The liquid gold of MRI

Known to most as an inert noble gas, helium is a multifaceted substance with diverse applications. The element owes its stoic nature to its fully occupied electron shells, which mean that it doesn’t readily bond with other substances. On account of this chemical property, helium was sometimes seen as an attractive lifting gas for airships as it is not flammable (unlike hydrogen). If we consider the use of helium in industry, the element can be found wherever there is a need for immense cooling. It adopts a liquid state at a temperature of -269°C – approaching absolute zero – and these extremely low temperatures form the basis for many of its technical applications.

The particle accelerator at the CERN nuclear research center in Geneva and the technology inside a magnetic resonance imaging (MRI) scanner have one thing in common: At the heart of these systems, superconducting coils are used to generate a powerful magnetic field. Extreme cooling with liquid helium is essential for the operation of these magnetic coils and for them to become what are known as superconductors – in other words, to conduct electrical current without resistance. Liquid helium is the only medium cold enough to rid metals of their electrical resistance, enabling them to generate powerful and stable magnetic fields.

About a quarter of the helium consumed worldwide is used for the extreme cooling of superconducting magnets, and demand is on the increase. At the same time, helium is a rare element – at least here on our planet. Produced by the decay of various radioactive elements in the Earth’s crust, it either accumulates in rocks or percolates into pockets of natural gas, of which it is a common constituent. From there, helium is brought to the surface by volcanic activity or must be recovered from natural gas using complex separation techniques. 

Given that helium is such a valuable resource, it makes sense to handle existing reserves prudently. With that in mind, efforts are underway in several fields not only to find alternatives but also to identify ways to recycle the element and, above all, to use it economically. This also applies to applications of helium in medical technology. Depending on the type of device, conventional MRI scanners can require over 1,000 liters of liquid helium for cooling¹ – reason enough to explore new possibilities.

In order to keep the need for liquid helium as low as possible, future technologies will focus on closed-circuit systems with a view to minimizing the mass of particles that require powerful cooling. At the same time, perfectly coordinated magnetic components mean that the system generates less thermal energy overall. Highly optimized thermal coupling is the final element of this innovative technology and allows exceptionally efficient conduction of any remaining heat in the system. Taken as a whole, these and other measures will reduce the amount of liquid helium required to less than one liter.²

Avoiding the need for helium has numerous advantages. Installations are more modern in the sense that they conserve valuable environmental resources, and new technologies are easier and cheaper to install than is usually the case for a conventional MRI system. For example, these machines used to require a long quench pipe. This was intended to allow cold helium to escape from the building safely and directly into the atmosphere in the event of an emergency shutdown, which led to an immediate collapse of the magnetic field. Depending on the location of the MRI scanner in the building, installing a “helium chimney” of this kind generally called for costly construction work – something that several MRI systems may not need in the future anymore.

New MRI systems will also have a smaller footprint in terms of their weight and dimensions. Whereas the installation of previous systems often entailed complicated work in order to open up hospital walls or roofs, a new type of system literally fits through the front door. This saves money and could also pave the way for delivering MRI systems to locations where access to this technology was previously considered impossible. A promising development for humans and the environment alike.