In this publication, a setup for fluorescence tomography is used to image nanoparticles in mice. The setup is based on a MetalJet D2 source and Montel optics that focus the 24.1 keV Indium line to a semi-monochromatic, 100 µm narrow beam with low divergence. As contrast agent, the mice are injected with molybdenum nanoparticles that are passively targeted to tumors but also show up in other organs. Spectrometers measure both the transmitted radiation and the x-ray fluorescence from the nanoparticles. The mice are scanned to perform tomography and the results are used to analyze how the nanoparticles accumulate in the mice after different circulation times. The scanning parameters are compatible with in vivo experiments.