We have designed an excitation part of the driving circuit of the fundamental mode orthogonal fluxgate (FG) to avoid an interference problem between fluxgates that may occur when individually operating fluxgates are placed closely. In the new design, three sensor heads are driven by a common excitation current while their outputs are processed separately to yield their own outputs. With magnetometers of this design we have built a 6ch FG array of a linear arrangement with the spacing of 3cm, as a step to a 6×6 fluxgate array. The excitation frequency was shared by two excitation circuits each of which provides a set of three sensor heads with the excitation current. Magnetocardiogram (MCG) was measured with the 6ch FG array by repeatedly sliding a top plate of the bed by 3cm that carrying a healthy volunteer lying on it. The distribution of the QRS complex observed on the 5×6 of the measurement points resembles that observed by a SQUID MCG measurement system.

抄録全体を表示

Magnetic force was utilized in the magnetic separation techniques. These techniques were established and applied valuable industrial systems. For example, in the environmental field, it was helpful on decontamination of discharging water. In this technique, magnetic force worked with paramagnetic materials such as minute metal which couldn't reject by filters. In contrast, present study tried applying the magnetic force with diamagnetic gas such as carbon-dioxide (CO₂) gas. By interfusing oxygen (O₂) gas which has paramagnetic characteristic with CO₂ gas, the distribution of CO₂ concentration in the aqueous container space was controlled by gradient magnetic field. In experiments, we tried observing the distribution of dissolved CO₂ gas and measuring CO₂ gas concentrations under gradient magnetic field.

抄録全体を表示

We developed a magnetic nanoparticle (MNP) imaging system that uses the harmonic signals of MNPs on the basis of their nonlinear magnetization curves. Since the interference of the excitation field can be significantly decreased by measuring the harmonic signals, the detection sensitivity can be improved. First, we have characterized the nonlinear properties of MNPs in order to evaluate the harmonic signals. We clarified what proportion of MNPs contributes to the harmonic signal. It is important to choose a sample having a large portion of MNPs with large magnetic moment and short relaxation time for the harmonic signal-based detection. Then, we measured a contour map of the signal field from the MNPs with our simple detection system using second harmonic signal. We could detect 100μg of MNPs located at z=25mm below the pickup coil with a high signal-to-noise ratio. Analyzing the contour map using a mathematical technique called singular value decomposition (SVD), we could clearly distinguish two MNP samples separated by Δx=25mm and located at z=25mm. This simple detection system will be useful for medical applications such as sentinel lymph node detection.

抄録全体を表示

Numerical simulation of human and xenopus myelinated nerve magnetic stimulation was executed to compare their excitation thresholds at Low Frequency (LF) band. Currently LF band magnetic field exposure is suppressed during Magnetic Resonance (MR) scanning to avoid possible unexpected sensation and motion, which limits the resolution of MR images. Recently, Weinberg and his colleague reported higher threshold of human peripheral nerve against magnetic field at LF band in their experimental study. Using equvalent circuits of human and xenopus myelinated nerves, their thresholds for LF magnetic field stiumulation were investigated. As a result, the excitation threshold of human nerve for LF magnetic field stimulation with biphasic cosine wave increased exponentially around 100kHz as the frequency increased, which is consistent with the finding of Weinberg et al. and was not observed in xenopus nerve equivalent circuit. The lower axoplasm resistivity of human nerve was considered to be the cause of this feature.

抄録全体を表示

In this paper, we have proposed two kinds of magnetic microactuators for a cytology brush built into a capsule endoscope. One is a moving-magnet linear actuator, in which rotational oscillation of a permanent magnet is converted into linear movement through friction. The other is a rotating-magnet actuator with a flexible push-pull wire. Both actuators can be driven by external magnetic field and rub the brush back and forth. As a result of the operation test, they successfully pushed and pulled the brush back and forth along the surface of raw meat. Furthermore, we have added a new function of angular positioning to the capsule by DC magnetic field perpendicular to the magnetic field for rubbing brush.

