Abstract: An image-reconstruction method in which interactions with particular crystal pairs are detected and a trans-axial component of a geometric system response matrix is retrieved from a storage medium. This component provides an estimate of an axial component of the geometric system response matrix. At least in part on the basis of the axial component and the trans-axial component, an annihilation site distribution of annihilations most likely to have resulted in the interaction with the particular crystal pair is estimated.

Abstract: In a PET scanner, a method for processing coincidence data includes associating a selected portion of the coincidence data with one of a plurality of subspaces of a coincidence space; deriving, from the coincidence data associated with subspace, a contribution to be used in forming an image; and weighting the contribution by an amount that depends on a likelihood that the coincidence data associated with that subspace includes data indicative of trues.