okay so: neurotransmitters are chemical messengers which go through neurons and their synapses (the gap between neurons). Hormones on the other hand are also chemical messengers but they go through blood instead that's the only difference.
PET scans and MRI scans are both non-invasive (require no surgery)
PET scans have an injected radioactive tracer where glucose produces positrons (don't have to know what they are) and then they travel to the most active parts of the brain and on the screen you will see that the redder the parts of the brain are, the more activity there is in that area so scientists can see which behaviours are initiated by which part of the brain.
Then MRI scans are similar but unlike PET scans they show the structure of the brain (in 3D also) and a dye is injected into the patient so that the whole brain structure can be visible on the screen.
You can see tumours with both MRI and PET scans but MRI scans have disadvantages purely because you get put in that long tube and it lasts a long time producing a really loud noise which sucks. So people can feel claustrophobic! x