Development of a new drug faces multi-faceted sequences in the pipeline. Once a drug candidate is identified, evaluation process can be accelerated by in vivo noninvasive imaging because there is a potential to use a smaller number of animals and human subjects. Radionuclide imaging techniques, such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) are directly translatable imaging modalities that can be used in both animal models of disease and humans. In addition, SPECT and PET provide a highly sensitive means to track radiolabeled drugs, for which the imaging process less likely perturbs biological functions of animals and humans. Quantification of SPECT and PET data when used for drug development is elusive. Often times, in vivo SPECT and PET images of any drug candidate are used as ‘flash’ show-and-tell scenarios while actual data are obtained from ex vivo analyses. However, once the need and the degree of quantification are defined carefully, quantification of SPECT and PET can play an important role in drug development and evaluation processes.