MRI PicturesWhen protons in a brain are placed in a magnetic field, they can receive and transmit electromagnetic energy. The strength of the transmitted energy is proportional to the number of protons in the tissue. The strength of the signal is modified by properties of the microenvironment of each proton, such as mobility and local homogeneity of the magnetic field. MR signal can be weighted to make some properties more noticeable than others.
For a futher understand of the different parts of the brains anatomy look at the interactive animation series under Sagittal, Coronal and Top.