PET Scanning Systems

In the first of these studies, the researchers identified the areas of the brain that are associated with normal sadness. They asked volunteer subjects to think about some very sad personal experiences - and about some emotionally neutral experiences - while their brains were being imaged in a PET scanner. When thinking about the sad experiences, the volunteers reported feeling intense sadness, and many of them became tearful. The PET scans showed the changes in brain activity that accompanied these sad feelings. They demonstrated increased blood flow in the limbic system - a part of the brain that is involved in the control of emotion - and decreased blood flow in parts of the brain that are involved in the control of attention. 

Wu and colleagues (188) have also reported on the results of a positron emission tomography (PET) scan study of 15 depressed subjects and 15 normal control subjects after a night of normal sleep and a night with sleep deprivation. The authors found evidence for overactive limbic system metabolism in a subset of depressed patients after sleep deprivation, who subsequently experienced reduced activity in this area, as well as a lessening of their depression. 

Long before PET scan studies revealed the dramatic shift in cortico-limbic balance (in favor of the limbic system in REM), affective neuroscientists like Richard Davidson had proposed just such shifts to account for data describing differences in the experience and expression of positive and negative affects. Some people are optimistic and outgoing, whereas others are pessimistic and introverted. Davidson s work has begun to explain these differences in terms of differential brain activation. 

The PET scan has been used to study specific parts of the brain in which the neuroleptics are known to produce dysfunction by blockade of the dopamine neurotransmitter system, including the basal ganglia. A variety of studies show that the basal ganglia of neuroleptic-treated patients develop abnormalities (Farde et al., 1988). However, there are also many negative PET studies (see Buchsbaum et al., 1992, and a lengthy summary table in Andreasen et al., 1992 see also Andreasen, 1988). 

An important advantage of a CT transmission scan in the PET/CT system is that the scan data can be used for attenuation correction of PET emission images, obviating the need for a separate lengthy transmission scan in the dedicated PET system. The use of CT scans for attenuation correction reduces the whole-body scan time significantly. CT attenuation correction and fusion of CT and PET images are discussed in detail in Chap. 3. 

The great sensitivity of the dual probe system made possible the administration of lower dose of the tracer. It was possible to carry out 20 studies at different times in a single person with the same radiation dose associated with a single PET scan. This reduced cost, improved statistical validity, and was far simpler to apply. 

PET scanning makes it possible to measure the availability of dopamine receptors in the patients with schizophrenia compared with nonschizophrenics. The striatum, limbic system, and the cortex are the principal locations of dopamine neurons. Studies of young, drug-naive schizophrenic patients failed to demonstrate abnormalities in the densities... 

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