Effects of Gravity on the Velopharyngeal Structures in Children Using Upright Magnetic Resonance Imaging

Abstract

Objective

The influence of gravity on the velopharyngeal structures in children is unknown. The purpose of this study is to compare the velopharyngeal mechanism in the upright and supine positions while at rest and during sustained speech production in children between 4 and 8 years old.

Methods

A 0.6 Tesla open-type, multipositional magnetic resonance imaging scanner was used to image subjects in the upright and supine positions. The scanning protocol included a T2 fluid attenuation inversion recovery and an oblique coronal turbo spin echo scan with short scanning durations (7.9 seconds) to enable visualization of the velopharyngeal anatomy during rest and production of sustained /i/ and /s/.

Results

The magnetic resonance imaging protocol used for this study enabled successful visualization of the velopharyngeal anatomy in the sagittal and oblique coronal planes at rest and during sustained phonation of /i/ and /s/. Positional differences demonstrated a small nonsignificant (P > .05) variation for velar measures (length, thickness, and height), retrovelar space, and levator veli palatini measures (length and angles of origin).

Conclusions

Gravity had a negligible effect on velar length, velar thickness, velar height, retrovelar space, levator muscle length, and levator angles of origin. Supine imaging data can be translated to an upright activity such as speech. This is the first study to provide normative levator muscle lengths for children between 4 and 8 years old. Upright imaging may be a promising tool for difficult-to-test populations.

Keywords

children levator MRI upright and supine imaging velopharyngeal mechanism

Introduction

Speech is a dynamic process typically produced in the upright position. The structures that constitute the velopharyngeal port play an important role in speech production, swallowing, and breathing. The velopharyngeal mechanism includes the velum, lateral pharyngeal walls, and posterior pharyngeal wall. Velopharyngeal closure is accomplished through the combined action of several velopharyngeal muscles, the most important being the bilateral levator veli palatini (levator) muscle. The levator, palatoglossus, and palatopharyngeus muscles are collectively responsible for determining the velopharyngeal positioning in the pharyngeal cavity (Moon and Canady, 1995). Structural characteristics alone cannot determine the functional status of the velopharyngeal mechanism (Tian et al., 2010b). Magnetic resonance imaging (MRI) data are traditionally obtained in the supine position but these data may be applied to an activity in the upright position, such as speech. Assessment of the velopharyngeal structures during speech in the upright position is important. Better understanding of gravitational effects on the velopharyngeal structures will allow better utilization of MRI data in speech analysis and modeling (Stone et al., 2007).

Studies have examined the effect of gravity on swallowing and speech structures, including the respiratory apparatus, tongue, hyoid bone, pharyngeal areas, and velopharyngeal structures. Hoit (1994) observed that during speech breathing in the supine position, inspiration was dependent on the efforts of the diaphragm and expiration on the efforts of the rib cage. In upright speech breathing, inspiration involves effects of the diaphragm and abdomen, but the latter predominates for expiration.

The effects of body position on swallowing have been studied. Perry et al. (2012) noted variations in the initiation of the pharyngeal swallow and coordinated velar elevation during a liquid swallow (7 cc). In the supine position, the velum continues to elevate after initiation of the pharyngeal swallow. In the upright position, the velum comes to a fully elevated position at nearly the same time as the pharyngeal swallow is initiated.

Buchaillard and Perrier (2009) found negligible differences in tongue shape and formant values between the upright and supine positions during production of French cardinal vowels. The absence of significant differences was attributed to the model having a fixed jaw position in both the upright and supine orientation. Badin et al. (2002) demonstrated increased backward displacement of the tongue for consonants and vowels in the supine position using MRI compared with the upright position on cineradiofilm images. The increased backward tongue displacement was attributed to tongue weight. Stone et al. (2007) observed acoustic spectra (formant frequencies) to be preserved despite varying tongue responses to gravity. Results indicated a significant subject effect. Stone et al. (2007) hypothesized a compensatory response of the tongue to gravity in which the tongue counteracts to body position to preserve the acoustic effect.

Oropharyngeal structures appear to be affected by gravitational influences. Suttiprapaporn et al. (2008) studied gravity-induced changes in the oropharyngeal structures using computed tomography scans on clinically normal adult subjects. The soft palate, epiglottis, and entrance of the esophagus moved caudally with the positional change from supine to seated upright and moved posteriorly when the position changed from an upright to a supine position. Kitamura et al. (2005) assessed the influence of body position on vowel articulation using an open-type MRI scanner. It was noted that in the supine position, the tongue was more retracted (particularly for back vowels), the lips were thinner, and the lower end of the uvula turned downward in the direction of gravity.

