Numerical simulations to determine the stimulation of the crista ampullaris during the Head Impulse Test.

The Head Impulse Test, the most widely accept test to assess the vestibular function, comprises rotations of the head based on idealized orientations of the semicircular canals, instead of their individual arrangement specific for each patient. In this study, we show how computational modelling can help personalize the diagnosis of vestibular diseases. Based on a micro-computed tomography reconstruction of the human membranous labyrinth and their simulation using Computational Fluid Dynamics and Fluid-Solid Interaction techniques, we evaluated the stimulus experienced by the six cristae ampullaris under different rotational conditions mimicking the Head Impulse Test. The results show that the maximum stimulation of the crista ampullaris occurs for directions of rotation that are more aligned with the orientation of the cupulae (average deviation from alignment of 4.7°, 9.8°, and 19.4° for the horizontal, posterior, and superior maxima, respectively) than with the planes of the semicircular canals (average deviation from alignment of 32.4°, 70.5°, and 67.8° for the horizontal, posterior, and superior maxima, respectively). A plausible explanation is that when rotations are applied with respect to the center of the head, the inertial forces acting directly over the cupula become dominant over the endolymphatic fluid forces generated in the semicircular canals. Our results indicate that it is necessary to consider cupulae orientation to ensure optimal conditions for testing the vestibular function.

Assessing morphology and function of the semicircular duct system: introducing new in-situ visualization and software toolbox.

The semicircular duct system is part of the sensory organ of balance and essential for navigation and spatial awareness in vertebrates. Its function in detecting head rotations has been modelled with increasing sophistication, but the biomechanics of actual semicircular duct systems has rarely been analyzed, foremost because the fragile membranous structures in the inner ear are hard to visualize undistorted and in full. Here we present a new, easy-to-apply and non-invasive method for three-dimensional in-situ visualization and quantification of the semicircular duct system, using X-ray micro tomography and tissue staining with phosphotungstic acid. Moreover, we introduce Ariadne, a software toolbox which provides comprehensive and improved morphological and functional analysis of any visualized duct system. We demonstrate the potential of these methods by presenting results for the duct system of humans, the squirrel monkey and the rhesus macaque, making comparisons with past results from neurophysiological, oculometric and biomechanical studies. Ariadne is freely available at http://www.earbank.org.

Geometrical and volume changes of the membranous vestibular labyrinth in guinea pigs with endolymphatic hydrops.

OBJECTIVE: To evaluate geometrical and volume changes of membranous vestibular labyrinths in guinea pigs after endolymphatic hydrops (EH). METHODS: The membranous labyrinths of normal guinea pigs and of those with EH for 4 and 8 weeks were reconstructed after being scanned using micro-computed tomography subseqent to being stained in osmium tetroxide (OsO4). The diameters and volumes of the semicircular ducts, ampullae, utricles and saccules were measured based on the three-dimensional models. RESULTS: The diameters of the ampullae and utricles of EH guinea pigs were greater than those of the normal guinea pigs, while there were no significant differences in the diameters of the semicircular ducts among all groups. The volumes of ampullae, utricles and saccules of the EH groups were greater than those of the control group, but there were no changes in volumes of semicircular ducts after EH. CONCLUSION: The dilations of the membranous vestibular labyrinth in guinea pigs with EH mainly occur at the ampullae, utricles and saccules.

Radiologic examinations in human temporal bone specimens using digital volume tomography and high-resolution computed tomography after implantation of middle ear prosthesis and cochlear implant electrode array.

INTRODUCTION: Adequate imaging of the middle ear and its surrounding structures is an essential preoperative part in ear surgery. In the past, the main disadvantage of computed tomography (CT) scanners was the decreased diagnostic quality due to metallic artifacts. Furthermore, these scanners showed mostly an inferior image quality compared to digital volume tomography (DVT) in the temporal bone. It was the aim of this experimental study to compare the image quality of a state-of-the-art dual-source 2 × 128-slice CT scanner to DVT in temporal bone specimen. MATERIALS AND METHODS: Metallic prosthesis (PORP, TORP, stapes piston, cochlear implant electrode array) and an autologous incus were implanted in temporal bone specimen to analyze the diagnostic quality concerning the characterization of anatomic structures. Three further temporal bones were scanned without any preparation. Independently, 2 otologists and 2 radiologists scored the image quality of defined anatomic structures, using a range from 4 (excellent) to 0 (no diagnostic value). RESULTS: The general score for DVT was 2.67, whereas CT reached a score of 2.76. The diagnostic value for hard contrast objects was 3.0 for DVT and 2.9 for CT, whereas the score for soft tissue was 1.1 for DVT and 2.3 for CT. Almost no quality reduction of the display of anatomic structures caused by metallic artifacts could be detected in both diagnostic modalities. DISCUSSION: Both DVT and high-resolution CT allow good overall image quality in temporal bones, with discrete advantages for digital volume tomographic scans in terms of the image quality of hard contrast objects like bony structures or metallic implants.

Assessment of the reuniting duct by three-dimensional CT rendering.

CONCLUSION: The rendering strategy sometimes induces misunderstanding of the image. We demonstrated a more accurate image of the bony groove of the reuniting duct using three-dimensional (3D) cone beam CT image, which was less affected by artifacts created by the rendering effect. OBJECTIVE: To obtain a suitable image of the groove of the reuniting duct for future morphological study. MATERIALS AND METHODS: The grooves of reuniting ducts in 10 healthy human subjects were analyzed by cone beam CT in comparison with a cadaver study. RESULTS: We could obtain more accurate 3D CT images of the bony groove in human subjects by checking the landmarks of 3D CT images.

Three-dimensional images of the reuniting duct using cone beam CT.

CONCLUSION: There is a bony groove under the course of the reuniting duct of the inner ear. Cone beam CT could show three-dimensional (3D) reconstruction images of this groove in a cadaver and living human subjects. OBJECTIVE: To obtain simple and universal images of the reuniting duct in humans for clinical use. MATERIALS AND METHODS: We investigated the reuniting duct macroscopically by observing the temporal bone in cadavers and living human subjects using cone beam CT. 3D reconstruction images of the duct were analyzed by the rendering software IVIEW. RESULTS: The reuniting duct showed a bony groove between the saccule and cecum of the hook portion of the cochlea that could be three-dimensionally visualized by cone beam CT. A bony groove image in a living human subject could also be visualized by cone beam CT.