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 use6 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.

0

10

20

30

40

50

60

70

OCL PCL VTL OCV PCV VTV

Len

gth

(cm

)

M6004-28-09

APh Imaging Difference

0

10

20

30

40

50

60

70

OCL PCL VTL

Len

gth

(cm

)

0

10

20

30

40

50

60

70

OCV PCV VTV

Vo

lum

e (c

m3 )

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.