Chronic liver disease can progress to cirrhosis, with death due to liver failure and cancer. Cirrhosis prevalence in the EU is 0.5%-1%. However, development of therapies that prevent progression to cirrhosis is hampered by the lack of a sensitive, non-invasive method to quantify fibrosis or fibrosis progression (fibrogenesis). Liver biopsy 1) is risky, 2) shows high sampling variability, and 3) is too insensitive to assess fibrosis progression in clinical studies. Conventional radiological imaging, serum markers, and ultrasound- or MR-elastography do neither permit exact fibrosis nor any fibrogenesis measurement.We plan to develop a clinically applicable methodology to quantitate fibrosis and fibrogenesis over the whole liver using imaging agents that target and thus quantify abundant fibrillar collagen or key cells that drive fibrogenesis (activated myofibroblasts and cholangiocytes). We demonstrated the feasibility of this approach using radiolabeled conjugates of high affinity that target integrin alphaVbeta6 and PDGFbeta receptor that are cell surface molecules of activated cholangiocytes and myofibroblasts. i.v. injection of the integrin conjugate allowed quantitative imaging of alphaVbeta6 expression and correlated with whole liver fibrogenesis. We intend to optimize nonpeptide and peptide ligands for integrin alphaVbeta6, PDGF beta receptor and fibrillar collagens using novel linkers and oligomerization, using PET-radioimaging with Ga-68, Sc-44 and F-18. The targeted imaging constructs will be validated in vivo using established rodent models with defined liver fibrosis and fibrogenesis, with and without antifibrotic drug therapy. Translation to phase I and II clinical studies is planned in years 4-5 of the project.The technology will for the first time allow for 1. individual risk assessment of fibrosis progression, and 2. rapid testing of antifibrotic drugs and their combinations in small groups of individual patients.