Variations in velopharyngeal structures as a result of body position have been investigated. An electromyographic study was conducted on 19 adults to examine the effects of gravity on activation levels of the levator and palatoglossus muscles during speech (Moon and Canady, 1995). Less peak (muscle) activity was observed in the supine position (gravity working in the same direction) compared with the upright position. Peak intraoral pressure and peak palatoglossus electromyographic activity showed no significant differences between upright and supine positions. The peak levator electromyographic activity showed significant differences between both positions. Perry (2011b) reported the effect of gravity on velopharyngeal structures using open-type multiposition MRI on four adult women. The subjects were imaged at rest and during two speech tasks (/i/ and /s/) in upright and supine positions. Differences in velar height during /i/ production between the two positions were significant for all subjects. There were no significant differences in velar thickness. Greater levator muscle shortening was observed on images obtained at rest (2.8 mm). Minimal variations were observed between upright and supine positions for velar measures (length and thickness), pharyngeal measures (retrovelar and retrolingual), and levator muscle measures (length and angle of origin). The overall results demonstrated that the velopharyngeal structures were not affected by gravity during speech for this select population.

No upright MRI studies have examined the influence of positional changes in the velopharyngeal musculature in children. The purpose of this study was to compare velopharyngeal structures in the supine and upright positions during rest and sustained speech production in children (4–8 years old) with clinically normal anatomy. The study further demonstrates the feasibility of using upright MRI in evaluating the velopharyngeal characteristics of young children.

Method

Subjects

In accordance with the institutional review board at East Carolina University, 12 healthy children (five boys and seven girls) between 4 and 8 years old (mean, 6.23 ± 1.27) were recruited to participate in the study. The mean height was 41.67 inches (SD, 4.60 inches) and mean weight was 20.42 lb (SD, 4.19 lb). Of the 12 subjects, nine were black and three were white. Although racial differences have been shown to affect velar length and thickness and angle of origin for the levator muscle, the effects of race are not significant for the levator muscle (Perry et al., 2013). The selected age range (4–8 years) is the critical age for determining secondary surgical needs in cleft palate and for speech, language, and communication development. Subjects were recruited by flyers placed throughout the community. A coloring book was mailed to the prospective subject 2–3 weeks before the MRI exam. The coloring book allowed the subject to become familiar with the process of an MRI exam. An oral mechanism examination and oral to nasal resonance balance assessment was administered on all subjects by a speech language pathologist.

All subjects were native English speakers and had no history of craniofacial anomalies, musculoskeletal disorders, swallowing disorders, sleep apnea, or neurologic disorders that could potentially affect the regions of interest for the study. All subjects had a body mass index under 19 (mean, 18.63 ± 3.01) to control for possible variations in the velopharyngeal area as a result of obesity.

Magnetic Resonance Imaging

MRI data were obtained using a 0.6 Tesla open-type multiposition MRI scanner (Fonar Corporation, Melville, NY) at Triangle Orthopaedic Associates, PA (Southpoint, Durham, NC). The scanner enabled multipositional imaging in the upright and supine positions. The subjects had to be positioned only once during the entire scanning session. The start position was alternated between subjects. The scanning bed allowed for a 90° rotation, which enabled each subject to be rotated the same exact degree.

Numerous steps were taken to ensure the comfort of the child during the scan. Before starting the MRI exam, the child was introduced to the sounds of the MRI scanner by listening to audio samples of MRI noise played on an iPad. The recordings were the same noises that they could expect to hear during the MRI scan. The subjects were given a panic button and were frequently asked about their comfort level. An adult (parent or researcher) was in the scanning room during the entire scan. Children were encouraged to watch another child being imaged before them and were provided 5 minutes before their respective MRI scans to explore the MRI machine (e.g., walk around the scanner). A head device with soft sponges and pressure clamps was used to minimize head movement. The subjects had a soft sponge on their lap to wrap their hands around and a sponge in which to place their feet to minimize hand and foot movements, which can create motion artifacts for the head. Head movement was further reduced by allowing the subjects to watch cartoons on the television while the scan was in progress. This enabled them to maintain a consistent forward gaze, minimizing any distractions. A speaker microphone between the control room and the scanning room enabled the examiner to communicate with the subject throughout the exam.

