A company has developed a new way to cool magnets for MRI machines to near absolute zero without the need for a continuous supply of liquid helium.
According to Wired.co.uk, helium supplies are said to be running out, despite being the second most abundant material in the universe, helium is scarce on Earth as its lightness means it is not gravitationally bound to the atmosphere and is therefore constantly being lost to space.
A typical MRI scanner uses 1,700 litres of liquid helium, which needs to be topped up periodically.
Cryogenic has developed a technique to cool magnets to close to absolute zero without needing liquid helium, only a small fixed amount of helium (equivalent of maybe half a liquid litre).
The company is offering its magnets for use in a variety of imaging techniques including MRI, Nuclear Magnetic Resonance spectroscopy and Electron Spin Resonance spectroscopy.
The magnets can be cooled to low temperatures using mechanical refrigerators which run using electrical power and cooling water.
The coolers rely on the compression and expansion of a fixed volume of helium gas supplied under pressure in a closed, self-contained circuit — much like how an airconditioning unit would work. The helium gas remains cold and doesn’t condense into a liquid.
Cryogenic’s “dry” system eliminates the need for skilled manpower to transfer and handle the liquid helium.
Cryogenic says that its system avoids a problem that sometimes occurs with MRI machines, called “quenching”.
This is when the wire in the electromagnet stops being superconducting and starts to generate a lot of heat. At this point, any liquid helium around the magnet rapidly boils off and escapes from the vessel housing the magnet.
For this reason places using liquid helium need special ventilation facilities.