First, let’s get the issue of non-ferromagnetic metals taken care of.

Metals that aren’t attracted to magnets are non-ferromagnetic. However, even if they aren’t attracted to the magnet, non-ferromagnetic metals do still interact with the magnetic field. They can cause local distortions which can mess up MRI scans (making it very difficult to image anatomy close to any metallic implant or object). Orthodontic braces may make certain facial / brain scans difficult. Orthopedic implants may disrupt the MR imaging of areas right around the pin / plate / screw / rod. Different materials will have different disruptive properties, so never assume that you can’t be imaged simply because you have an orthopedic implant. Check with a radiologist.

Also, MR imaging makes use of radio frequency (RF) energy. Like magnetism, RF is non-ionizing (doesn’t break down DNA and give rise to cancers as X-ray energies have been shown capable of), and like magnetism RF interacts with electrically conductive materials. If an electrically conductive element is the right shape and/or size, the material may inadvertently serve as an antenna for the RF signal and the energy may disproportionately collect in the conductor. As you may remember from high school physics, energy doesn’t just ‘go away,’ it converts. in the case of RF energy, it converts to heat. If you have the ‘ideal’ antenna length and/or configuration for a particular radio frequency, it can cause remarkable heating and that heat can cause damage.

But just as with the issue of image disruption, don’t assume that the presence of an electrical conductor inside your body is an automatic contraindication for an MRI exam. Consult your radiologist.

For these reasons, it is important to identify all electrically conductive materials on or in the patient. But even with these real risks associated with non-ferromagnetic materials, the greatest threat, both in terms of numbers of incidents and fatalities, is ferromagnetic materials.

Now, let’s move on to ferromagnetic materials. Some of this may seem familiar to you if you’ve read my prior post on MRI and Metal, but work with me here and you’ll find that we delve a little deeper into what happens that makes ferromagnetic materials such a concern.

When a ferromagnetic material enters a magnetic field, it becomes a magnet itself. A ferromagnetic material accepts an induced magnetic field. Many ferromagnetic materials give up the field almost as easily as they accept it, so they aren’t significantly magnetized. Think of them in the same way as I’m a baseball fan… when surrounded by baseball fans, I can pretend to be interested. Away from other baseball fans, I have almost zero interest in the game.

So, if a ferromagnetic material becomes a magnet when exposed to another magnet, we now have two magnets, and we all know what happens when we bring two magnets together… [SNAP]

Actually, when we bring two magnets together, two distinct things happen. The first is that the two magnets work to align themselves to one another. We know that two like magnetic fields (positive-to-positive) will repel each other, but opposite polarity fields will attract. The natural action is that the magnets will work to rotate themselves in order to align their fields positive-to-negative. Compass needles are the living illustration of this as we count on them to rotate to align with the North Pole.

In the case of a ferromagnetic object brought near an MRI, let’s compare our two magnets. One weighs perhaps 12 tons and is bolted to the floor, the other is a pair of scissors that weigh a few ounces. Which of these two things is going to rotate to align itself? Right, the scissors.

So the smaller ferromagnetic objects that we wear, carry, or have placed within our bodies, are going to be subject to intense forces that will be working to align the magnetic polarity of the object to the massive (in weight and strength) magnetic polarity of the MRI magnet. This results in torque forces that can twist, turn and even tear whatever may be trying to hold them in place.

The other mechanical force that develops between two magnets is the one we’re all very familiar with… attractive force. As we bring two magnets that have aligned themselves to one another (or, as it the case of sticking a magnet to your fridge door, the non-magnetized large ferromagnetic material develops a localized magnetic domain in order to receive the fridge-door magnet you’re sticking to it), they snap together, often with startling speed and strength.

We describe this phenomenon in MRI as the ‘missile effect’ because ferromagnetic objects, propelled by enormous amounts of magnetic energy, can launch across the room with tremendous force towards an MRI. While magnetic projectiles may look as though they’ve been launched from a cannon, unlike ‘launched’ projectiles, these magnetic missiles don’t lose their inertia just because they hit something. Their singular mission in life is to reach the strongest part of that magnetic field and, if interrupted in their flight, they will incessantly continue applying pressure to try and push their way towards the peak of the magnetic field (typically the center of the MRI).

