CTPA – CT Pulmonary Angiogram

If you think you might have a blood clot in your lungs, do not book a scan. Call 999 or go to A&E now. Warning signs include sudden breathlessness, chest pain that is worse when you breathe in, coughing up blood, or a racing heart, especially if you have recently had surgery, been in hospital, travelled for a long time, are pregnant or have a swollen, painful leg. A pulmonary embolism needs assessment and treatment in hospital the same day.

About a CT pulmonary angiogram

The pulmonary arteries carry blood from the heart to the lungs to collect oxygen. A CT pulmonary angiogram (CTPA) is a CT (computed tomography) scan of the chest taken while contrast dye is injected into a vein, timed so that the dye fills these arteries. This makes the blood vessels show up brightly, so any blockage, such as a blood clot, can be seen.

The main use of a CTPA is to diagnose a pulmonary embolism (PE), a blood clot that has travelled to the lungs, usually from a deep vein thrombosis (DVT) in the leg. NICE recommends a CTPA straight away for people who are likely to have a PE. Because of this, almost all CTPA scans are done in hospital as emergencies.

A booked CTPA is for planned questions from a specialist, for example:

• ongoing breathlessness some months after a pulmonary embolism, to look for clots that have not cleared
• as part of tests for high blood pressure in the lungs (pulmonary hypertension)
• to look at abnormal blood vessels in the lungs, such as arteriovenous malformations

A CTPA also shows the lungs and heart, but for general lung problems a standard CT of the chest is usually used. If you cannot have contrast dye, or are pregnant, a different test called a V/Q scan may be used instead.

What happens during the scan

A small cannula is placed in a vein in your arm. You lie on your back on the scanner bed with your arms raised above your head. The radiographer controls the scanner from the next room, but can see, hear and talk to you throughout. Contrast dye is injected through the cannula, and the scan is timed to take place as it reaches the lungs. You will be asked to hold your breath for a few seconds. The scan itself takes only a few seconds.

For some CT scans, an injection of contrast dye is given through a small cannula in a vein, usually in your arm or hand, to make blood vessels and organs show up more clearly. CT contrast contains iodine. As it goes in you may feel warm and flushed, notice a metallic taste, or feel as if you are passing urine; these feelings pass within a minute or two. Allergic reactions are uncommon, and you may be asked to wait for up to 30 minutes afterwards. Where contrast is needed, it is charged separately.

Is CT safe?

CT uses X-rays, which are a type of ionising radiation. A CTPA gives a dose similar to a standard chest CT (about 8 mSv, similar to around 3.6 years of natural background radiation). The breasts receive some of this dose, which is one reason a V/Q scan may be preferred for younger women and in pregnancy. The risk from a single scan is very small, and every CT scan is checked by a radiologist or radiographer to make sure the benefit of the scan outweighs the risk, as required by the Ionising Radiation (Medical Exposure) Regulations. If you have had other CT scans recently, tell us when you book.