The evolution of technology in laryngology.
AS A FIELD IN WHICH the relevant system is not immediately available for observation and palpation, laryngology has relied upon technology since its inception. The earliest developments allowing vocal fold visualization are well described elsewhere. (1) Briefly, Bozzini was the first to visualize the larynx in 1807 with his Lichtleiter, a device that used a mirror to reflect candlelight to illuminate and visualize the larynx. Babbington and Avery both also developed mechanisms for mirror visualization in the early 19th century. This technique did not catch on widely until Manuel Garcia popularized mirror visualization of the larynx in 1854. (2) Since then, laryngologists have been striving to coapt the technology of the day to advance the art and science of laryngology. The advent of the flexible fiberoptic laryngoscope in 1976 was perhaps the most dramatic technological advance the field has seen; (3) since that time, however, the development of new tools and techniques has continued to expand at an ever increasing rate. Only time will determine how much of the current cutting edge will become indispensible in future practice. This article presents various technologies that have already become ingrained in day-to-day clinical practice, as well as some of those with the potential to contribute substantially to the future evaluation and treatment of the dysphonic patient.
VOCAL FOLD IMAGING
The pursuit of accurate in vivo imaging of the normal and abnormal vocal fold has occupied laryngologists for decades. Traditional fiberoptic endoscopic images provide a wealth of information, but have limitations. These include relatively low resolution, two dimensional representation of a three (or four) dimensional system, and the inability to capture the rapid motion of the glottic cycle during phonation. A broad array of tools and techniques has been developed to aid in visualization of the larynx both during function and at rest. Several of these technologies are reviewed here.
The flexible nasopharyngolaryngoscope described by Silberman et al. relies upon the principle of fiberoptics, in which flexible glass fibers are used to carry an image from the tip of the scope to the eyepiece. (4) Separate bundles of fibers travel within the scope to provide illumination. A lens at the distal end focuses the image such that it may be picked up by the imaging bundles. The image quality is limited by the number of bundles that can be contained within the scope, as well as the size and curvature of the lens. The stress of flexing inevitably leads to broken fibers and subsequent loss of pixels.
In 1959, optical physicist Harold Hopkins developed the rod telescope, which vastly improved the optics obtainable with an endoscope. (5) This technology was coupled with fiberoptic illumination by Karl Storz to create the version of the Hopkins rod telescope that is ubiquitous in otolaryngologic endoscopy to this day. The lack of flexibility limits its application somewhat, but this can be overcome to an extent by the use of angled lenses. Placement of a 70 or 90 degree prism at the distal end of the scope allows visualization of the larynx in the vast majority of patients.
Beginning in the 1980s, videoendoscopes were created with a charge-coupled device (CCD) chip at the tip of the endoscope. The CCD converts electronic signals into clear, high resolution images on a video monitor. (6) These "distal chip" or "chip-tip" endoscopes currently provide the highest quality images of anatomic locations only reachable with a flexible scope. However, in spite of the quality of the images, distal chip scopes have been found to underrepresent certain vocal fold pathologies even when compared to standard fiberoptic scopes. (7) Examination with a rigid telescope, with or without videostroboscopic analysis, remains a more accurate diagnostic tool than either method of flexible examination for identifying pathology of the vocal fold. (8)
Vocal fold function relies upon the potential for vibration at a rate of 80 to more than 1,000 Hz, which is far too fast to be resolved by the human eye. An image perceived by the human retina is held for 0.2 seconds, meaning only approximately 5 images per second can be appreciated. (9) This holding of images, however, can be exploited. In the late 19th century, Oertel discovered that using pulsed light at a rate slightly different from the frequency of vocal fold vibration would capture images at slightly different points in the glottic cycle. Due to the persistence of images on the retina, these images are fused by the brain into what appears to be a slow-motion image. This phenomenon is known as the persistence of motion, and it is the principle behind film projection. Initially, a spinning disk in front of a light source was used to create this strobe effect. The development of a pulsed xenon light source and low-light camera has made stroboscopy much more practical and allowed use in conjunction with both rigid and flexible endoscopic systems. Stroboscopic light allows routine slow-motion evaluation of the mucosal cover layer of the leading edge of the vocal fold and represents a dramatic technological advance in the ability to examine the vocal fold during function and diagnose pathology. Stroboscopy permits detection of vibratory asymmetries, structural abnormalities, small masses, submucosal scars, and other conditions that are invisible under ordinary light even with high resolution. (10)
