MRI question

I’ve worked at two hospitals, and have been to many others, but never anything related to radiology. So I have a question about MRI’s. Why do I see portable trailers that provide MRI’s at hospitals. They will even rotate so that a different trailer may be there the next day. It seems reasonable that this would be a good service for smaller institutions, but even Massachusetts General Hospital, one of the biggest hospitals in the city of Boston, has them. I would have thought that they would just use their own MRI’s.

My experience has been that the MRI units are so booked that there is often over-flow and there is need of these portable units.

One reason they’re in a trailer, is because the unit is too big to install without building the “house” around it. Trailers are easier to modify.
They are also very expensive, so they are often owned by a third party that does nothing but MRIs, owning one or more units. They charge the hospital for use for X amount of time. The patient/insurance charge is separate.
Large hospitals will use the portable units until they have the wherewithall to build a building around one.

I’ve read that the units have to be in a totally shielded room, and most regular buildings are’t set up that way. So it’s easier to have the room separate from the main building.

I don’t know how sensitive an MRI unit is to outside noise, but I do know that the big NMR unit on campus regularly got false signals from cars driving outside the building.

(So they blocked off part of that path. False signals stopped.)

Also, perhaps a good reason for getting a portable MRI unit is that not only are they very expensive, but the technology also moves pretty fast. You buy a 1.5T unit one day, and two years later there’s a 3T unit available. Upgrade costs are massive, but that 3T will give you extra resolving power. If you lease the units, you can just ask the leasing company to get you the 3T for +/mo, and they will turn around and lease the old 1.5T to a smaller hospital someplace for -/mo. Everyone wins.

Like computers, MRI technology is advancing at a fairly rapid pace. MRI suites are also rather complicated things internally, but externally, they can be reduced to little more than a whopping big electrical circuit and a door.

So, a lot of hospitals have decided it’s simpler, and better to let General Electric or Siemens build MRI suites into trucks and park the thing in a corner of a parking lot. In a couple years when the system (either the scanner itself, or the racks of electronics) are looking as outdated as a 200 MHz Pentium running Windows 95, they can just swap the entire thing out in a day, rather than being out of service for several days or weeks.