Fine and fair enough. But that scan would be limited to the head and not cover the entire body. I'm also not convinced that MRIs are a great, general purpose

Fine and fair enough. But that scan would be limited to the head and not cover the entire body. I'm also not convinced that MRIs are a great, general purpose diagnostic tool, if it's not used to diagnose concrete issues. The experience of your friend, who I hope recovered from the tumor not withstanding.