Using common sense can prevent a lot of safety incidents around magnetic resonance imaging (MRI) technology, but part of the problem posed by exercising that simple precaution is that the invisible power produced by the device cannot be seen, heard, or felt—that is, unless an error has already been made.
Not understanding the function and concept of an MRI unit immediately intensifies its risks. OEM and facilities’ obligatory safety education should constitute only a portion of the learning and behavior training of service engineers, technologists, facility maintenance crews, emergency response personnel, and even patients. Even though OEM safety videos are useful education tools, and the department area is protected via badge-only accessibility and individual screenings from technologists, part of biomedical/clinical engineering’s responsibility is to proffer their own knowledge and safety practices in order to prevent their own or others’ slip-ups.
|Working around an MRI requires extreme caution. The pull of the magnet can transform a metal object into a projectile, often with dangerous consequences. Photo Courtesy of Moriel NessAiver, PhD, www.simplyphysics.com|
The invisible power produced by the device extends beyond its own structure into the MR suite, itself a containing chamber. Passing a strong electric current through coils creates a magnetic field, which is contained in supercooling liquid helium that is then encased in a container called a cryostat. This, together with the coldhead (used to recondense helium vapor back into main magnet system), present safety concerns from varying fronts, including the highly technology-related magnetic field and cryogenics to more general clinical engineering maintenance concerns over voltage, radio frequencies (RF), and lifting. Contrary to appearance, a ramped, superconducting magnet is always “on” and requires no outside power to keep the field sustained. Exposure to the field itself is generally safe in the absence of ferromagnetic implants, monitoring devices, or other peripheral tools or possessions.
During a patient scan, hydrogen molecules in our bodies’ tissues subtly respond to the field by aligning to the magnetic field that then provides detailed imagery, which can sometimes involve injecting the patient with a contrast serum. Most MRI service engineers do not directly deal with the contrast injectors involved in the patient procedures, “which have few service issues,” says Christopher Jones, biomed CT specialist, MCP, at Johns Hopkins Bayview Medical Center in Baltimore, who oversees the imaging services division. In many facilities, the manufacturer continues to maintain the contrast injectors.
MRI units are unique from a biomed’s perspective. “The devices don’t experience a lot of mechanical wear and tear like older CTs, for example, due to the lack of moving parts,” says Ray McClellan, owner of MRI Technical Services Inc, Marietta, Ga. “The toughest challenge continues to be, even with the improved technology of each generation, isolating causes of image-quality problems. Unlike digital equipment, the engineer can’t always simply run a diagnostic test to know what’s wrong; RF involvement and how the patient is coupled to the coil, even lying a certain way, can be the cause of image problems.”
Service engineers cannot run a self-test on themselves as easily as they comparatively are able to with an ultrasound unit in an attempt to eliminate such potential variables, making diagnostics only the start of the challenges faced.
When it comes to working around the attractive force—or pull—of the magnet, Grant Smith, CRES, assistant director of imaging engineering and diagnostic support at Duke University Health System, Durham, NC, says, “Not much trial and error is allowed in this kind of environment.” Bill Dale, imaging engineer at Duke, concurs.
Safety surrounding the single facet of the forceful magnetism can be threefold—the force of the pull, the correcting torque, and the potential side effect of dizziness.
The pull of the magnet increases exponentially as an item moves toward the bore, or opening. At a farther distance, the tug on an overlooked item being carried or worn, such as a watch, may be felt. Moving even a foot closer to the magnet can transform the item into a projectile, often with dangerous consequences. According to McClellan, the force to attract the ferromagnetic object can be up to 150 times its weight, depending on size, location relative to the field, and mass distribution.
Items positioned sideways to the magnetic field can also experience projectile torque, which tries to snap the ferromagnetic item back around in line to the generated field. McClellan advises that this is a greater concern with patients who have implants, which can cause injury by being heated or rotated inside them.
Small items are not harmful to the magnet, yet any ferromagnetic metal within the field can affect image quality during scans. Radiology service specialists must always recover latent screws, staples, or paper clips from the machine, according to Jones.
Items of larger mass, such as oxygen tanks, beds, gurneys, tools, office or wheelchairs, and even floor buffers, can injure anyone in between the object and the unit. These situations have unfortunately made headlines in the past and have often been demonstrated in controlled safety videos.
During installation, ferromagnetic tools and equipment could be in use, but would need to be removed from the area prior to ramping up the magnet. Engineers are issued nonmagnetic tools for servicing, usually titanium for any 3 Tesla (T) magnets, or brass for 1.5T (impermissible with a 3T), according to Dale. He adds that service engineers should periodically check that a rogue item has not mistakenly been incorporated into the tool kit.
