Using MRI for assessing velopharyngeal structures and function

Abstract

Objective: Direct visualization of the velopharynx and, in particular, the levator muscle is particularly important in the assessment of velopharyngeal function and normal speech production. The purpose of this study is to demonstrate the development of a static and dynamic magnetic resonance imaging protocol for evaluation of velopharyngeal structures and function.

Methods: A high-resolution, T2-weighted turbo-spin-echo three-dimensional anatomical scan (sampling perfection with application optimized contrasts using different flip angle evolution) was used to acquire a large field of view covering the velopharyngeal anatomy. Dynamic speech assessment was obtained using a fast-gradient echo, fast low-angle shot, multi-shot spiral technique to acquire 15.8 frames per second (FPS) of the sagittal and oblique coronal image planes.

Results: Using a three-dimensional data set, as opposed to two-dimensional data, the full contour of the levator muscle can be appreciated. Dynamic images were obtained at 15.8 FPS in the sagittal and oblique coronal planes, enabling visualization of the movements of the velum, posterior pharyngeal wall, lateral pharyngeal walls, and levator muscle during speech.

Conclusions: A three-dimensional magnetic resonance imaging sequence, such as that used in the present study, may provide better analyses and more precise measurements. A dynamic fast low-angle shot sequence allows for visualization of the levator muscle and the velum during speech at a high image rate. This protocol could have a significant impact in improving the process of visualizing pathology and promoting clinical treatment plans for individuals born with cleft lip and palate.

Keywords: MRI; cleft palate; dynamic MRI during speech.

FIGURE 1

Oblique coronal image showing the cohesive levator sling from origin (white arrows at the top) at the base of the skull to insertion in the velum (single white arrow at the bottom). The image in the lower right displays the sampling plane used to obtain the oblique coronal image. Note the dark circle just above the lowest portion of the levator sling, which is the musculus uvulae cut in cross-section.

FIGURE 2

Demonstration of the measures in the midsagittal image plane and coronal image plane. ANS = anterior nasal spine; PNS = posterior nasal spine.

FIGURE 3

Demonstration of the process of acquiring an oblique coronal image. A: The oblique line in the midsagittal image is used to acquire the view of the levator muscle. B: The levator muscle can be viewed as the U-shaped muscle sling inside the white box. The white box represents the selected region used to acquire the dynamic images. C: The levator sling can be visualized as the central U-shaped muscle sling in the dynamic images.

FIGURE 4

Series of MR images to represent the movement of the velopharyngeal structures in the oblique coronal (bottom row) image planes during “ansa” production. NC = nasal cavity; OC = oral cavity; Levator = levator veli palatini muscle.