Ferromagnetic Detector Utility and Magnetic Resonance (MR) Safety: MedSun Small Sample Survey Summary
MedSun: Newsletter #71, April 2012
Survey Topic: Ferromagnetic Detector Utility and Magnetic Resonance (MR) Safety - Summary of Responses
Year Conducted: 2011-2012
The number of Magnetic Resonance Imaging (MRI) procedures is rising. At the same time, the sophistication of implanted and accessory medical devices used in the MR environment is increasing. While Magnetic Resonance Imaging (MRI) is a safe imaging procedure, there are contributing safety hazards inherent to the MR environment. Magnetic attractive forces to the strong MRI magnet can cause objects to become projectiles. Although rare, when these events occur, they often cause serious injury or death. Projectile events have been reported to FDA as well as identified in medical literature and in the media. Most projectile incidents may be attributed to site-access issues where staff brought in ferrous devices or products, or screening methods that did not reveal metal that was present on the patients, i.e. jewelry, belts, etc. All solutions to overcoming risky projectile events must be considered to ensure the safety of patients, accompanying family members, healthcare providers and other personnel who routinely enter the MR suite.
Actions to reduce this hazard include conventional patient screening practices, site-access restrictions and markings, and facility-wide education. Additional actions to reduce these events may include broader use of Ferromagnetic Detectors (FD) to identify ferromagnetic objects not discovered by conventional screening methods or to guard the scan room entryway. However, wide-spread adoption of FD has been controversial. Opponents claim that FD provide a false sense of security or could potentially replace thorough screening practices (ACR Guidance Document for Safe MR Practices: 2007). The risks and benefits of FD systems needs to be assessed to better gauge their utility.
Special Study Purpose
This Special Study is a survey effort to learn about user facilities’ MR safety practices, particularly why and how the facility employs FD - archway or hand-held - in their MRI department and the role of FDs in screening practices. Survey questions aim to gather information about the FD system and the providers’ experiences with them, their FD Quality Control practices, and to learn about any projectile events sites encountered while using FDs, or ones that were prevented. The information that follows is a summary of responses. Seven* structured telephone surveys were conducted with healthcare professionals from hospitals participating in the Medical Product Safety Network (MedSun). Survey respondents include: Medical Physicists, Chief Technologists, MRI Coordinators and Supervisors, Imaging Directors and Managers, Biomedical and Clinical Engineers.
All survey respondents are affiliated with the MRI department in their hospital. Six facilities also have outpatient centers that perform MRI procedures. The number of scanners each facility uses ranges from 2 to 13 magnets. There is a direct association between the number of magnets and the number of patients scanned per day, which can be anywhere from 13 to 125 patients. The respondents specify their magnet strengths are either 1.5 or 3.0 Tesla. Pole-style, archway and handheld FD systems are used by survey respondents. For the most part, archway and pole-style systems are primarily used to screen staff; whereas handheld detection is primarily used to screen patients in addition to other screening methods.
Below is the breakdown of FD systems used by all respondent facilities (n=7):
• Only handheld system (2)
• Archway system (1)
• Archway and Handheld systems (2)
• Pole-style, Archway and handheld systems (1)
• Neither+ (1)
Of the hospitals that employ archway or pole-style FDs, respondents indicate they rely on the vendor to install and set sensitivity, which is set high, as even eyeglass screws can set off alerts. One facility indicates MRI staff had a training session with the FD vendor and, at this site the Lead Technologist performs routine adjustments to their archway system. Other respondents indicate that, for the most part, no formal training is provided by the vendor and they do not adjust sensitivity. Two facilities chose to reduce the archway’s sensitivity because staff routinely pass by the FD (they do not enter through) with medical equipment containing metal, which frequently set off alerts. Archway and pole-style detectors always remain on as these provide auditory and visual alerts when ferrous objects are nearby. However, one facility elected to turn off the system’s auditory alerts and only relies on visual alerts because FD alerts are common. Existing suite architecture is a problem for respondents who purchased archway FDs. MR suite design contributes to false FD alerts, mainly due to metal door hinges and knobs that set them off. In fact, to solve this problem one facility attempted to redesign Zones^ 3 and 4 to decrease false positives.
