  Geodesic shooting has been successfully applied to diffeo-morphic
registration of point sets. Exact computation of the geodesicshooting between
point sets, however, requiresO(N2) calculations each time step on the number of
points in the point set. We proposean approximation approach based on the
Barnes-Hut algorithm to speedup point set geodesic shooting. This approximation
can reduce the al-gorithm complexity toO(N b+N logN). The evaluation of the
proposedmethod in both simulated images and the medial temporal lobe thick-ness
analysis demonstrates a comparable accuracy to the exact point set geodesic
shooting while offering up to 3-fold speed up. This improvementopens up a range
of clinical research studies and practical problems towhich the method can be
effectively applied.
