MRI Club

[indian]

I would like to hear from other technicians that understand What happens with the MRI (Magnetic Resolution Imaging) equipment. We usually have air conditioning, chillers, and a touch of helium! We step up to the plate and swing!

[thehumid1]

I have no clue sign me up for that training.... big difference between a hospital and a homeowner they legally have to maintain their POS as oppposed to HO's where it can only be suggested.

So can u get me any of that funky milky green contrast stuff when u mix it with Jameson irish whiskey its like a
hi powered shamrock shake.

[wolfdog]

I have serviced chillers on a
Magnetic Resonance Imaging machine or two in the past.


I'm not sure if they are the same as them "resolution" machines you're talking about.

[klrogers]

I service lots of chillers that serve MRI's and CT's Linear accelerators and other medical equipment. But I don't understand the medical equipment side, I leave that to the experts in that field, and they leave me to provide them with chilled water. Yes the upkeep is better than most residential or even a lot of commercial equipment, but when there is a problem they want it fixed yesterday, downtime equals BIG money to the medical facility.

Kevin

[onetime]

Yours sound just like all the ones I've worked on, standard A/C units, chillers cooling deionized water or another medium to cool the magnet. Just make sure you leave all your metal in the truck when you go into the magnet room.

[flange]

i never tried to find out how those suckers work. never needed to, but i do know that there is only a period of roughly <48 hours in most cases that the magnet can be without cooling once fired. typically the process chiller we install will cool their cooling medium which in turn cools the magnet only. the ac is for the other heat loads in the room. isnt the helium there for the lab techs????thats how they abuse the previous patient, by snorting the helium and talking funny.

[wolfdog]

I know what you mean. Like the laser cutters. They've got liquid oxygen,liquid CO2, and sometimes other gases. I guess it depends on what they cut.I've seen them cut everything from plastic to titanium to copper.


I just make cold water and head on down the street.

[maxster]

the helium within the magnet is what has to be cooled as the power rises on the MRI,if the chiller trips and the magnet is up the heat absorbed by the helium will break it down and the helium...charge! must be replaced,big bucks

[indian]

I only work on the part I understand and can deliver on also. One MRI engineer told me the helium quench on the magnets only removes something like 14 or 18 watts of energy.

[maxster]

searching in altavista they say the average magnet charge of hellium is 1700 liters at $3.50 a liter.i have worked on air cooled chillers and single compressor air cooled splits set ups and when that chiller trips they power that thing down asap,so the helium doesn't get compramised.

[jimp]

I do repairs for Phlips medical div and don't get past the helium cooling head.

[indian]

Originally posted by maxster
searching in altavista they say the average magnet charge of hellium is 1700 liters at $3.50 a liter.i have worked on air cooled chillers and single compressor air cooled splits set ups and when that chiller trips they power that thing down asap,so the helium doesn't get compramised. Isn't that a little scary? The old unit in our area always had a big cylinder out back until I fixed a leak and found out the helium compressor was shot. Now i really feel like cheap help, who knows how much I saved them. Should we charge like doctors and get extra insurance?

[dapper]

The way I understand it is........ The MRI uses a ceramic magnet that operates at its peak in ultra low temps. I think around -170C. The magnet is submerged in liquid helium to maintain the temp. The units that I have worked on have an external helium compressor that cools the helium as it picks up heat from the magnet during the scanning operation. These are water-cooled compressors. The chillers associated with these cool the cooling medium (glycol) for the helium compressors. The trick is to keep the pressure of the helium below 6psi. The helium begins to boil off above this point. The MRI is vented to the outdoors and a small amount boils off continually requiring recharging every several months or so. A rapid rise in pressure will open the relief valve at about 7+ psi causing a catastrophic loss of helium. I've been told that if you are near the path of the 6 inch vent line it is similar to standing near the track as a freight trains passes by. A typical recharge after this is in the neighborhood of $10 - 15 G. Assuming that the magnet shut down properly to prevent a total meltdown.

[clydemule]

Dapper is right, about 10-15K when you boil off the helium

NOt only do the chillers cool the helium compressor, the also provide water to a bank of heat exchangers, which in turn cool deionized water which cools the electronics (gradient amplifiers) and some of the coils which control the scan (gradient coils).

Sometimes we have provided chillers that also cooled the mechanical room by running chilled water through a fan coil.

Some MRI mfg's use one big chiller for everything, some use a micture of chillers. Some systems have air cooled graidents. We used to build a crapload of 4 tons for Philips CT scanning machines, but now they are all aircooled.


Running out of helium due to chiller failure is a great way to get a doctor super pissed off. Next best thing is for the chiller to be screwed up jsut enough so they can't scan. Every facility should have a backup water supply to at least cool the helium compressor. It only takes 2 or 3 gpm.

Clyde

[dapper]

The doctor has good reason to be pissed. The average scan takes 30mins. The average fee is $1000. Some places scan from 6am til 10pm. That would average about 32k every day the machine is down.

[maxster]

any brand chiller can be used for an MRI appliication.these guys designed a total enclosed unit to deliver chilled water to the load end...hgbp,redundent scroll compressors, chiller tank,lead/lag pump setup http://www.arctichill.com/Medical.htm

[indian]

I was trying to coordinate a pump replacement this week on one of the newer units that use only a chiller and helium, when in middle of a technical discussion the owner hung up the phone! As it turns out he is the owner/operator, he had someone freaking out in the middle of a test, trying to leave town!

