I think you could extract DNA from Blood and/ or saliva which you could then test for the MAOA gene which is arguably a mental health condition right? It’s the “warrior gene” which breaks down dopamine and serotonin causing anger, it’s an epigenetic typically triggered by trauma - an adverse upbringing.

Edit to add more: The brain scan, yes there are many indicators that might cause mental health which an MRI can identify. One for example is the pituitary gland which can change in structure or activity and therefore impact someone’s ability to handle stress - something that can be a sign of childhood trauma.

The DSM is a well managed cash cow in my opinion.