The present invention relates to iso-centering an object of interest prior to computer tomography (CT) scanning for examination of a patient in a C-arm CT examination apparatus. In order to provide facilitated positioning and to overcome or at least minimize these drawbacks, a C-arm CT examination apparatus (10) for CT scanning for examination of a patient is provided. The apparatus comprises a patient support unit, an acquisition unit, a data processing and control unit, and a display unit. The patient support unit is configured to bed a patient, free of motion, on the patient support. The acquisition unit is configured to acquire scout images of the patient including the object of interest in a respective position of the apparatus having position parameters. The data processing and control unit is configured to store the images and at least one respective position parameter including the iso-center position relative to the image; and to adjust the position of the apparatus roughly into a present position for CT scanning of the object of interest; and to select at least one iso-centering image from the stored images and, by geometrical calculation using, firstly, the at least one stored position parameter of the iso-centering image including the stored iso-center position and using, secondly, at least one position parameter of the present position of the apparatus including the present iso-center, adopting the appearance of the at least one iso-centering image, such that the appearance of the iso-centering image is according to the present position of the C-arm including the present iso-center. The display unit is configured to display the at least one adopted image on a display device together with and relative to a representation of the present iso-center for iso-centering.