山越 芳樹¹, 山本 敦史², 弓仲 康史¹

Yoshiki YAMAKOSHI¹, Atsushi YAMAMOTO², Yasushi YUMINAKA¹

¹群馬大学理工学府, ²群馬大学医学部整形外科

¹Graduate School of Science and Technology, Gunma University, ²Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine

キーワード : shear wave, viscoelastic properties, elastography, nonlinear properties

せん断波（ずり波：shear wave）を用いた映像法は，組織の硬さの映像化ができるという期待から幾つかの製品が市販されている．その代表的なものは，強力な超音波を集束させて生体内部にせん断波を発生させ，組織中を伝わるせん断波の伝搬速度から組織の特性化を行う音響放射力法（Acoustic Radiation Force Impulse: ARFI）である．しかし，時に，測定したせん断波の伝搬速度や組織の弾性係数が予想以上にばらつくなどの印象を持たれた方も多いと思われる．本稿では，せん断波の波としての性質を概観することにより，せん断波を組織特性化に活用する上での課題や注意点について触れる．最後に，我々が開発を行っている簡便で定量性の高いせん断波の新たな映像法について紹介する．

Evaluation of tissue viscoelastic properties is a promising method in ultrasonic wave medical diagnosis, because shear wave propagation characteristics, such as shear wave velocity, shear wave absorption, and dispersion characteristics are closely related to tissue mechanical properties. Several imaging methods based on shear wave propagation have been proposed, and many studies have been done using these imaging systems. However, the estimated shear velocity often does not match with the tissue stiffness identified by hand, and the variation in the measured value is sometimes larger than expected. In this review, characteristics of shear waves are summarized and important points are discussed regarding use of shear waves for tissue characterization. In addition, a shear wave wavefront reconstruction method developed in our laboratory is presented, as well as some phantom and in vivo experimental results.