Spontaneous malignancies arising in pet dogs form the basis of comparative oncology: the study of naturally occurring cancers across species with the power to inform human cancer research and therapeutic development strategies. The inclusion of imaging technology should also be considered, as pet dogs have and will play a key role in the discovery and development of technologies that facilitate cancer detection, monitoring, and molecular imaging. Several key features of spontaneous canine malignancies that are not present in other laboratory animal models make pet dogs a vital component of any novel cancer imaging technology development plan. This chapter reviews the past, current, and future endeavors in which tumor-bearing pet dogs are informing clinical investigations of novel imaging technology from hardware and agent standpoints, emphasizing the types of comparative oncology research questions that form the basis for successful studies. We provide examples of how tumor-bearing pet dogs have enabled the exploration of novel combinations of different imaging agents, particularly those with variable radiopharmaceutical composition. These include translational studies with validated imaging signals against clinical findings and tissue histology, allowing for an exploration of imaging agents combined with dose and technique optimization for validation both in vivo and with ex vivo tissue obtained during surgical procedures.