Necessary tools for a routine, biannual coldhead replacement include the use of a motor, which cannot get anywhere near the magnet, as well as the use of special rigging to perform the swap. Ladders and rigging kits needed to transport components or get to the top of a machine are available in fiberglass or nonmagnetic metals, such as aluminum, and can be sold or loaned locally or from the manufacturer.
With newer-model magnets, the snatching pull is restrained within a few feet of the bore, which is useful especially in the veterinary world, according to McClellan.
From a service standpoint, engineers need to always remember to empty pockets of change, lighters, and pens; remove rings, earrings, belt buckles, and glasses; and leave wallets, badges, cellular phones, pagers, and watches outside the suite. Anything having a magnetic strip, like credit cards and access badges, will be rendered ineffective. Biomedical engineers required to normally wear steel-toed shoes would need to change out of them around an MRI.
Failing to leave behind all items that the magnet might draw can cause injury or create additional, unnecessary, even highly costly service repair problems. If something gets stuck to the magnet, depending on the size, it can either be pulled out by hand or require the magnet be ramped down if its mass is too great to be pried off with the help of trained individuals. Biomeds working on MRI equipment must guard against expertise-bred complacency, as familiarity cannot prevent seasoned engineers from avoiding another magnetic safety concern.
Differentiating between two magnet models, Dale explain that the older 1.5T magnets will remain in use alongside the newer 3T models, which are known to reduce patient scan times by up to half an hour. The field from a 1.5T to a 3T design is increased exponentially. The overall pull of a 3T can be 30,000 times that of the Earth’s magnetic field and is limited by a bucking coil that can restrict the field’s reach down to 3 feet on the sides and 6 feet off the front and back of the bore.
For service technicians the increased gradient strength, higher RF and power, or stronger magnetic field of a 3T do not present drastically differing service challenges. However, the physical effect of greater magnetism requires cautioned movements to prevent dizzying side effects. Technicians should avoid swinging their head around, getting up too quickly, or doing any kind of quick, unbalancing motion of their head or inner ear.
A more service-exclusive safety concern revolves around the cryogenics. Superconducting magnet coils require a super cooling of the liquid helium to eliminate resistance in the wire. Anytime service requires opening the magnet’s cryogenic interior or venting, engineers must utilize safety gear to protect against possible cold burns inflicted by the hundreds to sometimes thousands (depending on the model) of liters of liquid being kept at about -270°C.
At a minimum, Jones recommends cryogen gloves, goggles, a face mask, a long-sleeved shirt, or a borrowed lab coat during handling.
According to McClellan, the components being handled are often small in mass and typically warm up in the air rather quickly, unless the handling involves the massive coldhead. During annual to biannual helium fills, not only must the recommended items be utilized in protecting the engineers’ bare skin from burns, but the potential for a quench during a coldhead service event involves added risks.
A quench is the quick heating of the supercooling liquid—which ramps down the magnetic field in just seconds—but consequently results in a rapid expansion of the liquid to gas at a ratio of 1:750 that may last a minute or so.
McClellan pragmatically depicts a scenario explaining that a superconducting magnet full of liquid helium a few degrees above absolute zero needs to be insulated by a nearly perfect vacuum and carries hundreds of amps of current running through a closed loop that it can sustain with no outside power for years, which creates a huge electromagnetic field; so a lot of energy is involved.
“Now, if anything disrupts that environment—if you were to lose vacuum, for example—all the energy goes into this liquid helium, which immediately boils off,” McClellan says. At service events involving coldheads or helium fills, “you’re more prone to quench the magnet; it’s not common but not unheard of, either, nor is it usually a dangerous thing—except when the venting doesn’t work,” he says.
A deliberate quench, with the press of an emergency button in the MRI suite, may be an appropriate response to an incident involving too large of an item stuck to the magnet or when a patient’s safety is compromised. Smith and Dale both stress that technicians need to know the location of the emergency shutdowns, which can vary slightly from system to system. The electrical shutdown is found on the wall and attached to the keyboarding for shutting off the gradients in response to issues involving patient safety. Magnet rundowns are right inside the cabinet door, which are for quenching the magnet down.
Even if power to the entire building goes out, the electromagnetic field can continue running for up to 3.5 years. In the event of an emergency, response personnel—especially firefighters, who would require advance notice of the department’s restrictions—must know that all previous safety procedures still apply unless a quench—intentional or not—has already occurred. A massive volume of gas created in a controlled, deliberate quench properly vents up and out through a facility’s rooftop. Damaged venting that cannot properly accommodate the amount of pressure created from the gaseous helium release has dangerous consequences in the event of a quench.
