Elsevier

Medical Laser Application

Volume 21, Issue 3, 8 September 2006, Pages 185-190
Medical Laser Application

Optical characterization of vocal folds using optical coherence tomographyOptische Charakterisierung von Stimmlippen mit Optischer Kohärenztomographie (OCT)Caracterización óptica de las cuerdas vocales mediante el uso de Tomografía de Coherencia Òptica

https://doi.org/10.1016/j.mla.2006.05.002Get rights and content

Abstract

The current standard procedure to ensure the diagnosis, if tissue is malignant, is still an invasive one. Optical coherence tomography (OCT) is a new non-invasive method to investigate biological tissue. In this study, OCT was used on porcine and on human vocal folds. The optical penetration depth of the used radiation is up to 2 mm.

Three different OCT application systems were used. The first is a high-resolution OCT, which works in contact mode. It was used to examine porcine vocal folds ex vivo. Porcine vocal folds were assigned to defined areas and examined by OCT in contact mode followed by traditional histo-morphological analysis. The second OCT is fiber based. It also works in contact mode. Images of human vocal folds were done in contact mode. They were compared with a typical histo-morphological image of a human vocal fold. The third application system works in non-contact to the tissue. It was integrated in a conventional laryngoscope. Human vocal folds were examined in vivo.

Single layers of the vocal folds could be distinguished from each other with all used systems. Pathological alterations could be seen. Imaging is possible in real time. General anesthesia is not necessary. OCT makes it possible to get a view under the surface of the vocal fold without being invasive.

Zusammenfassung

Zur Unterscheidung zwischen gutartigem und bösartigem Gewebe ist ein invasives Vorgehen bis heute unabdingbar. Die Optische Kohärenztomographie ist eine non-invasive Methode zur Untersuchung von biologischem Gewebe.

In dieser Studie wurde OCT zur Untersuchung von Stimmfalten des Schweins und zur Untersuchung von menschlichen Stimmlippen eingesetzt. Die Eindringtiefe der benutzten Strahlung ist bis zu 2 mm.

Es wurden drei verschiedene OCT-Systeme zur Untersuchung von Stimmlippen eingesetzt. Das erste ist ein hochauflösendes OCT, das im Kontaktmodus angewendet wird. Es wurde zur Untersuchung von Schweine-stimmlippen ex vivo eingesetzt. Es wurden bestimmte Areale mit OCT untersucht und anschließend histo-morphologisch untersucht.

Das zweite OCT ist ein Faser-OCT. Es arbeitet ebenfalls im Kontaktmodus. Mit diesem System wurden gesunde humane Stimmlippen in vivo unersucht und anschließend mit einem histologisch-morphologischen Bild einer gesunden menschlichen Stimmlippe verglichen.

Das dritte System arbeitet im Non-Kontakt zum Gewebe. Es wurde in ein konventionelles Laryngoskop integriert. Mit diesem System wurden humane Stimmlippen in vivo untersucht.

Einzelne Schichten der Stimmlippen konnten in allen OCT-Aufnahmen bei allen verwendeten Systemen gut voneinander abgegrenzt werden. Pathologische Veränderungen konnten erkannt und zugeordnet werden. Die Aufnahmen sind in Echtzeit möglich, und es war in keinem Fall eine Vollnarkose notwendig. OCT ermöglicht somit den Blick unter die Oberfläche von Stimmlippen, ohne invasiv zu sein.

Resúmen

En la actualidad el procedimiento estándar utilizado para confirmar el diagnóstico sobre si un tejido es maligno o no, sigue siendo un método invasivo. La Tomografía de Coherencia Òptica (OCT) es un nuevo método no invasivo para el estudio de tejidos biológicos. En este trabajo, el OCT fue utilizado para el estudio de cuerdas vocales porcinas y humanas. La profundidad de penetración óptica de la radiación utilizada fue de un máximo de 2 milímetros.

