title: Design of hearing aid shells by three dimensional laser scanning and mesh reconstruction.
abstract: Hearing aid shells (or earmolds) must couple the hearing aid with the user's ear. Earmolds have to fit the subject's outer ear canal properly to ensure a good performance of the aid. Because of the great variability in the anatomical pattern of the ear, earmolds are custom made. At present, an impression of the subject's ear canal is taken and used to fabricate the silicon-made mold. The postimpression activities that typically are performed during the fabrication process modify the physical dimensions of the resulting earmold and thus affect the fit of the product. A novel system for 3-D laser scanning and mesh reconstruction of the surface of ear canal impressions is presented. The reconstructed impression can be digitally stored and passed directly to dedicated CAD 3-D printing machines to model the silicon earmold and thus achieve the best possible fit. The proposed system is based on a couple of cameras and a commercial laser for the surface digitization and on a straightforward algorithm, based on the deformation of a geometric model, for the reconstruction of the acquired surface. Measurements on objects of well-known geometric features and dimensions are performed to assess the accuracy and repeatability levels of this 3-D acquisition system. Robustness to noise of the proposed reconstruction algorithm is determined by simulations with a synthetic test surface. Finally, the first measurements (acquisition+reconstruction) of closed surfaces from ear canal impressions are reported.
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto di Ingegneria Biomedica, Piazza Leonardo da Vinci, 32, I-20133 Milan, Italy. Gabriella.Tognola@polimi.it
authors.forename: Gabriella
authors.initials: G
authors.lastname: Tognola
authors.forename: Marta
authors.initials: M
authors.lastname: Parazzini
authors.forename: Cesare
authors.initials: C
authors.lastname: Svelto
authors.forename: Manuela
authors.initials: M
authors.lastname: Galli
authors.forename: Paolo
authors.initials: P
authors.lastname: Ravazzani
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Grandori
mesh_terms: D000465:Algorithms; D017076:Computer-Aided Design; D004424:Ear Canal / Q000033:anatomy & histology*; D006804:Ergonomics / Q000379:methods; D006310:Hearing Aids; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007834:Lasers; D010780:Photogrammetry / Q000379:methods; D011474:Prosthesis Design / Q000379:methods*; D017755:Prosthesis Fitting / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity