True that mri brain scans usually require an injection of contrast?

Often: Because brain mri's are considered the cadillac of brain imaging, contrast is often used to improve sensitivity for detection of infection and tumor. However, if you have low kidney function or an allergy to gadnolinium (mri contrast) you should alert the ordering provider or MRI technologist.

Not really: It depends on your symptoms and what disease or problem your Doctor thinks you may have. In my practice, slightly less than half of all the brain studies are given contrast.