Use of magnetic resonance image registration to estimate displacement in the human earcanal due to the insertion of in-ear devices

Abstract

In-ear devices are used in a wide range of applications for which the device's usability and/or efficiency is strongly related to comfort aspects that are influenced by the mechanical interaction between the device and the walls of the earcanal. Although the displacement of the earcanal walls due to the insertion of the device is an important characteristic of this interaction, existing studies on this subject are very limited. This paper proposes a method to estimate this displacement in vivo using a registration technique on magnetic resonance images. The amplitude, the location and the direction of the earcanal wall displacement are computed for four types of earplugs used by one participant. These displacements give indications on how each earplug deforms the earcanal for one specific earcanal geometry and one specific earplug insertion. Although the displacement due to a specific earplug family cannot be generalized using the results of this paper, the latter help to understand where, how much, and how each studied earplug deforms the earcanal of the participant. This method is revealed as a promising tool to investigate further acoustical and physical comfort aspects of in-ear devices. V

Pressure induced by roll-down foam-earplugs on earcanal

“…We idealize our model here into a skin layer with thickness, s and a bony/cartilaginous/fatty part backing the skin with thickness B. Experiments showed that RD-foam earplugs induce insignificant earcanal deformation corresponding to a mean displacement <0.4 mm [38]. The surrounding tissue is therefore considered as elastic homogeneous materials with equivalent elastic properties much harder than skin or earplug (indicated as a hard substrate on Figure 2b).…”

“…In this section, we present FE simulations that account for actual curvatures of earcanal. To do so, we obtained a full 3D geometric model constructed from high-resolution MRI images based of a healthy human subject (a volunteer male participant of 29 year of age [38,51]) without any known hearing impairment or earcanal abnormalities. Figure 1a shows the CAD model constructed from those MRI images.…”

“…Moreover, final shape of the earcanal and the earplug inside the earcanal depend on the relative stiffness of earplugs to that of earcanal. As such, soft earplugs may simply take the shape of earcanal, while stiffer earplugs, for example push-to-fit earplugs, may excessively deform the earcanal [38]. Another study utilized earcanal medical images to infer mechanical stresses through inverse calculation based on measured deformation of MRI scans [33].…”

Towards a Holistic Model Explaining Hearing Protection Device Use among Workers

“…At the Fitting/positioning phase (F), questionnaires or observations are commonly used. At the Interaction phase (I), the use of field attenuation estimation systems [90] (FAES), microphones or medical images (e.g., from magnetic resonance imaging MRI scanners [91]) is possible. Visual inspections could also be used for assessing the fit quality, but this is a much less robust method [65].…”

Principle of an acoustical method for estimating the centroid position of the earcanal wall normal velocity induced by bone-conducted stimulation: Numerical evaluation

“…The latter requires the knowledge of the EC shape function between the eardrum and the coupling duct and the geometric dimensions (inner radius and length) of the coupling duct. The EC shape can be obtained from CT or MRI images [27], 3D scans [28], EC imprint [26] or estimated using indirect acoustic method [29]. In theory, the EA model also requires the tympanic membrane acoustic impedance.…”