A CTPA (CT pulmonary angiogram) is the main scan used to check for a pulmonary embolism — a blood clot in the lungs. It's a fast CT of the chest with an iodine contrast injection that lights up the lung arteries, so a clot shows as a gap. It's very good at finding or ruling out a clot quickly. It uses radiation and contrast, so pregnancy and kidney function are considered — sometimes a VQ scan is used instead.
Key takeaways
- A CTPA is the main scan for a suspected pulmonary embolism (lung clot).
- It's a fast chest CT with an iodine contrast injection.
- Contrast lights up the lung arteries so a clot shows as a gap.
- A VQ scan is an alternative when contrast or radiation is a concern.
If a doctor is worried about a blood clot on the lung (a pulmonary embolism, or PE), the scan they’ll usually order is a CTPA. It’s fast, accurate, and can quickly confirm or rule out a clot.
What CTPA stands for and does
CTPA stands for CT pulmonary angiogram. It’s a CT scan of the chest timed with an iodine contrast injection that fills the arteries of the lungs.[1] On the images, the contrast makes the lung arteries bright — so a clot shows up as a gap where the blood (and contrast) can’t get through. It can also show other causes of chest symptoms, like pneumonia or fluid.
What to expect
A small cannula goes into a vein for the contrast. During the injection, a brief warm flush and metallic taste are normal and pass in seconds.[2] The scan itself takes only minutes, and you’ll be asked to hold your breath briefly. It’s often done urgently in an emergency department.
Radiation and contrast — the considerations
A CTPA uses radiation and iodine contrast, so the team checks a few things:[2]
- Pregnancy — the small dose is weighed against the danger of missing a clot; a VQ scan is sometimes preferred.
- Kidney function — a recent blood test may be checked before contrast.
- Contrast allergy — tell staff about any previous reaction.
Because a missed PE can be dangerous, the benefit of the scan usually far outweighs the small risks — but where contrast or radiation is a concern, a VQ scan (a nuclear medicine lung scan) can answer the same question. See our guide to the VQ scan.
Frequently asked questions
What is a CTPA used for?
To look for a pulmonary embolism — a blood clot in the lungs. It’s the main, fastest test for that question.[3]
Does a CTPA use contrast dye?
Yes — an iodine contrast injection is essential, because it’s what makes the lung arteries (and any clot) visible.[2]
Can I have a CTPA if I’m pregnant?
It can be done if needed — the small dose is outweighed by the danger of missing a clot — but a VQ scan is sometimes chosen instead. Always tell staff you’re pregnant.[2]
Sources
- RadiologyInfo.org (RSNA & ACR) — Computed Tomography (Body CT) — www.radiologyinfo.org/en/info/bodyct
- RANZCR / InsideRadiology — Iodine-containing contrast medium (ICCM) — www.insideradiology.com.au/iodine-containing-contrast-medium/
- healthdirect (Australia) — Pulmonary embolism — www.healthdirect.gov.au/pulmonary-embolism
