In this lesson
- What MRI contrast is, and what it does
- What the injection feels like
- What to tell your team beforehand
What contrast is
Not every MRI needs contrast. When it is used, it is a clear liquid given through a small tube in a vein, usually in the arm or the back of the hand.
The liquid contains a substance called gadolinium. It is not a colour dye, and it is not radioactive. It is also not the same substance as the dye used for CT scans — that one is iodine-based, and the two are completely different drugs. This matters: if you have been told you react to “the dye”, or to iodine, that is not automatically a reaction to MRI contrast. Tell the team anyway, so they can work out which one it was.
Gadolinium travels in the blood and changes how nearby tissue looks on the pictures, so certain things stand out much more clearly — where blood is flowing, where there is inflammation, and the exact edges of some abnormalities.
Think of it as turning up the difference between two things that would otherwise look alike. Your doctor asks for it when that extra clarity answers the question better.
How it is given
A nurse, radiographer or doctor places a cannula — a thin plastic tube — into a vein. That feels like a normal blood test: a sharp scratch for a moment.
Some pictures are usually taken first. Part way through, the contrast is injected through the cannula while you stay on the table, and more pictures follow. The cannula comes out before you leave.
What it feels like
Most people feel very little. Some notice:
- A cool feeling travelling up the arm
- A brief metallic or odd taste
- A short-lived sense of warmth
These pass within a minute or two and are not a sign that anything is wrong. Tell the team what you feel — they would rather know.
Side effects, calmly
Gadolinium contrast is well studied and, for most people, uneventful. Serious problems are uncommon.
Common and mild. A little nausea, a headache, a cool or odd taste, or mild bruising where the cannula went in. These usually settle on their own.
Less common. An itchy rash or hives. Tell the team if this happens, at the time or later — it is easily treated.
Rare. A more serious allergic-type reaction, with breathing difficulty or swelling. This is uncommon — and it is exactly why the department has staff, equipment and a plan for it, and why you are kept nearby for a short while afterwards.
Leaking at the injection site. Occasionally contrast leaks into the tissue around the vein instead of the vein itself, causing stinging or swelling. Say something straight away if your arm hurts during the injection. It is usually managed simply.
What to tell your team
Please say clearly, before the scan:
- If you have ever had a reaction to contrast — for an MRI, a CT, or anything else — and what happened
- If you have kidney problems, kidney disease, one kidney, or have ever been on dialysis
- If you are pregnant, might be pregnant, or are breastfeeding
- If you have diabetes, severe allergies or asthma
Kidneys matter because they are how the contrast leaves your body. If your kidneys work slowly, the team may check a blood test first, choose a different agent, or decide the scan is better done without contrast. Your team will ask these questions — and the honest answer, including “I’m not sure”, is always the right one.
Afterwards
Unless you are told otherwise, eat, drink and take your usual medicines as normal, and drink fluids over the rest of the day. If you feel unwell, or a rash appears later, contact the department or your doctor — they will want to know.
What people often ask
Will it make me feel hot all over?
That strong flush is associated with the iodine-based dye used for CT scans, which is a different drug. MRI contrast is usually much less noticeable.
Can I refuse the contrast?
Yes. You can ask what the scan would and would not show without it, and decide with your team.
Does it stay in my body?
Most is passed out in the urine within about a day. Tiny traces have been found to remain in some tissues; this has been studied closely and has not been shown to cause harm. Your team can talk you through it.
One thing to remember
Contrast is a clear liquid that makes certain things stand out. Most people barely notice it — and the two things worth saying out loud are any past reaction and anything to do with your kidneys.
This is general information, not medical advice — your own imaging team knows your situation.
References
- RadiologyInfo.org (RSNA/ACR). Patient Safety — Contrast Material https://www.radiologyinfo.org/en/info/safety-contrast
- InsideRadiology (RANZCR). Gadolinium Contrast Medium (MRI contrast agents) https://www.insideradiology.com.au/gadolinium-contrast-medium/
- InsideRadiology (RANZCR). Contrast Medium: Using Gadolinium or Iodine in Patients with Kidney Problems https://www.insideradiology.com.au/contrast-medium/