The present invention relates to a photon scanning apparatus comprising a photon source (2) to emit a photon beam (4), a photon detector (6) to detect photons emitted from the photon source (2). The photon source (2) is adapted to emit the photon beam (4) in accordance with a predetermined pulse width modulation scheme at a predetermined flux rate, wherein the pulse width modulation scheme defines pulse widths of the photon beam (4) for respective positions of the photon source (2) and the photon detector around a central axis (R) and an object to be scanned. The photon detector (6) is adapted to start detecting photons with a delay relative to the photon source starting to emit photons and to finish detecting photons prior to the photon source stopping to emit photons. The photon scanning apparatus thus only has to be calibrated for the predetermined flux rate.