Methods and apparatus enabling a mobile device to receive paging notifications from multiple networks. In a preferred embodiment, a rotatable shutter with three positions is placed between a light source and a DMD. A segmentation module segments surfaces in the joint based on information contained within at least one of the data sets, and a registration module spatially registers, in three dimensions, information represented by a first of the data sets with respect to information represented by one or more further data sets for the same patient.