Abstract: The principle of PET (Positron Emission Tomography) and its image reconstruction methods are briefly reviewed, with emphasis on the FBP (Filtered Back-Projection) method and the OSEM (Ordered Subset Expectation Maximization) both are often used in modern PET. By PET clinical protocol, some parameters can be suitably chosen in order to obtain better reconstructed images. The 3D PET rebinning algorithms are also introduced.