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Updated 13 September 2021

What is a CT Scan? An Essential Patient Guide

Image of woman holding a CT scan in front of the CAT scan machine.

What is a CT scan?

A CT scan (also known as a CAT scan) is short for computed tomography. They are performed to help doctors and medical professionals identify any abnormalities in the region of interest. A CT scan machine will use x-ray and computer technology to create 3D images of the investigated area.

How long does a CT Scan Take?

Depending on the area and type of investigations requested by the doctor, scans can take anywhere between 10-20 minutes [1]. However, the total procedure can take anywhere between 30-60 minutes (when accounting for set-up and preparation) [2].   

What is a CT Scan used for?

Doctors will typically refer to CT scans for diagnosing, monitoring and helping guide treatment for specific conditions and injuries. Examples of why a CT scan may be ordered include:
  • Looking for tumours, blood clots and infections. 
  • Determining the presence of fractures in bones
  • Assessing for any injuries after any trauma or accidents (e.g. sports collisions, car accidents, etc.)
  • Investigating any abnormalities in major organs, such as the brain, lungs and kidneys
  • Planning for future medical treatments and investigations (e.g. biopsies, surgery, etc.)
  • Monitoring the effectiveness of medical treatments (e.g. chemotherapy, radiotherapy, etc.)

What does a CT scan show?

Compared to plain x-rays, CT scans provide a more detailed assessment of the body by highlighting structures, such as bone, soft tissue (e.g. muscle, blood vessels etc.), organs and abnormalities (e.g. cancer, tumours, etc.). Areas and reasons that doctors commonly use CT scans to investigate include [3]:
    • Back pain
    • Headaches
    • Sinusitis (i.e. inflammation of the sinuses)
    • Persistent abdominal pain and discomfort
    • Migraines
    • Neck pain and discomfort
    • Vertigo and dizziness
    • Assessing for risk of strokes in the future
    • Kidney pain and discomfort
 

How does a CT scan work?

As noted earlier, CT scans provide a more detailed 3D image of the area(s) being investigated. Compared to plain x-rays, CT scans can show different angles and snapshots of various structures, such as bones, soft tissue and blood vessels.  Numerous sections of the region are scanned and captured using x-rays. This is comparable to finely slicing an apple into many segments to see what’s occurring inside. Slices as thin as 1 millimetre [4] can be viewed through this type of investigation.  After processing the previous image, the next slice of the region will also be viewed and processed. When CT scans are developed, they can be shown as consecutive individual 2D images of these slices or combined into larger regions.   

CT Scan Risks

While CT scans are important investigations, they also come with some risks. One of the main risks is the radiation produced from the x-rays. They have been modified to ensure that the radiation produced is as little as possible. However, radiation does accumulate over time with multiple exposures. However, the benefits of CT scans outweigh most risks associated with it.   Other risks associated with CT scans include: 
      • Radiation exposure to unborn babies during pregnancy. 
      • Reactions to the contrast dye in those who have kidney problems. This should be brought up with your GP before undergoing a CT scan. 
      • Potential allergic reaction to the contrast dye. Any previous allergies to contrast, iodine, shellfish, or medications should be reported to your GP [5].
      • Children are more sensitive to radiation than adults. Any concerns should be discussed with your GP to determine whether any modifications can be made [6].
      • Those who are claustrophobic might be uncomfortable whilst lying in the CT scan machine or gantry. Alternative arrangements can be made, such as a larger machine or taking certain medications beforehand. 
      • Disruptions to the scans if any wearable metallic objects are present in or on the body, including pacemakers, piercings, medication pumps, etc. If applicable, these must be reported to your GP before the examination. 
 

CT Scan Procedure

Before the CT Scan

Before receiving a CT scan, your GP and/or machine operator will explain the procedure. Additional written information or pamphlet may be provided with any further instructions. During this period, you should inform your GP about any potential personal risks, including:
        • Whether you are or trying to become pregnant
        • Have any kidney health problems
        • Possess any allergies
        • Claustrophobia
If you also require a contrast dye, you may also have to fast for at least a few hours beforehand. Additionally, to prevent disruption to the machine, ensure any metal is removed from the body (e.g. bracelets, rings, necklaces, etc.).

During the CT Scan

During the scan, you will be required to lie on your back in the machine’s circle tunnel (also known as the gantry). The machine’s operator will sit outside the room to set up the investigation. They will be able to observe and communicate with you throughout the whole procedure. As a result, they will monitor for any side effects or unwanted symptoms, including breathing difficulties and numbness.

After the CT Scan

In most circumstances, those who undergo a CT scan will resume usual daily activities unless indicated by a GP. There may be some side effects if a contrast dye has been administered. Ensure that you report any of these symptoms or other concerns to your GP, including:
        • Itchiness
        • Swelling
        • Breathing difficulties
        • Digestive issues
        • Pain
 

Other Investigations

Other imaging investigations that can also be performed include:
        • Plain X-ray
        • MRI
        • Ultrasounds
Compared to these diagnostic tests, CT scans are known to be quick and accurate. However, they also emit the most radiation. 

CT Scan vs MRI

One of the most common comparisons to CT scans is MRIs. Differences between these two imaging investigations have been summarised in the table below.
CT Scans  MRIs
Results obtained as early as 24 hours.  Results can take up to 1-2 weeks to access.
A small volume of ionising radiation is emitted during the assessment. Strong magnets are used to generate images that do not emit any radiation. 
CT scans are quick. Most will take between 10-20 minutes. MRIs are slower and take up to 90 minutes to obtain the image(s) [7]
Detailed images of all structures are captured, including bone, soft tissue and blood vessels. A greater amount of information is taken compared to CT scans, particularly the inner organs (e.g. brain, reproductive regions, etc.).
 

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References

        1. https://www.nhs.uk/conditions/ct-scan/ 
        2. https://myhealth.alberta.ca/Health/aftercareinformation/pages/conditions.aspx?hwid=ug6606 
        3. https://www.racgp.org.au/afpbackissues/2006/200605/200605beach.pdf 
        4. https://www.livescience.com/64093-ct-scan.html 
        5. https://stanfordhealthcare.org/medical-tests/c/ct-scan/risk-factors.html 
        6. https://www.safetyandquality.gov.au/sites/default/files/migrated/CT-scans-for-kids-DL-brochure-WEB.pdf 
        7. https://www.nhs.uk/conditions/mri-scan/what-happens/