If the venting fails during a quench, extremely cold helium gas can rush into the suite, causing quick changes in pressure, or even displacing oxygen—placing anyone in the room at risk for asphyxiation. Oxygen readers in a room help detect any dangerous drop in oxygen levels—not that someone wouldn’t recognize a hard quench. According to McClellan, he likens the noise of a quench to that of a freight train.
Anyone in the room at the start of a quench, whether venting is compromised or not, should crouch low to the ground (where O2 levels would be slightly better had venting indeed failed) and immediately exit the suite; no one should be allowed to enter the suite during a quench.
To also avoid being trapped inside the room during such an event, suite doors should either be propped open during service events, unless installed to open outward. In some service events, such as common helium fills that situate an engineer on top of the machine or ladder, escaping cryogen splash or spray from a quench can burn an engineer and would require immediate medical attention.
If someone has gone unconscious in the suite, trained emergency safety personnel are to be summoned immediately. Another individual in the room or observing from the console during service can call emergency responders in the event of a safety incident. Even a “ramped down, deinstalled magnet going to recycling [or being moved] is not past the point of being a hazard,” McClellan warns. After a machine is deinstalled and in transit, ice can form and block the machine’s vents if left ajar and lead to structure breaks, even explosions, from the resulting pressure buildup. Manufacturers continue to update safety education concerning both in-room and machine contained venting safety precautions.
Smith cautions that amid these specialized safety concerns, service engineers cannot forget the most obvious safety basics. Ten thousand volts coupled with RF in MR technology introduce safety precautions, some for the service engineer and some for the patient. Equipment service manuals outline the proper use of personal protection equipment (PPE), such as PPE used to protect eyes against sparking, and basic safety FDA requirements. RF safety is not usually part of the engineer’s safety equation but it does affect patient safety during scans where peripherals need to be MR approved, affixed, buffered, and lain correctly to avoid skin burns.
The copper-shielded MR suite keeps outside RF noise out through the use of wave guides, which strategically permit physical shield “breaks,” such as for AC ductwork or nonconductive hoses, pipes or fiber-optics, without compromising the suite’s integrity. All maintenance personnel need to be aware of the integrity-maintaining profile of the suite’s branching design to avoid errors such as erroneously running a thermostat wire through a waveguide, which can ruin the integrity of the RF room and pose challenges for a service engineer needing to solve image quality problems, according to McClellan.
The second safety basic involves the system cabinet itself and the 220- to 300-pound weight-lifting functions that are more everyday functions than those involving the magnet itself. Proper rigging equipment and backup engineer assistance is necessary in hoisting heavy MR components out of the more than 7-foot-high cabinet in order to prevent potential physical injury and property damage. Typically, a purchased part can be accompanied by the use of rigging equipment that can be shipped or locally transported.
Other general precautions include using additional signage or other means of safely securing the area during a service event to prevent people who want to view the service process from wandering in. Although the department is a secured access area, even authorized personnel can casually make the mistake of wandering in unscreened under the assumption that the magnet has been powered down, which is a major concern, according to Jones. Even trained personnel may forget the obvious safety concerns of the seemingly banal environment.
Proper training represents another necessary precaution. According to McClellan, safety education can unwittingly get lost in the retelling when those first trained, usually the technologists, educate the next group, who educates the next, who educates the next. From a program standpoint, entrance-permitting safety screenings and periodic training seminars or demonstrations should maintain a keen awareness of the ever-present risks.
Understanding MRI technology is truly the foundation of practicing related safety. Once understood, precautions may seem like common sense, but in a situation that defies our senses, no one wants to or should have to learn from their mistakes.
Veronik Minassian is a contributing writer for 24×7. For more information, contact .
A Safety Checklist
Ineffectively screened patients create common service problems, resulting in small items like hairpins causing image artifacts. Having the technologist screen the patient with a hand magnet and by asking pertinent questions is highly critical, according to Bill Dale, imaging engineer at Duke University Health System, Durham, NC.
From the service perspective, and with any service task at hand regardless of modality, having a preliminary safety checklist can save time, trouble, headaches, even lives in the case of MRI. Depending on what Dale’s approaching, his core checklist includes making sure he:
- Has the right tools;
- Has the right equipment to transport this component;
- Is carrying everything needed to perform the service event;
- Reviews literature or manuals pertinent to the task, whether a replacement or removal; possibly carrying documentation to the service event;
- Is prepared to enter the environment by removing his watch, cell phone, and ID badge; emptying his pockets; remembering not to carry any ferromagnetic item having substantial mass into the suite, and being cognizant of any such item that is required; and understanding the force of attraction is proportional to the mass;
- Enters the environment using standard safety precautions, brings the proper PPE, and does not risk exposure; and
- Secures power by shutting off proper breakers, taking a system down if necessary.