入江 喬介^{1, 2}, 田川 憲男¹, 田邉 将之¹, 守屋 正³, 吉澤 昌純⁴, 飯島 高志⁵, 伊東 紘一⁶, 横山 卓⁷, 熊谷 秀規⁸, 谷口 信行⁹

Takasuke IRIE^{1, 2}, Norio TAGAWA¹, Masayuki TANABE¹, Tadashi MORIYA³, Masasumi YOSHIZAWA⁴, Takashi IIJIMA⁵, Kouichi ITOH⁶, Taku YOKOYAMA⁷, Hideki KUMAGAI⁸, Nobuyuki TANIGUCHI⁹

¹首都大学東京大学院システムデザイン研究科, ²マイクロソニック株式会社技術開発部, ³首都大学東京名誉教授, ⁴東京都立産業技術高等専門学校ものづくり工学科, ⁵産業技術総合研究所水素材料先端科学研究センター, ⁶常陸大宮済生会病院内科, ⁷常陸大宮済生会病院外科, ⁸常陸大宮済生会病院小児科, ⁹自治医科大学臨床検査医学

¹Graduate School of System Design, Tokyo Metropolitan University, ²Research and Development, Microsonic Co., Ltd, ³Professor Emeritus of Tokyo Metropolitan University, ⁴Monozukukuri Department, Tokyo Metropolitan College of Industrial Technology, ⁵Research Center for Hydrogen Industrial Use and Storage, National Institute of Advanced Industrial Science and Technology, ⁶Department of Internal Medicine, Hitachi-Omiya Saiseikai Hospital, ⁷Department of Surgery, Hitachi-Omiya Saiseikai Hospital, ⁸Department of Pediatrics, Hitachi-Omiya Saiseikai Hospital, ⁹Department of Clinical Laboratory, Jichi Medical University

キーワード : high-frequency ultrasonic wave, microscopic image, tapered fused quartz fiber, needle-type ultrasonic probe

目的：本論文では，細径音響導波路を用いて組織の高精細な超音波画像を直接観察可能とする研究について述べる．方法：まず，反射法を用いて石英ファイバ中を伝搬する超音波の挿入損失と周波数特性を測定する．次に，透過法を用いて石英ファイバ中を伝搬する超音波の挿入損失および周波数依存性減衰を調べるために，受信トランスデューサをファイバ端面の近くに設置し，音響カップリング材を媒体として伝搬した超音波の特性を測定する．最後に，上記の測定結果を用いて測定条件を最適化し，水中に置かれた反射体（硬貨）を超音波ビームで走査することによってCモード像を得る．結果：ファイバ端面から反射波が得られ，その周波数特性において最大値を示す周波数は約220 MHzであった．音響カップリング媒体を伝搬した超音波の周波数は約125-170 MHzの帯域で検出され，超音波の最大検出距離は100 MHz周波数帯で約1.2 mmであった．最終的には，テーパー状石英ファイバを用いて，水中の硬貨の高周波Cモード像を得ることができた．結論：実験結果から，微細組織像を得るためには，信号対ノイズ比（S/N）を改善し，挿入損失を減少させる必要があることが示唆された．

Purpose: This paper describes an investigation into direct observation of microscopic images of tissue using a thin acoustic wave guide. Methods: First, the characteristics of the ultrasonic wave propagated in a fused quartz fiber were measured using the reflection method in order to study the insertion loss and the frequency shift of the ultrasonic wave transmitted from the transducer. Next, a receiving transducer was placed close to the end of the fiber, and the characteristics of the ultrasonic waves propagated through the acoustic coupling medium were measured using the penetration method in order to study the insertion loss and the frequency-dependent attenuation of the penetrated waves. Finally, a C-mode image was obtained by optimizing the measuring conditions using the results of the above measurements and scanning the ultrasonic beams on a target (coin) in water. Results: A reflected wave with a peak frequency of approximately 220 MHz was obtained from the end of the fiber. The transmitted ultrasonic waves propagated through the acoustic coupling medium were detected with a frequency range of approximately 125-170 MHz, and the maximum detectable distance of the waves was approximately 1.2 mm within the 100-MHz frequency range. Finally, a high-frequency C-mode image of a coin in water was obtained using a tapered fused quartz fiber. Conclusion: The results suggest that it is necessary to improve the signal-to-noise ratio and reduce the insertion loss in the experimental system in order to make it possible to obtain microscopic images of tissue.