Metal jewelry should be removed because the strong magnetic field of an MRI can cause rearrangement, attraction, and heating. Research is underway to use alternative materials such as LCP to avoid this.
We’ve all seen the sign on the radiology department door that says, “Please remove earrings, necklaces, watches, and other metal items that interfere with the image before entering the MRI suite.” But why do we need to remove these items? To understand why, let’s first look at what an MRI is, how it works, and how the presence of metallic objects during an MRI is dangerous in relation to magnetic fields.
Magnetic resonance imaging (MRI) refers to a high-tech medical device that uses a powerful magnetic field to obtain cross-sectional images of the body, or the images produced by the machine. In this article, we’ll use the former term. Here’s how MRI works The atomic nuclei in the body”s tissues normally rotate, but in the strong magnetic field of the MRI machine, they spin. When a high frequency is applied, the nuclei are put into a high-energy state, and when the high frequency is removed, they return to their original state and release energy, which is collected by an antenna and imaged by a computer.
So why shouldn’t you wear metal jewelry during an MRI? There are three main reasons.
The first reason is the rearrangement of metallic materials due to the strong magnetic field. The strong magnetic field of an MRI causes metallic materials to reorient themselves in the same direction as the magnetic field. It’s not just metal jewelry, but metal objects installed inside the body that can tear the surrounding body tissue. In fact, a patient with a metal aneurysm clip inside the brain has been known to tear brain tissue during an MRI.
The second reason is ‘attraction by strong magnetic fields’. The strong magnetic field of an MRI affects not only the inside of the machine but also its surroundings. If you bring a metal object near the MRI, the magnetic field will suck it in like a bullet. There have been accidents where pistols, scissors, and patient beds have been sucked into the machine, and in one case, an oxygen tank brought by a doctor was sucked toward a boy in the MRI and hit him in the head. In addition, the magnetic field of an MRI does not disappear when the electricity is turned off. This is because the magnetic field is generated by the liquid helium inside the MRI. The liquid helium must be removed in order to dislodge the material stuck to the MRI machine, which takes a lot of time.
The third reason is “heating due to stray currents”. Eddy currents are swirling currents that occur in a conductor when it is placed in a changing magnetic field. The magnetic field generated by MRI causes stray currents to flow through the metal materials in the machine, and heat is generated by the resistance of the metal materials. Metal jewelry, as well as iron oxide ink tattoos and some nicotine patches, contain metals, and there is a risk of burns from the heat during an MRI.
As you can see, the presence of metallic materials in MRIs poses many risks. These risks become even more problematic in situations where urgent medical attention is required. For example, if you’re in a serious car accident and need to get a quick MRI of what’s going on inside the injured area, if you have a pacemaker or iron core in your body, you’ll need to remove it first, which will delay treatment.
So how can we reduce the risks of MRI? One existing option is to use a material called LCP (Liquid Crystal Polymer). By replacing the metal inside the body with LCP, there are fewer stray currents, which can reduce heating. Also, unlike metal, LCP does not rearrange itself and is not attracted by magnetic fields, which can greatly reduce the risk. Research is also underway to use polyaniline, an electrically conductive plastic, which, if commercialized, could revolutionize MRI risk reduction by replacing all bioelectronic systems, such as pacemakers, with this material.
