When doing a mri of brain does it check for all brain diseases or just the one that your doctor suspects it may be?

Not just one thing: Any imaging study looks for various types of pathology, but is limited by the ability of the test to see some abnormalities. Traditional MRI sees masses well. Changes in extracellular water content help us see MS, most cancers, strokes and even migraines. We see most vessel abns. like aneurysms. Functional MRI is a special type of MRI which is useful for seizures and even many mental illnesses.