DOI 10.1007/s00702-004-0272-2 J Neural Transm (2005) 112: 319–330 Micropet imaging: in vivo biochemistry in small animals  V. Sossi 1;2 and T. J. Ruth 1 1 University of British Columbia=TRIUMF PET Program, and 2 Physics and Astronomy Department, University of British Columbia, Vancouver, B.C., Canada Received May 12, 2004; accepted December 11, 2004 Summary. Significant technological advancements required for imaging phys- iological function in small animals have been achieved in the last few years. Dedicated small animals PET scanners are now achieving resolutions that approach the one obtainable by autoradiographic methods, while still maintaining enough detection sensitivity to reliably measure biologically relevant parameters such as binding potentials or rate constants. Such developments have enabled researchers to explore in-vivo rodent models of human disease. The future in imaging now lies in the development of multi-modality imaging approaches, while the big challenge in the next few years will be for the chemists to develop tracers that are more specific and reflective of the functional condition under investigation, while miniaturizing the chemical synthesis related instrumentation. Keywords: Small animal imaging, radiotracers, positron emission tomography. Introduction For years researchers have used small animal models of human disease to address questions by using radiotracers and autoradiography. While providing high spatial resolution, these techniques suffer from two major shortcomings: data can only be collected post-mortem and might not provide a true represen- tation of in-vivo processes. Likewise they do not allow for the performance of longitudinal studies on the same subjects. The temporal progression of a pro- cess under investigation is generally obtained by using a large group of animals, supposedly treated in an identical fashion, and by sacrificing a subset at partic- ular time points of interest. Such procedures are not only costly in terms of animal life, but also introduce inter subject variability into the results. Positron emission tomography (PET) is a functional imaging modality that overcomes both these shortcomings: functional information can be obtained in-vivo, on live animals. Repeated and thus longitudinal studies in the same animals (Nikolaus et al., 2003; Umegaki et al., 2003) now become possible. PET is based on the  Lecture, 11th IWCN Congress, September 14–16, 2003 (Campbell River, BC, Canada)