The present invention relates to X-ray imaging technology as well as image post-processing. Particularly, the present invention relates to a method for computer aided detection of structures in X-ray images as well as an X-ray system. A computer aided detection algorithm visibly determines tissue structures in X-ray image information and subsequently matches the shape of a determined tissue structure with a library of known tissue structures for characterizing the type of determined tissue structure. The determination of a tissue structure and thus the characterization of the type of the tissue structure may be enhanced when employing also spectral information, in particular energy information of the acquired X-ray image. Accordingly, a method (70,80,90) for computer aided detection of structures and X-ray images is provided, comprising the steps of obtaining (72) spectral X-ray image information of an object, wherein the spectral X-ray image information constitutes at least one X-ray image, detecting (74) a tissue structure of interest in the X-ray image by employing a computer aided detection algorithm, wherein detecting a tissue structure of interest in the X-ray image comprises the computer aided detection algorithm being adapted to evaluate the X-ray image for tissue structure shape and compare the tissue structure shape with a plurality of pre-determined tissue structure shapes and wherein the computer aided detection algorithm is adapted to evaluate spectral information of the X-ray image for detecting the tissue structure of interest.