A method of tooth superimposition on MRI data for accurate measurement of vocal tract shape and dimensions

Measurement of vocal tract area functions from MRI data requires a technique for tooth visualization because the teeth are as transparent as air in the images. In this article, a new method is proposed to accurately superimpose the teeth onto MRI volume data. Upper and lower tooth images with the surrounding bony structure are obtained by scanning a subject holding a contrast medium in the oral cavity. They are superimposed onto the target volume data via a three-dimensional transformation using landmarks sampled from the tooth images and target MRI data. The accuracy of the dental image superimposition is ensured by the minimization of the error volume, which is the mismatch volume of the dental image overlapping the surrounding soft tissue. The method is evaluated using five operators sampling the landmarks. Results show that the error volume is significantly reduced to a nearly constant value regardless of the operator’s skill.