The imaging protocol was modeled after a similar, previously published study on adult women (Perry, 2011b); however, shorter length of time was used for each scan. This ensured standardization and comparability between results obtained in the adult (Perry, 2011b) and child population. The scanning protocol (Table 1) included a three-plane localizer, midsagittal T2 fluid attenuation inversion recovery and an oblique coronal turbo spin echo scan. The plane that most clearly depicted the genu of the corpus callosum, hypophysis, and outline of the fourth ventricle was selected as the midsagittal plane. The levator muscle region was obtained by drawing an oblique coronal line through the midsagittal image. The oblique coronal slice, which depicted the levator muscle sling in its full thickness from origin to insertion, was selected. The sagittal and oblique coronal scans were obtained while the subject was at rest and during sustained /i/ and /s/ production. The scans were conducted in both upright and supine positions.

Table 1

Scanning Protocol (0.6 Tesla)

	Perry 2011b (Adult Women)	Current Study (Children)
Sagittal T2 fluid attenuation inversion recovery
TR; TE	7136.604 ms; 92.5 ms	987 ms; 160 ms
Slice thickness	4.8 mm	5 mm
Spacing	0.36 mm	0 mm
No. of slices	1	3
Length of scan	2 min, 7 sec	7.9 sec
Oblique coronal turbo spin echo
TR; TE	3686.304 ms; 22 ms	987 ms; 160 ms
Slice thickness	2.5 mm	5 mm
Spacing	0.1 mm	0.37 mm
No. of slices	6	3
Length of scan	3 min, 9 sec	7.9 sec

TR = repetition time; TE = echo time

Speech Tasks

Subjects were instructed to produce /i/ and /s/ in the upright and supine positions. Both speech productions were practiced by the subject with the examiner before staring the MRI exam. Subjects were instructed to produce /s/ as “ssss” (single consonant) and not “eees” (vowel-consonant combination). Subjects maintained a sustained production for the duration of the sound (7.9 seconds in oblique coronal and in midsagittal). Subjects were instructed to inhale deeply before initiating the speech sound production. Speech sound productions were carefully monitored by the researcher in the scanning room to ensure that it was an accurate representation of the required sound and was sustained for the duration of the scan.

Regions of Interest

A total of six measures were made from sagittal and oblique coronal images using Amira (version 5.4.5, Visage Imaging, Berlin, Germany) visualization software. Measurements were obtained in both upright and supine positions. Midsagittal measures (Table 2; Fig. 1) included velar length, velar thickness, velar height, and retrovelar space. Velar length was measured as a curvilinear line from the posterior nasal spine to the tip of the uvula. The distance between the velar dimple to the velar knee was measured as the velar thickness. Velar height was measured as the vertical displacement of the velar knee from a reference line through the hard palate. The distance between the velar knee to posterior pharyngeal wall was measured as the retrovelar space.

Table 2

Description of Measures (Perry, 2011b)

Measure	Definition
Velar length	Distance of a curvilinear line starting at the posterior nasal spine, coursing through the middle of the cross sectioned velum, and extending to the tip of the uvula
Velar thickness	Distance from the velar knee to the velar dimple
Velar height	Vertical distance of the velar knee from a reference line drawn directly through the hard palate to the posterior pharyngeal wall
Retrovelar space	Distance from the velar knee to the posterior pharyngeal wall
Levator veli palatini muscle length	Distance from the origin of the muscle at the base of the skull, through the middle of the muscle belly, and to the midline insertion at the velum
Angle of origin	Angle created between a reference line connecting the two origins of the levator muscle and the line drawn to measure the levator muscle length

Figure 1

Demonstration of the velar measures and retrovelar space in the midsagittal image plane. A = velar length; B = velar thickness; C = velar height.

The levator muscle length and angle of origin were measured on the oblique coronal images (Fig. 2). The levator length was calculated as the curvilinear distance from the origin at the base of the skull to the insertion in the middle of the velum. The total levator length was determined by adding the right and left levator lengths and calculating the average. A reference line was then drawn between the two origin points on the right and left muscle bundles. The angle formed between this reference line and the levator length at the point of its origin was determined as the angle of origin. The measurement definitions and boundaries used were the same as those described for a similar study on adult women (Perry, 2011b) to ensure consistency in measurements in the adult and child populations.

Figure 2

Measures taken on the oblique coronal image plane. The curvilinear white line courses through the levator muscle bundle. The arrow points to the angle of origin, which is determined by using a reference line connecting the levator muscle origins on the right and left sides.