Of the five sites that employ handhelds, three have no formal training on how to use them; one respondent indicates that new employee orientation includes detector training and another reports that their facility receives informal training from their local police department on how to ‘wand’ patients using a handheld detector. Respondents who use handheld detectors indicate they are off when not in use and that batteries are checked at least two times per day. Handheld detectors are used in interview rooms at Zone 2 or 3, mainly by the MR Technologists. One respondent indicates that handheld detectors can be invasive when used to screen a patient and that they are in the process of better understanding their sensitivity relative to the distance from a patient.
Respondents indicate that handheld systems are an adjunct to their patient screening practices. Typically, they are used as a secondary or tertiary method, after the screening questionnaire or after the FD has alerted staff to the presence of metal, i.e.: cell phones and pagers, lighters, shirt buttons, underwire bras, jewelry such as belly button rings, hair pins, glasses, metal on shoes, keys, paperclips, scissors, and pens. One facility requires that all employees screen themselves with handhelds and anyone else entering the area; this site also requires escorts depending on the hospital employee entering the MRI suite who may not have formal access or training. Three respondents indicate that staff, in addition to patients, must complete a screening questionnaire prior to entering the MR suite.
Most respondents still use paper-based questionnaire forms. Some sites use a combination of paper and electronic formats. For example, paper is used to gather information from patients initially; electronic methods are used for information storage and retrieval. Questionnaires are typically completed prior to scheduling and again prior to the scan. Respondents indicate that patients may be screened 3 times at the most: once by the physician when a scan is first ordered, then by phone, and a third time onsite. The individual that completes the questionnaire depends on inpatient versus outpatient status. For inpatients, it may be the ordering physician and the ‘competent’ patient; for outpatients, the scheduler completes the form preliminarily, followed by a more detailed questionnaire filled out by the MR Technologist when a patient arrives for the scan. If a patient is unable to answer questions, respondents say they use other sources, notably the referring physician or family members that may be able to answer questions to confirm whether a patient is a candidate for an MR scan. X-ray or CT may also be done to rule out presence of other devices or metal. Patients, family members, referring physicians, and hospital support staff may all play a role to assist in gathering patient information, but all respondents indicate it is the MR Technologist that reviews and verifies the information provided in the questionnaire. One respondent states that they have received negative feedback from referring physicians about the screening questionnaire forms because they are time consuming; however, they still require the physician to complete them. Another respondent indicates they do not allow the patient to fill out their form – it can only be completed by an MR Technologist. Five respondents indicate that all patients are gowned prior to an MRI scan. Two respondents add that finding gowns without metal snaps is challenging.
Staff MR Safety training is required, typically on an annual basis or may be included in general hospital orientation for all employees. Some respondents’ hospital policy requires specific MR Safety training for anyone who has access to the MRI suite in addition to imaging personnel, such as, specific nursing unit staff that take care of patients receiving MR procedures. Other respondents’ facilities require specific MR safety training for all staff with access to Zones 2 or 3. As a result of a recent projectile incident, one respondent has expanded their MR Safety Training beyond radiology to include critical care/ICU employees, respiratory therapy nurses, surgeons and surgical staff. Housekeeping staff also are included in annual MR Safety training, with the exception of one respondent who shared that they use a specialty MRI cleaning company due to housekeeping staff turnover. For the most part, respondents indicate that the MRI suite has site access controls to preserve patient and provider safety. Two facilities require a keycard or badge access to gain entry.
