Reliability of 3-D/4-D Ultrasound Contouring of Tongue Surface During Swallowing

The tongue has a critical role in swallowing, particularly related to bolus (i.e., food or liquid material) manipulation and propulsion through the oropharynx. Tongue contour (i.e., shape) is likely modulated based on the characteristics of the bolus material being swallowed, particularly pertaining to bolus containment prior to oral transport during swallowing. There are limited tools available to characterize tongue motion in a 3-D plane. The purpose of this preliminary study was to apply methodology for ultrasound imaging of the tongue to determine if lingual movement and contour can be reliably quantified during swallowing tasks.

Lingual 3-D/4-D ultrasound data of tongue movement during swallowing were collected from 8 young, healthy participants (4 male, 4 female) using a convenience sample. Participants were presented with 4 different bolus thicknesses, each repeated 5 times (20 swallows total). In this report, only liquid bolus presentations were analyzed using an open-source WASL toolbox (WASL 10.3.6) for MATLAB. Reliability was measured from 8 frames per swallow, and root mean square was used to quantify inter- and intra-rater reliability.

The preliminary findings showed that reliable tongue surface contouring using 3-D/4-D ultrasound is possible during swallowing. The average inter- and intra-rater reliability, using root mean square, was 0.15-0.16 for liquid bolus swallows (0 = perfect agreement), indicating that these methods were highly reliable across and within raters.

Lingual 3-D/4-D ultrasound can provide information about lingual movements in the 3-D plane. Our results demonstrate that tongue surface contouring during swallowing using 3-D/4-D ultrasound is reliable within and across raters. The work presented here lays the foundation for future work by establishing a method for tongue contour analysis during swallowing.