Weight-Bearing MR Imaging as an Option in the Study of Gravitational Effects on the Vocal Tract of Untrained Subjects in Singing Phonation

Abstract

Magnetic Resonance Imaging (MRI) of subjects in a supine position can be used to evaluate the configuration of the vocal tract during phonation. However, studies of speech phonation have shown that gravity can affect vocal tract shape and bias measurements. This is one of the reasons that MRI studies of singing phonation have used professionally trained singers as subjects, because they are generally considered to be less affected by the supine body position and environmental distractions. A study of untrained singers might not only contribute to the understanding of intuitive singing function and aid the evaluation of potential hazards for vocal health, but also provide insights into the effect of the supine position on singers in general. In the present study, an open configuration 0.25 T MRI system with a rotatable examination bed was used to study the effect of body position in 20 vocally untrained subjects. The subjects were asked to sing sustained tones in both supine and upright body positions on different pitches and in different register conditions. Morphometric measurements were taken from the acquired images of a sagittal slice depicting the vocal tract. The analysis concerning the vocal tract configuration in the two body positions revealed differences in 5 out of 10 measured articulatory parameters. In the upright position the jaw was less protruded, the uvula was elongated, the larynx more tilted and the tongue was positioned more to the front of the mouth than in the supine position. The findings presented are in agreement with several studies on gravitational effects in speech phonation, but contrast with the results of a previous study on professional singers of our group where only minor differences between upright and supine body posture were observed. The present study demonstrates that imaging of the vocal tract using weight-bearing MR imaging is a feasible tool for the study of sustained phonation in singing for vocally untrained subjects.

Recommendations for real-time speech MRI

“…Upright scanners can potentially overcome these problems, and there have been a few studies that demonstrate their utility in RT-MRI of speech research. [90][91][92] The use of iterative constrained reconstruction algorithms have been shown to improve the SNR from low field simulated measurements, and these hold great potential in future use of upright low field scanners for RT-MRI of the upper airway. 93 The clinical role of RT-MRI in the assessment of abnormal vocal tract and upper airway dynamics has not yet been determined, and remains an exciting area for investigation.…”

Acoustic and Aerodynamic Coupling during Phonation in MRI-Based Vocal Tract Replicas

“…This is the case for high-pitched singing or vowels with a wide mouth opening like the vowel /a/. Another focus was set on the effect of the body position during phonation as MRI-imaging is commonly performed in supine position [23,24]. The reports showed that the effect of the supine position is statistically insignificant for different registers of professional tenors, whereas 5 out of 10 untrained singers phonated statistically significantly different being unable to completely compensate the different direction of the gravitation force in the supine position.…”

Effect of body position on vocal tract acoustics: Acoustic pharyngometry and vowel formants

“…One of the most consistent observations is that the pharyngeal (nasopharyngeal and/or oropharyngeal) cavity is smaller in the supine as opposed to the upright position during speech, as determined from APh (Jan et al, 1994), computed tomography (CT; Sutthiprapaporn et al, 2008), MRI (Engwall, 2006;Kitamura et al, 2005;Traser et al, 2014), ultrasound (Stone et al, 2007;Wrench et al, 2011), x-ray microbeam (Tiede et al, 2000), and videofluoroscopy (Bae et al, 2014). This effect can be explained by gravity pulling the tongue root posteriorly when the subject is in the supine position, thereby reducing the size of the pharynx.…”

“…In an electromyographic study, Moon and Canady (1995) observed a reduced level of muscle activity in the levator veli palatine for phonation in the supine as opposed to the upright position. In a MRI study of untrained singers, Traser et al (2014) observed elongation of the uvula in the upright position.…”