The Brain 107
Functional PET
PET
The last scan we will look at is functional positron emission tomography, or f-PET. In this machine the scanner detects positrons given off by excited oxygen atoms.
As you think, you burn glucose by combining it with oxygen. The parts of the brain that are thinking hard use a great deal of oxygen and this shows up in scans. Again the consecutive slice trick is used to generate a 3D image that allows you to fly through the brain as it works ona problem.
There is one problem common to all these methods. X-rays, MRI and PET scans only show us the location of thoughts with an accuracy of a few millimeters. Each pixel in the image contains around 10 million neurons, so we can't see the details of thought. For a scale comparison it
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