Abstract
Magnetic particle imaging (MPI) is a new imaging technique that detects the spatial distribution of magnetic nanoparticles (MNP) with the option of high temporal resolution. MPI relies on particular MNP as tracers with tailored characteristics for improvement of sensitivity and image resolution. For this reason, we developed optimized multicore particles (MCP 3) made by coprecipitation via synthesis of green rust and subsequent oxidation to iron oxide cores consisting of a magnetite/maghemite mixed phase. MCP 3 shows high saturation magnetization close to that of bulk maghemite and provides excellent magnetic particle spectroscopy properties which are superior to Resovist® and any other up to now published MPI tracers made by coprecipitation. To evaluate the MPI characteristics of MCP 3 two kinds of tube phantoms were prepared and investigated to assess sensitivity, spatial resolution, artifact severity, and selectivity. Resovist® was used as standard of comparison. For image reconstruction, the regularization factor was optimized, and the resulting images were investigated in terms of quantifying of volumes and iron content. Our results demonstrate the superiority of MCP 3 over Resovist® for all investigated MPI characteristics and suggest that MCP 3 is promising for future experimental in vivo studies.
Highlights
Magnetic particle imaging (MPI) was first presented as a novel radiation-free imaging modality by Weizenecker and Gleich in 2005 [1]
The signal produced by multicore particles (MCP) 3 is still three to four times higher compared with Resovist®
The evaluation of the optimal regularization factor λ indicated the higher signal-to-noise ratio (SNR) for MCP 3. These results are consistent with the observed better resolution and better visualization of phantom geometry seen for MCP 3 versus Resovist®
Summary
Magnetic particle imaging (MPI) was first presented as a novel radiation-free imaging modality by Weizenecker and Gleich in 2005 [1]. As MPI only detects the tracer, combination of MPI with other imaging modalities such as magnetic resonance imaging (MRI) or computed tomography (CT) is necessary to obtain the corresponding anatomical information [5,6]. To further advance MPI as a medical imaging modality, there is still a great need for the development of new MPI tracers. Tracers with excellent MPI characteristics are especially crucial for the potential preclinical development of this imaging modality and the identification of new possible clinical applications. Thermal decomposition provides very good control over the MNP shape, and the achievable size distribution is very narrow This method is complicated and needs high temperatures in some cases over 300 ◦C plus an inert gas atmosphere and produces a lot of possibly toxic byproducts [26]. With this method, the MNP are synthesized in organic solvents and, for use in biological systems, need to be transferred into the aqueous phase
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