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3D Finite Element Model of Posterior Membranous Labyrinth from in Vivo

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3D Finite Element Model of Posterior Membranous Labyrinth from in Vivo Journal of Translational Science Research Article ISSN: 2059-268X 3D finite element model of posterior membranous labyrinth from in vivo MRI of human temporal bone, including sensory zones Chaney HV1*, Lamy M2, Baumgartner D3, Venkatasamy A4, Veillon F5, Rohmer D6, Riehm S7, Debry C8 and Charpiot A9 1Assistant, ORL, CHU Hautepierre, Avenue Molière, 67098 Strasbourg cedex, France 2Engineer, Strasbourg University, France 3MCU, Strasbourg University, France 4CCA, Radiology, CHU Hautepierre, Avenue Molière, 67098 Strasbourg cedex, France 5PU-PH, Radiology, CHU Hautepierre, Avenue Molière, 67098 Strasbourg cedex, France 6PH, ORL, CHU Hautepierre, Avenue Molière, 67098 Strasbourg cedex, France 7PH, Radiology, CHU Hautepierre, Avenue Molière, 67098 Strasbourg cedex, France 8PU-PH, ORL, CHU Hautepierre, Avenue Molière, 67098 Strasbourg cedex, France 9PU-PH, ORL, CHU Hautepierre, Avenue Molière, 67098 Strasbourg cedex, France Abstract Objective: The aim of this work is to create a three-dimensional (3D) finite element model (FEM) of the human posterior membranous labyrinth, based onin vivo inner ear magnetic resonance imaging (MRI). Study design and setting: We used T2 weighted gradient-echo 3T MRI of a human inner ear. Images were acquired in vivo, from a patient presenting a vestibular schwannoma with a preserved labyrinthine geometry. Indeed, in this context, the elevation of the perilymphatic protides level secondary to the obstructive vestibular schwannoma enables a differentiation between the endolymph (which remains hyperintense on T2 weighted images) and the perilymph (hypointense on T2 weighted gradient echo images). Results: A 3D reconstruction of the posterior membranous labyrinth was performed through manual segmentation of the endolymphatic and sensory spaces. A mesh of the labyrinth was realized, first of its outer surface and then of its interior volume. The different structures of the labyrinth are included through a compartmentalization of the mesh. Sensory zones are precisely defined, based on a radio-histological correlation study. The resulting mesh of the model included 124,701 elements. Conclusion: Dimensions are in agreement with those in the literature, which is in favor of the validity of the model geometry. This model also has a pedagogical interest and can be useful for the clinical reflexion in cases of atypical benign paroxysmal positional vertigos (BPPV). It can also serve as a base for mechanical studies of vestibular physiology. Key points 1. This 3D model is based on in vivo inner ear imaging. 2. It is a FEM of human posterior membranous labyrinth. 3. This model includes all the sensory zones of the posterior membranous labyrinth. Abbreviations: 3D: three-dimensional; BPPV: benign paroxysmal also prove useful in the learning process of vestibular positional positional vertigos; CT: computed tomography; FEM: finite element manoeuvers. Likewise, it presents a clinical interest, as it can serve model; FIESTA: Fast Imaging Employing Steady State Acquisition; as a basis for diagnosis reasoning in cases of atypical BPPV. MRI: magnetic resonance imaging; SCC: semi-circular canal; STL: stereolithography. Introduction *Correspondence to: Hella VUONG CHANEY, Otorhinolaryngology Service and cervico-facial surgery, CHRU Hautepierre, Avenue Molière, 67098 Strasbourg Cedex, A morphologically precise 3D model of the posterior France, E-mail: [email protected] membranous labyrinth of the inner ear is a powerful tool for a better understanding of the vestibular physiology. It also offers an Key words: inner ear, in vivo, finite element modeling educational interest for mental representation of the orientation of Received: December 17, 2018; Accepted: January 19, 2019; Published: January human semi-circular canals (SCC) and their sensory zones. It could 21, 2019 J Transl Sci, 2019 doi: 10.15761/JTS.1000307 Volume 6: 1-6 Chaney HV (2019) 3D finite element model of posterior membranous labyrinth from in vivo MRI of human temporal bone, including sensory zones Other 3D models of the complete posterior human labyrinth 3D reconstruction of the posterior membranous labyrinth have been created, but most of them have been constructed from In vivo images of the right inner ear were acquired from a post mortem human temporal bones or issued from animal models. patient with vestibular schwannoma (grade II), with a preserved Only a few 3D models of the human membranous posterior labyrinth membranous labyrinth geometry and no intralabyrinthite extension have been created. Teranishi and al [1] developed a 3D model of the of the tumor (Table 1). In the presence of schwannoma, the elevation endolymphatic and perilymphatic