Ferromagnetic resonance (FMR) holds promise for heating magnetic nanoparticles (MNPs) in cancer therapy, especially for rapidly heating MNPs. This study aims to enhance the FMR-based heating ...efficiency of multifunctional hybrid gold and iron oxide nanoparticles (Au-Fe3O4 NPs) as theranostic agents. We experimentally investigate the FMR-based heating properties of newly developed dumbbell-like Au-Fe3O4 NPs, which feature ∼5 nm gold and 15 nm iron oxide components, in comparison to our previously developed Au-coated Fe3O4 NPs (Fe3O4 core ∼5.2 nm, Au shell thickness ∼0.5 nm). For comparison, we also synthesize pure Fe3O4 NPs (∼11 nm) under the same experimental conditions as the dumbbell-like Au-Fe3O4 NPs but without 5 nm Au seeds. Temperature measurements are taken at various DC fields (HDC = 0‒1600 Oe) under a radiofrequency (RF) field (fAC = 4 GHz, HAC = 1.265 Oe) for ∼13s. The results reveal a rapid temperature rise during RF field ON, followed by a decline upon RF field OFF. Remarkably, dumbbell-like Au-Fe3O4 NPs achieve a peak temperature increase of 23.4 °C, corresponding to a heating rate of 1.73 °C/s at HDC = 400 Oe, surpassing the combined values of ∼11 nm Fe3O4 NPs (11.0 °C, i.e., 0.83 °C/s at HDC = 1000 Oe) and ∼5 nm Au NPs (3.5 °C). Comparing these results to our previously developed Au-coated Fe3O4 NPs, which achieved a heating rate of 1.29 °C/s (temperature rise 16.9 °C) under HDC = 1200 Oe with an RF field at fAC = 4 GHz and a significantly higher HAC = 4 Oe (i.e. for HAC = 1.265 Oe, the estimated heating rate was 0.129 °C/s with a temperature rise of 1.69 °C), the dumbbell-shaped Au-Fe3O4 NPs demonstrate a substantially higher temperature increase by 13.4 times. These findings highlight the exceptional potential of dumbbell-shaped Au-Fe3O4 NPs for application in magnetic hyperthermia.
We investigated the magnetization response and heat generation of magnetic particles exposed to high-speed pulsed magnetic fields (PMF) during magnetic hyperthermia cancer treatment. The ...magnetization measurements exhibited an asymmetric change in the shape of the hysteresis loop, attributable to the rapid and substantial changes in the short-duration PMF (75 mT/μs). We propose a novel parameter to evaluate heat efficiency. The parameter considered disparities in waveforms and served as a valuable metric for evaluating the effectiveness of heat production. Our findings affirmed a substantial enhancement in heat efficiency with the application of PMF. Furthermore, the heat generation stemming from the magnetic energy dissipation within the PMF exhibited direct proportionality to the square of the field amplitude. The heat efficiency is fourfold higher than that generated by conventional waveform.
Alternating magnetic fields can deliver magnetic energy deeper inside the body for magnetic hyperthermia cancer therapy by using magnetic nanoparticles (MNPs). In this study, we proposed a highly ...effective heat generation method for the MNPs by the application of an ultra-short pulse wave. We numerically evaluated the heating power with a variety of parameters, such as pulse width, field amplitude, and frequency. The hysteresis curve and magnetization dynamics clearly indicate larger energy dissipation. Hysteresis loss and the input energy increase with increasing field strength and duty ratio and there is a large efficiency power condition. To evaluate the effective heat generation and practical temperature increment, a larger imaginary part of magnetic susceptibility (χ″ > 30) and specific loss power (SLP > 105 W/kg) are required. In addition, larger intrinsic loss power (100 nHm2/kg) is achieved. The results indicate that the contribution of magnetic harmonics signals on the ultra-short pulse wave significantly enhances the heat generation of MNPs for cancer therapy.
Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique that has been clinically applied for neural modulation. Conventional TMS systems are restricted by the trade-off ...between depth penetration and the focality of the induced electric field. In this study, we integrated the concept of temporal interference (TI) stimulation, which has been demonstrated as a non-invasive deep-brain stimulation method, with magnetic stimulation in a four-coil configuration. The attenuation depth and spread of the electric field were obtained by performing numerical simulation. Consequently, the proposed temporally interfered magnetic stimulation scheme was demonstrated to be capable of stimulating deeper regions of the brain model while maintaining a relatively narrow spread of the electric field, in comparison to conventional TMS systems. These results demonstrate that TI magnetic stimulation could be a potential candidate to recruit brain regions underneath the cortex. Additionally, by controlling the geometry of the coil array, an analogous relationship between the field depth and focality was observed, in the case of the newly proposed method. The major limitations of the methods, however, would be the considerable intensity and frequency of the input current, followed by the frustration in the thermal management of the hardware.
