CT vs MRI Scan

Modern medicine has advanced well beyond x-rays. The two most commonly used tests besides x-rays are CT scans and MRIs, both of which provide more detail than simple 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. A CT scan is a combination of a series of X-ray images taken at different angles; the CT uses a computer to create images from these X-rays. An MRI is a scan that uses magnetic fields and radio waves to produce a detailed image of the body’s soft tissues and bones.

How does a CT scan work?

A CT scan works by taking multiple X-rays at various angles and then utilizes those X-rays to form a three-dimensional image of whatever organ system is being examined. A computer examines all of the various X-rays taken at different angles and synthesizes the images to form a three-dimensional computer model of internal organs.

How does an MRI scan work?

MRIs use and send superconducting magnet and radiofrequency waves into the body. The magnetic field lines up atoms either in a north or south position with a few atoms that are unmatched. When radiofrequency is added, the unmatched atoms spin in an opposite direction, and when the radiofrequency is turned off those unmatched atoms return to the normal position emitting energy. The energy emitted sends a signal to the computer and the computer uses mathematical formulas to convert the signal into an image.

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.
• 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.
• Chest – CT is much better at examining lung tissue and often used for follow up on abnormal chest x-rays.
• Joints – MRI is best at showing tendons and ligaments.

Which one is safer, CT or MRI?

In general, both CT and MRI scans are relatively safe. However, there can be some problems. MRI scans should not be done on patients that have aneurysm clips (clips of the vessels within the brain) unless these clips are known to be MRI safe, as these clips can be pulled off and the patient could die from bleeding into the brain.

Another problem with the MRI is the presence of some cardiac pacemakers or defibrillators because the magnets can cause malfunctions in these battery-operated devices. Any metal devices that can interact with a magnetic field such as the presence of metal shavings in an organ, the eye, or extremity may be pulled out by the magnetic field. Moreover, other canisters that are metal need to be kept away from MRI machines because they can be attracted to the magnet and injure or kill the patient.

CT scans do not have these problems; however, they do expose the patient to radiation, though it’s a relatively low dose. Certain types of CT scan may not be appropriate even during pregnancy.

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 upon 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.