1. A method for calculating a scatter estimate for annihilation photons in a subject having a distribution of attenuation for scatter correction of detection data from a positron emission tomographic scanner, using the following steps: select a first scatter point S 1 and a second scatter point S 2 , determine a first scatter probability for scattering of a photon at scatter point S 1 and a second scatter probability for scattering of a photon at scatter point S 2 , determine an integral of the attenuation over a line connecting S 1 and S 2 , multiply the integral and the scatter probabilities and use the product in the calculation of the scatter estimate.