Angiography CT or Computed Tomographic Angiography (CTA) is the imaging of arteries using CT Scan.
scan, IV (intravenous)
is injected into an IV. The IV is started before the CT Scan begins. At the right time during the scan, the contrast is injected into the IV through a machine called a power injector.
The contrast material acts like "dye" but it is not dye because it doesn't stain like dye. It just causes anatomy to show up brightly on x-ray and CT.
When the contrast is injected in to the vein, the CT scanner will acquire images of contrast filled arteries quickly before it moves on to fill veins and then pass on to be excreted out of the body by the kidneys.
This is how arteries are examined by angiography CT or CTA.
Multi detector or multi slice CT technology has enabled CT to replace, in many cases, but not all, the need to have a catheter placed into an artery for examining arteries.
Putting an IV catheter into a vein doesn't have the risk that putting a catheter into an artery does. Putting a catheter into an artery has its possible complications of excessive bleeding. This is what is done in a special procedures department in radiology in the event you would need to have an artery repaired for example. This would be a day long event because of the need for post procedure observation.
CTA uses a vein to inject the contrast. There aren't the same bleeding complications with veins as there are with arteries and so angiogram CT is less than 30 minutes including preparation time and scan time.
CT angiography is used only to examine arteries. If there is a need for stent placement into an artery or to repair an artery, a special procedures department in radiology or a cardiac catheterization department outside of the radiology department is where this is done.