Mads Sølvsten Sørensen

Estimation of Volume Referent Bone Turnover in the Otic Capsule after Sequential Point Labeling

Using fluorochrome labeling and a newly validated method for bone turnover estimation, we determined absolute values for canine perilabyrinthine bone remodeling. The overall capsular bone turnover was found to be 2.1% per year, compared to 13.9% per year for the neighboring cranial bones and 7.4% per year for the humerus compacta. This gross 2.1% per year conceals a vast range, from 0.13% per year for the innermost perilymphatic zone, through a centrifugal increment toward 8% to 10% per year in the periphery. The underlying individual bone remodeling units exhibit a similar centrifugal pattern in numerical density and size. These findings indicate an inhibition of remodeling, seemingly emanating from the perilymphatic spaces, and affecting both the activation of osteoclasts and the extent of resorption by the osteoclasts. These values satisfactorily explain the preservation of such fetal remnants as the globuli ossei, the interglobular spaces, and the skein bone. In humans, local ineffective inhibition of bone resorption may play a role in the initiation of otosclerosis.

The visible ear simulator: a public PC application for GPU-accelerated haptic 3D simulation of ear surgery based on the visible ear data.

Background: Existing virtual simulators for middle ear surgery are based on 3-dimensional (3D) models from computed tomographic or magnetic resonance imaging data in which image quality is limited by the lack of detail (maximum, ∼50 voxels/mm3), natural color, and texture of the source material. Virtual training often requires the purchase of a program, a customized computer, and expensive peripherals dedicated exclusively to this purpose. Materials and Methods: The Visible Ear freeware library of digital images from a fresh-frozen human temporal bone was segmented, and real-time volume rendered as a 3D model of high-fidelity, true color, and great anatomic detail and realism of the surgically relevant structures. A haptic drilling model was developed for surgical interaction with the 3D model. Results: Realistic visualization in high-fidelity (∼125 voxels/mm3) and true color, 2D, or optional anaglyph stereoscopic 3D was achieved on a standard Core 2 Duo personal computer with a GeForce 8,800 GTX graphics card, and surgical interaction was provided through a relatively inexpensive (∼

The visible ear: A digital image library of the temporal bone

2,500) Phantom Omni haptic 3D pointing device. Conclusion: This prototype is published for download (∼120 MB) as freeware at http://www.alexandra.dk/ves/index.htm. With increasing personal computer performance, future versions may include enhanced resolution (up to 8,000 voxels/mm3) and realistic interaction with deformable soft tissue components such as skin, tympanic membrane, dura, and cholesteatomas-features some of which are not possible with computed tomographic-/magnetic resonance imaging-based systems.

A downloadable three-dimensional virtual model of the visible ear.

High-fidelity computer-based modeling, simulation and visualization systems for the study of temporal bone anatomy and training for middle ear surgery are based on a sequence of digital anatomical images, which must cover a large tissue volume and yet display details in high resolution and with high fidelity. However, the use of existing image libraries by independent developers of virtual models of the ear is limited by copyright protection and low image resolution. A fresh frozen human temporal bone was CT-scanned and serially sectioned at 25 µm and digital images of the block surface were recorded at 50- to 100-µm increments with a Light PhaseTM single-shot camera back attachment. A total of 605 images were recorded in 24-bit RGB resolution. After color correction and elimination of image size variation by differential cropping to 15.4 cm × 9.7 cm, all images were resampled to 3,078 × 1,942 pixels at a final resolution of 50 µm/pixel and stored as 605 one-Mb JPEG files together with a three-dimensional viewer. The resulting complete set of image data provides: (1) a source material suitable for generating computer models of the human ear; (2) a resource of high-quality digital images of anatomical cross sections from the human ear, and (3) a PC-based viewer of the temporal bone in three perpendicular planes of section.

