Methods and systems are disclosed, including a method for confining an annihilation range of a positron, from a plurality of positrons emitted from an object being imaged in a positron emission tomography (PET) imaging system. Confining the annihilation includes applying a stochastic multidimensional time varying magnetic field on the positron. Optionally, the stochastic multidimensional time varying magnetic field includes components in each of three dimensions.