Nano-sized particles are widely regarded as a tool to study biological events at cellular and molecular levels. However, there are only a few imaging modalities that can visualize interactions between nanoparticles and living cells. A new technique -- pulsed magneto-motive ultrasound imaging, capable of in-vivo imaging of magnetic nanoparticles at improved depth and in real-time is introduced in this study. In pulsed magneto-motive ultrasound imaging, an external high-strength pulsed magnetic field is applied to induce motion within magnetically labeled tissue and ultrasound is used to detect the induced internal tissue motion. A laboratory prototype of a pulsed magneto- motive ultrasound imaging system was built, tested and optimized through modeling and experimental studies using tissue-mimicking phantoms, ex-vivo tissue samples and in- vivo mouse tumor model. The results demonstrated a sufficient contrast between normal and iron-laden tissue labeled with ultra-small magnetic nanoparticles. Finally, further modifications and research directions are discussed which can eventually lead to development of a clinically applicable pulsed magneto-motive ultrasound imaging system. / text