Framework for Indirect Spatial Calibration of the Horizontal Plane of Endoscopic Laryngeal Images.
Hamzeh Ghasemzadeh, Dimitar D Deliyski, Robert E Hillman and 1 others
PMID 34986994WHAT IT FOUND
Vocal fold width is the most reliable reference feature for measuring laryngeal lesions in endoscopic images.
Unlike vocal fold length, which changes with pitch, or blood vessels, which vary in visibility, vocal fold width remains consistent across different phonatory conditions, allowing for more accurate pre- and post-treatment comparisons.
Key findings
01Vocal fold width was identified as the most appropriate common attribute for indirect calibration because it best balanced registration accuracy, size consistency, and vertical distance similarity.
02Vocal fold length was found to be inconsistent between comfortable and higher pitches, making it an unreliable reference for calibration.
03Violations of the vertical distance condition can lead to significant measurement errors, such as a 50% underestimation of lesion size if the reference feature is at a different working distance than the target.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study had a small sample size, with only 11 participants contributing data for vocal fold attributes and 7 for blood vessel attributes. The evaluation of size consistency was limited to only two phonatory configurations (comfortable and higher pitch), so it is unclear how these reference features behave across a wider range of loudness or voice qualities. The framework assumes the imaging angle is perpendicular to the vocal folds; it does not account for errors introduced by flexible fiberoptic endoscopes or non-perpendicular rigid scopes, which can distort measurements. The method relies on the assumption that the lesion size does not change between the intraoperative image and the laboratory recording, which may not hold if the lesion is highly compressible or if significant time passes between sessions.
Declared interests
Drs. Robert Hillman and Daryush Mehta have a financial interest in InnoVoyce LLC, a company developing technologies for voice-related disorders. These interests were reviewed and managed by Massachusetts General Hospital and Mass General Brigham.
The easy way to misread this
Do not assume this method provides absolute precision in all clinical settings. The accuracy depends heavily on the reference feature (vocal fold width) being clearly visible and on the camera being positioned perpendicular to the vocal folds. If using a flexible endoscope or if the view is oblique, the 'indirect calibration' may still produce significant errors, particularly if the reference feature and the lesion are at different vertical distances from the lens.