Self-consistent magnetic properties of magnetite tracers optimized for magnetic particle imaging measured by ac susceptometry, magnetorelaxometry and magnetic particle spectroscopy

Ludwig, Frank; Remmer, Hilke; Kuhlmann, Christian; Wawrzik, Thilo; Arami, Hamed; Ferguson, R. Matthew; Krishnan, Kannan M.

doi:10.1016/j.jmmm.2014.02.020

Cited by 51 publications

(36 citation statements)

References 26 publications

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“…7, 16, 24, 57 Anisotropy constants for our nanoparticles have previously been measured to be on the order of 3.5 ± 3.0 kJ/m 3 for 25 nm SPIONs, well below bulk values of approximately 11 kJ/m 3 . 58, 59 …”

Section: Methodsmentioning

confidence: 99%

Synthesis of phase-pure and monodisperse iron oxide nanoparticles by thermal decomposition

et al. 2015

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Superparamagnetic iron oxide nanoparticles (SPIONs) are used for a wide range of biomedical applications requiring precise control over their physical and magnetic properties, which are dependent on their size and crystallographic phase. Here we present a comprehensive template for the design and synthesis of iron oxide nanoparticles with control over size, size distribution, phase, and resulting magnetic properties. We investigate critical parameters for synthesis of monodisperse SPIONs by organic thermal decomposition. Three different, commonly used, iron containing precursors (iron oleate, iron pentacarbonyl, and iron oxyhydroxide) are evaluated under a variety of synthetic conditions. We compare the suitability of these three kinetically controlled synthesis protocols, which have in common the use of iron oleate as a starting precursor or reaction intermediate, for producing nanoparticles with specific size and magnetic properties. Monodisperse particles were produced over a tunable range of sizes from approximately 2–30 nm. Reaction parameters such as precursor concentration, addition of surfactant, temperature, ramp rate, and time were adjusted to kinetically control size and size-distribution, phase, and magnetic properties. In particular, large quantities of excess surfactant (up to 25:1 molar ratio) alter reaction kinetics and result in larger particles with uniform size; however, there is often a trade-off between large particles and a narrow size distribution. Iron oxide phase, in addition to nanoparticle size and shape, is critical for establishing magnetic properties such as differential susceptibility (dm/dH) and anisotropy. As an example, we show the importance of obtaining the required size and iron oxide phase for application to Magnetic Particle Imaging (MPI), and describe how phase purity can be controlled. These results provide much of the information necessary to determine which iron oxide synthesis protocol is best suited to a particular application.

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Section: Methodsmentioning

confidence: 99%

Synthesis of phase-pure and monodisperse iron oxide nanoparticles by thermal decomposition

et al. 2015

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“…[219] for fine particles and only weakly dependent on δU [220]. Calculating τ N for idealized spherical particles of different radii with δU = Kv ( r ), one can find that there is a narrow range of radii, 10–12 nm, for which the relaxation times fall in the interval 0.01–100 s typical to most biological time scales.…”

Section: Theoretical Conceptsmentioning

confidence: 99%

Biological effects of the hypomagnetic field: An analytical review of experiments and theories

2017

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During interplanetary flights in the near future, a human organism will be exposed to prolonged periods of a hypomagnetic field that is 10,000 times weaker than that of Earth’s. Attenuation of the geomagnetic field occurs in buildings with steel walls and in buildings with steel reinforcement. It cannot be ruled out also that a zero magnetic field might be interesting in biomedical studies and therapy. Further research in the area of hypomagnetic field effects, as shown in this article, is capable of shedding light on a fundamental problem in biophysics—the problem of primary magnetoreception. This review contains, currently, the most extensive bibliography on the biological effects of hypomagnetic field. This includes both a review of known experimental results and the putative mechanisms of magnetoreception and their explanatory power with respect to the hypomagnetic field effects. We show that the measured correlations of the HMF effect with HMF magnitude and inhomogeneity and type and duration of exposure are statistically absent. This suggests that there is no general biophysical MF target similar for different organisms. This also suggests that magnetoreception is not necessarily associated with evolutionary developed specific magnetoreceptors in migrating animals and magnetotactic bacteria. Independently, there is nonspecific magnetoreception that is common for all organisms, manifests itself in very different biological observables as mostly random reactions, and is a result of MF interaction with magnetic moments at a physical level—moments that are present everywhere in macromolecules and proteins and can sometimes transfer the magnetic signal at the level of downstream biochemical events. The corresponding universal mechanism of magnetoreception that has been given further theoretical analysis allows one to determine the parameters of magnetic moments involved in magnetoreception—their gyromagnetic ratio and thermal relaxation time—and so to better understand the nature of MF targets in organisms.

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“…with H k (0.03 T/l 0 ) the field at which the energy barrier due to general uniaxial anisotropy is suppressed (equal to 2K eff / l 0 M s ) for magnetocrystalline anisotropy, K eff (5 kJ/m 3 ) is the effective uniaxial anisotropy, determined from previously published magneto-relaxometry, AC susceptibility, and MPS studies, 21 and V is the particle volume (8.18 Â 10 À24 m 3 ). According to Usov et al, 7,20 b ¼ 0.9, n ¼ 1.…”

Section: A Slew-rate Dependencementioning

confidence: 99%

Slew-rate dependence of tracer magnetization response in magnetic particle imaging

Shah

Ferguson

Krishnan

2014

Journal of Applied Physics

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Magnetic Particle Imaging (MPI) is a new biomedical imaging technique that produces real-time, high-resolution tomographic images of superparamagnetic iron oxide nanoparticle tracers. Currently, 25 kHz and 20 mT/l 0 excitation fields are common in MPI, but lower field amplitudes may be necessary for patient safety in future designs. Here, we address fundamental questions about MPI tracer magnetization dynamics and predict tracer performance in future scanners that employ new combinations of excitation field amplitude (H o ) and frequency (x). Using an optimized, monodisperse MPI tracer, we studied how several combinations of drive field frequencies and amplitudes affect the tracer's response, using Magnetic Particle Spectrometry and AC hysteresis, for drive field conditions at 15.5, 26, and 40.2 kHz, with field amplitudes ranging from 7 to 52 mT/l 0 . For both fluid and immobilized nanoparticle samples, we determined that magnetic response was dominated by Neel reversal. Furthermore, we observed that the peak slew-rate (xH o ) determined the tracer magnetic response. Smaller amplitudes provided correspondingly smaller field of view, sometimes resulting in excitation of minor hysteresis loops. Changing the drive field conditions but keeping the peak slew-rate constant kept the tracer response almost the same. Higher peak slew-rates led to reduced maximum signal intensity and greater coercivity in the tracer response. Our experimental results were in reasonable agreement with Stoner-Wohlfarth model based theories. V C 2014 AIP Publishing LLC. [http://dx

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Self-consistent magnetic properties of magnetite tracers optimized for magnetic particle imaging measured by ac susceptometry, magnetorelaxometry and magnetic particle spectroscopy

Cited by 51 publications

References 26 publications

Synthesis of phase-pure and monodisperse iron oxide nanoparticles by thermal decomposition

Synthesis of phase-pure and monodisperse iron oxide nanoparticles by thermal decomposition

Biological effects of the hypomagnetic field: An analytical review of experiments and theories

Slew-rate dependence of tracer magnetization response in magnetic particle imaging

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