1. A method of reconstructing projection data indicative of a plurality of portion annihilation events, the method comprising: (a) distributing each of a plurality of subsets of the projection data into at least a first portion and a second portion; (b) concurrently performing reconstruction operations on the first portion using a first processor and on the second portion using a second processor, the reconstruction operations being performed concurrently by each of the first and second processors including: (i) forward projecting an object estimate with each of the first and second processors, (ii) with the first processor, using the forward projection of the object estimate and the first portion of the subset of the projection data to calculate a first correction, and with the second processor using the forward projection of the object estimate and a second portion of the subset to calculate a second correction; (iii) backprojecting the first and second corrections and updating the object estimate in accordance with the backprojected first and second corrections such that the object estimate used by the first processor and the second processor is updated from backprojected corrections from both the first and second processors; (c) repeating steps (b)(i), (b)(ii), (b)(iii) a plurality of times on each of the plurality of subsets to iteratively update the object estimate; (d) repeating steps (a), (b), and (c) on each of the subsets to iteratively update the object estimate; (e) generating a human readable image indicative of the iteratively update object estimate.