Dynamic imaging of speech and swallowing with MRI

Identifying Predictors of Levator Veli Palatini Muscle Contraction During Speech Using Dynamic Magnetic Resonance Imaging

Purpose The purpose of this study was to identify predictors of levator veli palatini (LVP) muscle shortening and maximum contraction velocity in adults with normal anatomy. Method Twenty-two Caucasian English-speaking adults with normal speech and resonance were recruited. Participants included 11 men and 11 women (M = 22.8 years, SD = 4.1) with normal anatomy. Static magnetic resonance images were obtained using a three-dimensional static imaging protocol. Midsagittal and oblique coronal planes were established for visualization of the velum and LVP muscle at rest. Dynamic magnetic resonance images were obtained in the oblique coronal plane during production of "ansa." Amira 6.0.1 Visualization and Volume Modeling Software and MATLAB were used to analyze images and calculate LVP shortening and maximum contraction velocity. Results Significant predictors (p < .05) of maximum LVP shortening during velopharyngeal closure included mean extravelar length, LVP origin-to-origin distance, velar thickness, pharyngeal depth, and velopharyngeal ratio. Significant predictors (p < .05) of maximum contraction velocity during velopharyngeal closure included mean extravelar length, intravelar length, LVP origin-to-origin distance, and velar thickness. Conclusions This study identified six velopharyngeal variables that predict LVP muscle function during real-time speech. These predictors should be considered among children and individuals with repaired cleft palate in future studies.

Assessment of velopharyngeal function with dual-planar high-resolution real-time spiral dynamic MRI

PURPOSE

To develop a real-time dynamic MRI method for comprehensive evaluation of velum movement during speech.

METHODS

Dynamic MRI has been used to study velopharyngeal insufficiency (VPI) by imaging the movement of the velum during speech, because it can provide good anatomic details with no exposed radiation. To be able to comprehensively evaluate dynamic velum movement, a real-time spiral non-balanced SSFP sequence was developed with simultaneous dual-planar coverage and improved spatial and temporal resolution using a combination of parallel imaging and spatial and temporal compressed sensing to achieve 6 × acceleration. New off-resonance correction and post-processing methods were also developed to reduce blurring and slice crosstalk.

RESULTS

The method demonstrated good image quality for visualizing dynamic velum movement with reduced blurring and improved image homogeneity. Spatial resolution of 1.2*1.2 mm² with 150 mm FOV and temporal resolution of 20 frames-per-second with simultaneous dual-planar coverage was achieved.

CONCLUSIONS

This work describes a new technique for studying speech disorders using dual-planar accelerated spiral dynamic MRI.

Can Dynamic MRI Be Used to Accurately Identify Velopharyngeal Closure Patterns?

BACKGROUND

Dynamic magnetic resonance imaging (MRI) has been proposed as a non-invasive, child-friendly, reproducible, and repeatable imaging method providing a 3-dimensional view of the velopharyngeal structures and function during speech. However, the value of dynamic MRI as compared to imaging methods such as nasopharyngoscopy is not well understood. The aim of this study was to compare the ability of nasopharyngoscopy and dynamic MRI to accurately identify velopharyngeal closure patterns among adults without cleft palate.

METHODS

Participants included 34 healthy adults with normal anatomy between 19 and 33 years of age (mean = 23 years; SD = 4.1 years). Participants underwent dynamic MRI and nasopharyngoscopy studies and comparisons were performed to determine the intra- and inter-rater reliability for accurately determining closure pattern. The MRI acquisition was a dynamic acquisition of a 2D plane.

RESULTS

Strong inter- (κ = .824; P < .001) and intra-rater (Rater 1: κ = 0.879, P < .001, 94% agreement between ratings; Rater 2 with 100% agreement) agreement was observed for the identification of closure pattern using nasopharyngoscopy. Inter-rater agreement for ratings using MRI demonstrated moderate agreement (κ = .489; P < .004). Examining point agreement revealed only 27 of the 33 ratings of MRI showed agreement (80%).