Mastoidectomy performance assessment of virtual simulation training using final‐product analysis

Purpose: To develop a three-dimensional (3-D) virtual model of a human temporal bone and surrounding structures. Methods: A fresh-frozen human temporal bone was serially sectioned and digital images of the surface of the tissue block were recorded (the ‘Visible Ear’). The image stack was resampled at a final resolution of 50 × 50 × 50/100 µm/voxel, registered in custom software and segmented in PhotoShop® 7.0. The segmented image layers were imported into Amira® 3.1 to generate smooth polygonal surface models. Results: The 3-D virtual model presents the structures of the middle, inner and outer ears in their surgically relevant surroundings. It is packaged within a cross-platform freeware, which allows for full rotation, visibility and transparency control, as well as the ability to slice the 3-D model open at any section. The appropriate raw image can be superimposed on the cleavage plane. The model can be downloaded at https://research.meei.harvard.edu/Otopathology/3dmodels/

Volume-Referent Bone Turnover Estimated From the Interlabel Area Fraction After Sequential Labeling

The future development of integrated automatic assessment in temporal bone virtual surgical simulators calls for validation against currently established assessment tools. This study aimed to explore the relationship between mastoidectomy final‐product performance assessment in virtual simulation and traditional dissection training.

Temporal Bone Dynamics, The Hard Way: Formation, Growth, Modeling, Repair and Quantum Type bone remodeling in the Otic Capsule

In the compact bony otic capsule remodeling is low, and bone remodeling units are distributed centrifugally in relation to inner ear tissues and spaces. Fluorochrome-labeled bone remodeling units are scarce, abortive, and tortuous with no uniform direction of movement. This study presents a method for the estimation of volume-referent bone turnover based on measurements of the fractional area between labels after sequential labeling with osteofluorochromes. The applicability of this method is tested against a classical quantification method in undecalcified cortical specimens from the canine humerus, where both methods can be used. The estimate of bone turnover derived from the new sequential labeling in eight dogs is 7.4% (SEM 2.1%) per year and the classic estimate derived from calculations of the formative osteonal area and the formative period yields 6.9% (SEM 2.1%) per year. Agreement is sufficient to justify future measurements of absolute bone turnover in sequentially labeled perilabyrinthine bone.

Cognitive load in distributed and massed practice in virtual reality mastoidectomy simulation

This review presents studies in which temporal bone dynamics were monitored in undecalcified human and animal materials by combined microradiography and osteofluorochromic time labeling. The results are interpreted in accordance with modern concepts of spatial and temporal organization of bone behavior in an attempt to contribute to a new basis for understanding the structure and function of the bony otic capsule. In postcartilaginous development, perilabyrinthine bone formed a separate functional unit in which growth and modeling were absent. Consequently, all drift movements bypassed the bone present inside a narrow perilabyrinthine zone, which in effect maintained a so-called drift barrier enclosing the entire inner ear. In baseline bone remodeling and repair-associated remodeling transients, secondary osteons were distributed centrifugally with respect to inner ear spaces, and the average osteonal size decreased towards the inner ear, suggesting a progressive inhibition of bone resorption towards inner ear spaces. No histological capsular component proved resistant to bone resorption during modeling and remodeling. Instead the dynamic behaviour of any moiety of capsular bone appeared to depend on its spatial relation to the membranous labyrinth rather than on histological characteristics. This spatial organization of perilabyrinthine bone development and turnover is responsible for the unique histology of capsular bone and may explain the accumulation of fatigue micro-cracks which can be found in human perila byrinthine bone. These findings suggests the role of inner ear tissues as a functional matrix in control of capsular bone dynamics even beyond fetal life.

Gene expression of the endolymphatic sac.

Cognitive load theory states that working memory is limited. This has implications for learning and suggests that reducing cognitive load (CL) could promote learning and skills acquisition. This study aims to explore the effect of repeated practice and simulator‐integrated tutoring on CL in virtual reality (VR) mastoidectomy simulation.

Cognitive Load in Mastoidectomy Skills Training: Virtual Reality Simulation and Traditional Dissection Compared

Abstract Conclusion: The endolymphatic sac is part of the membranous inner ear and is thought to play a role in the fluid homeostasis and immune defense of the inner ear; however, the exact function of the endolymphatic sac is not fully known. Many of the detected mRNAs in this study suggest that the endolymphatic sac has multiple and diverse functions in the inner ear. Objectives:The objective of this study was to provide a comprehensive review of the genes expressed in the endolymphatic sac in the rat and perform a functional characterization based on measured mRNA abundance. Methods:Microarray technology was used to investigate the gene expression of the endolymphatic sac with the surrounding dura. Characteristic and novel endolymphatic sac genes were determined by comparing with expressions in pure dura. Results: In all, 463 genes were identified specific for the endolymphatic sac. Functional annotation clustering revealed 29 functional clusters.