Accuracy of measurements on digital videostroboscopic images of the vocal folds

Objectives: The reliability of objective measurements on digital laryngeal images was investigated. Methods: The magnitude of the error of measurement of surface areas by visually tracing the outline was determined for three different areas: the area of the lesion and, during vibration, the glottal area on maximal opening of the vocal folds and the glottal area on maximal closing of the vocal folds. Results: The errors in these areas were 10% to 30%. The results suggest that the error is mainly due to the uncertainty of the real outline of areas with a vague boundary. Correction for differences in magnification between two images (posttherapy and pretherapy) is of importance in about 25% to 65% of cases, depending on the area measured. Conclusions: Only when the magnification ratio is small (less than about ±10% from 1.0) may a correction not be necessary.