19 Apr, 2022

CT Scans: The Complete Guide (Updated 2023)

A CT scan is a fast and accurate diagnostic imaging method, used to generate pictures of the inside of your body. CT has a range of applications, from the study and treatment of suspected or confirmed cancer (oncology), to assessing bones, joints and complex fractures.

If you’ve never had a CT scan before, you might not know what to expect from the procedure. If you’re at a turning point in your healthcare journey, we can help provide the additional information and support you need to choose the right scan, and understand how a CT scan works.

 🩺 CT scans use ionising radiation, and must be medically justified to limit unnecessary exposure. When you book a CT scan with us, our expert clinicians will make sure it is the right type of scan for your needs, and can help recommend alternatives where required.

What does CT stand for?

CT stands for Computerised Tomography. You may also hear CT scans referred to as CAT scans, which stands for Computerised Axial Tomography. There is no difference between a CT scan and a CAT scan, they are the same thing, but CT is just a more modern term.

How does a CT scanner work?

  • CT scanners are doughnut-shaped, with a flat bed that moves in and out of the scanner. There is an X-ray source on one side of the scanner, and a detector on the other side.
  • During your CT scan, the X-ray beam circles around your body, and the detectors capture the strength of the rays passing through your bodily tissues. Bone tends to block more of the ray than softer tissues such as the muscles, and CT scanning technology uses this variation to create images of the inside of your body.
  • The images are collected in ‘slices,’ which are cross-sectional pictures of the body. They are more detailed than traditional X-rays, and the 2D slices can be stacked together by a computer to create a 3D image. The image can be rotated, or viewed as slices, which makes it easier for a medical professional to identify the exact location of an abnormality.

When is a CT scan needed?

You might need a CT scan in cases where an X-ray, ultrasound or MRI scan has not been able to capture enough detail of a particular body part to form a diagnosis.

Your doctor might suggest a CT scan in cases of suspected cancer, stroke, or issue with the blood vessels such as an embolism or aneurysm. CT scans are also highly accurate for assessing complex fractures and joint problems, and may be suggested for this purpose.

As CT scans are so fast to complete, they are commonly used in urgent care settings. CT scans can enable doctors to quickly assess trauma, injuries and abnormalities, and help give patients the care they need as soon as possible.

What can a CT scan be used for?

A CT scan can be applied to many different medical situations, and can be used for:

  • Locating, diagnosing and planning treatment of suspected cancer, or non-cancerous tumours
  • Detecting lesions, especially within the abdomen
  • Identifying stroke, embolisms and aneurysms
  • Imaging the lungs, to look for tumours, clots and other abnormalities
  • Imaging complex fractures, joint erosion and bone tumours

What can CT scans diagnose?

CT scans can be used as a diagnostic tool for a range of health conditions, to help you get the peace of mind you need. CT results help medical professionals diagnose and assess:

  • Aneurysms and embolisms
  • Cancer
  • Spinal trauma
  • Bone tumours and complex fractures
  • Joint abnormalities
  • Heart disease and other heart abnormalities
  • Injuries, tumours, stroke or haemorrhage in the brain
  • Emphysema, pneumonia, tumours and other lung abnormalities

How long does a CT scan take?

CT scans are very quick procedures, especially compared to an MRI scan. A whole-body CT scan can be completed in under a minute.

However, the total length of your appointment depends on the body part being scanned, whether a contrast agent is required, and any preparations such as getting changed and completing paperwork.

Are CT scans safe?

CT scans are generally safe and low risk for most patients. CT scans do use ionising radiation, which can be harmful in high doses. However, the amount of radiation used in a CT scan is carefully considered before your procedure, and the scan must be medically justified to ensure the benefits of a diagnosis outweigh the risks.

There are some cases where a CT is the most suitable option for a patient. For example, if their particular condition is best visualised using CT, or if they are unable to lie still for the longer duration of an MRI scan.

However, a CT scan would rarely be recommended for pregnant people, and, if a contrast agent is required, people with kidney problems may not be suitable candidates.

