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To both speed up the optimisation process and to avoid local minima, most
currently used registration methods employ some form of
multi-resolution optimisation. That is, a sequence of image pairs, at
progressively larger spatial scales are created from the initial pair
of images:
. The images at larger scales are subsampled
versions (often with pre-blurring) of the original high-resolution
images, and so contain fewer voxels which means that evaluating the
cost function requires less computation. In addition, as only gross
features of the images remain at these large scales, it is hoped that
there will be fewer local minima for the optimisation to ``get stuck''
in.
Peter Bannister
2002-05-03