Positron Emission Tomography , brain function study

Positron emission tomography (PET) makes use of a short-lived positron emitter such as fluorine-18 to image human tissue with a degree of detail not possible with x-rays. It has been used extensively to study brain function (see illustration) and in medical diagnosis. For example, when the hormone estrogen is labelled with fluorine-18 and injected into a cancer patient, the fluorine-bearing compound is preferentially absorbed by the tumor. The positrons given off by the fluorine atoms are quickly annihilated when they meet... 

Chugani, H. T., Phelps, M. E. Mazziotta, J. C. (1987). Positron emission tomography study of human brain functional development. Ann. Neurol 22, 487-97. 

Nevertheless, receptor studies in these areas are consistent with a role for biogenic amine function in the pathophysiology of major depression. Two of the most replicated findings are increased 5-FIT 2a receptor binding in the PFC and reduced 5-FIT receptor number and function in the brains of depressed suicide victims. These findings have led to positron emission tomography studies to quantitate the number of 5-FIT 2 and 5-FIT a receptors in the brain of patients with clinical depression (31, 32). This work has documented a 42% and a 27% reduction in 5-FIT a receptors in the raphe and mesiotemporal cortex, respectively, in unmedicated patients with primary, recurrent, familial major depression. 

A relatively new technique that uses radioactivity to study body processes and diagnose malfunctions is commonly called positron emission tomography (PET). In this technique radionuclides that decay by positron emission are incorporated into compounds. For example, brain function can be studied by incorporating 1gC into glucose, which is the main source of energy for the brain. By studying how this labeled glucose is metabolized in the brain, doctors can discover abnormalities caused by diseases such as cancer, Parkinson s disease, and epilepsy. 

Numerous studies of brain function in major depression have been undertaken. Studies using positron emission tomography generally show decreased metabolism in the frontal lobes of depressed individuals, more so on the left (Bench et al., 1992). This abnormality is not specific to depression, being observed in other psychiatric conditions such as bipolar disorder and obsessive compulsive disorder. The abnormalities reverse wdth successful treatment. 

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