"I'm picking up good vibrations" If you can remember when that Beach Boys song came out you are of the same vintage as me! In the thirty odd years since then we have been offered more advances in technology than at the height of the Industrial Revolution.

Many of those advances have been in the field of medicine, and one of the most notable of those has been the NMR scanner (also called an MRI, Magnetic Resonance Imaging), for which one of the developers won a joint Nobel Prize. These very expensive, very large machines give us incredibly detailed images of the interior of the human body that make Xrays look the pale shadows that they actually are.

NMR stands for "Nuclear Magnetic Resonance", let's take these in order.

Nuclear: our bodies are made from thousands of different substances, proteins, amino acids, lipids etc. etc. Each of those is made up of collections of atoms and each atom has a nucleus. Each nucleus is made up of two other components, protons and neutrons (except for the very important hydrogen, which is part of the water atom and only has a single proton). If we could "tweak" those protons, twist them out of place and then let go, they would then spin back to their original position. Certain of the substances in the body contain protons capable of doing this.

Magnetic: these protons are a little like compass needles, put them in a powerful enough magnetic field and they will turn to line up with the magnets. If you have seen an NMR machine it is a very large drum, and some of that bulk is insulation to protect the incredibly powerful magnet, cooled by liquid gas, that is used for this purpose.

Resonance: here we find those "good vibrations". If you "twang" a ruler that is hanging out over edge of a table it vibrates at its "resonant" frequency. Chose a thicker ruler and that note goes deeper, a thinner ruler and it goes higher. Each of those substances in the body that have protons capable of being twisted also has a unique resonant frequency. Subject the substance to that frequency and the protons all line up, go it and they all go back to where they were. So, play a series of "notes" to the body and, in turn, different substances will "twang" at different points on the scale. Though it has to be said that this "note" is more akin to that picked up by a radio than the human ear!

In this case the "ears" are radio receivers that can detect the direction the signal comes from. One checks the "up-down" direction, the other "left-right".

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