Radioisotopes and PET
PET scans require the injection of a small amount of biologically relevant material like oxygen or glucose (sugar) which have been labeled with radio nuclides such as carbon-11, nitrogen-13, oxygen-15 and fluorine-18 (fluorine-18 is the most common). To understand the function of isotopes in PET scans, let's talk briefly about radiation in general.
While working with uranium containing compounds in 1896, Henri Becquerel made an unexpected discovery: Covered photographic plates became partially exposed in the presence of his compounds. Becquerel hypothesized that the exposure was due to some kind of ray passing through the plate coverings. He went on to discover several materials other materials in addition to uranium that also emitted these rays. Materials that emit this kind of radiation are said to be radioactive and to undergo radioactive decay. Ernest Rutherford performed experiments in 1899 to determine that uranium compounds produce three distinct kinds of radiation. Rutherford used the penetrating abilities of each of these radiations to differentiate and name them. The first, α (alpha) radiation proved the weakest form of radiation. A sheet of paper can stop α- radiation, which Rutherford determined was the nucleus of a Helium (He) atom. The next strongest form of radiation is β (beta) radiation. β-radiation turns out to be electrons at high velocity, and one needs 6mm of aluminum to stop β particles. Finally, the most powerful radiation is γ (gamma) radiation. γ rays are high energy photons that one needs several millimeters of lead to stop. Gamma rays are thus a form of electromagnetic radiation, just like visible light or X-rays. However, γ rays have a much shorter wavelength and a much higher energy than visible light. Even X-rays with the shortest wavelength and highest energy only overlap into the the range of "long"-wavelength (lower energy) gamma rays. The distinction between X-rays and γ rays is not merely their energy, but also the source of the respective radiations. X-ray photons are generated by energetic electron processes and not nuclear decay. The gamma ray spectrum is usually defined as light having a frequency between 1018 and 1021 Hertz. All radiation, as you might have guessed, is the result of atoms losing some particle or particles. This process of atomic degeneration is radioactive d