Correct choice is (a) Positron
Best explanation: PET stands for Positron Emission Tomography. In a PET process, there is a nuclear reaction causing emission of a positron. This positron comes in contact with an electron, undergoes annihilation and gives out two gamma rays which are detected by the detector. On the gamma rays that are detected at the opposite ends are used to form an image. Rest are discarded as noise.
