1. An apparatus comprising: a projection data spatial truncator that spatially truncates positron emission projection data acquired in a positron emission examination of an object, wherein the projection data spatial truncator (i) selects projection data acquired along lines of response that intersect a region of interest of the object; or (ii) rejects measured projection data acquired lines of response that do not intersect the region of interest; an iterative reconstructor that reconstructs the truncated projection data to produce first image space data indicative of the object, wherein the truncated projection data consists of projection data acquired along lines of response that intersect a first transverse sub-region of the object, wherein the iterative reconstructor produces second image space data indicative of a second transverse region of the object located outside the first transverse sub-region.