A study looking at almost a half million injections of contrast doses used in imaging found few serious side effects.

Coming out in the October issue of the American Journal of Roentgenology, the Mayo Clinic study cataloged the effects of 456,930 injections of iodinated and gadolinium contrast agents, used in MRI and CT scans, over a four-year period from 2002-2006. Of these injections, only about one in 1,000 was associated with an adverse reaction, the most common being hives, accounting for over half of all reported side effects.

The second most common side effect was nausea, making up around a fifth of all reported problems.

There were few serious side effects. Of the hundreds of thousands of patients in the study, only nine needed adrenaline shots to fight an allergic reaction, and only two were transferred to the emergency room.

Contrast agents are blamed for only one death -- that of a 79-year-old man whose heart stopped 30 minutes into an imaging procedure after getting the injection. He showed no symptoms before he died.

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