MRI tells if you have depression or schizophrenia?

is this true? if so, lets say you get your MRI back and they say there are no signs of schizophrenia in the brain, does this mean you don't have schizophrenia or they just didn't find any chemical imbalance according to the results? Also since these all tie in with chemical imbalances, how do they tell if say there is a chemical imbalance whether its depression bipolar or schizophrenia?

An MRI generates an image of the brain. It is not used as a diagnostic tool for mental illnesses. Firstly, it is not sensitive to neuronal activity of the brain, secondly and most importantly, there are no noticeable changes in brain scans for 'normal' depression, bipolar or schizophrenia. I say normal, because some structural abnormalities of the brain can cause signs of mental illness (such as a tumour).

Most mental illnesses cannot be diagnosed by imaging, only the history of symptoms given. When you mention chemical inbalances, the primary one which 'can' be diagnostic of schizophrenia is the balance of dopamine- though every one is different so it is by no means reliable to go around screening everyone's neural dopamine and predicting who has/will have schizophrenia.

Depression and Bipolar disorder are mainly thought to be a condition of serotonin inbalance and cannot be diagnosed via imaging or screening , only symptoms.

A MRI does not tell you whether you have depression or schizophrenia at the present stage. Diagnosis is usually the physician asking the patient and his family members questions that indicate the presence or absence of mental illnesses.

However, a depressed person's MRI is somewhat different from a normal person. The colours in the MRI are different from a normal person, however it is not used in diagnosis of depression.

Similarly, a schizophrenic's MRI is also a little different from a normal person.

Hopefully, in the future, more sophisticated scans can tell us definitely the person is suffering from depression or schizophrenia.

With a PET scan, it can tell us more information about the patient too.

Chemical imbalance in the brain cannot be detected by MRI.

The use of MRI is still in the research labs of neurologists and psychiatrists and scientists. It will see huge gains in the next 10 years.