3-D shape modeling for hearing aid design [Applications Corner]

Abstract

This is the accepted version of the paper.This version of the publication may differ from the final published version. trauma, and exposure to damaging noise, the most common treatment is a hearing aid. Since a patient typically uses a hearing aid for many hours during the day, it must be comfortable to wear. Permanent repository linkHearing aids are typically custom-made to match the three-dimensional (3D) geometry of the patient's ear in order to achieve a comfortable fit.This article presents a software-based approach to interactive 3D shape modeling for geometric design of hearing instruments. We review various shape modeling operations that transform a raw impression to the final shape of the hearing aid device. In addition, we present state-of-the-art methods for automating the design process. HEARING AIDS Anatomical PerspectiveWhen designing a hearing aid, surface manipulations are often carried out with respect to anatomical features of the ear. In Figure 1 (a) and (b), we simultaneously an image of a right ear along with an impression (described below) to show the major relevant features. The canal is topmost portion of the surface and is the part that goes inside the ear canal. The aperture is a plane that separates the inner ear and the outer ear. The tragus is the small flap of cartilage near the aperture. Across from the tragus is the anti-tragus. The tragus and anti-tragus are protrusions of the ear geometry so they appear as indentations on the impression. Between the tragus and antitragus is the notch. Also near the aperture, the concha is the bowl-shaped cavity that appears as a hump on the impression. The crus is a ridge of cartilage on the ear and appears as a valley on the impression. The cymba is an indented region next to the crus, while the anti-cymba is the flap of cartilage above the cymba in the picture of the ear. On the impression, the cymba is a protrusion and the anti-cymba is an indentation. Please see Gray's anatomy [1] for more details.

Automatic Detection of Anatomical Features on 3D Ear Impressions for Canonical Representation

“…Once a mesh is constructed from the 3D scan of an ear impression, an operator carries out a sequence of surface modification operations (Fig. 2), to design an HA shell [6]. Typically, he relies on manual measurements (on sub-mm scale) implicitly using certain key anatomical features.…”

“…(b) Due to the varied nature of the features, a collection of algorithms are proposed to produce an overall system capable of their reliable detection. These methods enable automation in the HA manufacturing (HAM) [6] and have the potential of faster and more consistent design. (c) The resulting signature will serve as a foundation to a 3D digital atlas of the human ear.…”

Feature Driven Rule Based Framework for Automatic Modeling of Organic Shapes in the Design of Personalized Medical Prosthetics

“…In this section, we consider the modeling of HA shells [8]. Ear impressions are first acquired by an audiologist by inserting a mold through an injector deep in the ear canal.…”

“…HAM [8], for instance, requires tedious amount of manual involvement. In-the-ear HAs are generally custom made to ensure a comfortable fit to the ear(s) of a patient.…”

“…5). HA designers, therefore, have to rely on their experience along with lengthy work instructions for carrying out surface modifications [8] via interactive CAD tools (iCT) [1].…”