Vocal tract area functions from magnetic resonance (MR) images.
Patrick W. Nye · The Journal of the Acoustical Society of America · 1991
MR equipment was used to obtain axial, coronal, and sagittal images of the vocal tracts of two male subjects during sustained vowel production. Spaced at 0.5-cm intervals, the MR image sections sampled the region from the larynx to the lips. A computer algorithm traced the air-tissue boundaries of the tract sections, and the boundaries of intermediate sections were interpolated at intervals of approximately 1 mm. These boundary data were used in 3-D digital reconstructions of the tract shape. Two methods for determining the area function from a 3-D tract model were applied and the results compared. Based on the assumption that the tract could be approximated by two straight tubes connected by a gradual right-angled bend, method 1 resectioned the model with a systematic combination of radial and parallel gridplanes designed to intersect the tract at equal intervals along its midline [cf. J. M. Heinz and K. N. Stevens, J. Acoust. Soc. Am. 36, 1037 (A) (1964); P. Mermelstein, J. Acoust. Soc. Am. 53, 1070–1082 (1974)]. Method 2 made no assumptions as to tract uniformity and traced the midline with an area minimization algorithm applied to the 3-D data. A sequence of equidistant points along the midline was then found and the area function derived. Several differences between the area functions are found, a major one being tract length which tends to be longer by method 2 than method 1. Also, the precision that can be gained by method 2 depends on the presence of many high definition MR images to ensure minimization stability. [Work supported by NIH Grant DC-00121.]