surrounding structures in this case bone structures in the area of the skull or the spinal column as indicated by the arrows leading to box c from these two image data records or image data volumes a merged image representation is produced which shows the two image data volumes with a constant mixture ratio such a representation is not absolutely necessary for the method in accordance with the invention but can be produced for example to enable an operator to rotate the image data records suitably in order to obtain a desired view or to facilitate subsequent evaluation or to change them in some other way with regard to the alignment or view a disadvantage of the merged representation as in box c is that for example a localization of the pathology in the area of the artery as in box a is rendered more difficult by the fact that certain areas of the artery path i e certain details of the image data volume as in box a are concealed by bone structures of the image data record as in box b this is particularly the case in the area of the shadow of the jaw bone which is highlighted as a partial area here by circle d in this area the artery path is concealed to a large extent.