Brain & Nervous System Neurological Symptoms & Diagnosis Comparing MRI and CT Scans Assessing the Benefits, Risks, and Limitations By Peter Pressman, MD Peter Pressman, MD, is a board-certified neurologist developing new ways to diagnose and care for people with neurocognitive disorders. Learn about our editorial process Peter Pressman, MD Medically reviewed by Medically reviewed by Claudia Chaves, MD on January 19, 2020 Claudia Chaves, MD, is board-certified in cerebrovascular disease and neurology with a subspecialty certification in vascular neurology. She is an associate professor of neurology at Tufts Medical School and medical director of the Lahey Clinic Multiple Sclerosis Center in Lexington, Massachusetts. Learn about our Medical Review Board Claudia Chaves, MD Updated on January 22, 2020 Print The brain and nervous system can be visualized with computerized tomography (CT) scans and magnetic resonance imaging (MRI). When faced with a neurologic disorder, an experienced neurologist can often make a diagnosis without the need for additional tests. At other times, it can be helpful (or even urgent) to order a battery of neuroimaging tests to locate or evaluate disorders that are not so easily identified. Learn how and why these tests are performed. Morsa Images / Getty Images Comparison The term neuroimaging describes methods of visualizing the brain and other parts of the nervous system to either confirm or rule out the neurologist's suspicions. MRIs and CT scans are two such tools a neurologist will regularly turn to. Metaphorically speaking, an MRI is like an expensive, professional-grade camera while a CT scan is more like a cheap disposable camera. The comparison is even more relevant given that the cost of an MRI far exceeds that of a CT scan. This doesn’t necessarily mean that one is inherently better than the other. Some people assume that, because the imaging quality of an MRI is higher, it should always be the first choice. But that reflects a general misunderstanding about the technologies, both in terms of their capabilities and shortcomings. Broadly speaking, an MRI and CT scan differ in three distinct ways: When time is of the essence. An MRI can take around 45 minutes to complete whereas a CT scan may only take five to 10 minutes. In the time it takes to get an MRI done (for, say, a serious intracranial hemorrhage) a person could be dead or severely injured. An MRI also requires a person to be very still for a long period of time, which can be difficult in an emergency. A CT scan is often the better choice for such emergencies.The types of abnormalities they detect. In some situations, a CT scan can detect abnormalities more easily than an MRI, including acute bleeding and bone fractures. By contrast, an MRI is best at detecting small or subtle lesions such as multiple sclerosis plaques, acoustic neuromas, or low-grade astrocytomas.Interference with imaging quality. MRIs create images using strong magnetic waves. Certain metal implants and non-compatible devices can interfere with these waves, causing a distortion of the images. In the same vein, the beams of radiation used by a CT scan can be scattered by dense bone (say, around a brain stem), leading to a picture that is difficult or even impossible to interpret. While MRI and CT can be used when indicated for pregnancy, there have been concerns that radiation from CT and contrast dyes used in MRI may pose potential harm to the fetus. The current body of evidence suggests that the risk is likely low. Speak with your doctor to fully understand the risks and benefits of CT or MRI scans if pregnant. Comparing the Diagnostic Capabilities of CT and MRI Imaging Risks CT scans essentially use X-rays to create a rotating image. As such, the amount of radiation involved can be concerning, with some studies suggesting a 1 in 300 chance of getting cancer as a result of a scan. This is more of a concern in young people since the development of cancer usually takes decades to manifest. For this reason, doctors tend to be more cautious about performing a CT scan on a child than on an older adult. MRI, by contrast, uses a very powerful magnet to stimulate atoms in a person’s body. Those atoms are then detected by the scanner. The greatest risk of an MRI is that any ferromagnetic metal implant can become a magnetic under the influence of the MRI and try to align pole-to-pole This can cause an implant to be displaced or overheated. Contrast Agents In some cases, neurologists will use a contrast dye to better differentiate what is going on inside the brain. Contrast dyes can be useful in highlighting vascular abnormalities such as brain aneurysms or lesions associated with acute MS, hemorrhagic stroke, or cancer. In both CT scans and MRIs, the contrast agent may cause serious problems: CT scans use a contrast agent that may contain iodine. In some rare cases, iodine exposure can cause serious to life-threatening allergic reactions.MRI scanners use a contrast agent called gadolinium. In persons with kidney disease, exposure to gadolinium can cause a rare but adverse condition called nephrogenic systemic fibrosis (NSF). MRI Takes about 45 minutes No exposure to ionizing radiation Better at imaging soft tissue Requires a gadolinium contrast agent May not be used with certain metal implants Generally double the cost of CT scan Noisier CT Takes about 10 minutes Exposes you to ionizing radiation Better at imaging bone and blood vessels May require an iodine contrast agent Is not affected by metal implants Around half the price of an MRI Quieter A Word From Verywell There is a lot that needs to be considered before undergoing a neuroimaging exam. As the patient, it is always important to inform your doctor about any allergy, implant, and health issue (including cancer treatments) you have or may have had. You should also air any concern you have about the procedure itself, particularly if you have claustrophobia or have had a bad experience in the past. Alternatives may be available. If an imaging tool is chosen wisely and with the full input of the patient, it can contribute greatly to the ease and accuracy of a diagnosis. Speak with your doctor or get a second opinion, if needed. What Is a PET/CT Scan? Was this page helpful? Thanks for your feedback! Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Sistrom CL, Mckay NL. Costs, charges, and revenues for hospital diagnostic imaging procedures: differences by modality and hospital characteristics. J Am Coll Radiol. 2005;2(6):511-9. doi:10.1016/j.jacr.2004.09.013 Stallard J. CT vs MRI: What’s the difference? And how do doctors choose which imaging method to use? Memorial Sloan Kettering Cancer Center. Hill B, Johnson S, Owens E, Gerber J, Senagore A. CT Scan for suspected acute abdominal process: impact of combinations of IV, oral, and rectal contrast. World Journal of Surgery. 2010;34(4):699 doi:10.1007/s00268-009-0379-6 Hinzpeter R, Sprengel K, Wanner G, Mildenberger P, Alkadhi H. Repeated CT scans in trauma transfers: An analysis of indications, radiation dose exposure, and costs. European Journal of Radiology. 2017:135-140. doi:10.1016/j.ejrad.2017.01.007 Additional Reading Pearce M, Salotti J, de González A, et al. Articles: Radiation exposure from CT scans in childhood and subsequent risk of leukemia and brain tumours: a retrospective cohort study.The Lancet. 2012; 380:499-505. Foray N, Bourguignon M, Hamada N. Individual response to ionizing radiation. 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