Gas chromatography is a process to separate gas molecules of different size due to their different adsorption at macroporous surfaces, e.g. at activated charcoal. The separation is managed by the use of starting gas or heating up.

A gas trap is a closed system, used in ventilation scintigraphy to store the exhaled radioactive gas for radiation protection.

A gas ventilation scintigraphy is a diagnostic imaging test of lung ventilation with radioactive noble gases during breathing maneuvers, e.g. with krypton (81mKr) or xenon (133Xe).
The radioactive gas is administered by a mask and requires a special delivery and trapping system (gas trap). The radioactivity in the lungs is measured with a gamma camera and is subsequently evaluated.
The use of krypton or xenon gases involves problems like the relatively short half-lives (about 15-30 seconds) and relatively high costs of xenon and krypton. The short half-life requires that the scan is performed directly after administration of the gas. In addition, the gaseous radiopharmaceutical is expelled from the body almost quantitatively within a few minutes of completing the study.
A ventilation scintigraphy combined with a pulmonary perfusion scintigraphy is highly sensitive for the detection of pulmonary embolism.
Radioactive noble gases are widely used as a ventilation agent to diagnose pulmonary embolism. However, 81mKr and 133Xe are rare and expensive, which limits their continuous availability. Tc99m-Technegas can be an alternative ventilation agent with the advantage of being less expensive and available daily.

See also Inhalation Scintigraphy.

Gastrografin® is a water-soluble iodinated radiopaque contrast agent for x-ray examinations of the esophagus, stomach, proximal small intestine, colon and is also used for bowel visualization in abdominal computer tomograms.
The high opacification and delineation after oral or rectal administration is caused by a low absorption of the intact gastrointestinal tract. However, visualization of the distal small bowel is generally unsatisfactory, since the hypertonicity of the medium causes intraluminal diffusion of water with subsequent dilution.

Gastrointestinal bleeding scintigraphy is used to locate and estimate the extent of an active bleeding by using Tc-99m labeled red blood cells (RBCs).