'A revolution in mental health'

Upon reading the NewScientist today, I was drawn to one particular article. This outlined the change of diagnosis procedure of mental health away from a symptom based diagnosis, and toward biomarkers and brain scans. This stood out to me as an issue, not only because I suffer from mental health problems myself, but also because such a huge sector of healthcare has been seemingly left behind research wise. You wouldn't diagnose cancer on the basis of a lump- the tissue would be tested- so why have we been diagnosing mental health issues differently, purely based on on symptoms and not on any objective laboratory measure? This would give rise to more accurate diagnoses, and hence improved help for the patient- that is, if the underlying science is reliable. This shift in technique is desirable, but 'to understand the neuroscience in sufficient depth to build a diagnosis would take time'.