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Comment by aexaey | Hacker News Reader

  Helium [...] is critical to [...] MRI scanner

Is that still the case, now that high-temperature superconductors are available, which work just fine while being cooled with much cheaper liquid nitrogen instead of requiring liquid helium?

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It’s not as simple as that. Wikipedia says:

Some cuprates have an upper critical field of about 100 tesla. However, cuprate materials are brittle ceramics which are expensive to manufacture and not easily turned into wires or other useful shapes. Also, high-temperature superconductors do not form large, continuous superconducting domains, but only clusters of microdomains within which superconducting occurs. They are therefore unsuitable for applications requiring actual superconducted currents, such as magnets for magnetic resonance spectrometers.

IOW, we don’t have a high temperature superconducting material that’s suitable for use in an MRI scanner yet.

It seems there is High temperature superconducting wire entering the market:

https://en.wikipedia.org/wiki/Superconducting_wire#HTS.28Hig...

That's still just cuprate superconductors except flattened inside of a metal tube. It's still expensive, inflexible, and for reasons to do with the SC physics, behave differently than the kind of Type 1 superconductors needed for MRIs and NMRs (high temperature superconductors are Type 2 and are a drastically different phenomenon).

>we don’t have a high temperature superconducting material that’s suitable for use in an MRI scanner yet.

But I think we are getting closer all the time... http://www.superpower-inc.com/content/high-field-magnets

There are Type 1 superconductors (the first that were discovered), and those have the magnetic properties that are more useful creating MRI type fields. There have been breakthroughs in Type 1 superconductors and I believe GE is making an MRI using Hydrogen at 20 Kelvin for the cryogen. Although I couldn't find much more than this patent in a quick search:

https://www.google.com/patents/US20130104570

...and then there are Type 2 superconductors, of with the High Temperature (HTS) variety have been popular. There have been steady advancements in those materials, and someday there will be an MRI machine based on HTS materials. See the link to SuperPower below as well.

Do you know what is even cheaper than using Helium? Using cryogen free magnets: http://www.mrsolutions.com/news-events/news-item/mr-solution...

Also: http://www.oxford-instruments.com/products/cryogenic-environ...

I can only guess that the price of replacing an MRI scanner is more than the expected difference in operating cost of nitrogen vs helium. Everything I know about MRI suggests that the machine itself is fairly pricy.

Not at all. MRI machines have huge start up costs but that doesn't mean they cost any less to run because making and storing liquid helium is orders of magnitude more expensive than liquid nitrogen. According to [1], for a new MRI from the manufacturer, it costs about $2 million for startup costs (capex and training) and another $2.5 million over the next 5 years for operating costs. Considering these things easily last 20-30 or more years the lifetime cost of an MRI will be an order of magnitude greater than the acquisition cost. Don't know how accurate this document is but it fits my experience of about $1 mil start up with $0.5-1 million per year operating costs.

[1] http://proimagingservices.com/wp-content/uploads/2014/10/How...

I have a higher up comment but cryogen free magnets exist now. They still need water and electricity but much cheaper than the cost of helium (ant the cost of the nitrogen around the helium).

Just to add to this good comment. MR scanners are generally (here in New Zealand) considered to have a lifetime of 10 years. Some scanners use liquid nitrogen and liquid helium for cooling. The use of compressors to reuse the helium that boils off has dropped helium use dramatically, meaning refills are now uncommon and occur every year or two.

Most of the MRI machines in existence use Helium, and they're expensive machines, unlikely to be replaced until they must be.

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