are the decay formulas and half-lives for the three PET isotopes:carbon-11 > boron-11 + e* (half-life ~ 20 minutes)
oxygen-15 > nitrogen-15 + e* (half-life ~ 2 minutes)fluorine-18 > oxygen-18 + e* (half-life ~ 110 minutes)PET uses a fundamental property of the positron—it is the antimatter
particle (antiparticle) corresponding to the electron. When a particle
encounters its corresponding antiparticle, there is a complete annihi-
lation of the mass of both particles, converting all the mass into en-
ergy (according to E = mc). When a positron is emitted via radioactive
decay, it will very quickly encounter an electron (because electrons
are everywhere in normal matter) and annihilate. The resulting
energy of this positron-electron annihilation emerges as two high-
energy gamma-ray photons flying off in exactly opposite directions.
By placing gamma-ray detectors all around the region where the
radioactive material is located and watching for photons emerging si-
multaneously and exactly 180 degrees apart, it is possible, by a sort of
triangulation, to rather precisely determine the source of the radioac-
tive decay.
The first isotope used for PET was fluorine-18. A radioactive variant
of glucose can be made by replacing one of the oxygen atoms in the
sugar with fluorine-18. Glucose is transported via the blood through-
out the body, and all cells in the body use glucose as an energy source.
Cells that are working harder use more glucose. In particular, nerve
cells that are more robustly generating signals in the form of action
potentials require more glucose to make the ATP needed to operate
their Na/K pumps and maintain membrane potential. Thus, the more
active the neuron, the more glucose it will take up from the blood.
If glucose radioactively labeled with fluorine-18 is injected into a