A method for localising a target 2 (f.i. a tumour) in an object 4 (f.i. human tissue) by means of scanning the object with a fan shaped X-ray beam 6. In known methods the X-ray beam is scanned twice over the object. In the first scan a shadow image of the object 4 and the target 2 in it is projected on an X-ray detector 10. In the second scan the position and the orientation of the X-ray beam 6 differs from the position and orientation of it in the first scan. Also during the second scan a shadow image of the object and the target is projected on the X-ray detector, in such a way that the positions of the target on the detector are mutually different. In this way the height of the target above the detector surface 10 may be calculated from the distance between the two shadow images of the target if both positions of the X-ray beam as well as both orientations are known. According to the invention it is proposed to translate and simultaneously rotate the X-ray beam 6 during the scan, the translatory and rotational movements being connected in such a way that the shadow image 12 of the target 2 is kept on the surface 10 of the detector during the scan. In this way it is possible to measure the translation d of that image during the scan, from which translation in combination with the translation D and the rotation during the scan the height of the target 2 above the detector surface 10 may be calculated. In this way only one scan is needed.Cette invention concerne un procédé de localisation dune cible (2) (telle quune tumeur) dans un objet (4) (tel quun tissu humain) consistant à balayer lobjet avec un faisceau (6) de rayons X en éventail. Dans les procédés utilisés jusquici, le balayage par faisceau de rayons X est effectué à deux reprises sur lobjet. Lors du premier balayage, une image fantôme de lobjet (4) et de la cible (2) quil comprend est projetée sur un détecteur (10) de rayons X. Lors du second balayage, la position et lorientation du faisceau (6) de rayons X