CONCLUSION

This demonstrates that inter-rater reliability for determining closure patterns from nasopharyngoscopy is good; however, ratings using MRI was less reliable at determining closure patterns. It is likely that future improvements in dynamic imaging with MRI to enable 3D visualizations are needed for improved diagnostic accuracy for assessing velopharyngeal closure patterns.

Contributions of the Musculus Uvulae to Velopharyngeal Closure Quantified With a 3-Dimensional Multimuscle Computational Model

The convexity of the dorsal surface of the velum is critical for normal velopharyngeal (VP) function and is largely attributed to the levator veli palatini (LVP) and musculus uvulae (MU). Studies have correlated a concave or flat nasal velar surface to symptoms of VP dysfunction including hypernasality and nasal air emission. In the context of surgical repair of cleft palates, the MU has been given relatively little attention in the literature compared with the larger LVP. A greater understanding of the mechanics of the MU will provide insight into understanding the influence of a dysmorphic MU, as seen in cleft palate, as it relates to VP function. The purpose of this study was to quantify the contributions of the MU to VP closure in a computational model. We created a novel 3-dimensional (3D) finite element model of the VP mechanism from magnetic resonance imaging data collected from an individual with healthy noncleft VP anatomy. The model components included the velum, posterior pharyngeal wall (PPW), LVP, and MU. Simulations were based on the muscle and soft tissue mechanical properties from the literature. We found that, similar to previous hypotheses, the MU acts as (i) a space-occupying structure and (ii) a velar extensor. As a space-occupying structure, the MU helps to nearly triple the midline VP contact length. As a velar extensor, the MU acting alone without the LVP decreases the VP distance 62%. Furthermore, activation of the MU decreases the LVP activation required for closure almost 3-fold, from 20% (without MU) to 8% (with MU). Our study suggests that any possible salvaging and anatomical reconstruction of viable MU tissue in a cleft patient may improve VP closure due to its mechanical function. In the absence or dysfunction of MU tissue, implantation of autologous or engineered tissues at the velar midline, as a possible substitute for the MU, may produce a geometric convexity more favorable to VP closure. In the future, more complex models will provide further insight into optimal surgical reconstruction of the VP musculature in normal and cleft palate populations.

Velopharyngeal Structural and Functional Assessment of Speech in Young Children Using Dynamic Magnetic Resonance Imaging

OBJECTIVE

The purpose of this study was to demonstrate a novel method for examining the velopharyngeal mechanism using static and dynamic magnetic resonance imaging (MRI) at the sentence-level production in young children with normal anatomy. This study examined whether velopharyngeal events occurring in the midsagittal plane are correlated to muscle events occurring along the plane of velopharyngeal closure. Adenoid involvement in velopharyngeal function was also explored.

METHODS

A high-resolution, T2-weighted turbo-spin-echo three-dimensional anatomical scan was used to acquire static velopharyngeal data and a fast-gradient echo fast low angle shot multishot spiral technique (15.8 frames per second) was used to acquire dynamic data on 11 children between 4 and 9 years old.

RESULTS

Changes in velar knee height from rest to the bilabial /p/ production was strongly correlated with changes in the velar configuration (r = 0.680, P = .021) and levator muscle contraction (r = 0.703, P = .016). Velar configuration was highly correlated to levator muscle changes (r = 0.685, P = .020). Mean alpha angle during bilabial /p/ production was 176°, which demonstrated that subjects achieve velopharyngeal closure at or just below the palatal plane. Subjects with a larger adenoid pad used significantly less (r = -0.660, P = .027) levator muscle contraction compared with individuals with smaller adenoids.

CONCLUSIONS

This study demonstrates a potentially useful technique in dynamic MRI that does not rely on cyclic repetitions or sustained phonation. This study lends support to the clinical potential of dynamic MRI methods for cleft palate management.

