The Differences Between A MRI and CT Scan


If you’re suffering from a health-related issue that requires deeper investigation, or you live with a condition that needs to be regularly monitored, you’ll often be recommended an MRI or CT scan. In 2017/18, data from the NHS alone shows that as many as 5.15 million CT scans and 3.46 million MRI scans were carried out in England.

MRI and CT scans are used as both a diagnostic tool and to monitor ongoing health conditions. Both scans are particularly beneficial in detecting different types of cancer, as well as discounting cancer in some cases. They can also help in discovering the underlying causes of aches, pains and other abnormalities within the body. Despite how commonly these scans are recommended, people are confused about which one scan is best, whether they do the same job and if they pose the same risks. Find out more about the difference between an MRI and CT scan in this post.

The main difference between an MRI and CT scan…

The key difference between these two types of scans is the science behind them; the way the machines work to scan the body, and how they create imagery. An MRI scan uses radio waves and works by creating a magnetic field around the body. The radio waves emitted bounce off water and fat cells within the body, which creates the image that we see. CT scans on the other hand use x-rays, exposing the body to radiation in order to create the images.

Whilst both MRI and CT scans are relatively low risk, it’s important to understand the differences between the two, and why you may be recommended one over the other. It’s crucial to have the scan that is the best fit for your condition or to assist in your diagnosis.

What is an MRI scan?

MRIs, (Magnetic Resonance Imaging), offer a non-invasive method of gaining a deeper look inside the body, making MRI scans an excellent tool for aiding the diagnosis of various medical issues. As explained above, they use a combination of a magnetic field and radio waves to generate cross-sectional images of the human body. The high-quality images produced are ideal for diagnosing issues across the whole body, from the brain and spinal cord to bones and joints, as well as the heart and other internal organs. One of the main differences between a MRI and CT scan is that an MRI does not expose the body to radiation, making them an extremely safe procedure.

What is a CT scan?

Similarly, CT scans are an excellent diagnostic tool and are used as a method to monitor on-going health conditions. This method of scanning uses a rotating x-ray machine which is designed to create cross-sectional images of the body. During the CT scan itself, you will lie down on a table which will then move through the CT machine, enabling the image to be created. Compared to a traditional x-ray, CT scans are able to provide much more detailed imagery, allowing for investigation into a greater range of conditions. CT scans are particularly useful for scanning organs within the abdomen and chest, however, they can also be used to detect cancer, examine blood flow and soft tissue.

Quality of images

Whilst both types of scans enable us to gain a detailed view inside of the human body, MRI scans capture more detailed images than CT scans. This makes MRI scans preferable for specific cases, for example picking up on brain and bone abnormalities as well as diagnosing sports injuries. Due to the science behind the scan, there are some cancers, tumours or lesions that the CT scans simply can’t show, in which case an MRI is a better option.

However, CT scans are exceptionally useful for cancer cases; diagnosing and staging cancer, checking on the effectiveness of treatment, as well as being able to determine whether the cancer has come back. A CT scan is effective in scanning the entire body, which is hugely beneficial for doctors to be able to see if cancer has spread to other areas of the body.

Scan time

Another key difference between CT scans and MRI scans is the length of time it takes to carry out the scan. An MRI generally takes anywhere between 30 and 90 minutes, whereas a CT scan can be completed in as little as 10 – 30 minutes. The length of the scan completely depends on the area that is being scanned. A full-body CT scan, for example, will naturally take longer than scanning just one area of the body.

Whilst an MRI scan usually takes longer, this shouldn’t be a reason to choose a CT scan instead. It’s important to opt for the scan which is best for diagnosing/monitoring the issue you are facing. Your doctor will be able to advise which scan is best for you.

Diagnosis of medical issues

Your doctor will be able to refer you for either an MRI or CT scan; this recommendation will be based on your symptoms and the area of the body that requires deeper investigation. If your doctor needs a more detailed image of soft tissue, ligaments or your internal organs, it is likely that an MRI scan will be recommended. However, for a more generalised scan or for fractures and head traumas, for example, a CT scan will more commonly be recommended.

An MRI scan can help in the diagnosis of the following:

  • Aneurysms
  • Trauma
  • Disc Herniations
  • Fractures
  • Osteoporosis
  • Cancers
  • Arthritis
  • Tumours
  • Muscle Tears
  • Cartilage Problems
  • Inflammation and many more

On the other hand, a CT scan is more beneficial for bone and internal organ injuries, as well as looking at blood flow problems. Another key difference between a CT and MRI is that a CT is more beneficial for emergency cases, such as where a person has been involved in an accident. A CT scan enables doctors to quickly detect any serious internal injuries.


Like most medical procedures, CT and MRI scans don’t come without their risks. Therefore, it is important to consider the risk vs what the result of the scan could show.

MRI risks/considerations include:

  • Can cause issues with metal due to the magnets used in the machine, therefore MRIs are not suitable for those with pacemakers and some joint replacements
  • Not recommended for pregnant women, apart from in extreme circumstances
  • Can be difficult for those who suffer from claustrophobia
  • Body temperature can rise during the scan

CT scan risks/considerations include:

  • Not suitable for pregnant women, and not usually advised for young children due to radiation exposure
  • Exposed to a small amount of radiation
  • There is potential for a reaction to occur for the dyes used to show contrast

MRI and CT scan self referral

Whether you are clear on the difference between an MRI or CT scan, or you would like further information, LycaHealth is here to help. We understand that you know your own body better than anybody else, which is why we offer self-referral for our imaging and diagnostic services. This will enable you to bypass lengthy waiting times, and access exceptional healthcare when you need it most. Head over to our self-referral page to book your private CT scan or MRI with LycaHealth today.

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