A three-dimensional subtraction angiography image data set including a target region of the patient is acquired. A region of interest is selected. An imaging geometry is defined for monitoring the intervention using an X-ray device. The image-obscuring blood vessels that superimpose the region of interest in the imaging geometry and imaging zones that show fractions of the image-obscuring blood vessels in the imaging geometry are determined. Path information relating to the image-obscuring blood vessels is defined. The information relating to the path is input into a two-dimensional forward projection data set. A fluoroscopic image is acquired in the imaging geometry. Pixels showing the image-obscuring blood vessels in the fluoroscopic image are determined using the path information and image intensity information from the fluoroscopic image. A masked image of the image-obscuring blood vessels is subtracted. The fluoroscopic image that has been modified is displayed.