Statistical Methods

Comparisons between the upright and supine positions for each measure were performed using a paired t test. The Bonferroni correction was used to minimize the effect of multiple comparisons and to control for type I error. The significance thus calculated equaled 0.05/c (where c = number of comparisons), resulting in a .002 level of significance.

The Pearson product moment correlation (α = 0.05) was used to establish interrater and intrarater reliability measures. Measurements were done on six randomly selected data sets by the primary and secondary raters 4 weeks after the first measures were obtained. Both raters made independent measures on a previous data set before starting data analysis. Clear definitions of the measurement boundaries were made and confirmed on practice data sets 5 weeks before starting data analysis. Both raters have prior experience in measuring the areas and structures in this study. The interrater and intrarater reliability ranged from r = .97 to r = .99.

Results

The MRI protocol used for this study was successful in visualizing the velopharyngeal structures of interest in the sagittal and oblique coronal planes. All subjects who agreed to participate successfully completed the imaging protocol. Clear images of the tongue, velum, and pharyngeal cavity were obtained. Changes in velar movement across different tasks (at rest and on phonation) were analyzed. The differences due to body position across the six measures are shown in Table 3. These measures indicate that changes in body position (from upright to supine) had a nonsignificant effect on differences in the velopharyngeal structures of interest in this study during rest and phonation tasks.

Table 3

Group Means and Differences Across All Six Measures

	Rest		/i/		/s/		P value^* (Upright; Supine)
	(Upright; Supine)	Difference^†	(Upright; Supine)	Difference	(Upright; Supine)	Difference
Velar length (mm)	26.92; 27.44	+0.52	24.87; 25.46	+0.59	24.09; 25.13	+ 1.04	.004
Velar thickness (mm)	7.97; 7.86	–0.11	6.90; 6.73	–0.17	6.63; 6.74	+0.11	.750
Velar height (mm)	4.60; 4.50	–0.1	3.32; 3.10	–0.22	2.49; 2.62	0.13	.795
Retrovelar space (mm)	7.05; 7.16	–0.11	0.31; 0.23	–0.04	0.00; 0.00	0.00	.850
Levator muscle length (mm)	32.9; 31.8	–1.1	29.53; 29.32	–0.21	28.41; 28.86	+0.45	.226
Angle of origin (°)	60.04; 58.1	–1.94	54.25; 52.46	–1.79	54.60; 54.63	+0.03	0.065

α =.002.

†

For difference values, plus (+) values indicate a greater value in the upright position and minus (–) values indicate a lesser value in the upright position.

Velar Measures

Differences in velar length between upright and supine positions varied among subjects in the type of response to gravity. Five of the 12 subjects demonstrated an increase in length of the velum from the upright to supine position. The increase in length was consistent across rest, /i/ tasks, and /s/ tasks. The remaining seven subjects demonstrated variations in their responses (increase or decrease) across positions and across the tasks. Group mean differences between upright and supine indicated a minimal increase in velar length for rest (+0.52), /i/ (+0.59), and /s/ (+1.04). These differences, however, were not statistically significant at P = .004.

The thickness of the velum between upright versus supine positions varied among subjects in the type of response to gravity. Only three of the 12 subjects demonstrated an increase in velar thickness from the upright to the supine position. Group mean differences between upright and supine were −0.1 1mm for rest, −0.17 mm for /i/, and +0.11 mm for /s/. These differences, however, were minimal and were within 0.1 mm, demonstrating a nonstatistically significant finding (P = .750).

There were no consistent patterns or statistically significant differences in velar height between upright and supine position across rest, /i/, and /s/ (P = .795). The responses varied across subjects. Group mean differences across upright and supine positions were −0.1 for rest, −0.22 for /i/, and +0.13 for /s/.

As expected for children with clinically normal velopharyngeal mechanism, the retrovelar space was zero for 11 of the 12 subjects during speech tasks. Seven subjects demonstrated a decrease in retrovelar space from the upright to the supine position at rest. Group mean differences between upright and supine positions were minimal for rest (+0.11), /i/ (–0.04), and /s/ (0.00) productions. The differences across position for this variable were not statistically significant (P = .850).

Levator Veli Palatini Muscle Measures

For 11 of the 12 subjects, the levator muscle length minimally decreased (–1.26 mm) in length when moving from the upright to the supine position at rest. During production of /s/, eight subjects demonstrated a minimal increase (+1.12 mm) in levator muscle length in the supine position. Group means indicate an average muscle shortening at rest (–1.1) and for /i/ production (–0.21). A minimal increase was observed for /s/ production (+0.45). The differences noted, however, were not significant (P = .226).