However, stroboscopy is only a simulation of slow motion and relies upon the fact that vocal fold motion is periodic and regular, which is not always the case. Severe vocal fold pathology will result in irregular and aperiodic vibration, rendering stroboscopy ineffective. True slow motion images are very useful in such cases, and the technologies of high speed imaging and kymography have been developed to provide just that. (11)
High Speed Imaging
The technological advance that allowed for high speed imaging of the vocal folds was the development of the ultra high speed camera (UHSC) in 1937. Dr. Hans von Leden had witnessed the use of this camera to study explosions during his time in the U.S. Navy during World War II. He conceived the idea of adapting this technology for vocal fold imaging, and along with Dr. Paul Moore developed in the mid 1950s a system capable of photographing the functioning larynx. The system was rather complex and consisted of an intraoral laryngeal mirror, which reflected an image of the vocal folds onto another mirror, which was then photographed using the UHSC. Photographs were obtained at 2000 frames per second in color and faster in black and white. (12)
The system for obtaining these original images was complicated and cumbersome, and printing and analyzing the images was extraordinarily time consuming. However, the information generated was revolutionary and contributed greatly to the understanding of the normal and pathologic vocal fold. By imaging the complete glottic cycle, aperiodic vibrations can be analyzed (severe dysphonia, scar, cough, throat clearing, laughter), and the onset and offset of phonation can be seen, among other phenomena. (13) This work paved the way for the development of less cumbersome, more clinically applicable high speed imaging systems. The incorporation of videotape was a significant improvement and decreased the processing time to some degree. The advent of high speed digital imaging (HSDI) in the mid 1980s, however, was the true leap forward that made the incorporation of high speed imaging into clinical practice feasible. (14) This technology remains expensive, and its true clinical value is still being established, which has prevented its wide adaptation. However, it holds great promise for research, for severe dysphonia, and potentially for the evaluation of children who cannot comply with stroboscopy. (15) As this technology continues to become less expensive and more widely utilized, it is likely to find a niche in officebased laryngeal analysis.
Kymography was developed as a method of analyzing the vocal fold while transcending both the limitations of stroboscopy and the cumbersome analysis of high speed digital imaging. Although kymography was described initially by Gall in 1984, it was not until innovations were developed by Svec and Schutte in 1996 that the technology became clinically practical. (16) A kymogram is a picture generated by displaying a single pixel line perpendicular to the glottic axis over time. Therefore, vibrations of the vocal folds and surrounding tissues are displayed in a single image. Kymograms can be generated either independently, or extracted from digital images. The latter has been termed digital kymography (DK). Svec and Schutte's system has been incorporated into the KayPENTAX videostroboscopy system (PENTAX medical, Montvale, NJ) such that a digital image of the vocal folds is obtained and then a single line can be identified for kymography. A foot switch allows switching between the normal image and high-speed videokymography. (17)
The principal disadvantage of videokymography is that it displays only a single point along the vocal folds. However, this point is displayed in considerable detail at a speed of nearly 8000 images per second. The clinical value of kymography was initially reported in 1998. (18) Since that time, applications have continued to evolve. (19) Videokymography has proven useful in analyzing patients with aperiodic voices, scar, subharmonic vibrations, double or triple vocal fold openings in a single glottic cycle, and various other abnormalities. (20) Much of the information obtained with videokymography is similar to that obtained by HSDI, but at the present time it is less expensive and more expedient to analyze. Experience thus far suggests that videokymography can be a powerful tool in the diagnosis of vocal fold pathology and the assessment of treatment outcomes for selected patients.
