MRI 'brain atrophy' or just less activity?

Question

If someone was told they had significant brain atrophy, all over but especially the temporal lobes, from the results of an MRI, could this be caused by a lack of good quality sleep or be a temporary state of illness? Could brain function appear more normal at a later stage when health is improved? Or is the MRI able to tell that there has been an actual atrophy of brain tissue?

Answer 1

An MRI shows the structure of the brain tissue, not its activity.  If you want to see the activity of the brain, you need a PET scan.

Brain atrophy on an MRI means that there is an actual reduction of the tissue of the brain.  It is physically smaller than it used to be.  

If you have atrophy of a muscle, say in one of your thighs, it will be smaller than the other.

The MRI actually shows the reduction of the brain tissue.   However, atrophy of brain tissue is not necessarily related to loss of brain function.  It can be, but not always.