ACCURATE MEASUREMENT OF VOCAL-TRACT SHAPES USING MAGNETIC-RESONANCE-IMAGING

In this paper, a method is developed for an accurate measurement of th e three-dimensional shape of the vocal tract, using magnetic resonance imaging (MRI), aiming at the analysis of the features of the vocal tr act shape in the utterance by children, males and females. To derive t he precise data for the shape of the vocal tract, the data for the voc al tract of the oral cavity is derived from the coronal MR image from the lips to the atlas. The data for the vocal tract from the glottis t o the palate are derived from two kinds of horizontal MR images. High- speed photography is used, and the imaging time is 2.9 s for each slic e. The central line of the vocal tract is estimated from the mid-sagit tal MR image, and the vocal tract length is calculated. Based on the m id-sagittal MR image, the three-dimensional shape of the vocal tract i s reconstructed from the vocal tract contour in the three kinds of ima ges. To process the large amount of data, a method is developed that a utomatically extracts the vocal tract contour from the MR image. A cor rection method is proposed for the teeth shape which cannot be imaged by MRI, based on the MR image of the dental impression. The error of t he measuring method is evaluated quantitatively using a model for the vocal tract. The transfer function for Japanese /a/ are estimated by t he proposed measuring method, and the result is compared to the result of LPC analysis of the speech recorded at the site. It is seen as a r esult that the errors for F1, F2, and F3 are 8, 17, and 141 Hz, respec tively.