Yasuhiko Terada

Skeletal Age Assessment in Children Using an Open Compact MRI System

MRI may be a noninvasive and alternative tool for skeletal age assessment in children, although few studies have reported on this topic. In this article, skeletal age was assessed over a wide range of ages using an open, compact MRI optimized for the imaging of a childs hand and wrist, and its validity was evaluated. MR images and their three‐dimensional segmentation visualized detailed skeletal features of each bone in the hand and wrist. Skeletal age was then independently scored from the MR images by two raters, according to the Tanner–Whitehouse Japan system. The skeletal age assessed by MR rating demonstrated a strong positive correlation with chronological age. The intrarater and inter‐rater reproducibilities were significantly high. These results demonstrate the validity and reliability of skeletal age assessment using MRI. Magn Reson Med, 2013.

Development of a magnetic resonance microscope using a high Tc bulk superconducting magnet

We have developed the first magnetic resonance (MR) microscope using a high critical-temperature superconducting bulk magnet. The bulk magnet comprises six annular bulk superconductors (60 mm outer diameter, 28 mm inner diameter, 20 mm high) made of c-axis oriented single-domain EuBa2Cu3Oy crystals. The magnet was energized using a superconducting NMR magnet operating at 4.7 T. The inhomogeneity of the trapped magnetic field measured with MR imaging was 3.1 ppm (rms) in the ϕ6.2 mm×9.1 mm cylindrical region. Three-dimensional MR images of a chemically fixed mouse embryo acquired with voxels of (50 μm)3 demonstrated the potential of our system.

Development of a mobile magnetic resonance imaging system for outdoor tree measurements

By combining a 0.3 T permanent magnet with flexible rotation and translation mechanism, a probe with a local electromagnetic shielding, several electrical units, a mobile lift, and an electric wagon, a mobile magnetic resonance imaging (MRI) system was developed for outdoor tree measurements. 2D cross-sectional images of normal and diseased branches of a pear tree were acquired for measurements of T(1), T(2), proton density, and apparent diffusion constant (ADC). The ADC map clearly differentiated diseased from normal branches. A whole-day measurement of the ADC map demonstrated that microscopic water flow in the normal branch changed proportionally with solar radiation. Therefore, we have concluded that our mobile MRI system is a powerful tool for studies of plants in outdoor environments.

Longitudinal NMR parameter measurements of Japanese pear fruit during the growing process using a mobile magnetic resonance imaging system

Longitudinal nuclear magnetic resonance (NMR) parameter measurements of Japanese pear fruit (Pyrus pyrifolia Nakai, Kosui) were performed using an electrically mobile magnetic resonance imaging (MRI) system with a 0.2 T and 16 cm gap permanent magnet. To measure the relaxation times and apparent diffusion coefficients of the pear fruit in relation to their weight, seven pear fruits were harvested almost every week during the cell enlargement period and measured in a research orchard. To evaluate the in situ relaxation times, six pear fruits were longitudinally measured for about two months during the same period. The measurements for the harvested samples showed good agreement with the in situ measurements. From the measurements of the harvested samples, it is clear that the relaxation rates of the pear fruits linearly change with the inverse of the linear dimension of the fruits, demonstrating that the relaxation mechanism is a surface relaxation. We therefore conclude that the mobile MRI system is a useful device for measuring the NMR parameters of outdoor living plants.

Laser-combined scanning tunnelling microscopy for probing ultrafast transient dynamics

The development of time-resolved scanning tunnelling microscopy (STM), in particular, attempts to combine STM with ultrafast laser technology, is reviewed with emphasis on observed physical quantities and spatiotemporal resolution. Ultrashort optical pulse technology has allowed us to observe transient phenomena in the femtosecond range, which, however, has the drawback of a relatively low spatial resolution due to the electromagnetic wavelength used. In contrast, STM and its related techniques, although the time resolution is limited by the circuit bandwidth (∼100 kHz), enable us to observe structures at the atomic level in real space. Our purpose has been to combine these two techniques to achieve a new technology that satisfies the requirements for exploring the ultrafast transient dynamics of the local quantum functions in organized small structures, which will advance the pursuit of future nanoscale scientific research in terms of the ultimate temporal and spatial resolutions.

Optical doping: active control of metal-insulator transition in nanowire.

The reversible control of metal-insulator transition (MIT) in In/Si(111) nanowires is demonstrated by tuning the band filling of the one-dimensional surface state by optical doping. The control of MIT is carried out by regulating the Fermi level in the surface state around the half-filled position, depending on the carrier density introduced at the interface. We successfully achieved the reversible and active control of MIT via the charge doping by regulating the intensity of photoexcitation. This method is widely applicable to other low-dimensional systems and makes MIT more controllable and suitable for use in nanowires as an active element in future architectures of nanosized functional devices as well as nanoscale interdevice wiring.

Nanoscale probing of transient carrier dynamics modulated in a GaAs–PIN junction by laser-combined scanning tunneling microscopy

The modulation of carrier dynamics in a GaAs-PIN junction after photoexcitation by an ultrashort-pulse laser was probed by shaken-pulse-pair-excited scanning tunneling microscopy (SPPX-STM), which enables nanoscale mapping of time-resolved STM images. The effect of the built-in potential on the carrier dynamics, diffusion and drift, which cannot be probed by the optical pump-probe technique, was successfully visualized in real space.

Development of an outdoor MRI system for measuring flow in a living tree.

An outdoor MRI system for noninvasive, long-term measurements of sap flow in a living tree in its natural environment has been developed. An open-access, 0.2 T permanent magnet with a 160 mm gap was combined with a radiofrequency probe, planar gradient coils, electromagnetic shielding, several electrical units, and a waterproofing box. Two-dimensional cross-sectional images were acquired for a ring-porous tree, and the anatomical structures, including xylem and phloem, were identified. The MRI flow measurements demonstrated the diurnal changes in flow velocity in the stem on a per-pixel basis. These results demonstrate that our outdoor MRI system is a powerful tool for studies of water transport in outdoor trees.

Direct Probing of Transient Photocurrent Dynamics in p-WSe2 by Time-Resolved Scanning Tunneling Microscopy

We have carried out time-resolved scanning tunneling microscopy on a layered semiconductor with an indirect bandgap, p-WSe2, and the dynamics of nonequilibrium photocurrent generated by ultrashort-pulse-laser excitation was analyzed. The photocurrent dynamics reflecting the flow of excited photocarriers at the surface, which is determined by the balance between the diffusion and tunneling rates, was successfully probed. Furthermore, the excess minority carriers transiently trapped at the surface for a few nanoseconds, which produce a transient surface photovoltage and cannot be detected by conventional methods, were directly observed and evaluated.

Ultrafast photoinduced carrier dynamics in GaNAs probed using femtosecond time-resolved scanning tunnelling microscopy

The combination of scanning tunnelling microscopy (STM) with optical excitation using ultrashort laser pulses enables us, in principle, to simultaneously obtain ultimate spatial and temporal resolutions. We have developed the shaken-pulse-pair-excited STM (SPPX-STM) and succeeded in detecting a weak time-resolved tunnelling current signal from a low-temperature-grown GaNAs sample. To clarify the underlying physics in SPPX-STM measurements, we performed optical pump‐probe reflectivity measurements with a wavelength-changeable ultrashort-pulse laser. By comparing the results obtained from the two methods with an analysis based on the nonlinear relationship between the photocarrier density and tunnelling current, we obtained a comprehensive explanation that the photocarrier dynamics is reflected in the SPPX-STM signal through the surface photovoltage effect. (Some figures in this article are in colour only in the electronic version)