Frank G. Shellock, Ph.D.

Adjunct Clinical Professor of Radiology

University of Southern California, Los Angeles, CA

Founder, Institute for Magnetic Resonance
Safety, Education, and Research (

President, Magnetic Resonance Safety Testing Services

Los Angeles, CA

Article excerpted from with permission of Frank G. Shellock, Ph.D.


To guard against accidents, injuries, or damage to magnetic resonance (MR) systems, the general and immediate areas associated with the scanner (also referred to as the MR environment) must have supervised and controlled access. Supervised and controlled access involves having MR safety-trained personnel present at all times during the operation of the MR facility to ensure that no unaccompanied or unauthorized individuals are allowed to enter the MR environment.  In addition, the MR safety-trained personnel are responsible for performing comprehensive screening of patients and other individuals before allowing them to enter the MR system room.


Additionally, it is necessary to educate everyone who needs to enter the MR environment on a regular or intermittent basis (e.g., custodial workers, transporters, security personnel, firefighters, nurses, anesthesiologists, etc.) regarding the potential hazards related to the powerful magnetic field of the MR system. Unfortunately, even with proper MR safety procedures in place, many individuals and patients have inadvertently “wandered” unattended into the MR environment, and these situations have resulted in disastrous consequences.


As one means of helping to control access to the MR environment, the area must be clearly demarcated and labeled with prominently displayed signs to make all individuals and patients aware of the risks associated with the MR system. The content of these signs is particularly important. However, the information shown on most signs currently in use is out-of-date, erroneous, or not displayed in a prominent enough manner. Therefore, new signs with revised content and new information were designed recently to promote a safe MR environment. This article discusses the current “warning” signs, explains the need and rationale for new signs, presents the content of the new signs, and provides recommendations for the placement of these signs in order to help prevent incidents and accidents in MR facilities.

The Old “Warning” Sign
The sign that is utilized at most MR centers in the United States has information that states, the following:








Obviously, given the present state of knowledge pertaining to MR safety, much of this information is outdated or simply incorrect. In fact, according to the Food and Drug Administration document entitled, Guidance for the Submission Of Premarket Notifications for Magnetic Resonance Diagnostic Devices (issued November 14, 1998), Attachment B, states: “The controlled access area should be labeled "Danger - High Magnetic Field" at all entries.” Also, this FDA document indicates:

“Operators should be warned by appropriate signs about the presence of magnetic fields and their force and torque on magnetic materials, and that loose ferrous objects should be excluded. “


The New “Danger” Sign
Therefore, in consideration of the above, the old “warning” sign was recently revised and updated to include the guidance from the FDA as well as the most current findings for MR safety, especially with regard to implanted objects. For example, because the term “warning” does not convey the importance of a situation that may not only be potentially hazardous, but has been responsible for serious injuries and deaths, the newly revised sign now states (Figure 1A):



Additionally, to inform everyone about the powerful magnetic field associated with the MR system, especially individuals unacquainted with MR technology, the following information is prominently shown on this new sign:





With respect to the information for implants and devices, in addition to cardiac pacemakers, implantable cardioverter defibrillators (or ICDs) are also potentially hazardous for patients and individuals in the MR environment.  Therefore, this information is included on the new sign. Also, because recently published reports have indicated that certain neurostimulation systems are safe for patients undergoing MR procedures if highly specific guidelines are followed (Rezai et al. 2002; Finelli et al. 2002), the statement regarding neurostimulation systems was deleted to avoid undue confusion.


Notably, recent articles in the peer-reviewed literature have reported that many types of metallic implants are actually safe for patients undergoing MR procedures. Comprehensive information for over 1,100 implants, devices, and other objects is readily available to all MR healthcare professionals in a recently published textbook (Shellock, 2003) and on-line at, including information for more than 150 implants and devices tested at 3-Tesla. Accordingly, this information is now clarified on the revised sign. Furthermore, individuals and patients are informed to consult MRI professionals if there are any questions regarding this matter, as follows:


Persons with certain metallic, electronic, magnetic, or mechanically-activated implants, devices, or objects may not enter this area. Serious injury may result.


Do not enter this area if you have any question regarding an implant, device, or object.  Consult the MRI Technologist or Radiologist.