Narrow Band Imaging
For the identification of nonvibratory pathology of the larynx including inflammation and malignancy, several technologies have been developed. Narrow band imaging (NBI) is one particularly promising such technique. Introduced in 2004 by Gono et al., NBI uses a filter to narrow the bandwidth of reflected white light into specific blue (415 nm) and green (540 nm) wavelengths. (21) Due to the fact that hemoglobin absorbs light at these wavelengths, this filter causes superficial blood vessels to appear dark and blue-green relative to the surrounding mucosa. Hypervascular tissues containing hemoglobin, such as in neoplastic and inflammatory processes, are thus much more obvious with NBI. This technique was quickly adopted into gastroenterologic endoscopy, and only more recently have reports of clinical utility in otolaryngology emerged. This has primarily been investigated for the early detection and delineation of epithelial malignancies. (22) A role in the detection and monitoring of laryngopharyngeal reflux has also been proposed. (23) Other methods for enhancing endoscopic images to detect superficial abnormalities including iScan, zoom endoscopy, and confocal laser endomicroscopy have been developed and shown in the gastroenterologic literature to be superior to standard endoscopy. (24) Although these techniques show great promise, further large scale studies and in both gastroenterological and otolarygological settings are needed to determine their clinical utility.
Contact endoscopy was developed initially as a gynecologic diagnostic tool in the early 1980s, and it has been used in the larynx since the 1990s. (25) The technique involves placing a specialized endoscope in contact with the mucosa, typically after application of methylene blue. These images are then interpreted by the otolaryngologist or pathologist and accurately show the epithelium and microvasculature. Enhanced contact endoscopy with the addition of NBI and other image enhancing techniques also has been described. (26) This has been shown to aid in the diagnosis, treatment, and surveillance of premalignant and malignant laryngeal lesions, and further applications are being investigated actively.
Optical Coherence Tomography
The techniques and technologies discussed thus far provide the ability to evaluate the surface appearance, motion, and vibratory function of the vocal folds in great detail. While this analysis provides insight into what likely lies below the surface, this remains a matter of educated conjecture. MRI and CT scanning techniques provide excellent visualization of larger, deeper lesions, but do not have the resolution required to show subtle pathology at the submucosal level. Biopsy with histopathologic analysis had been the only method of detecting such pathology until recently, which is limited by invasiveness and the potential for scarring. Technologies allowing visualization just beneath the surface of the larynx provide a new and evolving frontier in laryngology. Optical coherence tomography (OCT) has shown great promise in this regard. OCT was first reported in 1991 by Huang et al. and has evolved rapidly since that time. (27) OCT has been described as the optical analog to ultrasound, as it uses the reflection of light instead of sound to generate cross sectional images of tissue. (28) An OCT system consists of a light source, a plate beam splitter that divides the light into two beams, and a detector. (29) This is known as a Michaelson interferometer. (30) One beam is directed into the tissue and the other into a reference pathway. An interference pattern is generated between the two beams based on the properties of the tissue, and this creates a depth profile known as an "A line." Multiple A lines are created by scanning across a tissue sample and combined to form a two-dimensional image of the tissue, with an appearance similar to a histologic section. This image can be obtained to a depth of 2mm, which is ideal for laryngology given that imaging to this depth may capture the structure of the lamina propria and identify many vocal fold lesions. (31) OCT is an extremely promising technology and has been used safely for several years. (32) However, commercial, office based systems are not yet available.
Radiologic imaging the vocal folds and larynx, in anatomic context, is an invaluable diagnostic tool. The basics of the various modalities used to image the larynx including x-ray, CT, MRI, xeroradiography, fluoroscopy, and PET-CT are described well elsewhere, as are the exciting technologies of virtual endoscopy and virtual dissection. (33)
New adaptations of these relatively old technologies are arising constantly. Real-time MRI has proven valuable for its ability to image the entire vocal tract during phonation and identify both anatomic and functional pathology. (34) Functional MRI, which maps the brain activity of patients during various activities, has also found laryngologic applications. (35) Additionally, ultrasound has become increasingly useful in the larynx with improvements in resolution and processing. Recently, ultrasound has been shown to be useful in identifying vocal fold masses and lesions as well as in diagnosing paralysis and monitoring nerve function. (36)
Perhaps the brightest frontier in imaging of the larynx and vocal folds is not any particular device that will obtain images, but the way images are analyzed. Advances in image processing software have made it possible to selectively amplify the slightest motions or color changes from previously obtained videos. This has allowed detection of the pulse rate of humans by amplifying color changes in the face, and recreating sound signals by amplifying minute vibrations in objects such as a bag of potato chips. (37) Exactly how this technology will be put to use in the field of laryngology remains to be determined, but the potential is great.
