You'll be exposed to some radiation during the test. The amount varies depending on the type of machine used. The risk of developing cancer from a CT angiogram isn't known, but it's small. However, you shouldn't have a CT angiogram if you're pregnant because of possible harm to your unborn child.
It's possible that you could have an allergic reaction to the dye used in the procedure. Talk to your doctor if you're concerned about having an allergic reaction.