Finally, the statement, “NO LOOSE OBJECTS” on the current “warning” sign is rather simplistic and does not address other aspects of concern with respect to bringing potentially problematic items into the MR environment. Accordingly, the new sign states:

Objects made from ferrous materials must not be taken into this area. Serious injury or property damage may result.  Electronic objects such as hearing aids, cell phones, and beepers may also be damaged.


Thus, this new sign is more prominent, the term “danger” rather that “warning” is used (which, hopefully, will make individuals and patients readily take notice), and the overall content is more accurate with respect to current MR safety information. A Spanish language version of this sign has also been created*.


Additional New Signs
Two other “danger” signs were created to help control access to the MR environment (Figures 2 and 3). One sign states:




This Magnet is Always On!



The intent of this sign is to prevent the inadvertent entry of individuals and patients into the MR environment.

Interestingly, many individuals fail to realize that the MR system’s static magnetic field is always on. In fact, investigations of various accidents that involved relatively large ferromagnetic objects like oxygen cylinders, chairs, IV poles, and wheelchairs revealed that the offending hospital personnel thought that the powerful magnetic field was activated only during the MR procedure. Therefore, a new sign (Figure 3A) was created that indicates:



Sign Placement

The strategic placement of signs in and around the MR environment is crucial to ensure that all individuals and patients see them before entering this area. In general, the new sign shown in Figure 1 should optimally be placed on the door or entrance to the MR system. The sign in Figure 2 should be placed doors that serve as exterior entrances to the MR environment. The sign that states: DANGER! THIS MAGNET IS ALWAYS ON! should be placed near the doorframe so that it can be viewed by individuals and patients, especially if the door to the MR system room is open (Figure 3B).

[*To obtain the new signs designed to help control access to the MR environment, please visit or contact Frank G. Shellock, Ph.D. at the Institute for Magnetic Resonance Safety, Education, and Research,]


Finelli DA, Rezai AR, Ruggieri P, Tkach J, Nyenhuis J, Hridlicka G, Sharan A, Gonzalez-Martinez J, Stypulkowski PH, Shellock FG. MR-related heating of deep brain stimulation electrodes: an in vitro study of clinical imaging sequences. American Journal of Neuroradiology 2002;23:1795-1802.


Rezai AR, Finelli D, Nyenhuis JA, Hrdlick G, Tkach J, Ruggieri P, Stypulkowski PH, Sharan A, Shellock FG. Neurostimulator for deep brain stimulation: Ex vivo evaluation of MRI-related heating at 1.5-Tesla. Journal of Magnetic Resonance Imaging 2002;15:241-250.

Shellock FG. MR safety update 2002: Implants and devices. Journal of Magnetic Resonance Imaging 2002;16:485-496.

Shellock FG. Biomedical implants and devices: assessment of magnetic field interactions with a 3.0-Tesla MR system. Journal of Magnetic Resonance Imaging 2002;16:721-732.


Shellock FG, Tkach JA, Ruggieri P, Masaryk T, Rasmussen P. Aneurysm clips: evaluation of magnetic field interactions using  "long-bore" and "short-bore" 3.0-Tesla MR systems. American Journal of Neuroradiology (in press).

Shellock FG, Tkach JA, Ruggieri PM, Masaryk TJ. Cardiac pacemakers, ICDs, and loop recorder: Evaluation of translational attraction using conventional ("long-bore") and "short-bore" 1.5- and 3.0-Tesla MR systems. Journal of Cardiovascular Magnetic Resonance (in press)

Shellock FG. Reference Manual For Magnetic Resonance Safety: 2003 Edition, Amirsys, Inc., Salt Lake City, UT ( and

U. S.  Department Of Health and Human Services, Center for Devices and Radiological Health Food and Drug Administration, the document entitled, Guidance for the, Submission Of Premarket Notifications for Magnetic Resonance Diagnostic Devices, Issued November 14, 1998.




Figure 1. New sign (enlarged to show detail) designed to help control access to the MR environment. This sign should be placed on the door to the MR system room.


Figure 1 A. Top part of sign.





Figure 1B. Bottom part of the new sign.








Figure 2. New sign designed to help control access to the MR environment. This sign should be placed at the entrances to the MR environment.



Figure 3A. New sign designed to help control access to the MR environment.






Figure 3B. This sign should be placed near the doorframe so that it can be viewed by individuals and patients, especially if the door to the MR system room is open.