At some points in survey respondents’ careers, they indicate experiencing a projectile event with one of the following items: floor buffers, stethoscopes, tools, wheelchairs, oxygen tanks, or ventilators. One respondent indicates there have been many close calls but staff caught them in time. At one facility, there is an equipment check that occurs at Zone 2 as this is the transition zone where equipment on a patient is exchanged for MR Safe or MR Conditional equipment before entry to Zones 3 or 4. Other facilities have invested in MR Safe or MR Conditional equipment, i.e. wheelchairs, stretchers, IV pumps and poles, anesthesia machines, which remain in MR suite at all times. However, even MR Safe or MR Conditional equipment has set off the FD alerts - respondents note that some cart wheel bearings are problematic because they contain metal.
Equipment may also be marked with stickers to indicate MR Safe or MR Conditional. Facilities often will create a device listing referencing MR safety designations, notably for implants. Often times, this information is obtained from the device manufacturer, from product catalogues, or online. One facility requires that the Biomedical Engineer and Physicist also test for safety because there is concern that some devices may become magnetized over time, which impacts their safety status. One site purchased oxygen tanks and fire extinguishers that are safe for use in the MR environment for use hospital-wide, not just in or near the MR suite. Another facility maintains what they term to be an MRI safe housekeeping closet.
Overall, respondents indicate that FD systems – archway, pole-style and handheld – are effective in preventing harm, yet want to emphasize they are only as good as the people who use them and policies in place. Respondents express the need for more information about FD sensitivity limits. There is concern that FDs provide a false sense of security and concern that staff may become habituated to regular FD alerts.
Respondents feel that current guidelines are open for interpretation and, consequently, want better defined recommendations about how FDs should be set up in MR suites because, in their opinion, FDs are best utilized when they are installed as a part of the architectural plan rather than as add on equipment. One facility that only uses handhelds feels that by using a thorough questionnaire-based screening process combined with handheld detection gives the provider more control and is a cost-efficient practice. The majority of respondents indicate that archway and pole-style FDs are expensive but can be worth the cost when best utilized. Regardless of FD utilization, all responses represent the various safety measures employed by hospital facilities prior to an MR procedure.
*An eighth facility was contacted for this special study. They indicate they do not employ any FD (archway or hand-held) at this time. To come to this decision, they evaluated the use of FD and found they were not necessarily sensitive enough to detect all metal. Their concern is that they [FDs] would give staff a false sense of security and, instead of an FD, elected to rely on diligent screening processes on multiple levels.
+One facility is in the process of purchasing an archway or pole-style FD system in response to a costly projectile event. This respondent feels strongly that the high investment for an FD detector outweighs the associated costs after a projectile event. Costs incurred include MRI scanner repair, unquenching the magnet in addition to lost revenue when a scanner is down.
^Zones are described in ACR Guidance Document for Safe MR Practices: 2007.
Special Studies and Surveys are two of many tools the Agency is using to evaluate the public health impact of the potential problems associated with the use of medical devices. Additionally, FDA continues to receive adverse event reports from its Medical Device Reporting program. FDA will also continue to make use of the literature and other published information. FDA scientific, medical, nursing and engineering staff are made aware of the survey results as needed. If FDA believes there is a significant risk of adverse events as noted from the survey, it will combine those results with data gained from the other sources. FDA will work with the manufacturers and health care professional organizations to make important information known to the clinical community. Additionally, FDA continues to work with manufacturers to ensure the development, testing and promulgation of methods for reducing the risk associated with these devices and to minimize the complications from adverse events that may occur in the course of normal usage. If the results of any survey raise serious concerns about the safety of these devices, FDA may convene an Ad Hoc group of clinical and manufacturing representatives to discuss further actions.
Kanal E, Barkovich AJ, Bell C, et al. ACR guidance document for safe MR practices: 2007. AJR Am Roentgenol. 2007;188:1447-1474. Retrieved from:
Public Workshop: Magnetic Resonance Imaging Safety. October 25-26, 2011. FDA Workshops and Conferences.