One of the major uses of helium is to keep superconducting magnets very cold. The coils must be kept at a chilly 450 degrees Fahrenheit below zero in order to achieve the strong magnet fields necessary for magnetic resonance imaging. MRI is a widely used medical imaging technique, partly because the radiation used is of much lower energy than that need for CT scans, for example. MRI is actually an application of a quantum mechanical phenomena called NMR (nuclear magnetic resonance). The energy states of the nuclei in a magnetic field can be changed by tickling them with very small amounts of energy (radio waves to be precise), and the changes in these states can be used to produce an image of living tissue. The stronger the magnet field, the more easily detected the energy changes are, hence the use of the strong field superconducting magnets.
So how strong are these magnets? They are on the order of 1 Tesla, thousands of times more powerful than your basic horseshoe magnet. If you're not careful with a superconducting magnet of this strength, it can suck up a lot of metal. See the photos here for some stunning examples.
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