponds to the voxels outside DR, i.e. the actual negative, and D C S
corresponds to the voxels not labeled in DS.