TABLE I.

Summary of notation

Symbol	Description
(Ai, Li)	Intensity and label images of the i-th atlas
(Ãi, L̃i)	Intensity and label images of the i-th atlas after non-rigid warping to a particular target
(T, LT, $L_T^{*}$ )	Target intensity image, estimated label image (by MAS) and ground-truth label image, respectively.
I	Index-set of the N atlases
t	Index to denote the atlas acting as target image in the training set
K	Scalar denoting the number of selected atlases to be used for MAS
$S_t^{*}$	Set of indexes of the K best atlases for segmenting target image At, according to ground-truth
ST	Set of indexes of the K best atlases for segmenting target image T
f (·,·)	Scoring function that maps a pair of affinely registered images to their expected segmentation performance
w⃗	Weighting vector learned by SVM-Rank
θ⃗i	Vector with the HOG features extracted from i-th image in the training set
M	Scalar denoting the total number of features
Θ⃗k	Vector with the k-th pairwise feature from all atlas-target pairs in the training set
Ψ⃗	Vector with the ground-truth DR from all atlas-target pairs in the training set
Φ(·,·)	Compact vector of pairwise features from a pair of target and atlas images
m′	Scalar denoting the size of the compact set of features