A system that requires technology for diagnosis and treatment presents unique challenges for education, as well. Early visualization systems, as mentioned earlier, required direct visualization, and they allowed only one person at a time to observe. As such, a student could not watch a laryngeal operation. Therefore, the development of endoscopes and microscopes with projection abilities allowing more than just the operator to visualize the larynx was a monumental technological advance in education of young laryngologists. Tardy's 1972 report on his experience coupling a TV camera to the surgical microscope may well describe the single most significant technological advance in laryngeal surgical education, and it allows singing teachers who visit the operating room to see the details of the surgery. (38)
Diagnosis of laryngeal disorders relies heavily on other nonimaging technology, as well. Laryngeal EMG has become the workhorse of neurolaryngology, both for diagnosis and for localization of specific muscles for chemodenervation. Laryngeal EMG is reviewed elsewhere. (39) The development of ultrathin flexible esophagoscopes has made transnasal esophagoscopy possible, which allows for office-based evaluation and treatment of esophageal pathology. The clinical voice laboratory relies heavily on various technologies to obtain objective voice measures. Such technologies include electroglottography, aerodynamic measures, and sound signal processing software for acoustic analysis. The clinical voice lab remains a technological frontier in laryngology. We are still left without the vocal equivalent of an audiometer with which to measure both dysfunction and treatment outcome, but the clinical voice laboratory is becoming ever better at providing similarly useful measures. It is the opinion of the senior author (RTS) that current clinical voice laboratory analysis is based on obsolete technology, and the true technology that will allow for accurate assessment will be based on technology similar to that which looks for meaningful radio signals in space, processed through self-educating computers.
One of the most powerful tools that has been developed for measuring treatment outcomes, the quality of life survey, is low tech, but very high impact. Measuring the effects of treatment in a quantitative way is vitally important for the satisfaction of the patient and surgeon, as well as for research purposes, and especially for outcome measures that allow us to identify and make improvements in diagnosis and treatment.
Advances in imaging and other diagnostic technology inevitably lead to the diagnosis of more pathology. While laryngology remains a multidisciplinary field in regard to treatment, surgery is often the only remaining option after other medical and behavioral interventions have failed. Perhaps the biggest advance in laryngeal surgery was Oscar Kleinsasser's refinement of the use of a microscope and specialized laryngoscopes for use in microlaryngeal surgery in the early 1960s. (40) The development of specialized microsurgical instruments occurred at approximately the same time. Since then, techniques and instruments have continued to evolve and be refined. The adaptation of lasers for laryngeal surgery represented another significant technological advance.
Injection medialization laryngoplasty began with Brunings performing paraffin injections in the early 1900s. Since then, various materials have been developed, and the continuing development of new materials for this purpose represents an evolving technology in laryngology.
Technology in Voice Therapy
The field of voice therapy has embraced the smart phone revolution with the development of a number of applications to allow patients to practice techniques and monitor their progress. (41)
Other Technologies and Future Directions
Larngology has become a field that is ever more driven by and reliant upon technology. Advances in the science and technology of genetics may hold the key to many laryngeal pathologies including prevention and restoration of scar. Also, the fields of stem cell therapy and regenerative medicine hold great promise in the treatment of laryngeal disorders, and multiple studies and trials are underway.
The technologies discussed herein represent a portion of the current state-of-the-art and promising future directions in the field of laryngology. Such techniques are invaluable in the diagnosis of pathology and assessment of treatment response, and they have potential value in the voice studio. Certainly, there are other technologies in existence in varying stages of development that hold great potential to advance the fields of laryngology and voice teaching that are not addressed here. Only time will tell which of these will become part of our day-today future practice, what secrets will be revealed, and what barriers will be overcome.
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(2.) Manuel Garcia, "Physiological Observations on the Human Voice," Proceedings of the Royal Society of London 7 (1855): 399.
