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High frequency hysteresis characterization of magnetic nanoparticles

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https://ir.library.oregonstate.edu/concern/graduate_projects/nz806370r

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  • Hyperthermia is a cancer therapy that relies on the local heating of a cancerous tumor to kill cancer cells and disrupt the future growth of the tumor. While hyperthermia is capable of killing tumors separately, physicians often combine it with other treatment methods, typically radiation therapy, for its synergistic effects [1]. Using hyperthermia alone requires specific targeting of the cancer location to avoid collateral damage to healthy cells, which is difficult to achieve with traditional hyperthermia methods [2]. To improve specific heating of cancer cells, specialized magnetic nanoparticles have been used [3]. The functionalized magnetic nanoparticles bind to the cancer cells and dissipate thermal energy when an alternating magnetic field is applied. The particles should generate a large amount of heat, characterized as the specific absorption rate (SAR), while minimizing the frequency and amplitude of the applied field. Magnetic particle imaging (MPI) is a tomographic imaging technique that utilizes the nonlinear magnetic characteristics of superparamagnetic particles for in vivo imaging [4]. The technique relies on creating a gradient field such that there is an area of no magnetic field, also known as a field free point (FFP). Particles within the FFP will respond to an applied ac magnetic field, giving off their own signal that can be detected. Particles outside the FFP are saturated and do not respond to the applied ac field. Scanning the FFP allows the particle concentrations throughout the patient to be mapped, giving a 3D image of particle concentrations. This method of imaging is being investigated as an alternative to traditional angiography techniques that use x-ray imaging combined with a contrast agent to evaluate blood flow in vessels throughout the body [4]. This reliance on ionizing radiation shows an increased risk of cancer, especially for younger patients [5]. Not using ionizing radiation and MPI’s fast imaging speeds make it an attractive alternative to traditional angiography. Another application for magnetic nanoparticles is biosensing e.g. MPI using functionalized magnetic nanoparticles to locate and track targets in vivo [6]. In order to effectively use magnetic nanoparticles with hyperthermia and MPI applications the magnetic nanoparticles need to be characterized at the field and frequency commensurate with the application. MPI and hyperthermia both use field amplitudes of 10 mT to 100 mT and operate at frequencies of 10 kHz to 100 kHz and 100 kHz to 1 MHz, respectively [7] [8]. Magnetic characterization of magnetic nanoparticles at the field and frequencies used in MPI and hyperthermia could allow magnetic nanoparticle synthesis to be optimized for the intended application. There are various methods available to characterize the ac magnetic response of materials [9]. One method of interest is ac magnetometry, which measures ac MH response [9]. Few instruments are capable of the high fields required to characterize magnetic nanoparticles for use in MPI or hyperthermia. This work discusses the design and construction of a high field ac magnetometer.
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