Magnetic particle imaging (MPI) recently emerged as a new tomographic imaging method directly visualizing the amount and location of superparamagnetic iron oxide particles (SPIOs) with high spatial resolution. To fully exploit the imaging performance of MPI, specific requirements are demanded on the SPIOs. Most important, a sufficiently high number of detectable harmonics of the receive signal spectrum is required. In this study, an assessment of commercial iron oxide-based MRI contrast agents is carried out, and the result is compared with that of a new self-synthesized high-performance MPI tracer. The decay of the harmonics is measured with a magnetic particle spectrometer (MPS). For the self-synthesized carboxymethyldextran-coated SPIO, it can be demonstrated that despite a small iron core diameter, the particle performance is as good as in Resovist, the best-performing commercial SPIO today. However, the self-synthesized particles show the lowest iron concentration compared with Resovist, Sinerem, and Endorem. As the iron dose will be an important issue in human MPI, the synthesis technique and the separation chain for self-synthesis will be pursued for further improvements. In evaluations carried out with MPS, it can be shown in this work that the quality of the self-synthesized nanoparticles outperforms the three commercial tracer materials when the decay of harmonics is normalized by the iron concentration. The results of this work emphasize the importance of producing highly uniform and monodisperse superparamagnetic particles contributing to lower application of tracer concentration, better sensitivity, or a higher spatial resolution.