Contrast agent: Meaning in a Radiology Report

A contrast agent is a substance given before or during a scan, usually into a vein, that makes blood vessels and some tissues easier to see.

What it means

Contrast agents make blood vessels and some tissues stand out on a scan. For CT and X-ray studies, the agent usually contains iodine. For MRI, it usually contains gadolinium. Most are injected into a vein, but some are swallowed or injected into a joint. A scan listed as "with and without contrast" has pictures from before and after the injection. With healthy kidneys, most of it leaves in the urine within a day.

When it matters

Most people feel little. CT contrast can cause a brief warm flush, and MRI contrast a cool feeling in the arm. Allergic-type reactions can occur but are uncommon, and most are mild. Before the scan, staff ask about earlier reactions, kidney problems, diabetes medicines and pregnancy. After a past reaction, the team may use a different agent, give medicine beforehand, or plan a scan without contrast.

Questions to ask your doctor

Why does my scan need contrast, and what would be missed without it?
Do I need a kidney blood test before the contrast injection?
I reacted to contrast before. What will be done differently this time?

General information, not medical advice. What a finding means for you depends on your symptoms, your history and the images themselves, so talk your results through with a doctor.