This group comprises X-ray, MRI and Ultrasound contrast media. The X-ray contrast media are subdivided into iodinated and non-iodinated compounds, and are further classified according to water solubility, osmolarity and nephrotropic/hepatotropic properties. High osmolar substances correspond mainly to ionic substances, except from ioxaglic acid, which is classified together with the non-ionic substances. MRI contrast media are subdivided according to magnetic properties.