Method and system for calibrating an X-ray imaging system

A method for calculating during use the geometric parameters of an x-ray imaging system, an object or a patient to be observed being placed between the x-ray source and a detector of x-rays having passed through the object or patient, wherein it includes at least the following steps: detecting at least one marker on the object or the patient or in proximity to the object, the marker being of unknown 3D position, acquiring a plurality of 2D images for a plurality of viewpoints of the imaging system, detecting the position of at least one marker in each of the acquired 2D images, estimating the projection matrices corresponding to the projections of the object at various viewing angles and reconstructing in 3D the position of a marker on the basis of the estimation of the projection matrices.