Magnetic Resonance Imaging (MRI) is a powerful diagnostic tool that uses a strong magnetic field and radio waves to create detailed images of the body’s internal structures. Because the equipment relies on intense magnetic forces, strict safety protocols govern everything brought into the scanning room, especially patient attire. Preparation regarding what you wear and carry is paramount, ensuring patient safety and the clarity of the resulting images. This minimizes the risk of injury and prevents image artifacts.
Approved Clothing Versus Gowns
Most imaging facilities require patients to change into a hospital-provided gown before entering the MRI suite. This practice eliminates the uncertainty of hidden metallic components within personal clothing. The gowns are typically made of cotton and contain no metal fasteners or threads that could interact with the magnetic field. Changing into a metal-free garment helps mitigate the risk of thermal burns, a major safety issue in MRI.
If a facility permits wearing personal clothing, the requirements are specific. Only loose-fitting garments made entirely of natural, non-synthetic fabrics, such as cotton or linen, are usually approved. Personal items must be completely free of metal components, including snaps, zippers, belt buckles, and bra underwires. Even small metallic logos or threads woven into the fabric can heat up and cause skin irritation or burns during the procedure.
Mandatory Removal of External Metal
Removing all readily detachable metallic items is a mandatory safety measure before entering the high-field environment of the MRI room. Jewelry, including watches, rings, necklaces, and body piercings, must be taken off because they present a significant hazard. Common accessories like eyeglasses, hairpins, barrettes, and hearing aids also contain metal and must be left outside the suite. Keys, coins, and wallets must be emptied from pockets, as these everyday objects can be violently pulled into the machine.
The danger posed by external metal objects is twofold: the projectile risk and the thermal risk. Any ferromagnetic material can become a projectile, accelerating toward the magnet and posing a serious impact risk to the patient or staff. Furthermore, the radiofrequency (RF) energy used by the scanner can induce electrical currents, causing localized heating and potentially severe skin burns.
Hidden Hazards in Personal Items
Beyond the obvious accessories, several personal items contain metal in less apparent forms that can still be problematic during a scan. Certain cosmetics, especially mascara and liquid eyeliner, contain metallic flakes, often iron oxide, which can cause image distortion if the scan involves the head or eyes. Patients with permanent makeup or decorative tattoos must alert the technician, as the inks used, particularly in older or darker tattoos, may contain iron-based pigments. These metallic pigments can react to the RF energy, resulting in a tingling sensation or, in rare cases, a localized burn at the tattoo site.
Transdermal medicated patches are another hidden hazard, as some types have a metallic foil backing designed to regulate drug release. This metallic layer can act as a conductor, causing an electrical current to be induced and leading to significant skin heating and burns under the patch. Patients must also disclose all internal medical implants, such as pacemakers, aneurysm clips, or joint replacements, during the initial screening. While many modern implants are considered MRI-safe or conditional, devices with ferromagnetic components can still move or malfunction, requiring specific screening protocols to ensure the patient’s safety.
Understanding the Magnetic Field
The reason for these strict protocols lies in the physics of the MRI environment. The machine generates an exceptionally powerful static magnetic field, which can be tens of thousands of times stronger than the Earth’s natural field. This intense field exerts a strong attractive force on any object containing ferromagnetic metal, pulling it toward the center of the scanner. This attractive force is why unsecured items are forbidden in the scanning room.
A second safety factor involves the radiofrequency (RF) coils that transmit and receive energy during the scan. This RF energy can induce electrical currents in conductive materials, causing them to heat rapidly. Whether the conductor is a metallic thread in clothing or a foil-backed patch, this localized heating poses a risk of thermal injury. Adhering to all preparation guidelines counteracts these powerful physical forces.