Imaging the tongue and vocal tract.

The internal structures of the vocal tract are difficult to measure without impinging upon their normal movement patterns. Imaging techniques overcome that difficulty because they measure internal movement indirectly, without direct contact with the structures. This paper examines four well-known imaging techniques: X-ray, computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound. Tongue and vocal tract researchers have employed all of these techniques. Imaging systems provide very different articulatory information from flesh point tracking systems. They provide information about the shape and position of the entire imaged structure, rather than a single point on the structure. In addition, images usually can be made in multiple planes, providing midsagittal, parasagittal, coronal, transverse and oblique sections of the structure. However, these systems have several limitations. CT and MRI create static images only. Ultrasound cannot image hard tissue. Radiation exposure limits the duration of X-ray imaging. This paper discusses the advantages and limitations of imaging systems, as well as the uniqueness of the measurements made with them.