Three-dimensional video of facial surface synchronized with videofluoroscopic swallowing study

Purpose: A videofluoroscopic swallowing study (VFSS) is the gold standard for the examination of swallowing function. A fluoroscopic unit and contrast medium are used to record an X-ray video of the patient's swallowing dynamics. This requires clinicians to observe three-dimensional swallowing movements on a two-dimensional video. In addition, the VFSS lacks facial surface information. In this study, we developed a method to synchronize the VFSS video with the three-dimensional movement of the facial surface. Approach: A 44-year-old man with no dysphagia was studied. Five smooth and one textured iron ball with a diameter of 3 mm were attached to the facial surface as markers at the tip of the nose, the upper and lower lips, the left and right corners of the mouth, and the chin. Using an X-ray fluoroscopic unit, the swallowing movements of gelatin jelly containing an iodine-based contrast media were recorded. The patient swallowed the jelly with mastication (right side, left side, both sides) and without mastication (open-mouth swallowing). At the same time, the movements of the facial surface were recorded using three video cameras. The four obtained videos were synchronized in terms of their start point, end point, and playback speed using a computer. Results: We created a synchronized video of the VFSS video and the three-dimensional video of the facial surface. This video could be observed from any viewpoint. In addition, we could analyze the velocity, distance, and angle of each point. Conclusion: This method can be used to objectively analyze mastication using numerical values.