**4. Magnetic particle imaging is a recent development in imaging technology**

A new imaging method called magnetic particle imaging (MPI) has just been developed to find iron oxide nanoparticles (NPs). Some MRI flaws, such as poor specificity (caused by other low signal regions in MRI, such as hemorrhagic regions or those containing air) and challenging quantification, can be resolved with MPI. High tracer specificity is made feasible by leveraging MPI's direct detection of iron oxide NPs, which offer positive contrast without any underlying background signal from biological tissues. Iron (Fe) concentrations of 550 pg./L in vitro and 7.8 ng Fe in vivo, as well as detection limits as low as 1.1 ng Fe, have all been demonstrated. A static gradient field with a single, field-free parameter identifies signals in MPI. (FFR), which could be a line or a point. Then, using the particles already present in the FFR, a signal is produced by an oscillating magnetic field. Raster scanning the FFR throughout the entire field of vision produces images. Outside of the FFR, superparamagnetic particles are still fully magnetized and do not increase the signal [27].

#### *Iron Oxide Nanoparticles: A Mighty Pioneering Diagnostic Tool But Is It Really Safe… DOI: http://dx.doi.org/10.5772/intechopen.112074*

Because MPI directly detects SPIO magnetization, the signal is very dependent on the SPIO tracer's physical characteristics. For NPs to be suitable for MPI, they must possess the following three characteristics: superparamagneticity, susceptibility to magnetic saturation, and a nonlinear magnetic curve.

Since many SPION agents for MRI have the aforementioned characteristics, their prospective application in MPI has been looked at. Resovist®, a previously developed MRI contrast agent for the liver, was used to produce the most efficient MPI [20]. Magnetic Insight, Inc. has unveiled VivoTrax®, a carboxydextran-coated iron oxide NP formulation, with the same reference standard. It is intriguing to note that MPI can locate the clinically approved ferumoxytol rapidly [28]. Other research teams are working to develop new MPI tracers as it was established that neither Resovist® nor VivoTrax® was the optimal MPI solution.

There are numerous MPI biological applications that are now being studied. Early cancers can be identified using MPI by utilizing the tumor's enhanced permeability and retention (EPR) impact [29, 30]. Due to the leaky capillaries with big holes that result in the EPR phenomena, tumor tissue is an excellent target for therapy with nanomedicines and nanosized contrast agents. As a result, MPI plays a crucial clinical role in the early detection of cancer.

Cell tracking is one of MPI's oldest and most promising applications due to its superior tissue penetration, absence of background noise, and high degree of sensitivity, which enables it to identify as little as 200 tagged cells. Recently, mesenchymal stem cells (MSCs) tagged with clinically relevant feromuxytol NPs have been found by Nejadnik et al. [31] using MPI. A noteworthy achievement for the therapeutic application of MPI technology was the precise in vivo identification and quantification of ferumoxytol-labeled stem cells.