If you do require a contrast agent for your scan, there are some risks including allergic reactions.

What is a contrast agent used for in CT scans?

Contrast agents are chemical substances, which improve the quality of CT images in certain situations. The contrast chemical is usually iodine-based, and can be administered orally as a drink, into the bloodstream via an injection, or rectally in the form of an enema. The kidneys will get rid of the substance from your body after your scan. If you have impaired kidney function or are pregnant, you may not be suited to having a contrast agent injection.

Contrast agents are most commonly used to highlight blood vessels, and distinguish between different tissues. Contrast agents can have some mild side effects, like nausea or headache, but these effects subside quickly. In rare cases, an allergic reaction can take place, and you should tell your doctor if you experience a skin rash, any swelling, high or low blood pressure, wheezing, or shortness of breath.

How do I prepare for a CT scan?

You might be wondering what to wear for a CT scan, or if you have to fast before a CT scan.

Our expert clinician team and partner scanning centres will provide all the preparation instructions you’ll need in advance of your scan appointment. Example preparations include:

  • Avoiding eating or drinking anything for a few hours before your scan
  • Wearing loose, soft, comfy clothing. You might be able to wear your own clothes for the scan, but, depending on the body part being imaged, you might need to change into a medical gown
  • Changes to how you take your medication on the day of your scan

Our consultant clinicians will have established your medical history, but you may be asked to fill in a form about your health on the day of your scan. You will also be asked to sign a consent form before the process begins.

What do the images from a CT scan look like?

CT scan images are black and white, with several different shades of grey. The shading helps radiologists to differentiate between tissues and bodily structures.

The image clarity and shading can depend on the strength of the X-rays used in the scan, and whether a contrast agent was administered for the scan.

CT images can be viewed as a series of 2D ‘slices’, or as a 3D image composed by a computer using all of the 2D pictures.

What is the difference between a CT and an MRI scan?

No one type of diagnostic scan is ‘better’ than another - they all complement each other and have different uses. The key differences between MRI and CT scans are:

  • CT scans use ionising radiation, while MRI scans use very strong magnets to generate images
  • CT scans are faster and quieter than MRI scans.
  • CT scans are more commonly used for assessing fractures, scanning larger areas quickly, imaging the lungs, and within oncology settings. Meanwhile, MRI scans generally tend to capture more detailed images of soft tissues, ligaments and certain organs compared to CT scans.
  • MRI scans tend to use Gadolinium-based contrast agents where required, while iodine-based contrast agents are used in CT settings as needed.

📌 Learn more about CT vs MRI scans in our dedicated news article on the topic

How much does a CT scan cost?

Our private CT scan prices vary depending on the body part and scanning centre selected, but start from just £359. The cost of your booking includes:

  • A 1-1 pre-scan consultation with a member of our expert clinical team, to assess your medical history and suitability for your chosen scan
  • A referral for your scan
  • The scan at your selected partner scanning centre
  • Digital access to your imaging report
  • Copies of your images available upon request
  • Post-scan 1-1 clinician consultation to discuss your results and recommendations for next steps

If you're looking to book a private CT scan near you, our platform offers access to over 100 scanning sites across the UK.

How soon do doctors receive CT scan results?

Our expert clinician team receive your CT scan images and report up to 7 working days after your scan, but usually within a few days. This gives enough time for your images to be prepared, and for a radiologist to write a report of their findings.

How long should you have to wait for a CT scan result?

After our clinical team receive your results, they will review the outcomes in relation to your individual needs. They will contact you for a follow-up call within 2 days of receiving your results, to explain the report and suggest any next steps required. You’ll also receive digital access to your report, which you can share with your GP, consultant or specialist.

Currently, around a quarter of people due for NHS scans are waiting more than 6 weeks for an appointment, and a further few weeks for their results. It is our mission to reduce this pressure and provide fast access to medically necessary CT scans for our patients.

📢 Next Steps:

    • Book a private CT scan near you, without GP referral - our medical team will provide a quick referral and fast results with no waiting lists.
    • Visit our news page to learn more about CT scans and how to prepare.


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