Saturday, October 25, 2008

MRI Scanning

MRI (or CT) scanning is a medical imaging technique that takes pictures of internal organs. I've had MRI scans to investigate migraines and severe back pain and, more seriously, I've had relatives who've been scanned to enable their surgeons to plan operations to remove cancerous tumours. All in all, I'd be very disappointed if we couldn't have MRI scans any more.

(MRI brain images, taken from here)

However, MRI scanning is crucially dependent on fossil fuels - more specifically, on natural gas.

The guts of the scanner is a very strong magnet whicht only works when it's very cold - around minus 270 degrees Celsius. The only way to keep it that way is to suspend the magnet in a special thermos filled with liquid helium. And, despite the thermos, the helium steadily evaporates away and usually has to get topped up every week or so. Similar superconducting magnets are used in the Large Hadron Collider and in the NMR machines widely used in molecular analysis by chemists and biologists, so helium is crucial there, too.

Helium is better known as the gas in lighter than air party balloons, but it is also used as an inert gas for overhead welding and in the manufacture of solar panels, in the helium neon lasers used in many barcode scanners, mixed with oxygen in the gas cylinders used by deep-sea divers and as a coolant in both industrial refrigeration systems and nuclear reactors. In the future it may even be used in commercial modern, safer versions of Zeppelin-style airships.

However, that's assuming there's any left. Helium, despite its low profile, is so important to our civilisation that the US until recently maintained a national helium reserve alongside of their strategic petroleum reserve. But, just like petroleum, it is a finite resource and it is running out.

So what is the connection between helium and oil?

Helium is found naturally in the air we breathe, but only at a concentration of 0.0005%, and it takes a lot of energy to separate it out. The only other terrestrial source of helium is in natural gas deposits, which are mostly made up of methane but can also contain up to 8% helium. You can find out why here. Because you can't take one out of the ground without the other, running out of natural gas in the ground is the same as running out of helium.

However, not all natural gas extraction facilities have the equipment to separate out the helium, so a lot of it is simply wasted, dispersing to the atmosphere as the methane is burned. On the other hand, while you can make natural gas out of waste plant and animal matter (so-called 'biogas' or 'landfill gas'), alternate sourcing of helium involves the either the highly energy-intensive process of concentrating it out of the air or such sci-fi technologies as nuclear fusion and mining the sun.

So maybe we should start thinking of natural gas wells as sources of helium (with methane as a useful byproduct) rather than the other way around, and make most of the methane we want for energy out of biological waste. That's what we're keen to do and, as we couldn't find a domestic biogas supplier near us, this summer we're going to have a go at making our own from kitchen scraps just like these people here:

(Participants in the marvellous domestic biogas programme of ARTI India in Pune)