MRI ニ テキゴウ スル イリョウヨウ キンゴウキン ノ カイハツ

Metal-artifact due to volume-magnetic-susceptibility (χ) mismatch between alloy and human-tissue is one of the serious magnetic-resonance-imaging (MRI) artifacts. Alloys of susceptibility close to that of human-tissue (approximately -9 ppm) are thus required for MRI-artifact-free metal-biomedical-devices. Au-28 mass%Pt alloy is a candidate because of its χ and high corrosion resistance. However, the mechanical properties are insufficient for various types of biomedical-device. The authors found that Nb addition could improve the mechanical properties and simultaneously keep the alloy MRI-artifact-free. The authors produced an Au-8Nb-5Pt alloy wire and found that the χ value for this wire increased because of contamination during the production process. To adjust χ, the Nb content in the alloy was optimized and an Au-7Nb-5Pt alloy wire was produced. The χ value of this wire was confirmed to be close to -9 ppm. The Au-7Nb-5Pt alloy wire demonstrates higher mechanical properties than those of Au-28Pt alloy wire, and good formability. Recently, the authors are successfully producing several kinds of experimental vascular devices, such as coils for cerebral aneurysm embolization, cerebral aneurysm clips, and vascular stents. The next step of the current development is to evaluate the mechanical properties of these experimental devices, and to optimize the device designs for clinical usage

イオン液体含有レジン添加型グラスアイオノマーセメントの通電によるせん断接着強度低下 : オンデマンド剥離可能な歯科用スマートセメントのコンセプトと実証

With improvement of bonding strength of recent dental cement, it is difficult nowadays to remove restorations without excessive force or vibration to tooth, occasionally resulting in damage of dentin, enamel, and dental root. Therefore, “smart” dental cement indicating strong bonding and easy debonding-on-demand simultaneously is required. In this research, resin-modified glass-ionomer-cement containing an ionic-liquid, tris(2-hydroxyethyl)methylammonium methylsulfate was produced, and the shear bonding strength before and after direct current application were evaluated. The prototype cement containing 15 to 20 mass% ionic-liquid indicated simultaneously no significant reduction of shear bonding strength from that of the original cement not containing ionic-liquid, and significant reduction of bonding strength to approximately 20% of that of the original cement after direct current application of more than 2 mmC/mm2. The prototype cement in this research demonstrated that the concept of smart dental cement electrically debonding-on-demand is feasible

Development of MRI Artifact-Free Alloys for Biomedical Applications

MRIで金属アーチファクトを生じない医療用デバイスを作製するには，周囲の組織に近い体積磁化率を示す反磁性の金属材料が必要である．我々は，生体親和性の高い反磁性元素であるAuをベースとし，目標磁化率と高強度を同時に発揮する合金の開発を進めており，Ti-6Al-4V合金やCo-Cr-Mo合金と同等以上の強さを示すAu合金が得られる可能性が見えてきた．MRI artifact-free biomedical devices require diamagnetic metals indicating small volume-magnetic-susceptibility mismatch between the metal and surrounding tissues. The authors have developed new alloys based on Au, a biocompatible diamagnetic element, demonstrating susceptibility values close to surrounding tissues and high strength, simultaneously. And they found candidate Au alloys exhibiting strength similar to or higher than Ti-6Al-4V alloy and Co-Cr-Mo alloy

ボールミリング法で改質したβ-TCPセメントの諸特性への粉液比の影響

The authors have developed a β-tricalcium-phosphate (β-TCP) powder modified mechano-chemically through the application of a ball-milling process (mβ-TCP). The resulting powder can be used in a calcium-phosphate-cement (CPC). In this study, the effects of the powder-to-liquid ratio (P/L ratio) on the properties of the CPCs were investigated, and an appropriate P/L ratio that would simultaneously improve injectability and strength was clarified. The mβ-TCP cement mixed at a P/L ratio of 2.5 and set in air exhibited sufficient injectability until 20 min after mixing, and strength similar to or higher than that mixed at a P/L ratio of 2.0 and 2.78. Although the mβ-TCP cements set in vivo and in SBF were found to exhibit a lower strength than those set in air, it did have an appropriate setting time and strength for clinical applications. In conclusion, P/L ratio optimization successfully improved the strength of injectable mβ-TCP cement

