A system and method for generating X-ray radiation. The system includes an electron source operable to generate an electron beam and an X-ray target for generating X-ray radiation upon interaction with the electron beam. The method includes moving the electron beam over an edge separating a first region and a second region of the X-ray target, wherein the first region and the second region have different capability to generate X-ray radiation upon interaction with the electron beam. The system allows for a lateral extension of the electron beam to be determined based on a change in a quantity indicative of the interaction between the electron beam and the first region and between the electron beam and the second region, and the movement of the electron beam.