The ultimate goal of any type of medical imaging procedure is to obtain the best image quality while delivering the smallest radiation dose possible to the patient. The best image quality though, does not necessarily give the correct diagnosis for a given medical condition at the lowest possible dose to the patient. Additionally the vast number of alternative diagnostic modalities available today and their rapid evolution make the choice of the most suitable modality for a particular medical condition very difficult, if dose to the patient is to be considered as a major constraint. It is therefore very important to know the dose received by the patient from the different modalities to arrive at the same diagnostic result. This is especially important in Nuclear Medicine where the different modalities produce images of the metabolic function of the human body and they are more likely to arrive at the same diagnostic outcome. The aim of this presentation is to give an overview of the methods used to optimise the diagnostic value of the images produced by Nuclear Medicine diagnostic modalities.