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MRI vs CT scan

By Aaron B. Welk, D.C.

There are many reasons that a doctor may decide to order advanced imaging of the spinecan such as MRI or CT scan. X-rays are often a good screening tool as well, however the drawback of x-ray imaging is the use of ionizing radiation to create the images. Although the radiation dose for a typical x-ray series is low, excess radiation exposure should be avoided when possible.

In some instances, a closer look may be warranted based on the presence or lack of findings on the x-rays and MRI or CT may be ordered. The decision between these two imaging studies is largely based on the patient’s symptoms.

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Time for an MRI?

MRI is more commonly used in the outpatient setting to diagnose degenerative disease such as disc herniations or spinal stenosis. MRI uses a powerful magnetic field to produce images. MRI produces very clear images of the vertebrae, discs, joints, and muscles of the spine in multiple planes. Because the images are produced using a magnetic field, there is no radiation dose to the patient.

Most MRI scanners require the patient to be placed in a tube that may make some patients uncomfortable. Open MRI scanners are available, but the magnetic field of open scanners is not as strong and less detailed images are produced. The time a patient is required to be in an MRI scanner is also a drawback. The time required in an MRI scanner may be around 30 minutes. MRI may also be contraindicated with certain metallic devices such as pacemakers or spinal stimulators.

The benefits and risks of each examination can be discussed with your doctor before an MRI or CT scan is ordered.


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Time for a CT Scan?

The main utilization of a CT scan is in the setting of acute trauma to rule out fractures of the spine, although special studies like CT myelography (contrast examination of the spinal canal) are still used. Like MRI, CT imaging produces very clear images of the bones, joints, and muscles of the spine in multiple planes of view. Unlike MRI, CT uses ionizing radiation to produce images. The presence of metallic devices does not contraindicate CT imaging and this study may be ordered in place of an MRI if any hardware is present in the patient.

A CT uses a high powered x-ray tube that rotates around the patient to produce the images. This causes more radiation dose to the patient than a conventional x-ray examination. The time required to acquire CT images is much lower than with MRI. A typical CT scan only requires a few minutes to complete the examination. The patient is still required to pass through a tube, but the translation is much faster and may be completed in a single breath hold.

The benefits and risks of each examination can be discussed with your doctor before an MRI or CT scan is ordered.


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