spaces of the inner ear, using sections of the protides concentration in the perilymph space, resulting in of human temporal bones with and without hydrops. Rajguru and a drop of the perilymphatic signal on gradient echo MR images, al [2] made a model of the human posterior membranous labyrinth, increases the contrast between the endolymphatic and perilymphatic by reconstructing human sections of temporal bones. David and al spaces, as the endolymph remains normal [9]. This makes possible developed 3D models of the human posterior membranous labyrinth by the tracing of the contours of the endolymphatic space. The using X-ray micro computed tomography (CT) and tissue staining with membranous labyrinth geometry is conserved in about 70% of the phosphotungstic acid and created a software toolbox for morphological cases, as we observed in our service about 30% of endolymphatic and functional analysis of the duct system [3]. hydrops associated with schwannoma. To our knowledge, our model is the first 3D FEM of the human The patient underwent an axial high-resolution T2W three- posterior membranous labyrinth that was reconstructed using in vivo dimensional (3D) gradient-echo FIESTA-C sequence at 3T (Signa MRI images, by segmentation of the endolymph and sensory zones. HDxt, General Electric, *BLINDED*), using an eight-channel head Moreover, that model specifies the position of all the sensory zones. coil. This sequence is a sort of modified steady state free precession sequence, which does not require any contrast injection. The study box Reconstruction of the posterior membranous labyrinth was was placed parallel to the orbital roof, extended from the orbital roof, realized by a segmention of human temporal bone images. They downwards on 2.3 cm. The acquisition parameters were as follows: were acquired in vivo, using a T2 weighted gradient-echo MR images echo time (TE) = 0.8–1.2ms, repetition time (TR) = 7ms, field of view acquired at 3T, from a patient presenting an obstructive vestibular (FOV) = 22× 19.80 cm, frequency × phase = 484 × 484, flip angle = 60°C, schwannoma with a preserved labyrinth geometry and without number of excitations (NEX) = 1, bandwidth = 83.3 kHz, partition labyrinthine extension of the tumor. In the presence of a vestibular thickness = 0.3 × 0.3 × 0.3 mm (isotropic voxel). The acquisition time schwannoma of the internal auditory canal, the geometry of the was 7 min 49 s. membranous labyrinth can be considered normal in approximately The reconstruction of the inner ear was performed through a 70% of the cases, but the elevation of the perilymphatic protides manual segmentation, on the images of the endolymphatic space and concentration, resulting in a drop of the perilymphatic signal on T2 of the sensory zones, using the software ITK-Snap [10,11]. As the weighted gradient echo images enables to differentiate the endolymph, endolymph appears in a normal hyperintense signal on T2 weighted which signal remains normal, and the hypointense perilymph. images, and the sensory zones appears hypointense, it was not possible After a 3D segmentation of the posterior labyrinth, the resulting to reconstruct the whole posterior membranous labyrinth volume with surface object (a net of points on said surface) was used to create the an automatic segmentation process. Therefore, we performed a manual mesh of a 3D FEM. FEM are powerful tools for the estimation of a voxel by voxel segmentation (as featured in Figure 1). Written informed numerical solution to complex problems, in particular in structural consent was obtained from the patient for this study, and the Ethic mechanics. In the FEM, the modeled system exists as a discrete committee approved the study (approval number FC/dossier 2017-31). representation of its whole volume. The points of discretization are Figure 1. Axial slice of the right horizontal SCC and utricle. The called the nodes: when interconnected, they are the vertices of cells. membranous labyrinth is manually segmented, in order to include the Those cells are the so-called finite elements. Elements can be attributed endolymph (hypersignal) and the sensory zones (hyposignal). mechanical properties, to describe the materials they represent, and In the canals themselves, the contrast between endolymph and can be submitted to exterior or interior inputs. This technique thus perilymph was less obvious. The segmentation had to rely on histological offers new insights to complex biomechanical problems, which would knowledge: the membranous duct occupies about one quarter of the be impossible to observe, measure or analyze in vivo. bone canal and is fixed on its external diameter [12]. This knowledge Materials and methods was used to confirm which voxels were to be part of the segmentation in the SCC. Preliminary histological and radiological studies of the sensory zones Table 1.
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