No reason for a brain scan. If your neurologist isn't telling you that a scan is necessary, listen to them. Have you seen an SLP who specializes in stuttering? Speech therapy IS the answer. But it takes finding the right program. It takes the same effort as learning to play the piano. You have to put in the time every day. And at 8 years old, your son might not be ready to work at speech therapy in such a way for it to be beneficial. Insurance companies often say "no" as their first answer. You can often get more therapy approved, but it requires an appeal process.