Most scans cause no side effects. Plain X-rays, ultrasound and MRI generally have none. The main thing people notice is the brief warm flush and metallic taste from an iodine contrast injection, which passes in seconds. Reactions to contrast or tracers do happen but are usually mild; serious reactions are rare, and staff are equipped to treat them.
Key takeaways
- Plain X-ray, ultrasound and MRI usually have no side effects.
- A warm flush and metallic taste from iodine contrast is normal and passes in seconds.
- Reactions to contrast or tracers are usually mild; serious ones are rare.
- Seek help promptly if you develop a rash, swelling or breathing difficulty after a scan.
For most scans, side effects are uncommon — and many tests have none at all. Plain X-rays have no short-term effects, and ultrasound and MRI generally cause nothing (provided, for MRI, you don’t have a contraindicated implant).[2] Where side effects do occur, they’re usually linked to a contrast injection or a nuclear medicine tracer, and are usually mild and brief.
What’s normal
The most common thing people notice is from an iodine contrast injection during a CT or angiogram: a warm feeling spreading through the body for about 20 seconds, often around the groin, plus a metallic taste.[1] This is completely normal and passes within seconds. After a nuclear medicine scan you might feel nothing at all; the tracer simply clears over the next day.[3] A small number of people get a delayed rash hours to days after iodine contrast, usually mild.[1]
What’s a reaction
Reactions to iodine contrast are usually mild — a flush, brief nausea, mild itch — occurring in about 1–3 in 100 people and settling in minutes. Moderate reactions are uncommon (fewer than 1 in 3,000) and severe reactions are rare (fewer than 1 in 25,000).[2] Reactions to nuclear medicine tracers are very rare and almost always minor.[3] In every case, radiology departments are equipped to treat reactions, which respond well to emergency medication.[1]
When to seek help
Tell the radiographer or nurse straight away if, during or soon after a scan, you develop:[1]
- a spreading rash or hives;
- swelling of the face, mouth or throat;
- difficulty breathing;
- dizziness or feeling faint.
If these come on after you’ve left, return to the radiology practice if it’s open and nearby, or go to your nearest doctor or emergency department.
Frequently asked questions
Is the warm feeling from contrast a side effect to worry about?
No. The warm flush and metallic taste from an iodine contrast injection are normal and expected, and pass within seconds.[1]
Which scans have no side effects?
Plain X-rays, ultrasound, and MRI generally have no side effects (for MRI, provided you don’t have a contraindicated implant).[2]
Can radiation itself cause side effects like hair loss or sickness?
Not at diagnostic doses. Those effects come from very high radiation doses (such as radiotherapy), far above what a diagnostic X-ray, CT or nuclear medicine scan uses.[2]
Sources
- RadiologyInfo.org (RSNA & ACR) — Contrast Materials — www.radiologyinfo.org/en/info/safety-contrast
- RANZCR / InsideRadiology — Iodine-containing contrast medium (ICCM) (Goergen) — www.insideradiology.com.au/iodine-containing-contrast-medium/
- RANZCR / InsideRadiology — Nuclear medicine (Cain) — www.insideradiology.com.au/nuclear-medicine/
