**2.2.2 Technique of skeleton PET imaging**

PET is one of the exciting tomographic techniques, and provides functional information of blood flow and metabolism. As a positron meets a free electron in the tissue, annihilation occurs and the two 511keV annihilation photons are detected by coupled opposing detectors in coincidence. PET is more sensitivity than SPECT, and differs from SPECT by "electronic collimation".
