In modern medicine, radiopaque substances are those that will not allow X-rays or similar radiation to pass. Radiologic imaging has been revolutionized by radiopaque dyes, or contrast media, which can be passed through the bloodstream, the intestinal tract, or into the cerebral spinal fluid and utilized to highlight computed tomography (CT) or X-ray images. Radiopacity is one of the key considerations in the design of various devices such as guidewires or stents that are used during radiological intervention. The radiopacity of a given endovascular device is important since it allows the device to be tracked during the interventional procedure. The two main factors contributing to a material's radiopacity are density and atomic number.