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Rights: The University of Waikato
Published 21 July 2007

Dr Richard Watts from the Department of Physics and Astronomy at the University of Canterbury explains why an MRI machine is so expensive.


The main cost of the MRI scanner is in generating this very large, very uniform magnetic field. And the way that we do that is using super conducting wires. So super conducting materials have this unique property that they have no electrical resistance. It’s not nearly nothing, it’s absolutely nothing. So once you start a current flowing through these coils that current will continue to flow essentially forever. So the main cost of the MRI scanner is this coil of wire, and to keep that coil of wire super-conducting, to keep it with zero resistance we have to keep it very cold. And we keep it cold using liquid helium. Liquid helium is four degrees above absolute zero, absolute zero is minus 273 degrees celcius. And when you look at the MRI scanner itself, what you’re looking at is a big tub that contains several thousand litres of liquid helium.