Eine Betrachtung über Kettenspannungsänderung durch Fachaushebung

Bei der Erzeugung eines aus chemischen Fasern bestandenen Gewebes erscheint es besonderes von grösster Wichtigkeit, zunächst den Einfluss der Fachaushebung auf die Kettfäden schärfer zu präzisieren und die Gewebequalität und ihre Einstellung vervollzukommen. Nämlich sollen sich alle Kettfäden während des Webens in einem Zustand gleichmässiger Spannung befinden, damit ein reines Webfach entsteht, in das der Schussfaden eingetragen und an den Warenrand angeschlagen warden kann. Im allgemeinen kann dies durch das Zusammenwirken von Kettenablass- und Warenabziehvorrichtungen eingestell t werden. Aus statischem Gesichtpunkt haben wir zunächst versuchsweise die Kettenspannungsänderung durch Fachaushebung untersucht. Hierbei haben wir zum Zweck gehabt, die geeignetesten Fachbildegetriebe fiir das Weben mit chemischen Fasern entwerfen zu können

Steady Rotation of Micropolar Fluid Sphere in Concentric Spherical Container

AbstractThe problem of slow steady rotation of a micropolar fluid sphere in concentric spherical container filled with viscous fluid is studied. The appropriate boundary conditions are taken on the surface of the sphere. The hydrodynamic couple and wall correction factor exerted on the micropolar fluid sphere is obtained. The dependence of the wall correction factor on the micropolarity parameter and spin parameter is presented graphically and discussed. The hydrodynamic couple acting on a solid sphere in a cell model and on a solid sphere in an unbounded medium are obtained from the present analysis

Leukemia autopsies in Japan

For the purpose to know whether the annual increase of leukemia incidence in Japan is due to some leukemogenic factors or due to the increased detection rate, the authors made some statistical survey of autopsy cases in which the diagnosis is reliable and not any type of leukemias escape the detection. The results showed that acute leukemias, which are found mostly in younger age, is actually increasing. In addition, it has been deduced that among the suspected factors the increase in ionizing radiation will be one of the most probable factors for the increase in leukemia incidence</p

MRIに適合した生体医療用Au-Ta合金とAu-Nb合金の体積磁化率設計と硬さ

The volume magnetic susceptibility (χv) and Vickers hardness (HV) of Au–Ta and Au–Nb alloys were investigated for use as magnetic resonance imaging (MRI)-compatible alloys for biomedical applications. χv of the Au–Ta alloys did not depend on the phase constitution but did depend on the alloy composition. Therefore, heat treatment hardly affected χv of the Au–Ta alloys, and only alloys with Ta contents near 15 were possibly MRI-compatible. In contrast, χv of the Au–Nb alloys depended on the phase constitution. Therefore, both the alloy composition and heat treatment can be used to widely control χv of Au–Nb alloys, and Au–xNb alloys (x≥6.8) can be made MRI-compatible by optimizing χv using heat treatment. HV of the Au–15Ta alloy was smaller than that of pure Ti even after heat treatment, whereas HV of the MRI-compatible Au–Nb alloys was possibly higher than that of pure Ti after heat treatment. The saturated χv values of the Au–Nb alloys after heat treatment at 800 °Care compatible with the hypothesis that χv of an alloy is the average χv of each phase of the alloy based on the rule of mixtures. This hypothesis supports the tailoring of χv by controlling the alloy composition and heat treatment

RADIATION EFFECTS ON METAL MATRIX COMPOSITES BY FISSION NEUTRONS FROM JMTR AND JOYO

Ceramics fiber reinforced composites are expected to be potential candidates as fusion reactor structural materials. Aluminum matrix composites reinforced with C or SiC fibers are investigated. The objectives of this investigation are to evaluate potential of Al matrix composites as low activation fusion reactor materials and to develop them for fusion applications. Mechanical properties were measured by three point bending test and mini size specimen tensile test for composite materials and mono-filament tensile test. Microstructure was inspected by means of SEM and TEM. The effects of radiation were studied using fission neutrons of JOYO(FBR) and JMTR(BWR) and 1 MeV electrons from a HVEM. Al matrix composites showed excellent stability under irradiation up to a certain fluence, named threshold fluence. For SiC fibers in the composites, increment of tensile strength and Young\u27s modulus and crystallization of amorphous SiC were observed below the threshold fluence. But at above the threshold fluence, strength drastically dropped. Alloying of Ni and Si to matrix aluminum alloys was suggested to be unfavorable for SiC/Al composite materials used under nuclear reactor environments