3.3 MRI: Producing an image
Although the basis of the MRI technique is , it is important to realise that it does not involve recording an NMR spectrum in order to analyse which molecules are present.
A complete spectrum of the human body would show a large number of signals from protons in different proteins (DNA, etc.) and from different parts of the body, and would be impossible to interpret.
So how is an image produced?
We start by looking at a real example.
Figure 7 shows a typical slice through the sagittal plane which clearly shows the skin, grey and white matter, cerebrospinal fluid and other components of the brain. The smallest detail in this image is a millimetre or smaller, and images such as this are used to provide vital information as a means of diagnosis or to identify the need for any surgical intervention.
How are different components, such as the grey and white matter and cerebrospinal fluid in the brain, identified using MRI? And how is the spatial localisation achieved, providing information about where in the brain the different components are located?
In the next section you will consider spatial localisation. A key component is the use of magnetic field gradients.