ホログラフィ干渉法による鼓膜振動の解析

A HOLOGRAPHIC STUDY OF THE EARDRUM VIBRATION

　I．はじめに

　最近の画像工学の進歩に伴い，レーザ光の干渉現象を応用したホログラフィが広く行なわれるようになつた。

　本技術の1応用法である時間平均法time-averaged-holography^1）は微小振動の特異な記録法として開発されたもので，KhannaとTonndorf^2）3）は本法によりネコ鼓膜の生理的および病的振動状態について最初に報告した。

　われわれも同じく本法を応用して生体組織の振動現象の解明の目的で研究に着手したが，今回はカエルおよびモルモットの正常鼓膜の振動状態の観察について述べる。

　Eardrum vibrations are studied in frogs (rana nigromaculata) and guinea-pigs by means of time-averaged holography.

　Images of the eardrum reconstructed with this method are superimposed by interference fringes. As the fringes represent iso-amplitude contours like those on geodesic maps, the mode of vibration is clearly discernible at a glance.

　This is the first merit of the technique. The second merit is that, as the amplitudes relating to each fringe are calibrated according to the wavelength of the laserlight, the value is most precise and submicroscopic, viz., 10^-5 cm order.

　In this study, the first fringe appeared at about 80dB sound pressure in both animals. The vibratory pattern appeared to be constant depending upon the number of frequencies involved which increased with the increase of the sound pressure. At low frequency the eardrum showed, rather, a simple pattern; with increasing frequencies the pattern became more complicated containing two or more mounds.