[indian]

I would like to share something I noticed that happened during the pump motor replacement yesterday. The MRI happens to be a traveling unit. It is the semi traler type that makes our town three days a week and alternates to two other towns on the off days, anyway the chiller motor was bad. The pump was being disassembled when I found that at some time the motor (460 three phase) had been reversed in what was an apparent attempt to diagnose and repair. I noticed that there has been some interest in this thread and in the true spirit of sharing knowledge I would only like to point out that if you are dealing with a threaded shaft impeller pump that reversing rotation on the motor will spin the impeller off the shaft only adding to the problem. Being a traveling MRI I can only wonder if at one of it's other service locations they may perhaps have the phases reversed.

[clydemule]

Indian,

That is a good observation that you made, and a common problem on mobile units.

Since these mobile systems are for users on a budget, they are rarely restarted by a professional HVAC tech.

Often times what happens is the backwards scroll compressor or condenser fan is noticed first (after generating a service call that the chiller isn't working). The fan and/or compressor is corrected, but not the pump. Some pumps will still pump water when running backwards. Had one customer whose pump ran backwards for 2 years before he noticed it.

The key to remember is that if the rotation is wrong on one motor, it is wrong on ALL motors. Change rotation at the disconnect and not at the motor.

I would say that half of the MRI chillers use Goulds (G&L) pumps. The smaller pumps (<2HP)can run backwards with mostly just a performance drop. The largeest pumps of the series generally used will unscrew like you described in as short as 30 seconds. It wedges the impeller so far into the casing that it stops the motor and wrecks the pump.

American Stainless pumps uses a reverse thread lock screw that prevents that from happening. It is a nice feature.

What brand of MRI chiller was this?

Clyde

[pabull]

A couple of weird things i've run into on mobile MRI units were; on a two fan condenser, the lead fan draws the other fan into turning the wrong way, then when lag starts it continues the wrong way. if you see this make sure someone hasnt replaced w/ a rev. rotating motor(on 460/1ph/60 motors. because even if its wired for the right rotation, the rev. rotation motor doesnt have the torque to overcome and turn the correct direction. You need a non-rev. motor to solve it.
Another helpful hint; if you find a hard to find part i.e. control board or similar, that has to be shipped, you can remove and cap the glycol in/out lines at the helium pump and run a water hose from the building into the inlet and a drain hose from the outlet, set water flow for 2.5-3 gpm and it will at least keep em running. (wastes water..but).
I'm sure alot of you know this, but for someone new to MRI's, it can help you in a pinch.

[indian]

This one was made by Phillips

[clydemule]

Indian

I didn't work much with the Philips mobile stuff, but for the stationary MR systems I have worked with all of their chillers. If the system is less than 3 years old it has a Schreiber chiller, more than that it is a Neslab.

If you have any questions about those units I would be happy to answer any questions. But you sound like you have it pretty well figgered out.

Clyde

[jimp]

Originally posted by clydemule
Indian

I didn't work much with the Philips mobile stuff, but for the stationary MR systems I have worked with all of their chillers. If the system is less than 3 years old it has a Schreiber chiller, more than that it is a Neslab.

If you have any questions about those units I would be happy to answer any questions. But you sound like you have it pretty well figgered out.

Clyde

Clydemule you work for Schreiber?

[clydemule]

Depends...

Are you pissed off at them??

I used to work for them. Tomorrow (3/5) will be my 1 year anniversary of my last day.

I was a "consultant" for them until the end of the year, but they never really called me much. I had my own stuff to do anyway. Still know everybody there, we are on good terms.

Do you work for Philips, or an He company like Air Liquide?

Clyde

[jimp]

Originally posted by clydemule
Depends...

Are you pissed off at them??

I used to work for them. Tomorrow (3/5) will be my 1 year anniversary of my last day.

I was a "consultant" for them until the end of the year, but they never really called me much. I had my own stuff to do anyway. Still know everybody there, we are on good terms.

Do you work for Philips, or an He company like Air Liquide?

Clyde

I do some work for them in the Tampa bay area sometimes, George and Jeff I have talked to several times.
The first job they sent me on was a brewery that had a leak in one of the tank's and the beer was backing up into the glycol.
I also do some work for Philips and I hate those Neslab chiller's, last month I did a old style 7.5 Tecumseh change over to a Copeland scroll.
After the change over it ran for over a hour and the LLS for the TXV hung up and down went the temp, turned the machine off and it filled the compressor with liquid.
A real bastard of a job.

[clydemule]

Jim,

I remember you! The chiller at Hopper's that was "making" glycol. You also work on Polycold units.

This is Jeff actually. I build brewery chillers and stuff now.

George is still there.

Those Tecumseh compressor were a real pain. Especially the 10 ton version. We would actually try to get people to buy a 15 ton instead of a 20 ton because the 10 ton SF's were such crap. We then switched to Copeland BR's, and now ZR scrolls. Only use tecumseh on 3 ton or less.

We have been building all of the Philips MRI chillers for a few years now. I spent 90% of my time the last couple years working on medical chillers, that is why I try to be active on the MRI threads. At least I try to be helpful.

Jeff

[jimp]

Jeff what are doing now since you left?

[clydemule]

jimp,

I am building chillers. Posted pics of the first few on wall of pride. They didn't get moved to wall of shame yet so I guess I am on the right track.

Up until a few months ago I still kind of did work for Schreiber; difficult service situations, special designs, etc. They have a pretty good crew there now so they don't really need me anymore.

I am moving to Idaho in two weeks, and getting a new shop in the process about 3 times bigger than I have now. Hope to step up production in the next couple of months.

http://www.johnsonthermal.com has contact info.

Thanks for asking.

[jimp]

Yea, get the hell out of Cali, your costs should be lower in Idaho. If you ever need anything here's my number and email, 813-926-9900, pjames1@tampabay.rr.com

good luck
jim