抄録全体を表示

Resonant circuit is expected to be used as heating source for hyperthermia implants because it can be effectively heated by an applied AC magnetic field. It was previously reported that the size of the implant was successfully miniaturized down to 0.9mm in diameter, which was less than the diameters of the 18G injection needle and catheter. However, after the implant is delivered in vivo, the temperature measurement of the implant is difficult. In order to realize a less-invasive treatment of cancer, the implant should have the capability to control its heating. The two types of resonant-circuit implants were prepared. A method to control the heating of the implant using a ferrite core is discussed in this paper.

抄録全体を表示

Two electromagnetic heating methods have been studied in the hyperthermic treatment of cancer: dielectric heating, and induction heating using magnetic substances. Dielectric heating devices heat even normal tissues around cancer. On the other hand, induction heating has an advantage that it can heat cancer selectively. However, so far effective induction heating has been difficult: enough heat was not generated in the body because of (1) the magnetic field generated by portable induction heating devices was not strong enough, and (2) non-existence of excellent magnetic substances, and (3) strongly invasive temperature measurement in the body. In this paper, we try to solve those problems.
Firstly, we develop an effective high-power induction heating device. Secondly, we obtain an excellent superparamagnetic substance known as magnetic fluid (MF) with large magnetic particles. Thirdly, we propose a detection technique of magnetic particle distribution in the body, using X-ray CT, from which the internal body temperature can be estimated. We confirm the validity of the proposed method in vitro. Finally, we do an experiment to heat the excellent MF injected into VX-2 bearing rabbits. A significant anti-cancer effect was observed. Such results suggest that our study would be quite useful for the development of induction heating hyperthermia.

抄録全体を表示

We have developed a very sensitive thin film sensor using a transmission line. The sensor element consists of a coplanar line fabricated from a ceramic substrate and amorphous-CoNbZr film (4μm in thickness). The ceramic substrate with high permittivity enhances the phase change of the carrier, phase change around 7000 degree/Oe being achieved. A small phase change was detected using a Dual Mixer Time Difference (DMTD) method when a weak magnetic field are applied. We applied the sensor for magnetocardiogram (MCG) measurement using the phase detection technique. We succeeded in measuring the MCG signals in multi point, including a typical QRS wave and T wave, and this signals were found to roughly agree with already reported MCG data by SQUID.

抄録全体を表示

Conventional functional magnetic resonance imaging (MRI) has a relatively low temporal resolution, because this method does not measure neuronal activity itself but observes blood flow. The detection of local magnetic fields in close proximity to the activating area leads to a novel functional MRI with ultrahigh temporal resolution. Magnetic fields arising from neuronal electrical activities are very weak.
The aim of this study is to evaluate the feasibility of detecting neuronal magnetic fields using MRI. The three-dimensional potential distribution in the rat brain was measured using a microelectrode array. Somatosensory evoked potentials were recorded during hind paw stimulation with a spatial resolution of 300μm. The intensity of the magnetic flux density was calculated from the measured result, and was estimated at 2.84pT.
Estimation of the theoretical limit of MRI sensitivity suggested that the calculated magnetic flux density was within the detectable range of MRI.

抄録全体を表示

Biogenic crystals such as uric acid crystals were investigated for the purpose of exploring a new solar energy transfer function in the structure of uric acid crystals. The plate-like uric acid crystals had a plane surface which is a kind of micro-mirror, showing Brownian motion under dark illumination. We discovered the magnetically induced light intensity changing in the uric acid crystals when they were exposed to the magnetic fields of more than 500mT. The magnetic control of light scattering in the micro-mirror was investigated for the purpose of exploring the new mechanism of optical energy transformation in photonic crystals.

抄録全体を表示

There are some reports about combined effects of electromagnetic fields with known carcinogens, toxic physical or chemical agents. In previous study, we observed that magnetic fields (60Hz, 50mT) enhance cytotoxicity of mitomycin C on E.coli bacterium. In this study, we manufactured combined exposure system of ELF magnetic fields and anticancer drug on human cultured cells for efficacy assessment of ELF magnetic fields on chemotherapy.

抄録全体を表示