- by Bill Mansfield
I took these photos because they show common damage which may not have corrupted MRI image quality if better shielding products were used.
Water damage of a hat and flat system floor. This is the number one problem for hat and flats. The core of a hat and flat is wood. Wood gets wet and it swells.Then it drys and it shrinks. This expansion and contraction will loosen the pressure seal and radio waves jump in.
Preventive solution #1: Use a good waterproof isolator under the floor. Heavy rubber, swimming pool liner, welded vinyl. Beware! thin sheet plastic is a joke. It is a vapor barrier at most. Any company that uses $20 dollars of plastic to protect a big dollar MRI should re think their business practice. Preventive solution # 2. Never let water in the room. No mop buckets , no drinks. Never let the frost during helium fills drip on the floor. Preventive solution number #3. Keep humidity in check. Run that A/C 24 7 365. Galvanized metal zincs at high humidity and that micro thin zinc corrosion is less conductive. Less conduction , less attenuation, shield failure? Install hat and flat room styles in the dessert not in the jungle or areas with 60% humidity. Beware! too dry causes an ESD or a STATIC situation which is very bad for hardware. Cure for the failed floor situation: rig out MRI and sand joints of slightly damaged panels and remove and replace badly damaged panels. It’s two weeks to a month of down time for the MRI.
Second picture wood rot. This is not a hat and flat room but a metal floor with wood on top and bottom. Hardboard , MDF , or maysonite they call it. Agin a thin sheet of plastic is normally on bottom and vinyl on top. Moisture gets to the hard board and it gets soft then rots with plenty of good black mold and mildew sometimes a few bugs will join in on the fun. Just what you wanted in your imaging department. All this under your vinyl floor getting nice and soft. Even if the metal doesn’t corrode through the moisture has shorted your room to failure. I was taught early this method of using wood was bad news. The only cure: tear it out! This floor was rotted so we replaced it with a totally better and water resistant non wood products. So remember never put wood products on the floor. I saw a company shoot nails through their shield in to the concrete floor through the isolation barrier. So why did they isolate at all? If they are bonding the metal to the concrete ground.
Picture three epoxy floors. A large company patent a system where they mixed silka Prouduct hymod- L-V epoxy and poured this on concrete floors. In minutes it hardened to a mirror yellow finish and sealed the floor. Then they used a two part Silka injection jell mix with a 1/8 inch notched trowel and rolled their copper on while it was wet. This was a solid bond and held the copper well. The epoxy was labeled corrosive and sure enough the copper in time was eaten as you can see. Often depending on the construction the lime of the surface concrete ate the copper faster than the epoxy. In this picture Fortifiber corp copper of Massachusetts was used as you can see the paper backing still on the floor. This patent floor system has a 7 year life span on average for low field magnets and much less for high fields. No repair is possible for this floor. You must tear it out and replace with a better floor that will last. While you do that solder the walls of this panel room and toss the aluminum jamb windows and doors and buy quality less expensive copper components.
I hope this helps you make good decisions.
- by Bill Mansfield
Let me quickly address this closed container security issue. If security is an issue with the soft tarp tops, then use a removable, hard, steel top as in the photos below. The best way to load a heavy magnet into a container is by using its lift rings.
The straps, cables or chains used to load the magnet into an open container keep the magnet suspended for easy loading. It can’t fall, unless something breaks (of course) and I have never seen a magnet hit the ground. To load a magnet into a closed container you can lift most magnets with a fork truck (lift). Some MRI gantries are fork lift friendly, too. Most are not when you use a fork truck on any terrain less than perfect. Think of the bumps and the bouncing… you get the idea. Of the many stories told, they all involve fork trucks.
Then you have to deal with the second rig, moving the gantry into the closed-top container. Not all containers can handle any set of rollers on their floor. Pushing or dragging an 18 to 25 ton magnet on a container floor can cost you a container repair.
When you’re anywhere inland overseas, getting a large enough fork truck to remove the MRI from the container can be difficult. So the MRI ends up being rigged at the customs dock by a non-MRI rigger and placed onto another truck to eventually be rigged at the final location by a crane. This second rigging cost has just negated the savings the customer thought they had of a standard vs open-top container.