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Fig. 7 End plate (red) and ridgeline (black) segmentation at baseline (left) and year 1 (right)
We used the iterative closest point (ICP) algorithm to register the surfaces of the
vertebrae segmented at baseline and year 1. Given 2 sets of points, the ICP algo-
rithm
finds the rigid transformation that minimizes the mean square distance
between them [
49
51
]. We added landmark matching to address the problem of
entrapment in local minima. Our ICP algorithm is performed successively on the
ridgelines, end plates and the complete surface, the result of each stage serving as
the initialization for the following stage [
52
]. Figure
8
shows some examples of
registration results.
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