Computer measurement of oral movement in swallowing

This article describes a computer program that automatically detects and tr acks small metal markers affixed to a subject's tongue and teeth in fluoros copic image sequences of swallowing. The program, written in Microsoft Visu al C++ using Windows NT 4.0 and the SAVANT imaging toolkit, involves marker detection and marker tracking. Marker detection is done by template matchi ng. A generic marker template was designed by extracting the grayvalues of pixels within an imaged marker. Template matching with a weighted center-of -mass calculation determined marker location with subpixel accuracy. Marker tracking employed a nearest-neighbor algorithm since (a) the movement of e ach marker was less than the distance between any two markers and (b) marke r trajectories did not overlap. Effects of head motion were attenuated by c omputing tongue trajectories with respect to a constant frame of reference given by reference markers on the maxillary teeth. Motions were converted f rom pixels/ frame to millimeters/second using a calibration ring secured to the subject's neck. Results for several image sequences showed that our pr ogram performs very well in terms of marker detection and trajectory determ ination. Comparison of automatic and manual tracking of the same image sequ ences indicated a high degree of correspondence. Automatic tracking of oral movement by computer is a useful tool in kinematic studies of swallowing.