I am writing to describe an incident we experienced at Connecticut Children’s Medical Center that has implications for MRI safety. Following inhalation induction inside the MRI scanner room of a 12-year old patient, I heard a few bangs that sounded like objects being sucked into the magnet. Upon closer inspection, I observed several ball bearings lying on the ground and others that had apparently rolled across the floor and were pulled up the side of the magnet. We evacuated the patient and woke her up uneventfully. We use a Dräger Fabius MRI compatible anesthesia machine which is located approximately 5–10 feet from the entrance of the 1.5T magnet. This machine is equipped with several drawers and a shelf all of which have slides and encased ball bearings. Dräger Medical and Siemens Medical have both been informed of the incident.
Michael Archambault, MD
Connecticut Children’s Medical Center
Dräger would like to thank the Anesthesia Patient Safety Foundation (APSF) for the opportunity to respond to the above submission.
The authors describe a situation where, after induction, the clinician heard a few bangs that sounded like objects being sucked into the magnet. The clinician looked to the ground and saw ball bearings lying on the ground. Upon inspection, one ball bearing was found attached to the MRI magnet. No patient injury was reported.
The clinician reported that the source of the ball bearings was believed to have come from one of the drawers, which utilizes ferromagnetic ball bearings. The facility wanted to continue using the device so all the drawers, the writing tray, and all the slides were removed from the machine as a precaution. The machine passed all self-tests, and the hospital personnel performed additional testing between Fabius MRI and MRI machine successfully.
The Fabius MRI anesthesia machine has been tested with magnets with field strengths of 1.5 tesla and 3 tesla by a fringe field strength of 40 mtesta (400 gauss). Use of the machine at higher strengths could result in ventilator and device malfunction. Additionally, unmanageable attractive forces could lead to serious injury.
Figure 1: Warning from Fabius MRI Instructions For Use (IFU).
Prior to outlining Dräger’s findings during the investigation, it is important to clarify that contrary to the Fabius MRI being reported as “MRI Safe” during this submission, the Fabius MRI is instead “MRI Conditional” (please see warning from the Fabius MRI IFU) in Figure 1. This clarification is important in that the Fabius MRI is cleared from use “with magnets with field strengths of 1.5 tesla and 3 tesla by a fringe field strength of 40 mtesla (400 gauss). The use of the machine at higher strengths could result in ventilator and device malfunction. Additionally, unmanageable attractive forces could lead to serious injury.“
To provide further clarity:
- MR Safe—the device, when used in the MRI environment, has been demonstrated to present no additional risk to the patient or other individual, but may affect the quality of the diagnostic information. The MRI conditions in which the device was tested should be specified in conjunction with the term MR safe since a device which is safe under one set of conditions may not be found to be so under more extreme MRI conditions.
- MR Conditional—An item that has been demonstrated to pose no known hazards in a specified MR environment with specified conditions of use. Field conditions that define the specified MR environment include field strength, spatial gradient, dB/dt (time rate of change of the magnetic field), radio frequency (RF) fields, and specific absorption rate (SAR).
In this case, upon inspection of the Fabius MRI, the Dräger Service technician found that the writing tray of the Fabius MRI was damaged, and this damage led to the ball bearings in the writing tray slide being “dislodged” from the Fabius MRI machine (Figure 2).
Dräger completed further investigations on the ball bearings in question and found that, even when outside of the anesthesia machine, the ball bearings are not attracted to the magnet when kept outside of the 400 gauss line. This is consistent with the findings reported by the clinician, which said that ball bearings remained loose on the floor (beyond the 400 gauss line). These findings lead Dräger to believe that upon the ball bearings being dislodged from the Fabius MRI, at least one ball bearing infringed on the 400 gauss line, leading to the ball bearing being attracted to the magnet.
Dräger has no explanation on how the writing tray slides were damaged, which is a requirement for the ball bearings to become dislodged from the anesthesia device. The slides are approved for 25kg, and the writing tray is labelled with a “max. 10 kg” load. Additionally, the writing tray passed a load test “four times” the labelled load. Finally, since the Fabius MRI was introduced 10 years ago, this is the only reported destruction of the writing tray slides.
In summary, Dräger would like to thank the authors for sharing this unique scenario to the anesthesia community. It underscores the importance of understanding the risk associated with utilizing equipment inside an MRI environment, and the difference between an “MRI Safe” and “MRI Conditional” device.
Director of Marketing, Dräger, North America
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