Photon counting detectors may suffer from pulse sharing effects and fluorescence photon generation, which may lead to a degradation of the measured signals. According to an exemplary embodiment of the present invention, a detector unit is provided which is adapted for performing a coincidence detection and correction by comparing detection events of neighbouring cells, thereby providing for a coincidence identification followed by an individual coincidence correction. In order to reduce the number of coincidence detection and corresponding units per detector unit, a specific detector cell geometry may be applied.