AC Susceptibility of Magnetic Fluid in Nonlinear Brownian Relaxation Region: Experiment and Comparison with Numerical Simulation

Yonetani, Takashi; Ogawa, Kotaro; Enpuku, Keiji; Usuki, Naoki; Kanzaki, Hisao

doi:10.1143/jjap.49.053001

Cited by 23 publications

(19 citation statements)

References 25 publications

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“…To understand the mechanisms of magnetic relaxation, the susceptibility has been measured [5,6,7]. The susceptibility measurements also reflect the MNP size distribution and the particle rotation associated with the MNP structures [6,7].…”

Section: Introductionmentioning

confidence: 99%

Rotation of Magnetization Derived from Brownian Relaxation in Magnetic Fluids of Different Viscosity Evaluated by Dynamic Hysteresis Measurements over a Wide Frequency Range

et al. 2016

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The dependence of magnetic relaxation on particle parameters, such as the size and anisotropy, has been conventionally discussed. In addition, the influences of external conditions, such as the intensity and frequency of the applied field, the surrounding viscosity, and the temperature on the magnetic relaxation have been researched. According to one of the basic theories regarding magnetic relaxation, the faster type of relaxation dominates the process. However, in this study, we reveal that Brownian and Néel relaxations coexist and that Brownian relaxation can occur after Néel relaxation despite having a longer relaxation time. To understand the mechanisms of Brownian rotation, alternating current (AC) hysteresis loops were measured in magnetic fluids of different viscosities. These loops conveyed the amplitude and phase delay of the magnetization. In addition, the intrinsic loss power (ILP) was calculated using the area of the AC hysteresis loops. The ILP also showed the magnetization response regarding the magnetic relaxation over a wide frequency range. To develop biomedical applications of magnetic nanoparticles, such as hyperthermia and magnetic particle imaging, it is necessary to understand the mechanisms of magnetic relaxation.

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Section: Introductionmentioning

confidence: 99%

Rotation of Magnetization Derived from Brownian Relaxation in Magnetic Fluids of Different Viscosity Evaluated by Dynamic Hysteresis Measurements over a Wide Frequency Range

et al. 2016

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“…One of the most promising uses of mNPs in medicine is as an imaging contrast agent. Significant research has resulted in the development of methods such as magnetic particle imaging (MPI) [3–6], magnetic resonance imaging MRI methods such as Sweep Imaging with Fourier Transform (SWIFT) [7, 8], magnetic relaxometry (MRX) [9–17] and AC susceptibility detection [18–23]. A particularly relevant study to the present work describes the use of magnetic relaxometry and an array of SQUID sensors and drive coils to spatially localize mNPs using excitation fields in the microtesla range [9].…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic AC susceptibility imaging (sASI) of magnetic nanoparticles

Ficko

Nadar

Diamond

2015

Journal of Magnetism and Magnetic Materials

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This study demonstrates a method for alternating current (AC) susceptibility imaging (ASI) of magnetic nanoparticles (mNPs) using low cost instrumentation. The ASI method uses AC magnetic susceptibility measurement to create tomographic images using an array of drive coils, compensation coils and fluxgate magnetometers. Using a spectroscopic approach in conjunction with ASI, a series of tomographic images can be created for each frequency measurement and is termed sASI. The advantage of sASI is that mNPs can be simultaneously characterized and imaged in a biological medium. System calibration was performed by fitting the in-phase and out-of-phase susceptibility measurements of an mNP sample with a hydrodynamic diameter of 100 nm to a Brownian relaxation model (R2 = 0.96). Samples of mNPs with core diameters of 10 and 40 nm and a sample of 100 nm hydrodynamic diameter were prepared in 0.5 ml tubes. Three mNP samples were arranged in a randomized array and then scanned using sASI with six frequencies between 425 and 925 Hz. The sASI scans showed the location and quantity of the mNP samples (R2 = 0.97). Biological compatibility of the sASI method was demonstrated by scanning mNPs that were injected into a pork sausage. The mNP response in the biological medium was found to correlate with a calibration sample (R2 = 0.97, p <0.001). These results demonstrate the concept of ASI and advantages of sASI.

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“…The results may even get worse, since the diamagnetic magnetization is frequency independent and linearly related to the excitation field, whereas the magnetic response of MNPs is strictly nonlinear and depends on the excitation frequency [11,12]. The assumption of a frequency independent linear MNP susceptibility in the present model is therefore the most optimistic case for MNP detection with conventional alternating fields.…”

Section: Discussionmentioning

confidence: 95%

Depth limitations for in vivo magnetic nanoparticle detection with a compact handheld device

Visscher

Waanders

Pouw

et al. 2015

Journal of Magnetism and Magnetic Materials

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a b s t r a c tThe increasing interest for local detection of magnetic nanoparticles (MNPs) during clinical interventions requires the development of suitable probes that unambiguously detect the MNPs at a depth of several centimeters in the body. The present study quantitatively evaluates the limitations of a conventional magnetometry method using a sinusoidal alternating field. This method is limited by the variability of the magnetic susceptibility of the surrounding diamagnetic tissue. Two different sensors are evaluated in a theoretical model of MNP detection in a tissue volume. For a coil that completely encloses the sample volume, the MNPs can be detected if the total mass contributing to the signal is larger than 4.1 10 7 × − times the tissue mass. For a handheld surface coil, intended to search for the MNPs in a larger tissue volume, an amount of 1 μg of iron oxide cannot be detected by sensors with a diameter larger than 15 mm. To detect a spot with MNPs at 5 cm depth in tissue, it should contain at least 325 μg iron oxide.Therefore, for high-sensitive clinical MNP detection in surgical interventions, techniques with increased specificity for the nonlinear magnetic properties of MNPs are indispensable.

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AC Susceptibility of Magnetic Fluid in Nonlinear Brownian Relaxation Region: Experiment and Comparison with Numerical Simulation

Cited by 23 publications

References 25 publications

Rotation of Magnetization Derived from Brownian Relaxation in Magnetic Fluids of Different Viscosity Evaluated by Dynamic Hysteresis Measurements over a Wide Frequency Range

Rotation of Magnetization Derived from Brownian Relaxation in Magnetic Fluids of Different Viscosity Evaluated by Dynamic Hysteresis Measurements over a Wide Frequency Range

Spectroscopic AC susceptibility imaging (sASI) of magnetic nanoparticles

Depth limitations for in vivo magnetic nanoparticle detection with a compact handheld device

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