Visualising hyolaryngeal mechanics in swallowing using dynamic MRI

In this study, coordinates of anatomical landmarks were captured using dynamic MRI (dMRI) to explore whether a proposed two-sling mechanism underlies hyolaryngeal elevation in pharyngeal swallowing. A principal component analysis (PCA) was applied to coordinates to determine the covariant function of the proposed mechanism. dMRI data were acquired from 11 healthy subjects during a repeated swallow task. Coordinates mapping the proposed mechanism were collected from each dynamic (frame) of a dMRI swallowing series of a randomly selected subject in order to demonstrate shape changes in a single subject. Coordinates representing minimum and maximum hyolaryngeal elevation of all 11 subjects were also mapped to demonstrate shape changes in the system among all subjects. MophoJ software was used to perform PCA and determine vectors of shape change (eigenvectors) for elements of the two-sling mechanism of hyolaryngeal elevation. For both single subject and group PCAs, hyolaryngeal elevation accounted for the first principal component of variation. For the single subject PCA, the first principal component accounted for 81.5% of the variance. For the between-subjects PCA, the first principal component accounted for 58.5% of the variance. Eigenvectors and shape changes associated with this first principal component are reported. Thus, it was concluded that eigenvectors indicate that two muscular slings and associated skeletal elements function as components of a covariant mechanism to elevate the hyolaryngeal complex. Also, morphological analysis is useful to model shape changes in the two-sling mechanism of hyolaryngeal elevation.