Magnetic Particle Imaging (MPG) is a new imaging method that emerged in 2005. Magnetic nanoparticles that can be administered to the body in different ways (vascular access, respiration, local injection, etc.) can be imaged using magnetic fields with MPG. MPG has advantages such as the use of iron oxide-based nanoparticles that do not harm the body, high resolution images can be obtained in real time or near real time, any part of the body can be viewed without depth constraints and ionizing radiation is not used. Research studies are ongoing for the use of MPG in a wide variety of medical applications such as angiography, tumor imaging, imaging of intra-body hemorrhages, stem cell monitoring, and functional brain imaging.
Basic Operating Principles of Magnetic Particle Imaging Method
Magnetic nanoparticles, ranging in diameter from 5 nm to 100 nm, usually consist of a core of iron oxide (Fe304 / Fe2O3) and a polymer coated around this core. Iron oxide shows superparamagnetic properties in these diameters. In other words, while their average magnetization is zero when there is no magnetic field in the environment, when the magnetic field is applied, they are rapidly magnetized in this field. Coating the nuclei with polymer prevents the particles from coalescing and prevents destruction by the body's immune system. In this way, the circulation time of nanoparticles in the body is extended. In addition, it is possible to functionalize nanoparticles by binding molecules such as antibodies, drugs, enzymes, nucleic acids to polymers. Thus, the particles can be given properties such as external display, binding to target cells (eg tumor cells), drug transport and release.
Magnetic Particle Imaging, due to its name, can be confused with Magnetic Resonance Imaging (MRI). However, these two methods are completely different from each other in terms of both the working principle and the images obtained. While tissues are viewed anatomically in MRI, tissues are not visible in MPG images, only magnetic nanoparticles given to the body are displayed. Thus, the anatomical image and the nanoparticle image do not interfere with each other and imaging can be performed depending on the absolute nanoparticle density.
In the MPG method, a zone (magnetic field-free zone - MAB) where the magnetic field is zeroed in the imaged region is created. Since the magnetic field density around the MAB is low, the magnetization vectors of nanoparticles in this region are in random directions. The further away from the MAB, the greater the intensity of the magnetic field. The magnetization of nanoparticles in the intense magnetic field is aligned in the same direction as the applied magnetic field (magnetic saturation state). When a time varying homogeneous magnetic field is applied, this magnetic field cannot react because nanoparticles other than MAB are in a saturated state. Nanoparticles around the MAB react rapidly and become magnetized. This magnetization signal is received using receiving coils. The MAB is scanned electronically and / or mechanically within the imaging region to obtain an image proportional to the nanoparticle density.
Studies in ASELSAN
There is no human-sized commercial MPG device in the world yet. A unique prototype MPG system has been developed at the ASELSAN Research Center. Considering the interventional applications, a new open-edge system architecture was proposed and a US patent was obtained. In this system, a linear magnetic field-free region is scanned in the tissue, thus a high signal to noise ratio is obtained, and it is possible to scan large areas faster. However, open-sided configurations are much more comfortable for patients than closed systems. It will be possible to conduct small animal experiments in the ASELSAN MPG prototype system, which can scan an area with a diameter of 60 mm. Resolution and sensitivity measurements were made in the system, and phantom experiments were carried out to show the feasibility of detecting vascular occlusion.
With a self-funded project launched in August 2020, work to develop a human-sized MPG scanner has been initiated. Research is also planned for the use of this scanner for Magnetic Resonance imaging. In this way, anatomical information can be obtained with MR images and nanoparticles can be viewed with MPG.
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