Applications of Superconductors
Chris - Now we've heard from Tim all about the science of superconductivity and we began to explore some of the applications, but this is an area where you're really pushing the boundaries.
Ed - Probably the most successful application of superconductors is some of the medical imaging scanners you were talking about earlier. The long tube-like scanners that people often experience these days are actually based on superconducting magnets.
Chris - Like MRI; magnetic resonance imaging, for example.
Ed - Exactly.
Chris - Why do they need a superconductor?
Ed - They need a superconductor because you want to produce a very large magnetic field. What you're trying to do is line up all the protons in the water atoms in your body and get a big enough noise to sound ratio in the end. To do this, you need a very large magnetic field. You could do that with a magnet based on copper wire, but then the amount of heat that would be generated would be too large for the patient to be inside. You'd have to do a lot of cooling. The advantage of having a superconducting magnet is that the superconducting wires are cooled anyway, and you can have a much larger current without the patient being exposed to large amounts of heat.
Chris - Is it just patients that you can explore using this technology? Are there other things that you can image and where this technology is useful?
Ed - It's been used for a whole range of things. I believe that in Cambridge they've looked at the defrosting of courgettes inside an MRI scanner.
Chris - And why is that useful?!
Ed - Because you can look at the inside of the object that you're trying to examine as well as the outside, so you can do a section of the structure inside.
Chris - So while it's frozen, without having to chop it up and ruin it?
Ed - Exactly.
Chris - Oh I see. So you can see what would happen if you dumped that thing into the freezer?
Ed - Or what would happen when you take it out and let it defrost.
Chris - Now what about actually increasing the resolution of MRI. It's all very well that it gives us these images of gross areas of the brain in a way that we could never have dreamt of before, but now there's a way that's referred to as SQUID that allows you to look at what the brain is doing almost nerve cell by nerve cell.
Ed - Well not quite nerve cell by nerve cell. But certainly with a superconducting interference device, or SQUID, you can image the location of activity inside the brain by detecting the magnetic fields generated by the currents flowing inside the brain.
Chris - And what sorts of questions does that enable you to ask?
Ed - Well one question you can answer is that if you imagine a patient who has a brain tumour and you want to remove the brain tumour and work out the best way to go into the brain without damaging the sense of hearing and so on. What you can do is put the patient inside what's called a magnetoencephalography (MEG) scanner and play a tune into the patient's ear. Because this MEG has an array of SQUIDS around the head, you can map the distribution of magnetic fields associated with that piece of brain activity and work out exactly where in the brain the auditory complex is. When the surgeon wants to remove the tumour, they can do so without causing damage.
Chris - What about turning away from the brain and to other tissues such as the heart?
Ed - Yes. Again, by using an array of SQUIDS you can image the current distribution in the heart and therefore look for short-circuits. When the heart beats, the cells generate voltages. But certain conditions generate circuits in different parts of the heart and you can see those by using an array of SQUIDS.