The swallowing movement is a rapid, continuous and invisible movement constructed in the mouth, pharynx and larynx. Therefore, 2D images cannot achieve suitable resolution of the swallowing mechanism. This paper reports our successful visualization of the swallowing movement using 4D-MRI.
The synchronized sampling method was applied for 4D-MRI. Each of 9 slices of 4D-MRI had 35 images with the frame rate of 66 msec. The subject was a normal volunteer who swallowed 2 ml of liquid 128 times.
Though any section in the X, Y, Z directions could be used in 4D-MRI, we selected images of the sagittal section of the whole, and axial section of the velopharyngeal and glottic plane, and coronal section of the laryngeal plane. These images were useful to depict the complicated movement of organs during a swallow.
The results proved that adduction of vocal cords and laryngeal elevation started immediately after the liquid was infused into the subject's mouth, and then 198 msec after the infusion the pharyngeal lateral walls moved inward and the soft plate elevated. The velopharynx closed 132 msec after the elevation of the soft palate, and then its closure continued for 594 msec. Both the glottis and the larynx closed 66 msec after the velopharyngeal closure. After the time that the esophagus opened, the velopharynx gradually started to open. The esophagus opened for 198 msec, while the larynx continued to close for 462 msec. The glottis continued to close for 594 msec.
This first study of 4D-MRI for the swallowing movement simultaneously visualized the closure of the velopharynx, larynx and the glottis as well as opening of the esophagus. The 4D-MRI yielded detailed images of a normal swallow, which will help to clarify the mechanism of swallowing movement.