For medical research, approximately 115 million animals are needed every year. In medical imaging, rodents are used to test possible applications and procedures for diagnoses of anatomical and physiological diseases. However, working with living animals increases the complexity of an experiment. Accurate experimental planning is essential in order to fulfill the 3R rules (replace, reduce, refine). Especially in tracer-based imaging modalities, such as magnetic particle imaging (MPI), where only

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... nanoparticles give a positive contrast, the anatomical structure of the rodent is not visible without co-registration with another imaging modality. This leads to problems in the experimental planning, as parameters such as field of view, rodent position, and tracer concentration have to be determined without visual feedback. In this work a 3D CAD rat model is presented, which can be used to improve the experiment planning and thus reduce the number of animals required. It was determined using an anatomy atlas and 3D printed with stereolithography. The resulting model contains the most important organs and vessels as hollow cavities. By filling these with appropriate tracer materials, the phantom can be used in different imaging modalities such as MPI, MRI or CT. In a first MPI measurement, the phantom was filled with superparamagnetic nanoparticles. The tracer concentrations in the different organs were determined assuming a steady state that mimics an even distribution of particles in the blood of a living rat. The perfusion of the organs was imitated by calculating the ratio of the blood volume contained in the respective organ to the entire organ volume of the model. Finally, a successful visualization of all organs and vessels of the phantom was possible. This enables the planning of the experiment and the optimization of the experimental parameters for a region of interest, where certain organs would be localized in a living animal.