Undergraduate Research Symposium Madison, Wisconsin 13 April 2018 http:// waisman.wisc.edu/vocal / Measuring the Vocal Tract Using MRI and Acoustic Pharyngometry: A Comparison Abigail Lamers, Ying Ji Chuang, Katelyn Tillman, Julie Eichhorn and Houri K. Vorperian Vocal Tract Development Lab, Waisman Center, University of Wisconsin - Madison REFERENCES : (1) Corey, J. P., Gungor, A., Nelson, R., Fredberg, J., & Lai, V. (1997). A comparison of the nasal cross-sectional areas and volumes obtained with acoustic rhinometry and magnetic resonance imaging. Otolaryngology - Head and Neck Surgery, 117(4), 349-354. (2) Corey, J. P., Nalbone, V. P., & Ng, B. A. (1999). Anatomic correlates of acoustic rhinometry as measured by rigid nasal endoscopy. [Research Support, U.S. Gov't, P.H.S.]. Otolaryngology - Head and Neck Surgery, 121(5), 572- 576. (3) D'Urzo, A.D. , Lawson, V.G. , Vassal, K.P. , Rebuck, A.S. , Slutsky, A.S. , & Hoffstein, V. (1987). Airway Area by Acoustic Response Measurements and Computerized Tomography. American Review of Respiratory Disease, 135(2), 392-395. (4) D'Urzo, A. D. , Rubinstein, I. , Lawson, V. G. , Vassal, K. P. , Rebuck, A. S. , Slutsky, A. S. , & Hoffstein, V. (1988). Comparison of Glottic Areas Measured by Acoustic Reflections vs. Computerized Tomography. Journal of Applied Physiology, 64(1), 367-370. (5) Eccovision Acoustic Phayngometry [Operators Manual]. (2009). North Miami Beach, FL: Sleep Group Solutions. (6) Fredberg, J. J., Wohl, M. E., Glass, G. M., & Dorkin, H. L. (1980). Airway area by acoustic reflections measured at the mouth. [Research Support, U.S. Gov't, P.H.S.]. Journal of Applied Physiology, 48(5), 749-758. (7) Min, Y. G., & Jang, Y. J. (1995). Measurements of cross-sectional area of the nasal cavity by acoustic rhinometry and CT scanning. [Comparative Study]. Laryngoscope, 105(7 Pt 1), 757-759. ACKNOWLEDGEMENTS : This work was supported by NIH research grant R01 DC006282 from the National Institute on Deafness and other Communication Disorders (NIDCD), and core grants P30 HD03352 and U54 HD090256 from the National Institute of Child Health and Human Development (NICHD). Extracting Quantitative Measurements: • The VT-APh path was then used to execute a script that travels through the path and finds the orthogonal planes between each landmark and its subsequent increment. Intersection between the orthogonal plane and the 3D pharynx model was extracted as boundary vertices and edges used to obtain CSAs and volumes throughout the VT. • The CSAs produced were then plotted as a function of distance from the lingual aspect of the incisors/front teeth to the glottis, where the distance between the two points represents the APh VTL. • The resulting CSA plot was then superimposed on the acoustic pharyngogram by having both overlap at the level of the glottis. This approach was used to infer the anatomic equivalent location for the OPJ on the midsagittal plane of the imaging study, and selected to divide the overall OPV into OCV and PCV. • In addition, the cavity length measurements are obtained from the VTL: • 1) PCL: the curvilinear distance from the OPJ, as referenced by the data from APh study, to the level of the glottis. • 2) OCL: the curvilinear distance from the alveolar incisor along the palate to the OPJ. IV. RESULTS : Figure 3: Bar graphs comparing APh (blue) and MRI (orange) measurements for oral-cavity length (OCL), pharyngeal cavity length (PCL) and overall vocal tract length (VTL); also, oral-cavity volume (OCV), pharyngeal cavity volume (PCV) and vocal tract volume (VTV). Absolute differences in measurements, plotted in gray, reveal that APh yields volumes for PCV and subsequently VTV that are somewhat inflated. V. CONCLUSION : • APh is a non-invasive clinical tool that is being increasingly used as a research tool to gather VT measurement from typically and atypically developing individuals (who may not be imaged or cannot be imaged due to medical concerns). • Present findings confirm that APh may be used as a research tool and can be a useful approach to study the development of the upper airway in typically and atypically developing individuals (provided the participant is able to follow APh instructions, and the pediatric APh mouthpiece fits). • APh is a technique that may be used to gain information about the developmental changes in the oral and pharyngeal cavities. Such information may be used in VT modeling efforts to assess how changes in the oral and pharyngeal regions of the VT alter speech acoustics; also assess the role anatomic growth plays in speech intelligibility. II. OBJECTIVE : The purpose of this study is to determine comparability of APh measurements against MRI measurements for both the oral and pharyngeal portions of the VT. III. METHODS : Participants: Six adults (3 males, 3 females) between the age of 22 years and 30 years participated in both the APh and MRI components of this study. Participants had no health issues, specifically no pathology in the head and neck region including no history of speech/language or hearing difficulties. Also, they had no contraindications to undergo an imaging study. APh Protocol: • Each participant exhaled into a mouthpiece by Eccovision® (Sleep Group Solutions) 5 attached to the APh wave tube in the supine body position (to simulate MRI scanner table). • The wave tube emitted a