Measurements of ear-canal geometry from high-resolution CT scans of human adult ears
•Method to measure ear canal geometry from CT scans•First objective definitions for canal length and first bend location•Canal cross sectional area appears to increase with adult age cohorts along majority of canal length•Mean canal areas and lengths larger than previously reported, with large popul...
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| Published in | Hearing research Vol. 434; p. 108782 |
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| Main Authors | , , , , , , , , |
| Format | Journal Article |
| Language | English |
| Published |
Netherlands
Elsevier B.V
01.07.2023
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| Subjects | |
| Online Access | Get full text |
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| Summary: | •Method to measure ear canal geometry from CT scans•First objective definitions for canal length and first bend location•Canal cross sectional area appears to increase with adult age cohorts along majority of canal length•Mean canal areas and lengths larger than previously reported, with large population variations
Description of the ear canal’s geometry is essential for describing peripheral sound flow, yet physical measurements of the canal’s geometry are lacking and recent measurements suggest that older-adult-canal areas are systematically larger than previously assumed. Methods to measure ear-canal geometry from multi-planar reconstructions of high-resolution CT images were developed and applied to 66 ears from 47 subjects, ages 18–90 years. The canal’s termination, central axis, entrance, and first bend were identified based on objective definitions, and the canal’s cross-sectional area was measured along its canal’s central axis in 1–2 mm increments. In general, left and right ears from a given subject were far more similar than measurements across subjects, where areas varied by factors of 2–3 at many locations. The canal areas varied systematically with age cohort at the first-bend location, where canal-based measurement probes likely sit; young adults (18–30 years) had an average area of 44mm2 whereas older adults (61–90 years) had a significantly larger average area of 69mm2. Across all subjects ages 18–90, measured means ± standard deviations included: canals termination area at the tympanic annulus 56±8mm2; area at the canal’s first bend 53±18mm2; area at the canal’s entrance 97±24mm2; and canal length 31.4±3.1mm2. |
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| Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Author Contributions: Auden P. Balouch took the lead role in designing and developing the measurement method. She completed an undergraduate thesis at Smith College that included complete development of the method and extensive measurements on 6 ears. Authors Douglas Keefe and Susan Voss oversaw the thesis and had frequent meetings about the methodology development and testing. Auden also helped draft the manuscript, both writing and figures.Karen Bekhazi, Hannah E. Durkee, Rebecca M. Farrar, and Mealaktey Sok each learned the method developed by APB, made suggestions for improvements within the method, tested the method for repeatability, and approved the written document. To be specific, each author made measurements on the following number of CT scans, where multiple measurements were made on many of the ears: Karen Bekhazi: 29 earsHannah Durkee: 21 earsRebecca Farrar: 26 earsMealaktey Sok: 25 earsDouglas H. Keefe supervised the thesis of Auden Balouch on the method development within this manuscript, made fundamental suggestions for its improvement, and played an active role in editing and improving the manuscript.Aaron K. Remenschneider helped define the project and identified CT scans as a promising method to study ear canal geometry, leading to the thesis of first author Balouch. He also provided essential input based on his radiological expertise, he reviewed the scans to ensure they represented normal ears, he periodically reviewed the results as the project progressed, and he helped draft and edit portions of the manuscript.Nicholas J. Horton provided statistical analysis, data organization structure suggestions, and substantial edits to the writing.Susan E. Voss guided the project at all stages, oversaw coordinating the work of all of the coauthors, compiled all of the data and corresponding analyses, and had the lead role in drafting the manuscript. |
| ISSN: | 0378-5955 1878-5891 1878-5891 |
| DOI: | 10.1016/j.heares.2023.108782 |