Magnetic particle imaging is a new approach to visualizing magnetic nanoparticles. It is capable of 3D real-time in vivo imaging of particles injected into the blood stream and is a candidate for medical imaging applications. To date, only one particle type has been imaged at a time, however, the ability to separate signals acquired simultaneously from different particle types or from particles in different environments would substantially increase the scope of the method. Different colors could be assigned to different signal sources to allow for visualization in a single image. Successful signal separation has been reported in spectroscopic experiments, but it was unclear how well separation would work in conjunction with spatial encoding in an imaging experiment. This work presents experimental evidence of the separability of signals from different particle types and aggregation states (fluid versus powder) using a 'multi-color' reconstruction approach. Several mechanisms are discussed that may form the basis for successful signal separation.

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In assessing the safety aspect of future clinical magnetic particle imaging (MPI), this novel imaging technique can refer to expertise that is cumulated in the IEC standard for magnetic resonance imaging (MRI) safety. Both imaging techniques employ strong dynamic magnetic fields and therefore have to take caution to refrain from physiological effects such as peripheral nerve stimulation (PNS) or excessive tissue heating. This paper starts with an outline of the differences between MPI and MRI. Then, the basics of PNS and tissue heating are reviewed and applied to the specific MPI case. Finally, sequences for MPI are presented that will allow rapid MPI imaging at 150 kHz while being safe for the patient. Index Terms-Magnetic particle imaging (MPI), magnetic stimulation, peripheral nerve stimulation (PNS), specific absorption rate (SAR).

After realizing the worlds' first preclinical magnetic particle imaging (MPI) demonstrator, Philips is now realizing the worlds' first whole-body clinical prototype to prove the feasibility of MPI for clinical imaging. After a brief introduction of the basic MPI imaging process, this contribution presents an overview on the determining factors for key properties, i.e., spatial resolution, acquisition speed, sensitivity, and quantitativeness, and how these properties are influenced by scaling up from preclinical to clinical instrumentation. Furthermore, it is discussed how this scale up affects the physiological compatibility of the method as well as hardware parameters such as power requirements for drive field generation, selection and focus field generation, and the design of the receive chain of the MPI device.