Positron Emission Tomography (PET) imaging is a functional exploration technique for humans and animals invented in the early 70s, based on the administration of a specific radioactive labeled molecule. The first large part of this work reports theoretical aspects of the technique, including the problem of image reconstruction and corrections based on physical models necessary for the realization of 3D PET imaging. PET has gained large adoption in the clinics today, especially in the field of oncology. Considering this new availability, the question of standardization arises. As a consequence we explore and compare absolute performances of a unique panel of >30 PET-CT cameras based on a recognized standard. We write some proposals for further standardization, and for extension to evaluation of a novel commercial feature: time-of-flight imaging. We further develop image processing techniques for spatial resolution recovery based on a general analytic model, adapted to small lesions (MBPVEC). Another related development concerns larger lung lesions when respiratory motion is present. Quantitative corrections based on CT are evaluated, and a proposal is made for a novel technique alternative gating technique. The adaptive amplitude gating (AAG) methodology both improves detection and quantitative results for this lesion type. This work characterizes further the PET modality from instrumentation, physics and image processing perspectives. It was driven by a medical and clinical question and multiple collaborations with clinical institutions, what justifies its classification as multidisciplinary.