pulsing sound into the VT as the participant exhaled. The acoustic pharyngometer then used the reflected acoustic waves to calculate and display the cross- sectional areas (CSA) of the VT as a function of distance from the glottis to the teeth (pharyngogram). • Each participant completed eight breathing trials. Four slow exhale (inhale through nose, exhale through mouth) and four nasal (inhale and exhale through nose). Graphs/pharyngograms depicting the CSA were saved for each breathing trial. • The slow exhale pharyngograms were used to make VT length and volume measurements. • The nose exhale pharyngograms were used to identify the smallest CSA to mark the location of the oral-pharyngeal junction (OPJ). The pharyngometer then used the OPJ to calculate the oral and pharyngeal length and volume measurements. • APh waveforms were analyzed for both length and volume measurements of the oral cavity, pharyngeal cavity and VT. • The measurement definitions are as followed: • Oral cavity length (OCL-APh: teeth to OPJ) • Pharyngeal cavity length (PCL-APh: OPJ to glottis) • VT length (VTL-APh: teeth to glottis • The corresponding cavities’ volumetric measurements are: oral cavity volume (OCV-APh), pharyngeal cavity volume (PCV-APh), and vocal tract volume (VTV-APh). I. BACKGROUND / INTRODUCTION • Vocal tract (VT) measurements are typically made using medical imaging studies such as X-ray radiography, magnetic resonance imaging (MRI) and computed tomography (CT) scans. MRI is used when detailed visualization of the soft tissue is needed, and therefore optimal for making measurements of the oral and pharyngeal regions of the VT. • Acoustic Pharyngometry (APh) is a non-invasive technique that uses the reflection of acoustic waveforms to calculate the cross- sectional areas (CSA), length, and volume of the VT or upper airway. Despite its long standing clinical use 6 to assess patency of the upper airway in sleep studies, a very limited number of studies have examined APh measurements against actual anatomic measurements; and such studies have only used select APh measurements taken in the pharyngeal region (at the level of the glottis and trachea or of the nasal cavity) to compare against anatomic measurements obtained through MRI to confirm comparability of measurements 1, 2, 3, 4, 7 Figure 1. Participant exhaling into the Acoustic Pharyngometer wave tube while in the supine body position. Measurements of vocal tract length and volume were obtained from the reflection of the acoustic waveforms. M6004-28-09 APh Imaging Difference 0 10 20 30 40 50 60 70 OCL PCL VTL Length (cm) 0 10 20 30 40 50 60 70 OCV PCV VTV Volume (cm 3 ) Figure 2. Cross- sectional areas (CSA) of the oral-pharyngeal cavity from APh (red) and MRI (blue) as a function of distance from the glottis (0 on the x-axis) for one adult male participant. The MRI (top) image from the same participant depicts the corresponding anatomic regions for the CSAs. MRI Protocol: Each participant underwent a MRI study in the supine body position after confirming that the APh mouthpiece was in place and their head was in the neutral position such that the external auditory meatus and shoulder were horizontally aligned, and the angle between the canthomeatal line and orthogonal line was no more than 18 degrees. 3D oral-pharyngeal model rendering: • The posterior nasal cavity was set as the upper constraint while the opening of the trachea was set as the lower constraint of the oral-pharyngeal or VT model. • A set of 44 anatomic landmarks were digitally placed along the 3D VT model using multiplanar visualization of the sagittal, coronal, and axial views of the MRI study. • The landmarks were then used to establish a path that represents the likely pathway the APh waveform will take to travel through the VT. The path entailed establishing an oral cavity (OC) path and a pharyngeal cavity (PC) path that were created based on several landmarks and user-determined input, followed by manual smoothing and interpolation. • Findings from all six participants were similar to those of participant M6004 showcased in this poster. • Figure 2 showcases that APh (red plot) trend is representative of the detailed CSAs (blue plot) from MRI despite noted differences in actual measurements where APh CSAs are noticeably larger than MRI. • Figure 3 depicts the above noted observation where differences plotted in gray highlight that APh can capture length measurements accurately, but tends to inflate volumetric measurements particularly in the pharyngeal region. Abstract: The size and shape of the mouth and throat contribute to the unique way each person sounds. Acoustic Pharyngometry (APh) is a non-invasive technique that uses the reflection of sound waves to measure the airway and assess its patency. To assess APh measurements’ accuracy, we compared it against MRI measurements. Three men and three women performed APh in the upright and supine body position and had MRI scans in the supine body position. Findings revealed that length measurements were comparable. However, APh cross-sectional areas and volumes were noticeably larger than MRI. Although MRI measurements represent anatomic measurements more accurately, APh does successfully capture the overall oral and pharyngeal measurements and may be a useful method for the study of speech development and speech disorders.