The Measurement of 2D Curvature of In-Vivo Human Ear Canal

Abstract

Problem To non-invasively measure the 2D curvature of human ear canal and produce the earmold by the non-invasive 3D ear impression. Methods The images of external ear were scanned by high-resolution computed tomography (HRCT). The resolution for each slice was 512⋉512 pixels. The pixel size was 0.188⋉0.188mm and the slice thickness was 0.625mm. The boundary between tympanic membrane and external auditory meatus was enhanced by image processing. Additionally, 3D model of ear canal was reconstructed by 2D images. The length and angle of first and second bends of canal were measured based on the 3D model. 2D curvature of first and second bends of canal was then computed by sine and cosine laws. Results The volume of ear canal was 862.0 cubic mm. The angle and curvature of superior wall of first bend at axial view were 121.5 degrees and 0.0685; of inferior wall of first bend were 246 degrees and −0.1102; of superior wall of second bend were 227.8 degrees and −0.0332; of inferior wall of second bend were 143.1 degrees and 0.0130 respectively. 2D curvature of superior and inferior wall of first and second bends was diagrammed. Conclusion The 2D curvature of ear canal at first and second bends could be measured and produce the ear impression non-invasively. The geometry of canal changed by tumors is a common syndrome in ear disease. Therefore, the geometry of ear canal can be tracked after the otoplasty. Significance The 3D geometry of canal can help physicians diagnose the syndrome of external canal before otoplasty. Moreover, the hearing aid earmold can be made by non-invasive ear impression instead of invasive ear impression.