The high mortality in the final stage of certain liver diseases and the lack of whole organ donors for liver transplantation require alternative therapeutic approaches. Cell based therapy has been one of the promising approaches for treating liver diseases. Hereby, the utilization of hepatocytes or stem cells differentiated towards functional hepatocytes has been studied intensively. In order to validate the success of those approaches, it is necessary to monitor the location, homing and functionality of engrafted cells longitudinally and non-invasively. This has been possible with the help of imaging modalities like magnetic resonance imaging, positron emission tomography and optical imaging methods. All those methods require contrast agents, tracers or imaging reporters that track not only the location of transplanted cells but also visualize their functional status in vivo.
In this review, we provide an overview of possible contrast agents and tracers for liver imaging, an outline of imaging approaches for tracking transplanted cells in the liver and discuss imaging strategies to assess liver function non-invasively. Hereby, a strong focus will be on the assessment of imaging markers for the different modalities in experimental models for normal and diseased liver. We conclude the review with the possible advantages of such markers for diagnosis and monitoring of disease progression and therapy assessment over currently available imaging modalities.