Circle of Willis (C.O.W.)

MRI at Envision

What is a C.O.W?

A C.O.W scan uses CT Technology to provide detailed, 3D images of the blood vessels that supply blood to your brain. This scan may be combined with a carotid artery angiogram which looks at vessels in your neck.

What happens during a C.O.W scan?

A. Before your scan

Preparation – The day before your scan

Continue taking all of your current medications. Please inform us before the day of your scan if you have an Iodine allergy or if your kidney function is impaired.

What to bring

  • Your request form
  • Any relevant previous imaging
  • Your Medicare card and any concession cards

Preparation – On the day of the scan

You will be asked to fill out a questionnaire regarding your health status, medication, and any known allergies. If there is any chance you may be pregnant, please inform us before your scan. You may also be asked to change into a gown and remove some jewellery for your scan.

B. During your C.O.W scan


When you are transferred to the CT room you will be made comfortable on the examination table. The examination table slides you into the centre of the CT machine and some preliminary pictures are taken to confirm the scan position.

X-ray dye (contrast) will be injected into a vein via a cannula (a thin plastic tube, like a flexible needle) in your arm. The scan is then performed while the dye is passing through your blood vessels. You may feel flushed during this injection.

You may be asked to hold your breath for a short time so that you are completely still while the scanner takes a series of pictures.

The scan will take approximately 15 minutes.

Risks and side effects

A C.O.W scan is a very low-risk procedure. Find out about CT Risks and Side Effects.

Who will perform my scan?

Our specialist medical imaging team will perform your C.O.W scan.

What happens after a C.O.W scan?

How do I get my results?

After your appointment, the information from your scan is processed and interpreted by Envision’s medical imaging team before delivery of a report to your doctor.

Post procedural information

At the end of the procedure the cannula will be withdrawn carefully from the vein and a band aid applied. The dye will be flushed naturally by your body over the following 24 hours without you noticing it. You are free to eat and drink normally.  We recommend you continue to drink plenty of fluids to assist your body in flushing the contrast. You will be able to return to your normal daily activities after your scan.

Download an Information and Consent Form