山口 匡

超音波による組織性状の定量診断技術が近年盛んに開発されているが，より高精度な診断のためには各種の生体組織が有する固有の音響特性と病理学的性質との詳細な関係性についての理解が必要不可欠である．本研究では，音波伝搬に関わるパラメータである音響インピーダンスと音速に着目し，病態の異なる4種類のラット肝臓（正常・脂肪肝・非アルコール性脂肪性肝炎（NASH）・硬変肝）について、中心周波数が80 MHzの振動子を搭載した超音波顕微鏡を用いて組織学的微細構造との関係を検討した．病理写真との比較により脂肪肝およびNASHでは脂肪滴が多数認められ，音響インピーダンスおよび音速はどちらも正常肝と比較してわずかではあるが統計的に低値，線維肝は高値となった（<i>p</i><0.01）．この結果は，肝臓内に脂肪および線維が沈着することによる組織変性を反映していると考えられる．以上より，肝組織の変性状態を音響特性を指標として判定できる可能性が示唆された．

<p>Phantoms for ultrasonography have been widely used to improve skills of physicians and techniques of ultrasonic scattering. Several kinds of phantoms for ultrasonography have already been developed using gelatin, Polyacrylamide. In the development of biomodel for ultrasonography that covers human soft tissue, to change the mechanical properties widely is useful. We chose a poly (vinyl alcohol) hydrogel (PVA-H) to mimic human soft tissue. The purpose of this study is to measure the mechanical properties with varieties of concentration of solvent of PVA solution. The ratio of the mixed solution of Dimethyl sulfoxide (DMSO) and water was changed. The measurement of the static viscoelasticity, the dynamic viscoelasticity, and the loss tangent of PVA-H were performed. In addition, we measured the transverse wave velocity for the phantom to which graphite was added. In conclusion, the variety of mechanical properties of PVA-H is shown by the change of solvents, and especially the loss tangent is twice higher than the conventional PVA-H. And the transverse wave velocity has also a relation to the solvents.</p>

Non-invasive diagnosis of non-alcoholic steatohepatitis (NASH) can be achieved by quantitative ultrasound (QUS), which requires a detailed understanding tissue-specific acoustic microstructure at cellular scale (i,e., 10 mu m). This study focuses on obtaining speed of sound (c) of organelles (i.e., nucleus, cytoplasm, and fibers) using 250-MHz ultrasound in rat livers. Three different pathological stages were investigated in rat models: normal (control: n = 2), NASH (n = 3), and fibrosis model (n = 6). After animal sacrifice, each liver was fixed in formalin and a 7-mu m thin section was affixed to glass slide using a microtome. A scanning acoustic microscopy system equipped with a 250-MHz center-frequency transducer was employed to obtain two-dimensional (2D) maps of c with a spatial resolution of 7-mu m. The histological images were used to detect the positions of the nuclei, cytoplasm and fibers, and the corresponding c values from obtained from the co-registered 2D c map. For all organelles, Kruskal-Wallis test reveals a significant difference (p &lt; 0.01) between all paired stages. These results reveals that c is the highest in fibrosis livers for all organelles. Additionally, in NASH livers, c of nuclei and cytoplasm were the lowest, which could be due to intracellular fluid or ballooning of the whole cell. As expected, c in fiber changes with pathologic state. Results reveal that c of the nucleus and cytoplasm also changes with pathologic state and that we were able to carefully assess these differences using 250-MHz ultrasound. These results could prove invaluable to improve in vivo QUS investigations of livers.

Giant cluster-like vesicles (GCVs) encapsulating near-infrared fluorescent liposomes and X-ray contrast agents coated with lipids can play a multifunctional role, e.g. preoperatively and intraoperatively localizing tumors and reservoir of a fluorescent tracer for detecting sentinel lymph nodes if they are destroyed. We propose the method to assess the destruction of GCVs using the interaction between the ultrasound (US) and ultrasound contrast agents (UCAs). The GCVs were exposed to 2.8 MHz ultrasound with commercial UCA solution. The negative peak pressure of ultrasound was 0, 0.06, 0.56, 1.1 and 1.6 MPa. The measurements of radii of GCVs was conducted after ultrasound exposure. The result demonstrated that bigger GCVs are split to become many smaller GVs. The results indicated that the interaction between US and UCA enhances the destruction of bigger GCVs and increased the amount of smaller GCVs.