梅村 晋一郎¹, 工藤 信樹²

Shinichiro UMEMURA¹, Nobuki KUDO²

¹東北大学大学院医工学研究科, ²北海道大学大学院情報科学研究科

¹Graduate School of Biomedical Engineering, Tohoku University, ²Graduate School of Information Science and Technology, Hokkaido University

キーワード : ultrasound field, visualization, Schlieren, shadowgraphy, phase contrast, diagnostic ultrasound, therapeutic ultrasound

本論文では，光学的手法を用いて医用超音波の音場を可視化する3つの手法について述べる．1つは光源とカメラのみからなる単純な光学系で可視化を実現するシャドーグラフ法である．本手法で取得した音場可視化像を従来のシュリーレン法と比較するとともに，超音波診断用の短いパルス超音波の音場可視化における有用性を示す．続く2つの手法は，ハイドロホンによる音場測定の置き換えを目指して開発した定量化シャドーグラフ法と位相コントラスト法である．各手法の原理を解説するとともに，超音波治療に用いられる連続超音波の集束音場を可視化する実験を行い，ハイドロホン計測との比較を通じて3次元音場の精密計測における有用性を示す．

Three optical techniques for visualizing ultrasound acoustic fields used for medical applications are described. The first technique is a type of shadowgraphy that can be realized using a simple optical system consisting of only a point light source and a camera. Characteristics of the images acquired using this technique are compared to those acquired using the Schlieren technique, and the advantage of this technique is demonstrated by visualization of an acoustic field of diagnostic short-pulsed ultrasound. The other two techniques are quantitative shadowgraphy and the phase-contrast technique. These techniques are designed for visualization of three-dimensional (3D) pressure distributions to replace hydrophone measurements. Their principles are explained in detail, and experimental results for visualization of a focused ultrasound field are discussed. The acquired images were quantitatively investigated with comparison to hydrophone measurements, demonstrating the usefulness of the techniques in quantitative evaluation of 3D ultrasound fields.