Question: How does the magnetic fields and radio waves transform into a scan on a screen in relatively simple terms?

anon answered on 19 Mar 2015:

This is going to be tough as this type of physics is very difficult to understand..so bare with me.

1. Why we need a big magnet.

Our bodies have millions and millions of hydrogen atoms.. and this is what we use to create our pictures. The hydrogen atom consists of a proton and electron, but we are interested in the proton.

If you remember – a magnet will have a magnetic field – these are lines around a magnetc (remember the iron filings and magnets) so when a proton is put into a magnet it will align with its field. This property of allowing the proton to do this is called spin..
https://upload.wikimedia.org/wikibooks/en/5/5d/SpinningProtonMagnet.gif

2. Radiowaves.

We then add radiowaves to these aligned protons. When we add these radiowaves to the proton it gives them energy, we say that the protons become excited ( imagine if I gave you a huge bag of sweets.. you’ll get excited!). But once I stop adding these radiowaves this energy is lost – the proton releases radiowaves. These released radiowaves it what we need to create a picture.

We use a special detector to pick of these radio signals – this detector is called a coil. The coil is placed next to the body part we want to look at.

Now if you look inside your body you know that we are made up of different tissues.. water, fat, muscle. When you excite these protons in fat/water/muscle they will release different radiowaves because of their structure. Water is a fluid and the protons are moving freely around while fat and muscle the protons (hydrogen atoms) will be packed tightly together.

The computer (super smart computer) will receive these radiowave signals and arrange them to create an image.

I hope this is ok.. MRI is very tough to explain!