1. A method for in-time registration of images from temporally separated image acquisition sessions using imaging apparatus, the method comprising: retrieving a stored three-dimensional (3D) image of a portion of a living subject acquired at a prior acquisition time by a first 3D image acquisition system positioned away from the living subject, the stored 3D image indicating a guide 3D position corresponding to a relative 3D offset between a prior subject location and a prior acquisition location computed as a function of 3D point cloud data of the living subject acquired by the first 3D image acquisition system at the prior acquisition time; measuring a live 3D position of a second 3D image acquisition system positioned away from the living subject, the live 3D position corresponding to a real-time relative 3D offset between a present subject location and a present acquisition location computed as a function of volumetric data derived from real-time 3D point cloud data of the living subject being acquired by the second 3D image acquisition system; displaying, in a viewfinder window of the second 3D image acquisition system, a live view being acquired of the portion of the living subject in real time; overlaying a 3D guide on the viewfinder window during the displaying, the 3D guide being semi-transparent and generated from the stored 3D image and graphically positioned on the viewfinder window as a function of the computed live 3D position; and acquiring a present 3D image of the portion of the living subject.