Non-contrast vs contrast CT scan – what’s the difference?

Non-contrast vs contrast CT scan – what’s the difference?

Your doctor might write a referral for a CT scan, either with or without contrast. What is the difference between a non-contrast and a contrast CT scan, and when is contrast necessary?

A CT scan, or a computed tomography scan, is a medical imaging procedure that uses X-rays and computer technology to create detailed cross-sectional images of the body.

A contrast-enhanced CT scan

This is when a contrast agent (typically iodine-based) is injected into a patient’s bloodstream, usually through an IV line, during the scanning procedure. The contrast agent contains substances that absorb X-rays differently from surrounding tissues, making blood vessels, organs and abnormalities more visible on the CT images. As the contrast agent circulates through the body, it highlights blood vessels and other structures, enhancing their visibility on the images.

A non-contrast CT scan

Unlike contrast-enhanced CT scans, which involve the injection of a contrast into the bloodstream to highlight certain structures or abnormalities, a non-contrast CT scan is performed without the use of any intravenous contrast.

Many scans are routinely done without contrast, when visibility would be sufficient for a diagnosis. Non-contrast CT scans are also useful in situations where the use of contrast agents may be contraindicated, such as in patients with kidney problems or allergies to contrast.

Why do you have it?

Contrast-enhanced CT: Produces enhanced detail of blood vessels, organs and abnormalities, aiding in the diagnosis of conditions such as tumours, vascular diseases or inflammation.

Non-contrast CT: Is used to assess a variety of conditions, such as brain bleeds, sinus conditions, complex fractures, and kidney stones.

What to remember

  1. An appointment is needed for any CT scan.
  2. If you are pregnant, please inform the radiographer before the scan.
  3. Some scans require specific preparation, such as fasting or refraining from exercise prior to the scan.
  4. Please inform the radiographer of any allergies, in particular to contrast agents, prior to the scan.

What to expect

  • You may be asked to change into a hospital gown and remove your jewellery, as metal objects like zippers, buttons, belts and jewellery can affect the image quality.
  • During the scan you will lie on a motorised table that slides into the CT scanner. The radiographer will leave the room but communicate with you through an intercom. It’s essential to remain still during the scan to ensure clear images. The scanner itself might make buzzing or whirring noises, but it’s totally painless.
  • Most scans can be performed in a few minutes. Occasionally additional scan phases may be required, in which case the scan will take longer to complete.
  • After the scan, most people can resume their normal daily activities unless instructed otherwise by their healthcare provider or the radiographer.


The scan is available for your doctor to view. A radiologist will also provide a formal report to your doctor, who will discuss the results with you.

This article is part of a series aimed at decoding medical jargon. Visit our news section for more.