The torque from rotating ferromagnetic materials and the force of flying ferromagnetic materials have each killed people in the MRI, and caused many injuries, and done horrific damage to MRI machines and their components. This presents two major problems…

First, metal is everywhere. It’s in our shoes. It’s in the shiny filaments in our clothes. Our belt-buckles. It’s in the stuff in our pockets. It’s often in thing that are labeled ‘sand bags’. It’s in stuffed animals and even often in hospital pillows. Metal is an unavoidable part of modern life.

Second, as I described in my prior post on metal and MRI, it’s impossible to visually distinguish between magnetic and non-magnetic metals. Even if we know something is made out of wood, for example, doesn’t mean that we can be confident that it isn’t held together with steel screws or reinforced with a steel rod. So, not only is metal ubiquitous, but ferromagnetic metals are perhaps the most widespread types of metal used in contemporary life.

Because of the torque and attraction risks of ferromagnetic materials, many tools and devices made for use in the MRI environment that require the strength and durability of metal use of aluminum, titanium, brass and other non-magnetic materials.

It is the intersection of these concerns – that all types of metal are everywhere and that we usually want to admit non-ferromagnetic metals into the MRI room – that generates the need for a detection system that distinguishes only ferromagnetic material.

The name of this blog is the MRI Metal Detector for precisely this reason… while I frequently digress and discuss many things relevant to MRI safety, at the heart this forum is about the specific risks associated with ferromagnetic metals and, equally importantly, the contemporary tools that can be effectively deployed to help reduce those risks.

To help protect patients, staff, and millions of dollars of MRI equipment, I recommend (as do the VA, the ACR and others) that every MRI provider avail themselves of ferromagnetic detection to help more effectively screen people and equipment intended to enter the MRI suite.

That’s right, a guy getting an MRI in Colorado had a nail, purportedly stuck in his nasal cavity for approximately 30 years, wriggled loose and he coughed it up shortly after the exam! Follow the link below to view the video (after a short, but annoying commercial):

News video on MRI’s and nails in noses!

Ferromagnetic detection systems have caught a variety of unusual and unsuspected magnetic objects before they entered the room with the giant MRI magnet, but at the time I write this, no ferromagnetic detection system has been approved for finding things internal to the body of a person… even nails.

Would it have been possible for a ferromagnetic detection instrument to find an inch-long nail at a distance of an inch or two, say buried inside a beef roast? Yes, but it would depend greatly on the instrument and the conditions in which it was operated.

I don’t recommend sticking ferromagnetic materials in orifices just to test the sensitivity of your detector (a friend of mine did this with a BB in his ear… took several days to get it out). If you have questions about your instrument, ask the manufacturer.

And whatever you do, don’t go putting nails (or anything else, for that matter) up your nose!

As far as the MRI machine is concerned, there are two different types of metal, ferromagnetic and non-ferromagnetic. You may remember back to high school chemistry and the periodic table of elements where many of us learned (and then promptly forgot) that Fe is the symbol for iron.

Fe - Iron from the Periodic Table

“Fe”, the symbol, is derived from ferrum, the Latin word for iron. Ferromagnetic does not mean that a metal contains iron, but rather that the material has magnetic properties as iron can.

Ferromagnetic metals are iron, cobalt and nickel. These raw ingredients are common in many, many things made from metal, including (likely) the steel grommets in your shoes, to the zipper in your pants, to components in your wristwatch. Another common area to find these metals is in batteries, such as those found in your hearing aid, cell phone and iPod. There are a few non-metal ferromagnetic materials, but these are not very common.

Alright, alright, already… enough chemistry. What does this mean?

When exposed to magnetic fields, ferromagnetic materials become magnets themselves. You can prove this yourself with a fridge-door magnet and a few paper clips. You’ll probably find that paper clips right out of the box aren’t capable of magnetically ‘sticking’ to one another. If you stick one to a chunky fridge-door magnet, however, that paper clip is now magnetized and will likely be able to magnetically ‘stick’ to another paper clip. The length of the magnetic chain of paper clips you can create is a function of how strong the fridge-door magnet is and the magnetic properties of the paper clip steel.

