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CT scan vs. MRI: What’s the difference?

Modern medicine has advanced well beyond x-rays. At Medical Imaging of Fredericksburg, we have ultrasounds, mammography, CT scans, several types of MRIs, PET scans, and PET-CT scans. The two most commonly used tests besides x-rays are CT scans and MRIs, both of which provide more detail than x-rays. If you need specialized imaging, it can be helpful to understand the operation and uses for a CT Scan vs. MRI.

In some ways, these two tests are similar to one another. They both show cross-sectional pictures of the body, but they accomplish this with different techniques. CT (computerized tomography) uses multiple x-rays, taken at different angles, to produce the cross-sectional imaging. MRI (magnetic resonance imaging) uses magnetic fields and radio frequencies. Because of the differences in techniques, the tests show the same parts of the body in different ways and are selected based upon the possible diagnosis.

Differences: CT scan vs. MRI

CT scans

  • Radiation – Since CT scans are created by multiple x-rays, there is radiation exposure, although minimal. It is not usually appropriate during pregnancy.
  • Uses – Excellent for looking at bones, but very good for soft tissues, especially with intravenous contrast dye.
  • Cost – Usually less expensive than MRI
  • Time – Very quick. The test only takes about 5 minutes, depending on the area that is being scanned.
  • Patient comfort – The machine is very open, so concerns about confined space is rarely a problem.
  • Reactions – The intravenous contrast rarely causes allergic reactions. It does have the potential to injure kidneys, especially with people who already have kidney problems or diabetes or those who are very dehydrated.
  • Limitations – Patients who weigh more than 300 pounds may have to be sent to a location with a table designed to handle their weight.

A true Open MRI provides a more comfortable experience for many patients.

MRI

  • Radiation – None
  • Uses – Excellent for detecting very slight differences in soft tissues.
  • Cost – Often more expensive than CT scans.
  • Time – The time depends on the part of the body being examined and can range from 15 minutes up to 2 hours.
  • Patient comfort – The narrow tube can cause anxiety. Open MRI machines have been developed to handle patients who aren’t comfortable with the regular machine.
  • Reactions – Very rare allergic reactions to the IV contrast.
  • Limitations – Size of the tube may limit the size of the patient, although large patients may be handled with the open MRI machine. Certain metal objects implanted in the body, such as pacemakers, some prosthetic joints and rods and even some tattoos, may be affected by the magnetic field, preventing the test.

Uses for CT Scan vs. MRI

    • Abdominal pain – CT is the preferred test. It is more readily available on an emergency basis and is very accurate. Ultrasound is used for children and pregnant women.
    • Trauma – CT is present in most emergency departments and is the best at showing bone fractures, blood and organ injury.
    • Spine – MRI is best at imaging the spinal cord and nerves.
    • Brain – CT is used when speed is important, as in trauma and stroke. MRI is best when the images need to be very detailed, looking for cancer, causes of dementia or neurological diseases, or looking at places where bone might interfere.
    • Chest – CT is much better at examining lung tissue and often used for follow up on abnormal chest x-rays. Low dose CT Scans are available and used with high-risk smokers who need to be screened annually.
    • Joints – MRI is best at showing tendons and ligaments.

Your doctor will explain the choice of test, and he or she will consult with the RAF radiologist and MIF technologists to ensure that the imaging meets your needs. Both types of scan can help determine the source of your problem and get you closer to a solution.

Considerations for the cost of different imaging studies are an important element in planning for imaging studies. There are differences in the costs for these studies based on where they are completed as well as differences in the quality of radiology and staff support. It pays to compare these factors before completing either MRI or CT imaging. An imaging study completed in a location outside the major metropolitan area could create big cost savings with the study shared digitally with whatever medical professionals are providing care.

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