Some respiratory face masks are unsafe for MRIs, study finds
Many filtering face piece (FFP-3) respiratory masks, commonly used in MRI settings during the COVID-19 pandemic, can be unsafe for MRIs, according to a new study accepted for publication in Clinical Radiology.[1]
The safety risks stem from the presence of ferromagnetic components, which were found in five out of eight commercially available masks tested. Risks include artifacts on the MRI, deflection or displacement of the mask, risk of projectile effects, and radiofrequency-induced heating that could potentially cause burns. The masks deemed MRI-unsafe caused observable grid distortion of up to five centimeters.
“This study has demonstrated the importance of assessing respiratory FFP3 masks for use in and around MRI machines,” wrote first author Bethany Keenan, MD, and co-authors.
In addition to better understanding safety risks and grid distortion, the study also aimed to determine which masks can be considered safe for use in an MRI setting, as it isn’t obvious through outward observation alone. While some metallic components—such as metal nose strips—are immediately visible, others—such as silver or copper antimicrobial coatings—are difficult to observe. Additionally, the study notes that not all face masks are labeled appropriately.
“It is therefore important to not assume that the mask is safe prior to an MRI examination, and to conduct a safety evaluation to determine which components are made of ferromagnetic metals (such as steel) and which are non-ferromagnetic metal (such as aluminium),” the authors wrote.
To make their safety determinations, researchers placed each FFP-3 mask on a 3D head phantom and put it into the MRI machine at the Cardiff University in the United Kingdom. They compared the images to images of the 3D head phantom without a mask to measure displacement, considering the model with the mask as a “moving” image and without the mask as a “fixed” image.
Additionally, the researchers positioned temperature strips at the nasal bridge of the phantom. While they did not observe local heating for any of the masks—including one with an aluminum nose strip—they could not rule out the risk of local heating if using a higher specific absorption rate or a head and neck coil.
In general, the authors noted, pandemic-related requirements to wear a respirator or facemask were quickly put into place, meaning that many practitioners did not previously consider the potential risks or complications of wearing one.
“As a result, hospital staff may not be aware of the potential hazards these masks could pose and that MRI safety documentation does not exist.”
One best practice that the authors recommended is to order “MRI safe” surgical masks in a separate color for easy identification.
References:
1. Keenan, BE, Lacan, F, Cooper, A, et. al. MRI safety, imaging artefacts, and grid distortion evaluated for FFP3 respiratory masks worn throughout the COVID-19 pandemic. Clinical Radiology, 2022. DOI: https://doi.org/10.1016/j.crad.2022.05.001.
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