Four subjects demonstrated a decrease in angles of origin from the upright to the supine position at rest and during production of /i/ and /s/. Differences across subjects indicate that nine subjects had a decrease in angles of origin in the supine position for the production of /i/. The differences in angle between upright and supine positions were not significant (P = .065)

Differences Across Condition

A one-way analysis of variance (ANOVA) was performed to compare the effects of the three treatments (rest, /i/ production, and /s/ production) on levator length and angle of origin. The ANOVA results for the levator length were F_2,35 = 10.1121 (P = .0004) in the upright position and F_2,35 = 4.0855 (P = .026) in the supine position. The ANOVA results for the angle of origin were F_2,35 = 5.8381 (P = .0067) in the upright position and F_2,35 = 3.8631 (P = .0311) in the supine position. As expected, the changes across the three treatments were statistically significant at the .05 level of significance.

The percentage of levator muscle contraction during production of /i/ and /s/ across upright and supine positions was calculated. For the production of /i/, the percentage of levator contraction was 10.3% in the upright position and 7.68% in the supine position. For /s/ production, the contraction was 13.7% in the upright position and 9.04% in the supine position. The percentage of contraction for both /i/ and /s/ production was greater in the upright than in the supine position.

Discussion

Overall, the effect of gravity on the velopharyngeal structures in young children during rest and sustained speech production tasks demonstrates no significant differences (P < .002) from the upright to the supine position. The responses of the variables of interest were different across subjects. There is not enough evidence to validate the use of upright MRI over the traditional supine imaging methods to reduce effects of gravity on the structures that were investigated. Supine imaging can be used to relate to upright speech gestures in this targeted child population. This study protocol demonstrated 100% success rate in that all children who volunteered for the study successfully completed the study. Similar studies using supine imaging only for children between 4 and 7 years old showed an average success rate of 96% (Tian et al., 2010a; Tian et al., 2010b). Although these differences are negligible, the behavioral and imaging protocol development for this study can be adopted for future imaging studies involving children.

Velar Measures (Length, Thickness, and Height)

The velum remained nearly the same in thickness and height for rest, /i/ production, and /s/ production during upright and supine position. There was a consistent increase in velar length at rest, /i/ production, and /s/ production between the two positions. Although these findings are consistent with those of Perry (2011b), they are not consistent with findings of Ingman et al. (2004). Of the three measures of length, thickness, and height, velar length exhibited most differences between the upright and supine positions. The incidence of increase in velar height that one might assume in the supine position due to the effects of gravity was observed only in the production of /s/. This finding is consistent with that of Perry (2011b) for adult women. However, Perry (2011b) showed statistically significant difference in velar height between upright and supine position. The findings in the present study related to velar height during /s/ were not statistically significant. This may be due to the greater sample size used in the present study (N = 12) compared to Perry (N = 4). The increase in velar length, thickness, and height during the production of /s/ could be attributed more to the sound production characteristic of /s/ rather than to a significant response to gravity. The mean velar muscle length (mean, 26.01 mm) and thickness (mean, 7.11 mm) in the present study (in the supine position) were similar to those reported in studies of Chinese children (mean length, 25.52 mm; mean thickness, 9.15 mm) during rest and sustained phonation (Tian et al., 2010a; Tian et al., 2010b). Although studies by Tian et al. (2010a and 2010b) examined numerous speech tasks, the data in these articles were not reported separately for each phoneme. The phonemes used in these studies, /a/,/i/,/z/, /m/, and /f/ (Tian et al., 2010a) and /a:/,/i:/,/ts/, and /m/ (Tian et al., 2010b) for the sustained phonation speech tasks vary significantly in their place and manner of production.

The distance between the velar knee to the posterior pharyngeal wall showed variable differences across subjects between the upright and supine positions. This finding is not consistent with that of Perry (2011b) for adult women, where all subjects showed narrowing of the retrovelar space in the supine position. These differences could be due to variations in the adenoid pad size in the velopharyngeal cavity that are common in children in this age range. One subject presented with a mild gap during phonation of /i/. Because all subjects were judged to have clinically normal resonance, it is possible that, unknown to the researcher, this subject took a breath during the scan.

