Catheters, x-ray
It is possible to inject the contrast media (CM) directly into a particular blood vessel. However, because not all of our blood vessels are conveniently located near the surface, where we can easily get at them, we use catheters - thin plastic tubes about 1-2 mm in diameter and 60-120 cm long.
The catheter is inserted into an artery on the inside of the thigh. It is introduced over a thin metal wire that stiffens it and allows the catheter to be guided to where a given blood vessel to be examined branches off from its "parent" vessel, reaching this location in 30-60 seconds. The end of the catheter that is still outside the body is connected to a syringe containing CM, which is then injected at high speed and pressure. The larger the blood vessel, the more blood it contains - and the greater the rate of flow through the vessel, the larger the amount of CM that is needed, and at a high delivery rate. The X-ray must be taken just when the CM is in the area to be examined, and before it gets washed away. In order to synchronise the exposure with the injection of CM, and because the pressure of injection is fairly high, automatic injectors are most often used - although the injection can be done by hand as well.
GE Healthcare Glossary