An apparatus (A) and a method for controlling collimation operation of a collimator (COL) in an x-ray imager (100) during an intervention carried out by an operator (R). A first medical device (GW) is made to progress through a patient (PAT) in an exploratory phase of the intervention. A path is recorded in a scout image (CI； CI1-CI4) formed from footprints (GWF) of the first device (GW) as recorded in a sequence of projection images (F； FI-F4) acquired by imager (100) during the exploratory phase. Apparatus (A) uses the path in the scout image (CI； CI1-CI4) to control collimation of the x-ray beam during a subsequent delivery phase where a second medical device (BC) is made to progress through patient (PAT), said second device (BC) following the first device (GW) substantially along the same path.
