Spatiotemporal visualization of the tongue surface using ultrasound and kriging

Analyzing the motion of the tongue surface provides valuable information about speech and swallowing. To analyze this motion, two-dimensional ultrasound images are acquired at video frame rates, and the tongue surface is automatically extracted and tracked. Further processing and statistical analysis of the extracted contours is made difficult by: 1) arbitrary spatial shifts and data loss resulting from ultrasound transducer positioning; 2) difference in tongue lengths over time for same utterance (or swallow) and across subjects; and 3) differences in the sampling locations. To address the above shortcomings, we used kriging to extrapolate and resample the tongue surface contours. Kriging was used because it does not lead to wild oscillations associated with traditional polynomial fitting. For our kriging implementation, we used the generalized covariance function and linear drift functions that are used in thin place splines. Further, we designed a dedicated user interface called "SURFACES" that exploits this extrapolation to visualize the contours as spatiotemporal surfaces. These spatiotemporal surfaces can be readily used for statistical comparison and visualization of tongue shapes for different utterances and swallows.