Recommendations for real-time speech MRI

Real-time magnetic resonance imaging (RT-MRI) is being increasingly used for speech and vocal production research studies. Several imaging protocols have emerged based on advances in RT-MRI acquisition, reconstruction, and audio-processing methods. This review summarizes the state-of-the-art, discusses technical considerations, and provides specific guidance for new groups entering this field. We provide recommendations for performing RT-MRI of the upper airway. This is a consensus statement stemming from the ISMRM-endorsed Speech MRI summit held in Los Angeles, February 2014. A major unmet need identified at the summit was the need for consensus on protocols that can be easily adapted by researchers equipped with conventional MRI systems. To this end, we provide a discussion of tradeoffs in RT-MRI in terms of acquisition requirements, a priori assumptions, artifacts, computational load, and performance for different speech tasks. We provide four recommended protocols and identify appropriate acquisition and reconstruction tools. We list pointers to open-source software that facilitate implementation. We conclude by discussing current open challenges in the methodological aspects of RT-MRI of speech.

Real-time magnetic resonance imaging and electromagnetic articulography database for speech production research (TC)

USC-TIMIT is an extensive database of multimodal speech production data, developed to complement existing resources available to the speech research community and with the intention of being continuously refined and augmented. The database currently includes real-time magnetic resonance imaging data from five male and five female speakers of American English. Electromagnetic articulography data have also been presently collected from four of these speakers. The two modalities were recorded in two independent sessions while the subjects produced the same 460 sentence corpus used previously in the MOCHA-TIMIT database. In both cases the audio signal was recorded and synchronized with the articulatory data. The database and companion software are freely available to the research community.

Using MRI for assessing velopharyngeal structures and function

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.

Effect of posture on deglutitive biomechanics in healthy individuals

The purpose of this study was to assess displacement of oropharyngeal structures, particularly the hyoid bone and velum, and variations in timing of the pharyngeal stage of swallowing in the upright versus the supine position. Twelve Caucasian adult subjects between 19 and 27 years of age participated. Subjects were recorded swallowing 7 cc of liquid barium in the upright and supine positions. The hyoid bone had a significantly greater amount of anterior displacement while in the supine position compared to that of the upright position (p < 0.01). While in the upright position, the velum comes to a fully elevated position at nearly the same time as the initiation of the pharyngeal swallow (within an average of 27 ms of each other), whereas in the supine position the velum continues to elevate on average 115 ms after the initiation of the pharyngeal swallow. Results indicated a significant difference (p < 0.05) in the amount of velar movement from rest to the fully elevated position between the upright and supine positions for female subjects. The results from the study demonstrate variations in hyoid displacement, velar movement, and bolus movement through the pharynx with respect to the two body positions and the subjects' gender.

Novel 16-channel receive coil array for accelerated upper airway MRI at 3 Tesla

Upper airway MRI can provide a noninvasive assessment of speech and swallowing disorders and sleep apnea. Recent work has demonstrated the value of high-resolution three-dimensional imaging and dynamic two-dimensional imaging and the importance of further improvements in spatio-temporal resolution. The purpose of the study was to describe a novel 16-channel 3 Tesla receive coil that is highly sensitive to the human upper airway and investigate the performance of accelerated upper airway MRI with the coil. In three-dimensional imaging of the upper airway during static posture, 6-fold acceleration is demonstrated using parallel imaging, potentially leading to capturing a whole three-dimensional vocal tract with 1.25 mm isotropic resolution within 9 sec of sustained sound production. Midsagittal spiral parallel imaging of vocal tract dynamics during natural speech production is demonstrated with 2 × 2 mm(2) in-plane spatial and 84 ms temporal resolution.

Flexible retrospective selection of temporal resolution in real-time speech MRI using a golden-ratio spiral view order

In speech production research using real-time magnetic resonance imaging (MRI), the analysis of articulatory dynamics is performed retrospectively. A flexible selection of temporal resolution is highly desirable because of natural variations in speech rate and variations in the speed of different articulators. The purpose of the study is to demonstrate a first application of golden-ratio spiral temporal view order to real-time speech MRI and investigate its performance by comparison with conventional bit-reversed temporal view order. Golden-ratio view order proved to be more effective at capturing the dynamics of rapid tongue tip motion. A method for automated blockwise selection of temporal resolution is presented that enables the synthesis of a single video from multiple temporal resolution videos and potentially facilitates subsequent vocal tract shape analysis.