Over the past few decades, immuno-PET has demonstrated its value by enabling both visual and quantitative investigations of the immune system in vivo (1). In the development of monoclonal antibody (mAb)-based therapy, immuno-PET helps answering important questions related to 1) the pharmacokinetics of the drug or molecule: “What is the distribution of the drug or molecule?”, 2) study optimisation: “What is the optimal imaging mass dose and time point?”, and 3) target engagement: “Does the drug or molecule reach and interact with the target?”.