Zero Boil-off Magnets and Helium Loss
"Zero boil-off" means that a magnet that does not lose helium during the normal course of operation. Zero boil-off magnets generally consist of systems that are designed to have very low heat leak. That, and also the cryocooler is designed to liquefy the vapor that boils off from the cryogen and return it to the reservoir, similar to boiling a pot of water with a lid. When one puts a lid on a pot of the boiling water, the water evaporates and collects as water droplets on the pot lid, it then gets heavy enough to fall back into the pot instead of boiling off. This does not mean that helium cannot be lost from various other issues and failures in parts of the cooling system, like the cold-head. If your MRI magnet is zero boil-off but is losing helium, call an expert engineer to check out what could be going on. Please contact us if you need to find an engineer to service your MRI.
Below you will see a list of six common magnets with various boil-off helium rates. This list does not include all magnets but it does include the magnet types you're most likely to come across when you are looking to buy a used or refurbished MRI.
Common zero-boil off magnets:
1. GE: CXK4 LCC
2. Siemens Avanto: OR105
3. Siemens Espree: OR122
Other Magnet's Boil-off Rates:
1. Philips Intera and Achieva 1.5T: (IGC) F2000 .02-.04% per day or about 1% per month.
2. Siemens Symphony: OR70 .1%-.2% per day
3. Toshiba Vantage or Titan: OR76 .1% - .14% per day
Cost To Refill An MRI
Helium is a commodity and like other commodities in the marketplace, the price per liter changes often. If you want to work to keep your helium prices lower, find a helium provider and sign a contract with them to get their preferred rates. There still might be variability in your helium rate per liter, but getting a preferred customer rate is better than not getting one!
How Much Helium Should I Add To My MRI?
Consult your MRI manual to find out to what percentage your MRI should be filled. If your MRI is about to be de-installed, you might need to add helium to account for helium loss during the de-install.