Levator Veli Palatini Muscle Measure

The length of the levator muscle was found to be shorter in the upright versus the supine position only for production of /s/, although differences were not statistically significant. This minimal effect of gravity on levator muscle length (shortening) was observed at the rest position primarily instead of during speech production tasks. This is consistent with findings of Perry (2011b). The percentage of contraction for both /i/ and /s/ productions was greater in the upright than in the supine position. The smaller percentage of contraction demonstrated for /i/ and /s/ productions in the supine position could be due to the caudal displacement of the soft palate and epiglottis when moving from the upright to the supine position, as described as Sutthiprapaporn et al. (2008). In a similar study (supine position only) on Chinese children, only the extravelar lengths were reported (Tian et al., 2010a). The present study is the first study to provide the complete levator muscle length measurement for children in this age group. The levator muscle length obtained in this study is less than that reported by Ettema et al. (2002) on adult male and female subjects. Although Kuehn et al. (2004) analyzed the levator muscle in children using MRI, no quantitative data were reported.

The findings for angles of origin (Table 4) were similar to that observed on levator muscle length (Ettema et al., 2002; Perry et al., 2011b). There was a decrease in angles of origin for rest position and production of /i/ in the supine position. Although nonsignificant, the decrease in the angle was observed only for /s/ production. Mean levator angles of origin (mean, 55.06) and levator origin widths (mean, 45.30) were similar to those reported in a previous study (mean, 52.23; mean, 55.0, respectively) on Chinese children (Tian et al., 2010b).

Table 4

Comparison of Group Means for Levator Muscle Morphology Analyses Between the Current Study and Similar Studies Using MRI

	Current Study: 12 Black and White Children (4–7 years old)	Perry (2011b): Four White Women (30–36 years old)	Ettema et al. (2002) 10 White Men and Women (21–53 years old)
Angle of origin (°)
Rest	60.04	58	63
/i/	54.25	48	53
/s/	5.60	44	52
Levator muscle length (mm)
Rest	32.9	44	45
/i/	29.53	37	40
/s/	28.41	36	37
Muscle contraction (%)
/i/	10.3	17	15
/s/	13.7	21	18

Clinical Implications

The findings of this study provide applications to clinical practice. No studies have examined the feasibility of using upright MRI imaging to assess the velopharyngeal area in young children. In cleft palate, the major muscle of interest is the levator. MRI enables direct visualization of the levator muscle. Traditional supine imaging has been associated with the feeling of claustrophobia, and children younger than 4 years have to be sedated. However, modifications to the imaging protocol, such as acclimating the subject to the process involved (through audio samples, rehearsals, and consistent reinforcement), can achieve successful results. In the present study, children as young as four years old were imaged without any sedation at rest and during speech tasks. MRI is a promising diagnostic tool for enabling presurgical decisions in young children (Perry et al., 2011; Kuehn et al., 2000).

Limitations of the Study

Although the magnetic resonance images were obtained with good resolution, motion artifacts were present. In instances where motion artifacts might have affected the image clarity for analysis, the scans were repeated. This was more evident on the sustained phonation tasks than for the scans taken at rest. Noise was noticeable on the sagittal and oblique coronal images. However, the levator muscle sling and the velar muscle boundaries could still be identified. It is likely that the scan time needs to be reduced to less than 5 seconds to be applicable to younger (3–4 years old) populations. There is a trade-off, however, between spatial and temporal resolution that must be addressed to provide a more useful clinical protocol. Poor image quality can lead to less clear anatomic boundaries, which may not be useful when there is just a small gap. Another limitation of the study is the unequal division of subjects on the basis of race. There were more black subjects than white subjects; however, Perry et al (2013) reported no racial differences for the levator muscle length and angle of origin.

Conclusion

In cleft palate research, the primary population for secondary surgery is children. This is the first study to provide normative levator muscle lengths for children between 4 and 8 years old. This study demonstrates successful imaging of children in an upright magnetic resonance scanner. The modified child-friendly protocol used in this study enabled successful scanning of all enrolled subjects. The results from this study indicate that positional variations do not significantly affect the velopharyngeal structures and musculature. Overall, the effect of gravity on velar (length, thickness, and height) and levator (length and angle of origin) muscle measures were minimal. Data obtained on a supine imaging scanner can be applied to an upright activity such as speech. Further benefits of upright imaging should be investigated in this difficult-to-test population.

Footnotes

Acknowledgments

I would like to thank Dr. John Greenhalgh, Ms. Juanita Brame, and Mr. Rudolph Andrews at the Triangle Orthopaedic Associates, PA, Durham, North Carolina, for providing the facility and technical support for implementation of the study.

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