Se utilizaron tres sistemas diferentes de aplicación de OCT. El primero de ellos fue el OCT de alta resolución, el cual trabaja por contacto. Fue utilizado para examinar cuerdas vocales porcinas en un estudio ex vivo, analizando áreas definidas por OCT de contacto, seguido del análisis histomorfológico de rutina. El segundo OCT basado en fibras, también trabaja por contacto. Con este sistema se tomaron imágenes de cuerdas vocales humanas, las cuales fueron comparadas con la imagen histomorfológica de un cuerda vocal humana normal. El tercer sistema de aplicación trabaja sin contacto con el tejido y fue integrado a una laringoscopía convencional. Las cuerdas vocales humanas fueron examinadas in vivo.

Los tres sistemas utilizados permitieron distinguir láminas individuales en las cuerdas vocales. También fue posible observar las alteraciones patológicas. La proyección de imagen es posible en tiempo real. El uso de anestesia general no es necesario. OCT permite obtener una visión por debajo de la superficie de la cuerda vocal sin ser un método invasivo.

Introduction

Optical coherence tomography (OCT) is well suitable for application on vocal folds. The depth relevant for its examination correlates well with the penetration depth of the applied weak infrared laser beam, which is approximately 1–2 mm. The three layers of the lamina propria mucosae of the vocal fold differ from each other by their varying content of elastic and collagenous fibers. The so-called Reinke space, the superficial layer of the lamina propria mucosae, has a fibrous contingent which is loosely organized. The epithelium of a human vocal fold has a diameter of about 0.1 mm. The lamina propria mucosae has a diameter of about 1 mm (Fig. 1).

According to the well-accepted “body-cover-model” introduced by Hirano and coworkers [1], [2], [3], these layers perform certain movements as a function of vocal fold tension. Vocal fold activity also relies on a functional separation of muscle (body) and the lamina propria mucosae (cover). This separation has to be respected whenever performing surgery [4], [5], [6], [7], [8].

To indicate phonosurgery it is of key importance to differentiate the quality of structural changes on vocal folds beforehand, such as the expansion of lesions into the depth or tissue loss. The latter results in a concave vocal fold, which concomitantly leads to a loss of aerodynamics. The voice becomes instable and will be limited in performance of frequency and dynamic range. Moreover, due to scaring of the tissue, the already present voice deficit becomes worse by a stiff glottis [6]. So it becomes evident that an exact preoperative diagnosis is a prerequisite for optimizing protection of the epithelium.

OCT is already well established in dermatology and ophthalmology [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. First clinical studies in the respiratory and digestive tracts were also already performed at the Nizhny Novgorod Medical Academy in Russia [11], [23]. The most detailed and comprehensive study of laryngeal tissue was done by the medical academy and the Semashko Regional Clinical Hospital in Nizhny Novgorod [24].

Section snippets

Materials and methods

OCT is a method for imaging different layers of transparent or scattering tissue by scanning the area of interest with a weak (<1 mW) laser beam. The measuring principle is similar to ultrasound imaging. The measurement signal consists of light which is directly reflected from the surface of the tissue as well as light which is back-scattered from different layers from inside the tissue. As a typical light source, superluminescent diodes with a broad emission band (several tens of nanometers)

Results

Fig. 5 shows a comparison of an OCT image, which was taken from the porcine vocal fold and a histological section from the same area. The image clearly shows the distinction of the epithelium mucosae from the loose collagenous structure of the lamina propria mucosae. In these pictures, the epithelium mucosae has a thickness of approximately 50 μm. Inside the loose collagenous layer, structures can be detected which can be interpreted as vessels (arrows). Since the resolution of the OCT image is

Conclusion

During laryngoscopy, the question whether or not a lesion is malignant is a common challenge. One of the main criteria for the decision between phonosurgery versus tumorsurgery depends on the depth extension of the lesion. This cannot be decided by sole examination of the surface structure. It is important to get a view under the surface of the vocal fold. Alterations which penetrate the lamina propria mucosae into the deep layer are defined to be malignant. The diameter of the lamina propria

Acknowledgements

We thank H. Gasse, R. Koch from Hanover Vetenary School for preparing the histological sections, and we thank ISIS Optronics as well as Carl Zeiss Surgical Instruments for enabling us the OCT measurements and we thank H. Nawe from Hanover Medical School for preparing the human histological section.

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