[en] A numerical simulation of diffusion-weighted imaging (DWI) experiments, based on the Bloch-Torrey equation, provides an additional insight into diagnosis using MRI. However, simulation of DWI for largesize models has not been performed because huge computing power is required. We have recently developed a high-speed MRI diffusion-weighted simulator. Here we extend this simulator to the diffusion tensor imaging (DTI). To simulate DTI, as a first step, one needs to calculate DWI along several directions of MPG generated by synthesis of multiple gradients. However, the simulator allows to apply a single gradient at a time to employ the speed-up techniques. To overcome this limitation, the numerical model is rotated by an angle to make MPG always directed toward the same direction. As a result, the synthesized gradients become equivalent to the single gradient and could be treated by the simulator. Finally, the calculated DWI image is rotated back to the original coordinate system. A two-dimensional DWI simulation was performed for a human brain size model and a DTI image was calculated from the obtained images. The results showed that the errors were less than 2%. (author)

[en] An electron energy-loss spectrometer was designed and constructed. It consists of a stainless-steel collision chamber, two sets of hemispherical electron energy analyzers, four sets of electrostatic lenses, an electron gun, a sample compartment, a Celatron detector, two turbomolecular pumps, power supply units and a set of electronics for counting, controlling and data analysis. The electron energy analyzers, one is for selection and the other is for analysis, are made of oxygen-free copper and their diameters are 90 mm along the electron path. The electrostatic lenses have three or four components and were designed on the basis of a trajectory calculation. The scattering angle can be varied from -5deg to 110deg. The energy resolution of the spectrometer was determined to be 60 meV from a half-width of the 1s-2p transition of He. The spectra and its angular dependence of He agreed with the previous results. The spectra of nitrogen and methanol at low electron energies and at various scattering angles were measured, and several features have been assigned as singlet-triplet transitions. (author)

[en] Effects of main magnetic field time-variation upon MR (Magnetic Resonance) images are presented. In permanent magnet MRI system, main magnetic field strength varies linearly with time according to the magnet's temperature variation. The effects of this field strength time-variation upon MR images are simply. (author)

[en] Previously we proposed a new application of NMR to measure biological materials in human body noninvasively, using the magnetic focusing technique on the measuring target (MT). The present paper considers how to generate the magnetic focus and demonstrates this technique by using the low-field NMR spectrometer. In the first parts of this paper, the signal error due to the fringe region of MT is evaluated theoretically and the constant field contours for several arrangements of multiple coils are calculated so as to generate the magnetic focus. Simple results are obtained analytically for the axisymmetric field especially. Furthermore, a new approach which enlarges the zero-flux region is proposed to achieve a high S/N ratio. In the latter parts, the construction of 100 kHz NMR spectrometer, whose static field H₀ is generated by the main solenoid 70 cm long and 40 cm in diameter with two compensation windings, is described. The proton resonance signals from 1 cm³ sample water are obtained with a S/N ratio of 15, which is more than ten times better than the value estimated from the relation S/N proportional to H₀sup(2/3). By using the separate samples under the gradient field, a separate signal corresponding quantitatively to each sample is obtained. The signal from a certain specified area near the surface of a large sample has a shifted resonant frequency and an emphasized magnitude when the magnetic focusing technique is applied. (auth.)

[en] Optimization of an antenna for magnetic resonance imaging (MRI) requires an acurate analysis of antennas located inside a conducting cylindrical RF shield. A Galerkin-moment method analysis which can be used for an arbitrary shaped shield is employed. Surface current on a conducting plane is expanded using surface patch segments based on the method of Richmond. Numerical results are compared with measured input impedance confirming the validity of the proposed method. Furthermore relation between the dimension of shield and the sensitivity of the antenna is discussed theoretically. (author)

