What can an MRI scan show that a PET scan cannot?
In general, PET scans are used to look at the functions of various brain regions while MRI scans provide information about the structure of the brain. PET scans are comparatively simple instruments, showing which parts of the brain are active at any one time. To do this, a small amount of radioactive tracer (usually glucose, which is the primary fuel source of neurons) is injected in the bloodstream. Those cells which are most active take in these radioactive tracers, and these active regions are detected by the PET scan. MRIs are usually more time-consuming and are not generally used monitor brain activity. But MRIs provide images that more clearly show the structure of different brain regions, and are invaluable for diagnosing brain abnormalities such as those caused by tumors or disease.