Now, the exact same thing happens with ferromagnetic metals approaching the MRI, but a crucial difference is the distance at which the materials get attracted. With your fridge-door magnet test, the paper clip needs to be touching (or very nearly so) the magnet before the attractive effects are felt. MRI’s, by virtue of the fact that they’re both 1,000′s of time stronger and larger than your fridge-door magnet, can exert profound attractive force at a good distance away from the magnet.

The size and strength of MRI magnets is so great that people have been trapped, injured, and even killed by the force of ferromagnetic objects attracted to the MRI. From concealed roller-skate tennis shoes, to steel-reinforced furniture, to conventional hospital wheelchairs and gurneys, to steel oxygen cylinders, all of these normally harmless (outside the MRI suite) items become life-threatening when subjected to the enormous pull of the MRI’s magnet.

Not all metals are ferromagnetic. In fact, in an MRI suite a concerted effort is usually made to rid the area of ferromagnetic materials and use non-ferromagnetic replacements whenever possible. Non-ferromagnetic metals include aluminum, titanium, brass, copper, and many others. These (and other) non-ferromagnetic metals can present other problems and hazards during MRI imaging, but that’s a topic for another day.

It is almost impossible to determine whether a material is ferromagnetic just by looking at it. In fact, even sometimes when you know what an object is made of, it still isn’t enough to know whether it’s ferromagnetic or not. Stainless steel, is one of these examples.

Stainless steel is not a metal, but rather a family of recipes for metal. Some stainless steel ‘recipes’ (alloys) call for ingredients with ferromagnetic properties. Others which include ferromagnetic ingredients are specially formulated to change the structure of magnetic materials into non-magnetic versions of the material. These special ‘de-magnetized’ stainless steels can become ferromagnetic if the steel is manipulated (shaped, bent, heated, or stressed), so even magnetically ‘safe’ stainless steels can become ‘unsafe’ under certain circumstances (a change that isn’t observable to the eye).

It is remarkably difficult to distinguish magnetically ‘safe’ metals from magnetically ‘unsafe’ metals, either by simply looking at them or, sometimes, even if you know what the metal is. As a result, MRI facilities must assume all metals to be magnetically unsafe unless and until they’ve been verified to be non-magnetic.

So, how do MRI facilities distinguish magnet-unsafe metals? They can use magnets, which shouldn’t be used on patients or sensitive equipment, limiting their applicability. The safer option (and arguably more effective, to boot) is to use a ferromagnetic detector, at least on patients and sensitive equipment.

Ferromagnetic detection instruments, such as the Mednovus products, should be used to help identify magnetically-unsafe materials. This is the standard established by the American College of Radiology, the VA’s MRI Design Guide, and even recommended by the Joint Commission in Sentinel Event Alert #38.

As a patient, it is vital to take seriously the admonitions against wearing or carrying metal into the MRI suite. If you have shrapnel, penetrating metal injuries (particularly in the eye), or any surgeries, implants or prosthetics, it’s critical to have the full information on each to share with your MRI provider. Metal inside the body may not fly across the MRI room like a loose oxygen cylinder (don’t believe what you see on House), but the twisting an pulling that the magnet will exert on an internal ferromagnetic object can be just as dangerous. Active implanted devices, such as pacemakers or nerve stimulators, present particular problems because of both the magnetic attraction and potential interference with the normal function of the device.

Patients should also actively seek out MRI providers that conform with the contemporary safety recommendations, including the use of ferromagnetic detection. You can even contact Mednovus when you want to find providers near you who have this technology available.

Providers of MRI services should make sure that the pre-screening and safety services they provide are in accord with the contemporary best practices, including the use of ferromagnetic detection. With available ferromagnetic detection products equal in cost to only a few hours worth of technical revenue, there’s no financial rationale for not providing this valuable safety benefit to patients and staff. Plus, when weighed against the costs of ferromagnetic object accidents, these instruments of safety are clearly effective risk-management investments.

In all cases, metal brought to the MRI suite (either inside or outside the body of the visitor) should be scrutinized by a trained MRI staff person. This investigation should be aided through the use of ferromagnetic detectors, both to help characterize the hazards of any particular object and to help find ferromagnetic materials that weren’t caught in the prior screening process.