24.3

Magnetic Nanoparticles for Magnetic Particle Imaging

Magnetic particle imaging (MPI) is an emerging tomographic imaging technique

that provides the fast acquisition of 3-D volumes with high temporal resolution for

in vivo imaging. The principle of MPI is based on the nonlinear magnetic suscepti-

bility of MNPs (Paysen et al. 2019). In the presence of an oscillating magnetic field,

there is a shift in the magnetization of MNPs, which leads to the generation of

response signal from MNPs. MPI performance for clinical diagnostics strongly

depends on the type of the magnetic material assessed. Amongst a variety of

available MNPs, iron oxide NPs (IONPs) have the potential to be used as MPI

tracers attributed to its superparamagnetic nature, tendency for magnetic saturation,

and nonlinear magnetization curve. Additionally, IONPs are metabolizable and

nonradioactive, induce linearly qualitative images, and assist in long-term tracking

of targeted cells. As MPI directly locates and produces images of the IONPs in the

targeted area, thereby, the concentration of IONPs governs the intensity of the MPI

signal obtained (Meola et al. 2019). Moreover, MPI signal is only originated from

MNPs without signal contributions from anatomical structures as human body

tissues are diamagnetic in nature and thus cannot produce any signal that might be

deemed as background noise (Tomitaka et al. 2019). MPI has an edge over other

diagnostic techniques as it does not employ any source of radiation for imaging

purposes. To summarize, MPI offers a potential biomedical imaging technique with

same protection as magnetic resonance imaging, speed as of X-ray computed

tomography, and sensitivity that of positron-emission tomography (Khandhar et al.

2017).

These attributes offer a plethora of clinical applications such as cardiovascular

imaging, cancer diagnosis, brain injury detection, lung perfusion imaging, and

in vivo tracking of magnetically labelled stem cells. Moreover, the in vivo preclinical

diagnosis by MPI is reckoned clinically safe due to the biocompatible nature of

IONPs and nonemployment of any ionizing source for imaging purposes.

Additionally, MNP, has the potential to label the cells and these MNP-labelled

cell can be visualized by MPI, generating three-dimensional view of distributed

MNP-labelled cells in the body. On the basis of this, Song et al. tailored Fe3O4 NPs

encapsulated

by

fluorescent

semiconducting

polymers

to

create

Janus

Fe3O4NPs@semiconducting polymers which were assessed for the in vivo labelling

and tracking of cancer cells. In comparison with fluorescence imaging and MRI,

Janus Fe3O4NPs@semiconducting polymers by MPI offered superior sensitivity,

deep tissue penetration, and excellent linearity between the tracer amount and the

signal intensity (Song et al. 2018). Similarly, Jung et al. labelled exosomes released

by both hypoxic tumor cells and normal tumor cells with superparamagnetic

particles. The labelled exosomes were then traced by MPI (Jung et al. 2018).

Furthermore, Zheng et al. utilized standard superparamagnetic iron oxide (SPIO)

particles for the labelling of mesenchymal stem cells (MSCs) in order to trap them in

the target tissue. This experiment was performed on the mice in which labelled stem

cells were injected into the mice through the tail vein and then these distributed stem

cells were tracked through MPI (Zheng et al. 2016).

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Recent Progress in Applications of Magnetic Nanoparticles in Medicine: A Review

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