探討聲帶分層構造在超音波影像之呈現

Abstract

音聲醫學（phoniatrics）是從解剖、生理、病理等醫學的角度，來探討人類發聲的學問。到目前為止，文獻中對於人體聲帶的功能障礙仍然沒有準確的評估方法。 要研究聲帶發聲之生物力學需要深入軟組織去看，以目前非侵襲性的影像檢查儀器 ( 例如：電腦斷層掃描儀、核磁共振儀、超音波儀 ) 都是很好的選擇。但是要檢查振動中的聲帶組織，對於上列儀器都是相當大的挑戰。超音波擁有高解析度且為非侵襲性的檢查優點，已廣泛地應用臨床醫學上，透視活體組織在低頻率的運動 (f < 10Hz) 。但是超音波在耳鼻喉科臨床及聲帶研究方面實在很少。因為喉部周圍組織有空氣界面與軟骨，超音波傳遞受到阻礙，且聲帶的振動是一個高頻的運動，超音波影像在時間上及空間上解析度都不足，無法觀察高頻率的運動。所以到目前為止，超音波在聲帶方面的研究，大部份都侷限於型態學上。 本研究擬開發超音波影像應用於人體聲帶的臨床診斷。鑒於聲帶的顯微構造以及其病變尤其是Renike’s space的狀態與音聲障礙息息相關，我們利用更精密、解析度高的超音波儀器，由聲帶的分層構造著手，配合組織學檢查確定，確立聲帶各分層構造在超音波影像上之正常圖像及特徵，期待以此為基礎開拓超音波影像在音聲障礙診斷的新視野。 在本研究中我們經由將聲帶分層構造一層一層剝離，並加上組織學在光學顯微鏡下的確認，我們得以完成聲帶各分層構造在超音波影像上之圖像特徵與確認。由上面的結果我們可以得到下面幾項重要的結論： （1）證明聲帶的分層構造的確可以在超音波影像上清楚的表示出來。 （2）各分層在超音波影像上之特徵如下：Reinke’s space在B-mode超音波下是組織-空氣介面下一層低超音波回音的區域。聲帶韌帶為Reinke’s space之上較薄一層稍微不均勻稍為高一點回音的區域。而聲帶肌則為甲狀軟骨下一層緊密且較高回音的區域。 有了本研究的結果，對於將來能夠正確的評估cover層的狀態將有極大的幫助。並期望超音波影像這項具有非侵入性、安全、方便、即時（real time）、檢查時不影響正常發聲等優點的好工具能夠真正成為臨床上常規檢查音聲障礙的利器。

Although clinical ultrasound imaging has been widely used in various fields of practice, its application on the laryngeal examination has been limited due to the spatial resolution and the dynamic response to tiny high frequency movements. Among the basic functions of human larynx, phonation is one of the most complex and the least understood activity. The 3D vibratory movements of the vocal folds（VF）, the stiffness of the mucosa and the aerodynamic forces acting on the VF play important roles in the formation of voice. Therefore, sophisticated noninvasive technologies that combine photoglottography (PGG), electroglottography (EGG) or video laryngostroboscopy with aerodynamic methods need to be developed to investigate the laryngeal function and the neurophysiology of phonation.

To visualize the laryngeal activity in vivo under normal articular movements, fiberoptics were inserted into the lower pharynx via the nasal cavity. The ultrasonography of the larynx would provide further details of the VF cartilaginous and endolaryngeal structures. The true vocal folds and the vocal muscles appeared as hypoechoic structures that could not be adequately visualized in US scanning (Raghavendra et al. 1987). Morphologically, the use of B-mode US is not superior to other imaging techniques, such as CT or MRI in visualizing laryngeal structures, especially the true VF. Therefore, the studies of phonation have been limited.

The vibration of VF periodically interrupts the glottal airflow and forms the acoustic signal that is perceived as the voice. Due to its unique multilayered structures, the VF can be divided into the “cover” and the “body”. The cover includes mucosa and the superficial layer of lamina propria, called the Reinke’s space. The body consists of vocal ligament and vocal muscle. Functionally, the vibration of VF is confined mainly to the cover and the mucosal wave is propagated vertically from the lower to the upper margin of the VF. The vertical mucosal traveling wave is the summation of sequential horizontal tissue displacement waves from the infraglottic to supraglottic extent of the VF structure. The status of the VF cover, especially the stiffness of Reinke’s space, plays the key important role in the pathogenesis of dysphonia. In this study, we use the new generation ultrasonography scanner with higher resolution (HDI-5000, ATL, Bothell, WA) and higher frame rate (33 Hz) in B-mode to study the multilayered structures of vocal folds from fresh excised human larynx after laryngectgomy. We studied the echogenic features of each layer. The multilayered structure of the vocal fold was stripped off layer by layer and was confirmed by histopathology. And the multilayered structures of vocal folds in ultrasound imaging were verified. The cover of the vocal folds was an almost nonechogenic band. The medical ultrasound imaging is easy to perform and analyze, safe, non-invasive, well tolerated, generally available, real-time and with a minimum disturbance to the voice production. It seems to be one of the best choices to meet the requirements for routine laryngeal examination. This is the first time the multilayered structures of vocal folds, especially the cover were verified by medical ultrasound imaging. By doing so, we hoped that medical ultrasound imaging can someday become a promising tool in diagnosing the causes of dysphonia in routine laryngeal examination.