Hazard [Health Devices Jul 1998;27(7):266-7]

Problem

A member hospital reported that a sandbag containing ferromagnetic pellets was inadvertently brought into the magnetic field of a 1.5-tesla magnetic resonance imaging (MRI) unit. The sandbag, which had been placed in the vicinity of a patient's groin for site compression and the control of bleeding, had been obscured from the MRI staff's view by a blanket. As the patient was brought toward the MRI unit, the sandbag was violently pulled from its position and became pinned to the wall of the MRI tube. The patient received bruises to her chest and head. Although the MRI unit sustained no damage, two men were required to remove the sandbag from the bore of the magnet.

MRI units use strong magnetic fields and radio-frequency waves to image anatomic structures such as the brain and spine. The magnetic field generated by an MRI unit will attract ferromagnetic objects with considerable force. This attraction, usually referred to as the "missile effect," poses a significant risk to anyone in or near the unit who is in the path of one of these objects. ECRI is aware of several serious injuries caused by patients being struck, pinned, or lacerated by a ferromagnetic object pulled into the magnet. These objects include oxygen bottles, tools, chairs, ladders, patient lifts, traction weights, IV poles, laundry carts, pens, hair barrettes, and scissors.

In addition to possibly causing injuries, a ferromagnetic object pinned deep within a tight MRI bore may be hard to reach, and generating sufficient force for its removal may be difficult. Extensive downtime may also ensue: in an emergency, the magnet may need to be turned off quickly (i.e., quenched) to extract sizable ferromagnetic objects, putting the MRI system out of service for up to three days and entailing substantial financial loss. In the worst case, damage could require replacement of the magnet, a repair that could cost more than $500,000.

Careful screening of all objects and persons is crucial in ensuring the safety of the MRI area.

While sandbags are often assumed to contain only sand, some contain ferrous pellets or iron oxides that add weight to the sandbag without increasing its size. Several journal articles report cases of a sandbag containing ferrous pellets creating a hazard in an MRI environment. Reports include dislocation of, and other damage to, the magnet, as well as damage to the gantry, fan blower, and body coil antenna. And in an incident similar to the one reported by the hospital, the force needed to remove a 5 lb ferromagnetic sandbag (dimensions: 5 x 5 x 1½ in) was estimated at 500 to 700 lb.(1)

MRI staff must ensure that sandbags (as well as other objects used for patient positioning, patient immobilization, and site compression) are brought into an MRI environment only if they are MRI compatible—that is, nonmagnetizable. Sandbags should be assumed to be ferromagnetic and should be barred from entering the MRI area unless they are specifically labeled for MRI use. This restriction includes sandbags that may have come from other departments (e.g., physical therapy, cath lab). While some facilities have advocated testing sandbags with a magnet or a metal detector (e.g., a handheld sensor), ECRI does not believe that this is a reliable or cost-effective screening method.

If sites have existing sandbags not specifically labeled for the MRI environment and wish to keep using them, they should contact the sandbag supplier to verify that the component materials are MRI compatible. And if a variety of compatible and noncompatible sandbags are used throughout a facility, a marking system should be implemented to identify the ones that are compatible.

The above precautions should also extend to all other possibly ferromagnetic items, including wheelchairs, stretchers, and IV poles.

1. Purchase and use only sandbags that are known to be MRI compatible and that are so labeled.
2. If unsure of the content of a currently owned sandbag, do not allow it in the MRI environment until it is verified as nonferromagnetic. Do not bring it near the MRI unit to determine whether it is ferromagnetic.
3. Alert MRI staff of the need to check whether ferromagnetic sandbags have been brought into the area from other hospital departments (e.g., a site compression sandbag carried in on a patient from the cath lab). These sandbags could be obscured from view by a sheet or blanket.
4. Follow the typical precautions used in MRI environments:

• Alert users and other appropriate personnel to the risks posed by ferromagnetic materials.
• Ensure that the area immediately surrounding the MRI unit is placarded with the appropriate warnings.
• Ensure that trained staff members are responsible for physically securing the area.
• Carefully screen for ferromagnetic materials; this includes removing metallic objects belonging to patients and staff.

1. Chu WK, Sangster W. Potential impacts of MRI accidents. Radiol Technol 1986 Nov-Dec;58(2):139-41.

UMDNS Terms

• Sand Bags [13-439]
• Immobilizers [12-093]
• Magnetic Resonance Imaging (MRI) Units [16-260]
• Positioning Aids [16-223]

Device factor: Design/labeling error

User error: Incorrect clinical use

Support system failures: Poor prepurchase evaluation; Use of inappropriate devices

Mechanical