“…The methods in Adler et al, 2014, Adler et al, 2012), Yushkevich et al (2006) are also causal sequential, but the neighbor that I i is registered to is not necessarily . Non-causal algorithms that align I i to a bilateral neighborhood (Gaffling et al, 2015, Guest and Baldock, 1995, Saalfeld et al, 2012, Wirtz et al, 2004) cannot converge in one sweep, because after I i is registered to , those neighbors get transformed too. Instead, repeat sweeps (forwards or back and forth) can be used to increasingly smooth the stack, but this increases the computational cost, particularly if the algorithm depends on expensive registration operations.…”