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CT Angiography of the Circle of Willis — With or Without Intravenous Contrast

Published: August 9, 2026Updated: August 16, 2026

A CT imaging study of the major arteries at the base of the brain, performed with and/or without injected contrast to evaluate the cerebral circulation.

Quick summary

["This test uses CT images to look for narrowing, blockage, or bulging vessels in the arteries at the base of the brain."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
75671-8
Short code
CTA Circle of Willis WO+W contr IV
Synonyms
CTA Circle of Willis WO+W contr IV
Category
liver
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ct-angio
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What is this test?

CT angiography of the Circle of Willis is an imaging test that shows the major arteries supplying the brain. Intravenous contrast may be used to make these blood vessels easier to see, depending on the examination ordered.

Why might I need this test?

This test may be ordered to evaluate suspected aneurysms, narrowed or blocked arteries, or other blood-vessel problems. It may also be used to assess the brain's circulation after trauma, surgery, or a stroke-related concern.

How is the test performed?

You lie on a CT scanner table while the machine takes detailed pictures of your head. If contrast is used, it is given through a small intravenous line, and the scan is repeated as the contrast moves through the blood vessels.

How do I prepare for the test?

Follow the imaging center's instructions about eating, drinking, and medications. Tell the care team about any prior contrast reaction, kidney disease, thyroid condition, or pregnancy possibility before receiving contrast.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Circle of Willis CTA

Frequently asked questions

Does this test require intravenous contrast?
The study may be performed with contrast, without contrast, or both, depending on the specific order. The imaging center can confirm what will be used before the examination.
Is CT angiography the same as a routine head CT?
No. A routine head CT primarily evaluates the brain's tissues, while CT angiography is designed to show blood vessels in greater detail.
What should I do if I have had a bad reaction to contrast before?
Tell the imaging center and your clinician before the appointment. They can review your prior reaction and determine what precautions or alternative imaging are appropriate.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy