Elasticity of human vocal folds measured in vivo using color Doppler imaging

Noninvasive measurement of human vocal fold (VF) vibratory length was made during normal phonation to calculate the corresponding elasticity. A fixed-ends rubber string phantom that was driven by a vibrating motor was built to simulate the horizontal VF movement. The vibratory artefact of color Doppler imaging (CDI) was used to characterize and quantify the high-frequency tissue vibration with small amplitude. Because the frequency and the length of vibrating VFs were obtained simultaneously, the stress-strain relation and the Young's moduli of the VFs could be calculated. For the six vocally normal adult volunteers (3 M, 3 F, ages from 19 to 51 years old), the effective vibrating lengths of the vocal fold in low pitch were about 1.4 to 1.6 cm and 1.3 to 1.5 cm for men and women, respectively. The VFs lengths extended to about 1.7 to 1.8 cm in pitch over an octave higher and the stress-strain relation was nonlinear. However, in the range of lower pitch, the VF stress was relatively linear with respect to the strains and the Young's moduli were about 30 to 120 kPa in men and 120 to 300 kPa in women.