**1. Introduction**

Nuclear Medicine is a medical speciality that involves the application of small amounts of radioactive materials, known as radiopharmaceuticals, for the diagnosis and treatment of disease, without causing any physiological effect.

Drug‐delivery strategies have been steadily being developed in order to obtain better therapeutic results, enhance adhesion to treatment, and mitigate side effects. The ever‐ increasing complexity of the systems, combined with the regulatory demands by the Medi‐ cines Authorities, made the *in vivo* analysis of those systems' behavior almost compulsory.

The unique characteristics of Nuclear Medicine and Radiopharmaceuticals make dynamic, noninvasive studies and therefore are frequently used in the evaluation and development of new drug‐delivery systems. This chapter aims to review the different techniques available, their rationale and applications, using, whenever possible, examples from the literature as well as from the authors' own experience.
