Prevention of projectile accidents (RTMR)

• Projectile events (also known as missile events) are among the most significant dangers of strong magnetic fields, such as those within an MRI scanner, and can cause critical injury to MRTs, patients and the MRI system.
  • The most common MRI scanner uses a superconducting magnet whose magnetic field is always considered “on” or “active.” Turning off the magnets can be done by ramping down or through a process called quenching. A Quench is a highly complex and potentially dangerous undertaking which does not occur often.¹
• There have been a number of serious patient injuries caused by metallic objects becoming projectiles, which in some cases resulted in fatalities (see Prevention Projectile Accidents: Examples from Practice).
  • Ferromagnetic materials and magnetic materials that are not ferromagnetic (e.g., paramagnetic materials) can be pulled into the magnet bore. Examples include medical devices, oxygen tanks, cleaning supplies, ferromagnetic sand, paper clips, and coins.¹
• Facilities employ strict policies to ensure screening procedures are implemented for the detection of potential projectiles prior to their entry into the MRI environment.
  • All individuals entering the MRI environment are screened before each procedure (regardless of whether they have been screened in the past).
  • All equipment is verified for MRI safety before being allowed into the MRI environment by a Level 2 trained MRI Personnel.
    • Level 2 MRI personnel are those with MRI safety education to ensure safety of all individuals and facility resources within the MRI environment. An MRI Technologist is classified as a Level 2 MRI safety-trained personnel.
  • Additional attention must be given to objects made from conducting materials, as these may pose hazards under certain conditions.^1,2

*For more details about MRI screening in general, see BPG guideline MRI screening (RTMR)

• The most effective measure to prevent patients carrying potential projectiles into the MRI suite is to require they change into hospital gowns, which includes the removal of all clothing, undergarments, and any other items worn on the body.¹²
  • MRI-safe hospital gowns are made of cotton and do not contain pockets or metal snaps.
  • Use of other clothing in the MRI suite may be potentially dangerous if the garment contains metallic threads, objects, or synthetic conductive materials capable of producing thermal burns.¹
• Non-ambulatory patients may only enter the MRI environment in an MRI-safe wheelchair or gurney which has been inspected specifically for¹:
  • Ferromagnetic oxygen tanks and IV poles¹
  • Sandbags with metallic contents³
  • Ferromagnetic objects concealed under blankets, in pockets or folds of clothing or stowed on transport equipment¹
• The MRI fringe field is clearly demarcated and secured by trained staff.¹

• Equipment and objects are labelled according to the ASTM (formerly known as the American Society for Testing and Materials) standards for safety in the MRI environment as follows:
  • MRI safe – objects that pose no known hazards in all MRI environments
  • MRI conditional – objects that are acceptable when used in a specific manner within specific MRI environments, with limitations on usability or the testing that was performed on it
  • MRI unsafe – objects that pose a known threat or hazard in all MRI environments
• A list of MRI safe and MRI conditional objects is maintained in the department, including details of restrictions for use.
  • Information not contained within the document can be obtained from the manufacturer’s guidelines for use in MRI environments

• All MRI staff and other personnel who may enter the MRI environment are provided with formal training at regular intervals on MRI safety, including:
  • Discussion of objects that can and cannot be allowed into the MRI environment³
  • The importance of effective screening
  • A reminder that the magnetic field is always ‘on’¹

1. Shellock FG. Reference Manual for Magnetic Resonance Safety, Implants, and Devices. Biomedical Research Publishing Group; 2020. Accessed August 7, 2020. http://www.mrisafetybook.com/
2. ACR Committee on MR Safety. ACR manual on MR safety. Published online 2020. Accessed August 7, 2020. https://www.acr.org/-/media/ACR/Files/Radiology-Safety/MR-Safety/Manual-on-MR-Safety.pdf
3. Barkovich EJ, Jernstedt Barkovich M, Hess C. Ferromagnetic sand: A possible MRI hazard. Neuroradiol J. 2018;31(6):614-616. doi:10.1177/1971400918795865