The supporting cells and hair cells (HCs) in the organ of Corti (OoC) are highly organized. The precise 3D micro-structure is hypothesized to play a critical role in cochlear function. Recently, we combined two techniques to obtain the organ of Corti cytoarchitecture. Two-photon imaging allowed us to perform in situ imaging without subjecting the tissue to other potential distortions, while genetically engineered mTmG mice have a fluorophore embedded in the cell membranes. In this contribution we discuss the parameterization step necessary to compare structures obtained with this technique at different locations and in different specimens. <p> </p>First, the z-axis is chosen perpendicular to the basilar membrane. Subsequently, base and apex of cells are indicated by landmarks. As such, the cells are approximated as a stick representation. This representation is used to calculate the 3D lengths and angles of all imaged cells. Since the OoC is not straight but spiral-shaped, the radial (y) and longitudinal (x) directions differ at each location. Therefore, circular arcs are fitted through the 3 rows of outer HCs to define the local radial (y) and longitudinal (x) direction. Novel in this approach is the 3D data of the cell position in the organ of Corti. Cell diameters and tissue areas cannot be quantified with this stick representation and need to be measured separately.
Greater understanding of tympanic membrane (TM) biomechanics has the potential to guide future advances in medical
technology related to its surgical repair (myringoplasty). The pars tensa of the TM is a composite structure with two
collagen fiber layers that provide the main scaffolding for the TM. The external layer is arranged in an approximately
radial configuration, and the other is arranged in an approximately circumferential configuration. A more detailed
knowledge of collagen fiber orientation and volume fraction could greatly improve existing mechanical simulations of
the TM. To address this, we employed multiphoton microscopy (MPM) imaging of the TM in two modalities: second
harmonic generation (SHG) and two-photon fluorescence (TPF). The unique spectral signature of SHG allows selective
imaging of collagen fibers. TPF also produces images of fibrillar-type collagen but lacks the specificity of SHG. Both
the SHG and TPF images show patterns of collagen organization in the TM that match expected results with respect to
both orientation and size. Through MPM, we intend to accurately determine the collagen fiber layer thickness, density,
and orientation as a function of radial position and quadrant location.
Understanding the biomechanics of the middle ear is important for surgical reconstructions. As the output of the
middle ear, the stapes plays a key role in transferring acoustic vibrations to the cochlea. In order to develop anatomically-based mathematical models, which are needed to improve our understanding of stapes dynamics, detailed morphometry
of the stapes is required. High-resolution micro-CT imaging techniques were used to generate three-dimensional
reconstructions of cadaveric temporal bones from 5 species commonly used in experimental middle ear research: the
chinchilla, human (relatively mid-frequency hearing limit), cat, guinea pig, and gerbil (relatively high-frequency hearing
limit). From the standard discretizations of micro-CT images and corresponding 3-D volume reconstructions, the centers
of mass, principle axes, stapes head areas and stapes footplate areas were calculated. Mechanical relationships were
estimated between the capitulum area and the footplate area and inter-species comparisons were performed between the
cross-sectional shapes of the anterior and posterior crura. Quantitative dynamic properties were estimated from the rigid
body motion calculations. The parameters estimated in this study will be useful for building biocomputational models of
the stapes for a variety of species.
A novel micro computed tomography (μCT) image processing method was implemented to measure
anatomical features of the gerbil and chinchilla cochleas, taking into account the bent modailosis axis.
Measurements were made of the scala vestibule (SV) area, the scala tympani (SV) area, and the basilar
membrane (BM) width using prepared cadaveric temporal bones. 3-D cochlear structures were obtained
from the scanned images using a process described in this study. It was necessary to consider the sharp
curvature of mododailosis axis near the basal region. The SV and ST areas were calculated from the μCT
reconstructions and compared with existing data obtained by Magnetic Resonance Microscopy (MRM),
showing both qualitative and quantitative agreement. In addition to this, the width of the BM, which is the
distance between the primary and secondary osseous spiral laminae, is calculated for the two animals and
compared with previous data from the MRM method. For the gerbil cochlea, which does not have much
cartilage in the osseous spiral lamina, the μCT-based BM width measurements show good agreement with
previous data. The chinchilla BM, which contains more cartilage in the osseous spiral lamina than the
gerbil, shows a large difference in the BM widths between the μCT and MRM methods. The SV area, ST
area, and BM width measurements from this study can be used in building an anatomically based
mathematical cochlear model.