Today, those observing the Thanksgiving holiday in the U.S. may mark the occasion by watching celebratory parades of large inflated balloon turkeys and other characters floating down city streets. Next Tuesday November 28, a team of cryogenics experts will go live from a lab where they use helium to make MRI machines. This is the first episode in a new series – Lab Invaders LIVE – that sneaks us behind the scenes, into the minds and machines shaping science and medicine.
Today’s Question: We asked one of those cryogenics experts, Dr. Stuart Feltham, to explain if and how the helium used in these famous balloons is the same or different than that used in MRI scanners?
Dr. Stuart’s Answer:
It is the same gaseous chemical element Helium — He, atomic number 2, the first of the noble gases on the periodic table – that’s used in both balloons and MRIs.
There are many intricacies in how helium is used depending on its ultimate use, but I would highlight two key differences to note in this case. First, the grade of helium used and second, the form the helium is in.
Let’s start with the grade. Helium itself is graded on a very precise scale of purity, measuring the true composition of the gaseous element in any given situation. A grade of six is the closest to pure perfect helium you can get and a grade of four and below is the lower end. This is simplifying somewhat – it’s also possible to have further variations within each grading, due mostly due impurities like carbon dioxide, nitrogen, oxygen, and water.
This highest grade is often reserved for the tiny chips found in your smartphone and other high-tech electronic products. The superconducting magnets that are crucial to running MRI machines also have very specific and secure ways that they must be created, which is what we do in the factory where I work in Florence, S.C. We almost always use a grade of 5.5 to six for MRI magnets because of this, but also because we mostly buy helium in its liquid form, which is pretty much always 100% pure.
The lower grades of helium are most often reserved for balloons. While it’s technically possible to use nearly any grade in balloons, more often than not they are filled with the gaseous element at a purity of four and below due to a number of factors, including the scarcity of helium (in fact we are hard at work to find ways to use less of this precious element in the creation of MRI magnets).
The other key difference is the form in which the helium is used.
Anybody who has held a balloon can ascertain that it’s filled with a gas – helium in its innate gaseous form. This is what makes it lighter than air and able to float.
In MRIs, the only way to cool the magnets to the necessary “superconducting” temperature is to use liquid helium – mined from below the earth’s crust.
There you have it: the difference between what’s keeping the balloon afloat and making an MRI magnet is often the grade of helium and the form of helium (although there’s always exceptions and intricacies – that’s why we love science!).