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Magnetic resonance imaging (MRI) is generally considered to be safer than X-ray or computed tomography (CT) scanning because it does not use ionizing radiation, so does not increase the patient’s risk of developing cancer. Instead, MRI uses magnetic fields and radio waves to cause the hydrogen protons within the body to resonate and emit radio waves, which can be detected by receiver coils and translated into images using computer software. MRI causes no known biological damage and can create clearer and more detailed images of soft tissue than other imaging techniques.[1]
Ferromagnetic Objects
Because of the powerful magnetic field used in MRI, however, it is important to take great care to screen for any metal objects that may be within or on a patient’s or accompanying caregiver’s body or in the MRI scanning area. Ferromagnetic objects (those with magnetic properties) will not be allowed in the scanning room because the magnet in the MRI can turn them into dangerous projectiles (in the case of objects outside of the body) or pull on metal objects within the body, potentially causing them to move suddenly and with great force.[2] Although there are several non-ferromagnetic metals, it can be very difficult to determine by inspection, or in some cases, even by knowing what the metal is, whether it is ferromagnetic. For this reason, all metals will typically be excluded from the room unless it can be verified that they are MRI safe.[3]
Many everyday items can be ferromagnetic, including jewelry, cell phones, and elements of clothing, such as zippers, hooks, or metallic threads. Less common items that can present danger during an MRI scan include aneurism clips, medication pumps, and bullets or shrapnel embedded in the body. Medical equipment such as pacemakers or neurostimulators may malfunction or cause injury. Some newer medical devices are made to be MRI safe, so not all patients with these types of equipment will be excluded from MRI scanning.[4] For more information about MRI contraindications, see our blog post on the topic. Be sure to be thorough in your reporting of all items during your MRI screening prior to the exam so that your radiologist can take all necessary precautions to keep you safe.
Tattoos and Cosmetics
Pigments used in tattoos may also be of concern, as some contain iron oxide. Although the iron oxide particles are very small and do not pose the same kind of danger as objects such as ferromagnetic implants or embedded shrapnel, they can become heated during MRI scanning and cause first- or second-degree skin burns similar to sunburn. If you have tattoos or permanent makeup, be sure to mention them so the technologist can take steps to prevent or alleviate this potential side effect. Even in cases where minor skin burns have occurred in tattooed skin, the effect has resolved fairly quickly and without lasting effects.[5] Some conventional cosmetics also contain metal particles, so patients receiving MRI scans of the head should remove any makeup prior to scanning.[6]
Gadolinium-Based Contrast
Some MRI procedures will use a gadolinium-based contrast agent to enhance the information obtainable from the images. Unlike the iodine-containing contrast agents used in X-ray exams, the contrast used for MRI rarely causes allergic reaction. However, patients with medical issues such as impaired renal function or liver disease may have an increased risk of complications resulting from use of the contrast agent. Your doctor may order a blood test to assess kidney function prior to administration of gadolinium-based contrast.[7]
The information contained in the Iowa Radiology website is presented as public service information only. It is not intended to be nor is it a substitute for professional medical advice.You should always seek the advice of your physician or other qualified healthcare provider if you think you may have a medical problem before starting any new treatment, or if you have any questions regarding your medical condition.
Iowa Radiology occasionally supplies links to other web sites as a service to its readers and is not in any way responsible for information provided by other organizations.
[1] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1121941/
[2] http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_mr
[3] http://mrimetaldetector.com/blog/2009/03/mri-and-metal/
[4] http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_mr
[5] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3445217/
[6] http://www.hopkinsradiology.org/patient_care/Patients/Radiology Procedures/MRI Prep
[7] http://www.vhl.org/wordpress/patients-caregivers/living-with-vhl/diagnosis-and-treatment/screening-and-testing-protocols/an-uncommon-side-effect-of-mri-contrast-agents/
