What is the difference in Oxygen-15 Positron Emission Tomography and 18-flourodeoxyglucose Positron Emission Tomography in terms of results in blood flow studies?

Answer 1

The difference is one between an cumulative signal vs a transient signal. Oxygen uptake reflects metabolic activity in the neurons. Areas of the brain that participate in a task will be preferentially marked by the tracer, but that signal will dissipate fairly quickly as the oxygen leaves the cell as carbon dioxide. The FDG-PET-CT is a cumulative signal as the active tissue will have an increased glucose transport into the neurons, but as the glucose is cleaved inside the neuron to supply metabolic needs the tracer part of the molecule stays inside the active neurons. So since most of the brain is active at some level this results in a background staining and a poor signal to noise ratio.