I’ve seen pictures of PET scans of bipolar illness and schizophrenia. What exactly is a PET scan and how is it administered? Are these scans used to diagnose these illnesses?

Positron emission tomography (PET) is a sophisticated imaging technique that can effectively and non-invasively measure brain metabolism and cerebral blood flow (CBF), which are indicators of brain function. These studies can be conducted at rest or after a task or drug administration to show which areas of the brain become more active. The picture it shows of brain function is created when a molecule, such as glucose, is synthesized using tiny amounts of radioactive carbon, for example (sugars are made out of carbon and other atoms). The PET camera detects this tiny amount of radiation (a fraction of the amount of radiation that would be received simply by living in Denver for a year). All of this information about brain activity is assembled into a composite picture by the computer system. PET is a research tool. It cannot yet provide a yes/no diagnostic categorization in psychiatric disorders, although imaging is close to being able to do that with Alzheimer’s Disease.

However, PET provides quantitative information on many important physiological variables in the brain including neurotransmitters and receptors. This is of primary interest in the field of psychiatry, because the manifestations of psychiatric illness are thought to reflect biochemical and physiological dysfunction. PET has research potential for shedding light on the underlying mechanisms and for evaluating treatment effects of schizophrenia, depression and bipolar disorder. Studies of patients with major depression and bipolar disorder have demonstrated a reduction of glucose metabolism in the prefrontal brain cortex, which may correlate with severity of illness. Investigators have found a profound CBF decrease in prefrontal areas and a relative increase in metabolic activity in subcortical regions, particularly in the basal ganglia when schizophrenia is present. This pattern of decreased frontal activity, coupled with increase in subcortical regions in schizophrenia may be consistent with the model for the simultaneous generation of positive symptoms (such as hallucinations) and negative symptoms (such as less emotional expression).

Schizophrenia affects almost 1% of the world’s population with similar prevalence throughout different countries and geographic areas. The financial burden of schizophrenia exceeds that of all cancers in the USA and it was reported to be the world’s fourth leading cause of disability. Bipolar disorder, also called manic-depressive illness, is another very serious disorder of the brain. More than 2.3 million American adults, or about 1% of the population in a given year, have bipolar disorder. Abnormalities in brain biochemistry and in the structure and/or activity of certain brain circuits are responsible for the extreme shifts in mood, energy and functioning that characterize bipolar disorder. Finally, major depression affects approximately 15% of the population at any given point in time and produces a vast burden of suffering and decreased productivity. For these illnesses, PET can identify regional brain activity changes and identify how they change with treatment. In studies using labeled neurotransmitters, such as dopamine and serotonin, PET can provide information about what are the underlying abnormalities in neurotransmitters and the degree to which these abnormalities return to normal with a particular treatment. In our studies of depression, we have identified changes in brain serotonin binding which normalize with treatment.

Yvette Sheline, MD
Washington University
School of Medicine

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