Imaging
CT Pulmonary Angiogram
A CTPA is a specialised CT scan with contrast dye used mainly to look for a blood clot in the lungs (pulmonary embolism).
Quick answer
CT Pulmonary Angiogram: what it is and what the results mean
A CT pulmonary angiogram (CTPA) is a CT scan of the chest timed to capture contrast dye as it fills the arteries of the lungs, producing clear images of the pulmonary blood vessels.
- Why it is done: Its main use is to diagnose or rule out a pulmonary embolism — a blood clot that has travelled to the lungs — in people with sudden breathlessness, chest pain or a raised D-dimer.
- Understanding results: A radiologist looks for clots (filling defects) in the lung arteries.
What it is
A CT pulmonary angiogram (CTPA) is a CT scan of the chest timed to capture contrast dye as it fills the arteries of the lungs, producing clear images of the pulmonary blood vessels.
Why it is done
Its main use is to diagnose or rule out a pulmonary embolism — a blood clot that has travelled to the lungs — in people with sudden breathlessness, chest pain or a raised D-dimer. It can also show other causes of chest symptoms.
What to expect
A cannula is placed in an arm vein and contrast dye is injected as the scan runs. You lie on the scanner table and hold your breath for a few seconds while images are taken; the whole appointment usually takes 15–30 minutes.
Understanding the results
A radiologist looks for clots (filling defects) in the lung arteries. A normal scan makes a pulmonary embolism very unlikely, while a positive scan confirms it and prompts blood-thinning treatment.
Good to know
Risks and limitations
CTPA uses radiation and iodine contrast; it may be avoided or replaced with a VQ scan in pregnancy or contrast allergy. Kidney function is usually checked first.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
CT Pulmonary Angiogram: frequently asked questions
Why did I have a CTPA instead of other tests?
A CTPA is the most common test for pulmonary embolism because it directly shows clots in the lung arteries. A D-dimer blood test and a clinical score are often used first to decide who needs the scan.
Is a CTPA safe in pregnancy?
It can be done in pregnancy when needed, but doctors weigh the radiation carefully and sometimes choose a VQ scan or leg ultrasound instead. Always tell staff if you are or could be pregnant.
Related tests
Other imaging investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Royal College of Radiologists / relevant professional body
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