CT scan vs MRI: Key Differences Explained

When it comes to medical imaging, CT scans and MRI scans are two of the most common techniques used by doctors to diagnose and monitor various conditions.

While both provide detailed images of the inside of your body, there are some key differences between these two types of scans. This article will explain the main distinctions between CT and MRI scans to help you better understand these important diagnostic tools.

What are CT scans and MRI scans?

Although the procedures for undergoing a CT scan and an MRI are similar — both requiring the patient to lie on a table that moves through a large, doughnut-shaped machine — there are several key distinctions between the two that will be discussed below.

1. CT scan

   • A CT (computed tomography) scan uses X-rays and computer processing to create detailed cross-sectional images of your body. 

   • The scan is usually quick, lasting only a few minutes.

2. MRI scan 

   • An MRI (magnetic resonance imaging) scan uses powerful magnets and radio waves to generate images of organs and structures inside your body.

   • MRI scans are typically longer, taking 30-60 minutes to complete.

Book an appointment with our Thomson Medical health screening specialists today.

Key differences between CT scans and MRI scans

1. Imaging methods

   • The technology used in CT scans uses X-ray technology, while MRI scans use magnetic fields and radio waves.

2. Exposure to radiation

   • Radiation exposure CT scans involve exposure to ionising radiation, whereas MRI scans do not use any ionising radiation.

   • This makes MRIs a preferred option for patients who need repeated imaging over time as repeated radiation can cause cell damage and risk of cancer. 

3. Image detail

   • MRI scans generally provide more detailed images of soft tissues, organs, and the nervous system compared to CT scans.

   • However, CT scans are often better for imaging bones and can more easily detect issues like fractures.

4. Imaging speed

   • Imaging CT scans are much faster than MRI scans. 

   • A CT scan can be completed in just a few minutes, while an MRI scan typically takes 30-60 minutes.

5. Volume of sound 

   • CT scans may be more suitable for people who are sensitive to loud noises, as MRI scanners produce loud noises during the imagine process, and CT scanners are relatively quiet in comparison.

6. Comfort

   • Some patients find MRI scans more uncomfortable due to the enclosed space and longer scan time. 

   • CT scanners are more open and the procedure is quicker, which may be preferable for those with claustrophobia.

When are CT scans preferred?

• CT scans are often used in emergencies due to their speed and ability to quickly detect issues like internal bleeding or head injuries.

• CT scans are excellent for detailed imaging of bones, making them ideal for diagnosing fractures or joint problems.

• For examination of lung tissue and detection of lung cancer, CT scans are typically the preferred method.

• CT scans are very effective at identifying and locating kidney stones.

When are MRI scans preferred?

• Imaging MRI scans provide detailed images of the brain and spinal cord, making them ideal for diagnosing conditions like multiple sclerosis or brain tumours.

• During the examination of soft tissues like muscles, ligaments, and tendons, MRI scans often provide clearer images than CT scans.

• MRI scans are sometimes used in addition to mammograms for breast cancer screening, especially in high-risk patients.

• MRI scans can provide detailed images of the heart and blood vessels without using radiation.

Safety considerations for MRI and CT scans

1. Radiation exposure 

   • While the radiation dose from a single CT scan is generally considered safe, repeated CT scans may increase the risk of radiation-related health issues.

   • Your doctor will weigh the benefits against the risks when recommending a CT scan.

2. Metal objects and implants 

   • Due to the strong magnetic fields used in MRI scans, patients with certain metal implants or devices (such as pacemakers) may not be able to undergo an MRI.

   • Always inform your healthcare provider about any implants or metal in your body before an MRI.

3. Contrast agents 

   • Both CT and MRI scans sometimes require the use of contrast agents to enhance image quality. While generally safe, some patients may have allergic reactions to these substances.

To receive personalised advice on what safety considerations apply to you, get in touch with our Thomson Medical health screening specialists.

Choosing between CT and MRI

The choice between a CT scan and an MRI scan depends on various factors, including:

• The part of the body being examined

• The condition is diagnosed or monitored

• The urgency of the situation

• The patient's individual circumstances (e.g., presence of metal implants, claustrophobia)

While both CT scans and MRIs have some similarities, their differences in technology, speed, and imaging capabilities make each one better suited for certain situations. By understanding these differences, you can have more informed discussions with your doctor about your diagnostic imaging options.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Book an appointment with Thomson Medical today.

FAQs

Is a CT or MRI scan safer??

Generally, MRI scans are considered safer than CT scans because they don't use ionising radiation. However, both procedures are considered safe when used appropriately. 

MRIs may be preferred for patients who need repeated scans over time to minimise cumulative radiation exposure. That said, CT scans are sometimes the better choice depending on the medical condition being investigated. 

Are CT scans or MRI scans painful?

Neither CT scans nor MRI scans are painful. However, you may experience some discomfort from lying still for an extended period, especially during an MRI scan.

Can I eat before a CT scan or MRI scan?

This depends on the specific scan and whether contrast material will be used. Your healthcare provider will give you specific instructions on eating and drinking before your scan.

How long do I have to wait for the results of my CT or MRI scan?

The time it takes to receive results can vary. In some cases, preliminary results may be available within hours, but a full report typically takes a few days. Your doctor will inform you when to expect your results.

Are CT scans and MRI scans safe during pregnancy?

CT scans are generally avoided during pregnancy due to radiation exposure. MRI scans are considered safer during pregnancy, but they are usually only performed when necessary. Always inform your doctor if you are pregnant or think you might be pregnant.

Can children have CT scans or MRI scans?

Yes, both CT and MRI scans can be performed on children when necessary. However, special precautions may be taken, such as using lower radiation doses for CT scans or sedation for MRI scans if the child has difficulty staying still.