Apparatus and methods are described including acquiring 3D image data of a targeted vertebra. A processor indicates the targeted vertebra within the 3D image data. A radiopaque element is positioned on the body of the subject with respect to the spine and a radiographic image is acquired. The processor (a) generates a plurality of 2D projections of the targeted vertebra from the 3D image data, (b) for each vertebra that is visible in the radiographic image, identifies if there exists a 2D projection of the targeted vertebra that matches the radiographic image of the vertebra that is visible, and (c) in response, indicates on the 2D radiographic image the vertebra for which a match with a projection of the targeted vertebra was identified, such that a location of the targeted vertebra is identified with respect to the radiopaque element. Other applications are also described.