An intrauterine device (IUD) is a small, T-shaped form of contraception placed inside the uterus for long-term pregnancy prevention. Magnetic Resonance Imaging (MRI) is a powerful diagnostic tool that uses strong magnetic fields and radio waves to create detailed internal body images. The concern regarding IUDs and MRI stems from the presence of metal, even in small amounts, within the device. A strong magnetic field can potentially interact with metallic components, leading to movement, heating, or image distortion, which makes verifying device safety before a scan mandatory.
Understanding MRI Compatibility Classifications
Medical devices, including IUDs, are labeled with one of three compatibility categories established by regulatory bodies to standardize safety in the MRI environment. The designation “MR Safe” applies to a device that contains no metal or only non-magnetic materials, posing no known hazard in any MRI system. This means the device can be brought into the scanning room without restriction.
The most common designation is “MR Conditional,” which indicates the device is safe only if specific limits on the magnetic field and scanning process are strictly followed. These conditions are determined through rigorous testing and must be clearly documented by the manufacturer. If a device is labeled “MR Unsafe,” it contains ferromagnetic material that poses a definite hazard; it should never enter the MRI scanning room.
MR Unsafe devices carry the risk of being pulled out of position by the powerful static magnetic field, an effect known as magnetically induced displacement force or torque. This could cause internal injury to the patient. Furthermore, the metal in an Unsafe device can significantly heat up during the scan due to the radiofrequency energy used to generate images.
IUDs Designated as MR Unsafe
The IUDs designated as truly MR Unsafe typically contain a significant amount of highly ferromagnetic material, such as certain types of stainless steel. The most widely referenced example is the “Chinese ring IUD,” a stainless-steel ring-shaped device distributed in China, predominantly between 1988 and 2000. When exposed to the intense magnetic field of an MRI scanner, the steel in these older devices can experience significant magnetic torque and displacement forces. This forceful movement presents a clear danger of tissue damage or device perforation inside the body.
Additionally, the presence of this ferromagnetic material causes massive image artifacts that completely obscure the area of interest in the scan. While these stainless-steel IUDs are rare in many Western countries, the MR Unsafe classification remains relevant for patients who may have received the device abroad or many years ago.
Parameters for MRI Conditional IUDs
Most modern hormonal and copper IUDs are classified as MR Conditional, which means they can be safely scanned under specified conditions. Hormonal IUDs, such as Mirena, Skyla, and Liletta, are primarily constructed from plastic and contain minimal or no metal, sometimes only a small silver ring marker, making them highly compatible. Copper IUDs, like ParaGard, rely on a copper wire wrapped around a plastic T-frame.
The “Conditional” status requires specific constraints on the MRI system to prevent slight warming or movement of the device. For instance, testing has demonstrated that many copper IUDs can be safely scanned in systems up to 3.0 Tesla (T), which refers to the strength of the static magnetic field.
The conditions also relate to the magnetic field gradient and the radiofrequency energy deposition. The spatial magnetic field gradient limit is often specified, such as up to 36,000 Gauss per centimeter (360 T/m) or 40 T/m, which measures how quickly the magnetic field changes over distance. The Maximum Specific Absorption Rate (SAR), a measure of radiofrequency power deposited into the body, is also limited, often to a whole-body averaged SAR of 4 Watts per kilogram (W/kg).
As long as the MRI system parameters do not exceed these specified limits, the risk of significant torque, device displacement, or temperature rise (which is typically less than 1° Celsius) is negligible. The vast majority of IUD users can safely undergo an MRI scan when necessary.
Pre-Procedure Screening and Documentation Requirements
Before any Magnetic Resonance Imaging procedure, a patient with an IUD must undergo a thorough screening process to confirm the device’s compatibility status. The patient must provide the exact make, model, and date of insertion of their IUD to the MRI technologist and radiologist to verify the device’s specific MR Conditional parameters. The most reliable way to confirm the device type is to present the patient ID card or documentation provided at the time of IUD insertion.
Healthcare providers must then cross-reference this information with the manufacturer’s official safety labeling for the device. If the specific IUD model is not known, or if the documentation is unavailable, the MRI procedure may need to be postponed. If the IUD cannot be positively identified as compatible under the scanning conditions, the procedure is often deemed too risky and an alternative imaging modality, such as ultrasound or Computed Tomography (CT), may be used instead.