p> There are also several points of comparison relative to PET (Powers & James, 1984, p. 187). With the use of PET, there are required radionuclides that decay by means of positron emission. These positrons rapidly combine with electrons that are oppositely charged and closely located. Following annihilation, they generate two 511 keV photons that travel in opposite directions, and are detected by the positron camera which can localize their site of origin. Given the use of radionuclides that have decaying emitting positrons, PET can use such isotopes as carbon, nitrogen, oxygen, and fluorine in that they meet this requirement. As such PET can be used to produce the labelling, and study the distribution, of numerous physiologic substances (e.g., glucose, amino acids, etc.). There is then permitted the quantification of parameters, including local blood flow, the rate of,glucose metabolism, and the utilization of amino acid. The cost of PET can be prohibitive, given that the short half-lives of
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