Nuclear Medicine is a medical specialty that allows modern diagnostics and treatments using radiopharmaceuticals original radiotracers (drugs linked to a radioactive isotope). The radiopharmaceuticals are considered a special group of drugs and thus their preparation and use are regulated by a set of policies that have been adopted by individual member countries. The radiopharmaceuticals used in diagnostic examinations are administered in very small doses. So, in general, they have no pharmacological action, side effects or serious adverse reactions. The most serious issue with their use is the potential for diagnostic mistakes due to changes in their biodistribution. The appearance and development of new radiopharmaceuticals in both the diagnostic and therapeutic domains, as well as the impact of new multimodality imaging techniques, are all having a significant impact on nuclear medicine (SPECT-CT, PET-CT, PET-MRI, etc.). It is crucial to understand the techniques limitations, radiopharmaceutical distribution and potential physiological changes, radiological contrast contraindications and bad responses, and the possibility of both interfering. The process of generating radiopharmaceuticals is introduced and relevant interactions of radiation with matter are discussed. Diagnostic nuclear medicine instrumentation is explained, and future trends in nuclear medicine imaging technology are forecasted.