Over the past few years, I’ve had a handful of MRIs (magnetic resonance imaging) done to investigate the condition of my neck and back. I’ve got more herniated discs than I have fingers. :mad: But that’s not the real question.
Every MRI I’ve had was done in a truck. At one location, they’d done a very nice bit of construction to conceal that you were walking out of the radiology suite and the building itself and stepping into a large truck parked alongside the hospital. Others made no such effort, and you’d simply walk out of the building, down some steps to ground level and over to the truck.
But, why are these things in trucks? The one that was camouflaged was at a hospital building that was only five years old, so MRI wasn’t exactly a new concept. That the hospital designers simply forgot to leave a space in the radiology suite for the MRI machine seems unlikely, so there must then be a reason for putting the things in trucks.
• Portability seems an unlikely reason - I’m assuming the hospitals either lease or buy the things outright with no intentions of moving or loaning them.
• Does MRI technology change often enough that they’re left semi-mobile to be more easily upgraded?
• Are the devices fickle enough that they’re allergic to other stuff in a building such as CT scanners or regular Xray rooms?
• Are the machines hazardous? I know they use enormous magnetic fields - the last one I was in was a 3-Tesla beastie - 3T is a LOT of magnetism, so perhaps they need to keep it outside? But this was the one that was physically attached to the building, so perhaps not?
I expect that they are sooo expensive and not required often enough for the hospital to have one permanently manned and running on site (you can’t just turn them on and off…the superconducting magnets have to be contsantly cooled with liquid helium).
It makes more economic sense to share the cost with several hospitals and just truck the thing around. All the MRI tests at your hospital are scheduled for the same day…cause tomorrow the thing is going to be several miles away at the next hospital.
What Sigene said. In the early days of MRI, government regulators decreed which institutions could have an MRI, and which would have to share. So many were built to be hauled around. And in some less-populated areas, demand is still not so high as to make having a permanent one feasable for many hospitals.
Hmmm… Guess the ones that get shuffled around are done in the dark of night or by the same mythical people that re-stock vending machines. I’ve never seen an MRI on the move, not that I’ve been watching, but they’re fairly distinctive compared to regular 18-wheeler-type trailers and often have a big GE/Philips/Siemens logo on them. (OK, I have no life…I’ve been looking too closely at MRI machines!) And no, it never occurred to me to ask when I was in any of them why they had wheels.
But… the 3T one that was all but bolted to the building was set up in an area that’s not exactly accessible to be pulled out, unless they chopped down some of the trees nearby - this thing was pretty much sitting on its own concrete pad amid shrubs and trees. Also, this particular hospital would appear to have at least two of them as I was given the option of either “campus” on the same day. This is in San Francisco, so we’re not exactly a small city.
As for your third bullet point: they don’t seem to be aversely affected by other equipment, since the MRI at the National Cancer Center in Tokyo was immediately below the CT Scanner. I suppose there could have been some thick shielding in that floor, but if it were really sensitive you’d think they’d move it further away.
I asked a visiting friend who happens to be a radiologist in Canada. He isn’t familiar with truck-mounted MRI scanners, but his speculation is that the hospital wasn’t originally designed to house an MRI scanner. Apparently the shielding and support equipment require a major renovation to the building, so it may be cheaper to buy a stand-alone factory-built MRI lab and park it next to the hospital.
I work in a prison. We have an arrangment with an outside contractor for MRI services. They bring an MRI trailer into the prison about once a month for us to use. So at least some of them are actually on the road being used at different locations.
The hospital in my home town used one of these mobile MRIs. It would come once a week I believe. They parked it out behind the radiology department (or Diagnostic Imaging as they call it now). Eventually, though, demand was high enough to install a permanent machine. There was an extensive overhaul of a room complete with EM shielding etc. I believe the whole renovation, installation, etc was around $1million.
Incidentally, they still have a mobile cardiac catheter truck that comes once a week complete with a cardiologist. That’s a little more scary than just a magnet to sit in.
I asked the techs the same thing. Its just that the MRI equipment is too expensive to maintain at many smaller hospitals, apparently. In an area with several hospitals instead of one large one, they just decided it was more cost-effective to have a unit travel to the hospitals than have each equipped with their own machine.
Well, it sounds like there were a lot of mobile MRIs at first, but now more are starting to become available for permanent use in hospitals. Well, I guess it’s possible that the hospital bought one of the old mobile units to be used as a permanent unit, and due to space issues, or other logistical issues, it was easier to attach the truck to the side of the building than move the equipment.
Slight hijack…you can’t shield an electro-magnetic field, can you? I mean you can shield things from one, a la Farraday cages, but you can’t contain the field itself, right? If this is true, with such huge magnetic fields in use, how do they protect areas around an MRI machine?
Well, I don’t know, but it seems that if you can surround something in a particular substance and it protects it, then if you surround the generator it would effectively contain/block it.
hobbes730 is correct: You can’t put shielding around an electromagnetic monopole, or at least, not effective shielding. But magnetic monopoles are at least very rare, and possibly non-existant, so the magnetic source in an MRI is at least a dipole (and possibly quadrapole). And I’m pretty sure that you can shield a dipole.
Also, dipole fields fall off as the inverse cube of distance, not the inverse square like monopole fields, so plain old distance is a pretty good way to “shield” against magnetism.
I’ve heard that in Massachusetts, getting approval for an MRI (for a hospital to purchase one) was difficult, and the route around the struggle with the state was to have an outside company bring one to the hospital in the truck. The MRI scanner was never moved around, it was just a way that an outside company could provide the equipment and operate it.
That’s exactly it – it’s a capital allocation/ regulation decision. MRI’s can be in a hospital, on a truck, or in a non-hospital facility. Which one is a result of market demand for them and on the competitive decisions made by the service providers.
I have also seen mobile ultrasound systems for stones.
An MRI setup (not including real estate costs for a fixed unit) costs about 1.4 - 2.0 million for the hardware. It’s expensive and costs in may areas may need to shared amoung several hospitals to justify it’s use.
