What Is the Difference Between a CT Scan and MRI?

A CT scan and MRI are both non invasive and low risk tools used by doctors to diagnose specific conditions. They both produce images of the inside of our body, but what are the differences between a CT scan and MRI, and when are they used?

How a CT Scan and an MRI Work

A CT scan, also known as a CAT scan, stands for computerized axial tomography using X-rays, and is more widely used than an MRI. CT scans rotate on an axis taking 2D images from all different angles. The images become 3D when the cross sections are put together and shown on a computer screen.

MRI refers to magnetic resonance imaging using radio waves. Unlike a CT scan which use X-rays, an MRI scan uses powerful magnetic fields and radio frequency pulses to produce more detailed images of organs, soft tissue, and bone.

What Do a CT Scan and an MRI Show?

CT Scans

CT scans help to diagnose serious injuries to the head, chest, abdomen, spine, and pelvis. This imaging technology can also determine the size and location of tumors and monitor the progression of cancer. In addition, a CT scan can show bone fractures and locate the source of internal bleeding.

Your doctor may order a CT scan to evaluate the following:

  • Fractures or broken bones
  • Fever or unknown pain
  • Heart, kidneys or liver problems
  • Changes in tissues that can trigger a spread of disease
  • Trauma


An MRI is typically used to diagnose issues with joints like the wrist and ankle. Your doctor can determine herniated discs, torn ligaments, and problems with a patient’s soft tissues by referring to various MRI scans.

An MRI can also show issues of the heart, breast, and blood vessels. It is most often used after other tests fail to provide sufficient information for a diagnosis.

Your doctor may also order an MRI to investigate the following potential conditions:

  • Tumors or cysts
  • Disease of the liver, bile ducts, pancreas, and gallbladder
  • Endometriosis

Practical Differences

A CT or CAT scan is more widely used, takes less time, and is less expensive than an MRI, although an MRI is more detailed.

A normal CT scan takes approximately 5 minutes whereas an MRI can take over 30 minutes.

An MRI is also very loud and can cause hearing issues. If someone is claustrophobic these scans can be quite problematic since you must stay immobile for the entire test.

Risks For Both

Although a CT scan uses a very small dose of radiation, it can be harmful to unborn babies.

There can also be a possible reaction to the dyes that are often used during both an MRI and a CT scan.

MRI magnets can cause potential reactions and safety issues like the following:

  • A very long MRI can cause a rise in a person’s temperature
  • The magnets can cause certain things to malfunction like a pacemaker or defibrillator.
  • Likewise, brain aneurysm clips can be a serious safety risk. They can be pulled out and the person can suffer from bleeding in the brain.

You should not have an MRI if you have metal components in joints, or metal shavings in an organ or eye.

It is imperative to speak with your doctor about any issues you may have ahead of a CT scan or MRI in order to lower all possible risks. When used appropriately, these imaging technologies can be extremely helpful in diagnosing and monitoring a variety of health conditions.

For more information, or to schedule your appointment, contact (214) 345-8300 today!