Originally Posted by
Ken Fitzgerald
Dan,
I installed and maintained 0.5 - 3.0 Tesla MRI scanners for 24 years. I have a little experience with them.
MRI scanners won't rip implants out of your body unless it was a large ferrous implant. Let's don't overstate the case and cause people unnecessary fear. You do need to be cautious, however.
The technologist who operate MR scanners actually have a reference book that states which and what type of implants can be scanned.
The most common magnetic field strength of MRI scanners is 1.5 Tesla or in another measure 15,000 gauss. Now to give you an idea of how powerful that magnet is, the earth's magnetic field strength is commonly accepted as field strength of 0.67 gauss. A disclaimer, however, physicists routinely argue this value. So the most commonly used magnetic field strength magnet is 25,000 times the earths magnetic field strength. Remember we are talking magnetic field strength...that which causes your compass needle to point to magnetic north. These MRI scanners typically are in special rooms with specially annealed steel in the walls to keep the magnetic field in the room or they are specially constructed magnets with reverse wound coil wires on the outside which keeps the magnetic field in the room.
Some MRIs are considered low field (0.2-0.5 tesla), mid-field (1.0 tesla) and others are high field, 1.5 tesla 3.0 tesla and above.
The reason they ask that question about whether you have ground steel or ferrous metals is potentially the magnet could move the metal in your eye and damage the surface of the eye in the process. Often if there is doubt, they will shoot a head x-ray prior to doing the MRI exam. If they can see the metal, they won't do the MRI. Don't be alarmed!
I have been scanned hundreds of times. There are imaging artifact problems that cannot be realized on test phantoms due to their homogeneity. Thus, to see if a problem has been resolved, a human body needs to be scanned. Often late at night it would be just myself and the radiological technologist there. So the tech scanned me. I had a piece of steel in my arm from an oil field accident. It was there for over 40 years. Only when I knew I was going to have to install and work on a 3.0 Tesla magnet did I have the steel chip removed from my arm. When working inside the bore 1.5 T magnets I could feel the small chip of steel twist and knew it should be removed before working on the 3.0 T magnet. In fact, my employer, a large manufacturer, required us to acknowledge any stainless steel in our bodies. If people had had surgery and had screws, they had to obtain a certificate from their surgeon with the type of screw and the quality of the stainless steel used. If the screw didn't meet certain specification, you weren't allowed to work on high field MRIs.
You will probably be asked if you have any implants like a pacemaker, cochlear implant and other implanted devices.
The reason they ask about pacemakers that the magnetic field is capable of resetting/erasing the cardiac pacemakers memory. I actually witnessed this once.
The reason a cochlear implant(CI) can't be scanned is because of the rare earth magnet that is part of the implant. The antenna of the CI sound processor which looks like a hearing aid has a rare earth magnet on it. The implant under the scalp has a magnet. The two magnets hold the antenna to the scalp. The sound processor takes sound, amplifies and modulates a radio signal which is goes down a small cable to the antenna and transmitted through the scalp to the implant. I can have MRI scans but ONLY if I undergo minor surgery first, the magnet is removed, the scan performed and then the magnet surgically reinstalled on the implant. I have a CI and a recent study says that I could possibly have a scan but I wear a medical alert necklace saying "Cochlear implant....No MRI....No mono-polar cautery"at my surgeons recommendation.
I won't bore you with details about what a 1.5 T magnet is capable of but....I saw a patient bed stuck to magnet.....I saw a large metal rolling tool cart being used as a anesthesia crash cart stuck to a magnet. Keep in mind, both of these items have a LOT of steel and were very close to the magnet before they attached to it. In either case, they shouldn't have been positioned that close to the magnet but the people who were moving them, neither of which were MRI trained radiologic technologists, were either unaware or inattentive to the rules when working around such devices.
Don't be worried....answer the questions. If in doubt, the MRI technologist won't scan you.
Don Orr, a fellow Creeker, IIRC operates MRI scanners and would be more knowledgeable.