A positron emission tomography (PET) data processing method comprises obtaining PET data from a PET detector, wherein the PET detector comprises an array of detector elements, and wherein the PET data is representative of a PET measurement of at least part of a subject. The method comprises identifying in the PET data a plurality of paired events, wherein each paired event comprises a first photon event in a first region of the PET detector and a second photon event in a second region of the PET detector. The first photon event comprises an energy deposition in a first detector element of the array or in a first detection region of the first detector element due to a scattering of a first photon at a first azimuthal scattering angle and an associated energy deposition by the scattered first photon in a second detector element of the array or in a second detection region of the first detector element or of the second detector element. The second photon event comprises an energy deposition in a third detector element of the array or in a third detection region of the third detector element due to a scattering of a second photon at a second azimuthal scattering angle and an associated energy deposition by the scattered second photon in a fourth detector element of the array or in a fourth detection region of the third detector element or of the fourth detector element. The method further comprises processing the PET data in dependence on the first and second azimuthal scattering angles for the paired events.