(3.) H. D. Silberman, H. Wilf, and J. A. Tucker, "Flexible Fiberoptic Nasopharyngolaryngoscope," Annals of Otology, Rhinology and Laryngology 85, Pt. 1 (September/October 1976): 640-645.
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(7.) Eller et al. (2008); Eller et al. (2009).
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(9.) Rosen, Amin, et al.
(10.) J. S. Ruben, R. T. Sataloff, and G. S. Korovin, Diagnosis and Treatment of Voice Disorders, 4th ed. (San Diego: Plural Publishing, Inc., 2014), 215-216.
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(13.) Izdebski et al.
(14.) Ibid.; R. A. Franco, J. G. Andrus, and R. T. Sataloff, "New Technologies: High-Speed Video, Videokymography, Optical Coherence Tomography, and 3D Holography," in C. J. Hartnick and M. E. Boseley, eds., Pediatric Voice Disorders (San Diego: Plural Publishing, Inc., 2008), 31-50; K. Honda, S. Kiritani, H. Imagawa, and H. Hirose, "High-speed digital recording of vocal fold vibration using a solid-state image sensor," in T. Baer, ed., Laryngeal Function in Phonation and Respiration (San Diego: College-Hill Press, 1987), 485-491.
(15.) Franco et al.
(16.) V. Gall, "Strip Kymography of the Glottis," Archives of Otorhinolaryngology 240, no. 3 (1984): 287-293; J. G. Svec and H. K. Schutte, "Videokymography: High-Speed Line Scanning of Vocal Fold Vibration," Journal of Voice 10, no. 2 (June 1996): 201-205; H. K. Schutte, J. G. Svec, and F. Stram, "Videokymography: Research and Clinical Application of Videokymography," Logopedics Phoniatrics Vocology 22, no. 4 (January 1998): 152-156; H. K. Schutte, J. G. Svec, and F. Stram, "First Results of Clinical Application of Videokymography," Laryngoscope 108, no. 8, pt. 1 (August 1998): 1206-1210.
(17.) Zietel et al.
(18.) Schutte et al.
(19.) J. G. Svec, F. Stram, and H. K. Schutte, "Videokymography in Voice Disorders: What to Look For?," Annals of Otolaryngology, Rhinology, and Laryngology 116, no. 3 (March 2007): 172-180.
(20.) Franco et al.
(21.) Izdebski et al.; M. J. Hawkshaw, J. B. Sataloff, and R. T. Sataloff, "New Concepts in Vocal Fold Imaging: A Review," Journal of Voice 27, no. 6 (November 2013): 738-743; K. Gono, T. Obi, M. Yamaguchi, et al., "Appearance of Enhanced Tissue Features in Narrow-Band Endoscopic Imaging," Journal of Biomedical Optics 9, no. 3 (May/June 2004): 568-577.
(22.) A. Watanabe, M. Taniguchi, H. Tskujie, et al., "Early Detection of Recurrent Hypopharyngeal Cancer after Radiotherapy by Utilizing Narrow Band Imaging--Report of a Case," Nippon Jiblinkoka Gakkai Kaiho 110 (October 2007): 680-682; Y. Orita, K. Kawabata, H. Mitani, et al., "Can Narrow-Band Imaging be Used to Determine the Surgical Margin of Superficial Hypopharyngeal Cancer?," Acta Medica Okayama 62 (June 2008): 205-208; T. Masaki, C. Katada, M. Nakayama, et al., "Narrow Band Imaging in the Diagnosis of Intraepithelial and Invasive Laryngeal Squamous Cell Carcinoma: A Preliminary Report of Two Cases," Auris Nasus Larynx 36, no. 6 (December 20009): 712-716; X. G. Ni, S. He, Z. G. Xu, et al., "Application of Narrow Band Imaging Endoscopy in the Diagnosis of Laryngeal Cancer," Zhonghua Er Bi Yan Hou Tou Jing Wai Ke Za Xhi 20, no. 2 (February 2010): 143-147; C. Piazza, D. Cocco, L. De Benedetto, et al., "Narrow Band Imaging and High Definition Television in the Assessment of Laryngeal Cancer: A Prospective Study on 279 Patients," European Archives of Otorhinolaryngology 267, no. 3 (March 2010): 409-414.