[en] An echo-time encoding proton NMR chemical shift imaging proposed by Dixon is extended to be applicable to low filed systems. The method utilizes the small phase angle between magnetic vectors of water and lipid protons to decrease the signal decays with spin-spin relaxation. The inevitable phase error caused by the static field inhomogeneity is corrected by using phase images of phantom measured under the same conditions as the actual measurements. The experiments were carried out using CuSO₄ doped water and vegetable oil at 0.5 T. Two chemical shift images could be clearly resolved with only one scan when the field inhomogeneity was larger than the chemical shift difference. (author)

[en] This report describes on the production of a line-shaped magnetic field and its application. The line-shaped magnetic field was produced by superposing static magnetic fields in the direction of parallel multi-wires. The field distribution in a field of parallel four wires was measured with the low magnetic field NMR system manufactured for trial, and the production of line-shaped field was confirmed. It was shown by using the line-shaped magnetic field that a signal in a specified region could be separated from a signal in other region by model experiment with pure water. The spin density imaging of a two-dimensional substance by NMR was made with the line-shaped magnetic field, and it was found that the present method gave better S/N ratio than the previous method. (Kato, T.)

[en] We have been investigating functional MRI (fMRI) using Student t-test analysis for selecting activated regions. This analysis is sensitive to the signal to noise ratio (SNR) level, so that a low SNR reduce the activated size. In this report we describe new analysis, a combination of Student t-test analysis and signal change analysis. This combination of two analyses is less sensitive to the SNR level. Experiments of fMRI were performed using a 1.5-T prototype MRI system with local gradient coils. Healthy volunteers carried out a left-finger tapping task in these experiments. Clinical images were acquired using spin-echo sequence to identify the structure of the brains. Functional images were acquired using two sequences, echo-planar imaging (EPI) sequence and interleaved EPI (IEPI) sequence. Each imaging sequence had the following parameters: EPI: T_E=15 ms, data acquisition time=75 ms, spatial resolution=4 x 2 mm and temporal resolution=2 s; and IEPI: T_E=15 ms, data acquisition time=75 ms, spatial resolution=2 x 1 mm, and temporal resolution=8 s. The SNR of IEPI is about a quarter that of EPI. The activated regions were selected by using Student t-test analysis and the combination of two analyses respectively. The activated size was calculated based on the number of pixels in the activated region and the pixel size. As a result of Student t-test analysis the activated sizes of IEPI reduced to less than half those of EPI. But there were not a significant differences in the activated sizes estimated by the combination of two analyses between EPI and IEPI. We conclude that our proposed combination analysis method can estimate the size of the activated areas more precisely. (author)

[en] A single crystal of a new ternary silicide U_1.2Fe₄Si_9.7 has been synthesized by the Czochralski method and characterized by X-ray diffraction, magnetization, specific heat and electrical resistivity measurements. It crystallizes in the hexagonal Er_1.2Fe₄Si_9.8-type structure characterized by a disordered two-dimensional layer of U-atoms. The lattice parameters are a = 3.956(1) A and c = 15.055(2) A. Magnetic susceptibility follows the Curie-Weiss law down to 40 K with the effective magnetic moment of 2.4 μ_B/U. The electronic specific heat coefficient, γ of 180 mJ/K²mol·U was obtained. A large residual resistivity due to the disordered structure of the U-Si layer was observed. (author)

[en] The slotted tube resonator for a magnetic resonance imaging diagnostic equipment was approximated with the line model which was corrected with a concentrated electrostatic capacity, and analyzed by using the moment method of Richmond, in this way, the input impedance characteristics, current distribution and electromagnetic field distribution have been elucidated. Moreover, by comparing with the measured values of the input impedance, the validity of the analysis was shown. Magnetic resonance imaging diagnostic equipment can obtain the tomograms of human bodies in any direction without invasion, and it is superior to X-ray CT and ultrasonic diagnostic equipment in the discrimination capability for the soft tissues of human bodies, accordingly attention has been paid to it as a new medical diagnostic equipment. The role of the resonator for MRI is to irradiate a subject with high frequency magnetic field and to receive the resonance signals that the subject generates, and the required performance is to generate a uniform, strong magnetic field. The analysis model and the method of analysis of a slotted tube resonator and the results are reported. (K.I.)