Spandex may be relaxing when posing in the downward facing dog yoga position — but for an MR exam, it's anything but.

Providers nationwide have introduced new policies in recent years that bar patients from donning standard yoga and athleisure gear in MR environments, many of which are likely to burn skin during exams due to the presence of metallic materials embedded in the garments. Some bans even extend to specific clothing brands.

“The use of metallic fibers or metallic nanoparticle treatments is becoming much more commonplace. You don’t necessarily have to see metallic flecks for it to have these electrically conductive properties and be potentially dangerous in the MR environment,” Tobias Gilk, the founder of Gilk Radiology Consultants and chairman for the board of directors at the American Board of Magnetic Resonance Safety, told HCB News. “What best practices have recommended for a number of years is to remove street clothing and provide patients with gowns and scrubs so the facility has control over what materials go into the MR and to the extent possible, eliminate what the patient may be bringing with them that they very likely don’t know.”

Designed to prevent the buildup of odors and bacteria, yoga gear consists of tiny metal threads that are likely to move due to the electromagnetism and radio waves of an MR scanner, creating thermal energy that burns patient skin in a process similar to magnetic induction cooking.

Though infrequent, such events cause patients to suffer from first- and second-degree burns. The risk even applies to metal fibers found in certain forms of underwear and certain tattoo pigments with metallic compounds, especially substances with iron oxides, such as certain black pigments.

To prevent the onset of incidents like this, providers such as Stony Brook University’s hospitals, UCLA and Mount Sinai have put up signs in radiology rooms and redefined clothing policies that advise patients to wear other garments, like paper gowns or cotton T-shirts.

UCLA has even prohibited specific brands, for example, Lululemon, whose products are created with Silverescent technology, a fabric composed of silver-bonded threads to prevent bacteria from building up. It has also banned clothes made by the Gap, Athleta and Columbia Sportswear.

Patients themselves can help prevent the onset of adverse events by checking to see if clothing labels for words such as "antimicrobial" or "antibacterial", signs that metals comprising "silver technology" are embedded within the garments.

This, however, can be challenging, as metal materials are not visible in clothing. Brands may also use unique terms from one to another, creating confusion, and are not required to label whether clothes are safe for MR environments.

Ferromagnetic detectors can help, but in a limited capacity, due to their inability to detect non- non-ferromagnetic substances, such as copper. Even regular metal detectors can prove inefficient due to the low quantity and concentration of metals embedded in clothing.

One example of this predicament involved an 11-year-old girl in 2012 who suffered second-degree burns from her undershirt, which contained silver microfibers that went undetected by a wand metal detector test prior to the MR exam, according to the American Journal of Neuroradiology.

Gilk says it is impractical for MR staff and technologists to have a comprehensive knowledge of the types of clothes and brands that pose risks like this and should focus on operational best practices, such as gowning patients, and focus on the specific area of the body being examined.

“We really have to resort to existing standard best practice, which is at least to get the clothing items in the area or region that is going to be receiving radiofrequency energy. If we’re doing the patient’s ankle, we’re probably not worried about the t-shirt they’re wearing but if we’re doing the head, then of course we are, because that’s close enough to the region that, depending on the particulars of the MR system, the t-shirt could receive a significant amount of radiofrequency energy.”

Other items at risk for setting off adverse events in MR environments include forms of compression wear, camping gear, and antimicrobial treatments that go into clothes.