Magnetic Resonance Imaging (MRI) is a non-invasive diagnostic test that uses a strong magnetic field and radio waves to create detailed pictures of the organs and soft tissues inside the body. For an MRI of the knee, preparation involves specific considerations for attire to ensure both patient safety and the quality of the scan. Since the procedure relies on a powerful magnet, the clothing worn during the scan is a primary factor in a successful appointment.
The Critical Rule: Why Metal is Prohibited
The fundamental safety requirement for entering an MRI suite is the complete absence of metal, particularly ferromagnetic materials. An MRI scanner generates a static magnetic field that can be tens of thousands of times stronger than the Earth’s natural magnetic field. This extreme force can turn even small metal objects into high-speed projectiles, a phenomenon called the missile effect.
Beyond this physical hazard, metal objects can also cause a dangerous thermal reaction. The radiofrequency energy used by the scanner is absorbed by metal, causing it to heat up rapidly and potentially cause severe skin burns. Hidden metal in clothing, such as metallic threads, zippers, snaps, and reinforced seams, all pose a burn risk. Underwire bras and clothing with metallic anti-bacterial compounds, often found in athletic wear, are common sources of this thermal hazard.
Recommended Clothing Choices
The safest choice is to select garments made entirely of natural fibers, specifically 100% cotton or linen. These materials are non-conductive and will not react to the scanner’s powerful magnetic or radiofrequency fields. The clothing should be loose-fitting to maximize comfort, as the patient must remain completely still for the duration of the scan, which may last 30 to 60 minutes.
A two-piece outfit is highly recommended, such as cotton sweatpants or shorts and a simple t-shirt, as this makes it easier to position the knee within the scanning coil. Shorts are often the most practical choice for a knee examination, as they allow maximum access to the area being imaged. The garments should be free of any metal fasteners, including zippers, buttons, snaps, or grommets.
It is important to check clothing carefully, as many modern athletic and “athleisure” wear fabrics contain embedded metallic microfibers for odor-wicking or anti-bacterial properties. Therefore, clothing labeled with terms like “silver technology” or “Coolmax” should be avoided completely.
When the Facility Provides Attire
Many imaging facilities require a change of clothes as a final safety measure. Most centers will provide a clean, loose-fitting cotton gown or disposable scrubs for the procedure. This is done to eliminate any doubt regarding the material composition of the patient’s clothing. The mandated change ensures that no hidden metallic fibers, which can be difficult to detect, are brought into the scanning room.
Some facilities have strict policies that require all patients to wear provided attire to protect against thermal burns, which are the most common reported MRI safety issue related to clothing. It is always advisable to call the imaging center before the appointment to confirm their specific policy on patient attire. Even if a patient arrives in acceptable clothes, they may be asked to change if the staff is unfamiliar with the brand or material. Changing into facility-provided scrubs offers the highest assurance of safety and compliance for the knee MRI.