(23.) Hawkshaw et al.
(24.) S. K. Amateau and M. I Canto, "Enhanced Mucosal Imaging," Current Opinion in Gastroenterology 26, no. 5 (September 2010): 445-452.
(25.) M. Klancnik, I. Gluncic, and C. Drasko, "The Role of Contact Endoscopy in Screening for Premalignant Laryngeal Lesions: A Study of 141 Patients," Ear, Nose, and Throat Journal 93, no. 4-5 (April/May 2014): 177-180.
(26.) R. Puxeddu, S. Sionis, C. Gerosa, and F. Carta, "Enhanced Contact Endoscopy for the Detection of Neoangiogenesis in Tumors of the Larynx and Hypopharynx," Laryngoscope 125, no. 7 (July 2015): 1600-1606.
(27.) D. Huag, E. A. Swanson, C. P. Lin, et al., "Optical Coherence Tomography," Science 254, no. 5035 (November 1991): 1178-1181.
(28.) Franco et al.
(29.) Izdebski et al.; Franco et al.; Hawkshaw et al.
(30.) Izdebski et al.
(31.) Hawkshaw et al.
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(33.) J. Abitol, A. Castro, R. Gombergh, and P. Abitol, "Laryngeal Computed Tomography: Virtual Endoscopy--Virtual Dissection," in R. T. Sataloff, ed., Professional Voice: The Sequenced Art of Clinical Care, 3rd ed. (San Diego: Plural Publishing, Inc., 2005), 440-447.
(34.) M. Echternach, M. Marik, and B. Richter, "Dynamic Real-Time Magnetic Resonance Imaging for the Analysis of Voice Physiology," Current Opinion in Otolaryngology & Head and Neck Surgery 20, no. 6 (December 2012): 450-457.
(35.) J. F. Galgano, K. P. Kyung, R. Branski, et al., "Correlation Between Functional MRI and Voice Improvement Following Type I Thyroplasty in Unilateral Vocal Fold Paralysis--A Case Study," Journal of Voice 23, no. 5 (September 2009): 639-645.
(36.) P. H. Tsui, Y. L. Wan, and C. K. Chen, "Ultrasound Imaging of the Larynx and Vocal Folds: Recent Applications and Developments," Current Opinion in Otolaryngology & Head and Neck Surgery 20, no. 6 (December 2012): 437-442.
(37.) M. Rubenstein, "See invisible motion, hear silent sounds. TED. November 2014; www.ted.com/talks/michael_rubenstein_see_invisiblemotionhear_silent_sounds_cool_creepy_we_can_t_decide?language=en (accessed December 20, 2015).
(38.) M. E. Tardy, Jr., "Microscopic Laryngology: Teaching Techniques," Laryngoscope 82, no. 7 (July 1972): 1315-1322.
(39.) R. T. Sataloff, S. Mandel., Y. Heman-Ackah, R. Mafien-Espaillat, and A. Abaya, Laryngeal Electromyography, 2nd ed. (San Diego: Plural Publishing, Inc., 2006), 1-149.
(40.) O. Kleinsasser, "Mikrochirugie im Kehlkopf," Archiv fur Ohren-, Nasen- und Kehlkopfheilkunde 183, no. 2 (November 1964): 428-433.
(41.) R. T. Sataloff, F. Chowdhury, J. E. Portray, M. J. Hawkshaw, and S. Joglekar, Laryngeal Surgery (New Delhi: Jaypee Bros. Publishing, 2014), 3-263.
Dr. Romak graduated from the University of Connecticut School of Medicine, received his residency training in Otolaryngology--Head and Neck Surgery at Mayo Clinic in Minnesota, and completed a fellowship in Laryngology and Care of the Professional Voice at the American Institute for Voice and Ear Research. He practices laryngology and otolaryngology in Wilmington, Delaware.
Robert T. Sataloff, Associate Editor
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|Title Annotation:||Care of the Professional Voice|
|Author:||Romak, Jonathan J.; Sataloff, Robert T.|
|Publication:||Journal of Singing|
|Date:||Jan 1, 2017|
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