Abstract: The coincidence technique employed in positron emission tomography (PET) to detect the two simultaneously, emitted annihilation photons of 511 keV that travel at a 180�angle to each other. Because of the scattered radiation, the scattered photons were also detected by the coincidence technique in PET. PET images uncorrected for scatter give inaccurate image data and, in addition, the scatter contribution could give rise to signal to noise ratio (SN R) and could produce highly structured errors or artifacts in the images. So, to understand of the effects of the scatter on PET imaging, and to master the measured and corrected methods of the scatter will improve the quality of image and accurately measure the biological parameters of the radiophamaceutical in vivo.