PAD FOR MRI MAGNET 2

[braves25]

I am designing a pad for a mri magnet that weighs about 10K. Vibration of the magnet will also be an issue, but I do not have any info for the vibration. Has anyone designed something similar to this? Thanks.

 

[pennpoint]

braves25
You have me wondering if steel rebar is even used in such a pad? if an alternate is used what is it.

pennpoint

 

[SperlingPE]

I have designed foundations for MRI's. The first thing that we usually do is hire a vibration specialist to do a site study. The room and the pad that the MRI sits on are typically isolated from surrounding structure. It is site specific. One MRI foundation that I designed was near the air ambulance landing pad. This greatly affected the operation of the MRI magnet. Another MRI was near a high traffic corridor and a mechanical room. Both affect the operation of the MRI magnet. I designed the pad foundation using fiberglass rebar. Any non-metal rebar can be used. Fiberglass rebar is manufactured locally so that was what swayed my decision to use fiberglass as opposed to carbon fiber rebar. Non-metallic rebars are not the same. Each has their own structural properties. Obtain information from the supplier and do not allow substitutes without verifying properties. Concrete design with non-metallic rebar is described in ACI 440. This is a valuable resource. The room (walls, ceiling, floor) will also be shielded. This makes for some tricky joint details. Hughes Brothers, Inc. in Seward, NE was the rebar supplier. There are other suppliers around as well.

 

[Senseloop]

I deal allot with MRI's and have seen Aluminum plates used as pad's, its not a matter of what kind of rebar is used, the key is how far the rebar is from isocenter of the magnet. One trick you might want to use to see if your room leaks is to take a battery powered radio in the room and see where you get a signal, most of the time its in the pin panel or at the door, be sure to close the door when your in the room. Also, the above response is correct when talking about traffic area's, any change in the magnetic field may cause image problems, cars passing by mobile units in parking lots have caused many people problems. Make sure you know where your 5 Gauss line is. I have seen changes in the field from an office next to the scanner that put a cabinet against the wall with a scanner in the next room.

 

[samdamon]

Braves25-

I have designed several pads for MRI equipment. If yours weighs only 10k, thats relatively light. The vibration issues are best left to experts. The manufacturer will set acceleration limits for all three dimensions and the proposed site will have to measured for conformance.

Whether your magnet has three support feet or four, the pad design (if its on grade) can be straightforward, but be careful that the top layer of pad reinforcement does not create a problem with the gauss fields of the magnet. Each manufacturer has specific limits on how much ferrous material can be within a certain distance of the magnet isocenter. Be sure to ask for this data.

I usually end up dropping the top of MRI pad elevation about two inches to allow installation of RF shielding around the base. Ask your client to provide the thickness of the shielding.

Also, in my neck of the woods (New Jersey), MRI mfgrs are not willing to fasten the MRI to its supports. I have asked manufacturers if they attach in California (I would think in CA they would be very strict about this) but I never get an answer. This is not a good situation (Who needs a 15k magnet sliding around during an earthquake?) but there is not much that can be done when the arch says "Hey we've been doing it this way for ten years and haven't had a problem with seismic yet".

Let us know how you make out. Good luck with the project.