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The videostroboscopy of the larynx has become a powerful tool for the study of vocal physiology, assessment of the fold abnormalities, motion impairments and functional disorders, as well as for the early diagnosis of diseases like cancer and pathologies like nodules, carcinoma, polyps and cysts. Since the vocal folds vibrate in the range of 100 Hz up to 1 kHz, the video stroboscope allows physicians to find otherwise undetectable problems. The color information is essential for the physician by the diagnosis e.g., of the early cancer stage. A previously presented 'general purpose' monochrome high-speed video stroboscope has been tested also for the inspection of the human larynx. Good results have encouraged the authors to develop a medical color version. In contrast to the conventional stroboscopes the system does not utilize pulsed light for the object illumination. Instead, a special asynchronously shuttered video camera triggered by the oscillating object has been used. The apparatus including a specially developed digital phase shifter provides a stop phase and slow-motion observation in real time with simultaneous recording of the periodically moving objects. The desired position of the vocal folds or their virtual slowed down vibration speed does not depend of the voice pitch changes. Sequences of hundreds of high resolution color frames can be stored on the hard disk in the standard graphic formats. Afterwards they can be played back frame-by-frame or as a video clip, evaluated, exported, printed out and transmitted via computer networks.
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