In prior studies focused on transcranial magnetic stimulator (TMS) coils, optimization of coil windings typically occurred on generic curved surfaces, such as planes or cylindrical shapes. However, ...these surfaces do not consider the challenge of coil misalignment, which arises due to variations in individual head geometries. This misalignment can significantly diminish the coil's effectiveness. To address this issue, we propose a novel coil design approach that identifies the 'best-fit' curved surface, minimizing the likelihood of mismatch with diverse skull geometries. We further enhance the coil winding pattern using the stream function applied to this custom curved surface. Numerical simulations using a hemisphere brain model demonstrate that the coil designed on this 'best-fit' curved surface exhibits a remarkable 22% increase in efficiency and a 41% expansion in stimulation area compared to the conventional butterfly coil. These findings underscore the advantages of our method in crafting high-efficiency and wide-ranging therapeutic TMS coil.
We developed a novel magnetometer that employs negatively charged nitrogen-vacancy (NV
) centers in diamond, to detect the magnetic field generated by magnetic nanoparticles (MNPs) for biomedical ...applications. The compact probe system is integrated into a fiber-optics platform allowing for a compact design. To detect signals from the MNPs effectively, we demonstrated, for the first time, the application of an alternating current (AC) magnetic field generated by the excitation coil of several hundred microteslas for the magnetization of MNPs in diamond quantum sensing. In the lock-in detection system, the minimum detectable AC magnetic field (at a frequency of 1.025 kHz) was approximately 57.6 nT for one second measurement time. We were able to detect the micromolar concentration of MNPs at distances of a few millimeters. These results indicate that the magnetometer with the NV
centers can detect the tiny amounts of MNPs, thereby offering potential for future biomedical applications.
New laparoscopic sentinel lymph node navigation using a dedicated magnetic probe and magnetic nanoparticle tracer for gastric cancer patients allows minimally invasive surgeries. By identifying the ...sentinel lymph nodes containing magnetic nanoparticles, patients can avoid excessive lymph node extraction without nuclear facilities and radiation exposure. This paper describes the development of the laparoscopic magnetic probe, ACDC-probe, for laparoscopic sentinel lymph node identification utilizing the nonlinear response of the magnetic nanoparticles magnetized by an alternating magnetic field with a static magnetic field. For highly sensitive detection, the ratio of static to alternating magnetic fields was optimized to approximately 5. The longitudinal detection length was approximately 10 mm for 140 μg of iron, and the detectable amount of iron was approximately 280 ng at a distance of 1 mm. To demonstrate the feasibility of laparoscopic detection using the ACDC-probe and magnetic tracers, an experiment was performed on a wild swine. The gastric sentinel lymph node was clearly identified during laparoscopic navigation. These results suggest that the newly developed ACDC-probe is useful for laparoscopic sentinel lymph node detection and this magnetic technique appears to be a promising method for future sentinel lymph node navigation of gastric cancer patients.
In this study, the theoretical feasibility of utilizing optically pumped magnetometers for on-board magnetoencephalography measurements was explored. Simulations were conducted to generate ...steady-state visually evoked response (SSVER) signals that incorporate vehicle noise, and a noise reduction strategy specifically designed for on-board applications is proposed. Upon engine activation, the magnetic field vibration of a conventional gasoline-powered vehicle measured in an urban environment was found to be approximately seven times greater in the vertical direction than in the horizontal direction. The maximum signal-to-noise ratio of the SSVER in an automotive environment was simulated to be −110 dB. A 350-mm side-length, 20-turn active compensation coil can achieve an attenuation rate of approximately 28 dB at a target frequency of 24 Hz for measurements inside the vehicle cabin. Therefore, an increase in the number of coil turns would result in a higher attenuation rate. Further noise attenuation to the level inside a magnetically shielded room requires approximately 80 dB.
In the surgical treatment of nonpalpable breast lesions, such as in early-stage cancer, a hook-wire is inserted into the lesion as a marker to enable surgeons to excise the tissue, along with the ...hook-wire, with a good margin. However, a benchmark technique for intraoperatively determining whether the excised tissue has an appropriate margin around the lesion has not yet been established. In this study, a method for locating a ferromagnetic stainless steel hook-wire inside the excised tissue using a magnetometer is proposed. The magnetometer is placed around a phantom along with the hook-wire at varied locations to map the magnetic field distribution. The three-dimensional coordinates of hook-wire are obtained by executing an optimization algorithm. The experimental results indicate that the location of the hook-wire is successfully obtained. Based on the information regarding the margin around the hook-wire, the surgeon can immediately evaluate the risk of whether some cancer cells still remain in the body.
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