Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging technique that uses strong magnetic fields and radio waves to generate detailed images of the internal structures of the body. MRI is especially useful for imaging soft tissues, such as the brain, spinal cord, muscles, ligaments, and organs, as well as detecting abnormalities such as tumours, inflammation, or injury.

MRI  involves a complex process involving the nature of the nucleus at the quantum level, the use of radio waves, and of resonance.

In essence, it utilises the hydrogen atoms in ones body.  if one could send a radio signal into the body and make these atoms 'respond', and the 'response strength' is determined by their concentration , then we could use them to differentiate between tissues types.

This is how MRI works

In order to understand how this happens we need to look at a number of concepts individually.

1. First we need to look at nuclear spin and why hydrogen atoms behave as little magnets. This is video 1
2. Second, we need to understand what happens when these atoms are put into strong magnetic field. This is video 2
3. Third, we discuss resonance and see how these atoms behave when 'hit' by a radio wave pulse.
4. Fourth we look at relaxation which is where these atoms now emit a radio frequency which is then picked up by the MRI machine= video 4
5. Finally we look at how the MRI machine determines the location of these pulse - video 5​​

Interactive
The following is a simulation of how an MRI works

1. Click on "Simplified MRI"
   
2. Start by applying the main magnetic field. What do you see occurring with the hydrogen nuclei? 
3. Increase the power of the radiowave source. What do you see occurring?

Now we alter the field by applying the gradient fields

1. Adjust the frequency until you get a response. What does this demonstrate?
2. Add a "tumor". What frequency is required to get a maximum signal from the tumor?