When Would You Need a CT Scan Instead of an MRI?

Q: When is a patient a good candidate for a CT scan instead of an MRI?

A: There are several scenarios in which a CT scan would be needed instead of, or in addition to, an MRI.

Often, arthritis or another abnormality is found on an x-ray, and further evaluation with higher-level imaging is called for. CT imaging shows many aspects of osseous (bony) detail better than an MRI.

CT imaging is often the most appropriate first choice in the case of a trauma. A CT is quick; it may take less than two or three minutes to obtain all the images. In comparison, an MRI can take 15 to 45 minutes.

Additionally, CT allows for assessment of spinal hardware integrity, including hardware positioning and loosening. Although most spinal hardware is safe for MR imaging, the metal creates significant artifact (misrepresentations) on MR images, and adequate hardware assessment is nearly precluded.

Some patients experience claustrophobia or have difficulty staying still in an MR machine. While there are many methods we can use to help patients better tolerate the MR experience, such as music, MRI goggles for viewing movies, relaxation techniques, and even anti-anxiety medications, some patients cannot tolerate the time or environment of an MRI scanner. These patients would benefit from getting a CT instead.

Additionally, patients with certain types of implanted medical devices cannot be exposed to the magnetism of an MRI scanner. As a patient, it is especially important to mention to the technologist or radiologist if you have any implanted devices as there are a few circumstances in which a patient cannot get an MR examination. A CT scan can be more appropriate for these patients.

MRIs are much less restricted than they were years 20-30 years ago. For example, many years ago, everyone who had a pacemaker was told they could not go near an MRI scanner. With pacemaker evolution and research, we now know that many pacemaker devices are completely safe for MRIs with proper monitoring. Patients with a pacemaker should only have an MRI in a facility where cardiologists (doctors specializing in the heart) can monitor them. This would typically be at a university-based health care center.

Radiologists (doctors who specialize in imaging) are experts in interpreting medical imaging. They are also trained to help healthcare providers, and patients determine whether an MRI or CT imaging is best. Never hesitate to call the imaging center ahead of time and ask to speak to a radiologist or chief technologist when you have any questions about imaging safety.

– Dr. Gayle Salama, Neuroradiologist and Director of Spine Imaging

This question was answered during the episode of Spine Time called “Neuroradiology: The Marriage of Diagnostics and Intervention.” A recording of this webinar held on September 22, 2021, is available on YouTube. To sign up for future episodes of Spine Time, where you can ask questions of our spine specialists, subscribe here.

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