Negative contrast media

The negative radiological contrast media are the gases air, oxygen, nitric oxide (N₂O) or carbon dioxide (CO₂) and they may be combined with water suspensions of barium sulphate for double contrast images of the gastrointestinal tract and with water soluble iodinated contrast media for double contrast investigations of joints. New technologies, such as computed tomography, magnetic resonance tomography and the use of contrast media in these techniques, have almost completely eliminated the use of gas in encephalography and myelography.

The use of gas as a contrast medium in the gastrointestinal tract has no other adverse effects than those induced by the volume of the gas.

Gas emboli may occur from unintentional intravascular injection of gas. The danger of injecting gas decreases with smaller gas volumes and higher water solubility of the injected gas. Carbon dioxide has the highest water solubility and there is an increased interest in using carbon dioxide in for example femoral arteriography because the digital subtraction technique may produce images of workable quality. An advantage is of course the low price of the gas. Gas may only be used in areas that the examiner considers will tolerate a transient reduction or transient interruption of blood flow.

Torsten Almén and Peter Aspelin