Imaging the cochlea by magnetic resonance microscopy

doi:10.1016/0378-5955(94)90058-2

Hearing Research

Volume 75, Issues 1–2, May 1994, Pages 75-80

https://doi.org/10.1016/0378-5955(94)90058-2 Get rights and content

Abstract

The isolated, fixed cochlea of the mustached bat was studied with three dimensional magnetic resonance (MR) microscopy. The cochlea of this animal is about 4 mm in diameter and its entire volume was imaged. With the field of view and matrix sizc used, the volume elements (voxels) making up the volume data set were isotropic 25 × 25 × 25 μm cubes. Three dimensional (3D) MR microscopy based on isotropic voxels has many advantages over commonly used light microscopy:

1.
1) it is non destructive;
2.
2) it is much less time consuming;
3.
3) no dehydration is required and shrinkage is minimized;
4.
4) the data set can be used to create sections in any desired plane;
5.
5) the proper alignment of sections is inherent in the 3D acquisition so that no reference points are required;
6.
6) the entire data set can be viewed from any point of view in a volume rendered image;
7.
7) the data is digital and features can be enhanced by computer image processing; and
8.
8) the isotropic dimensions of the voxels make the data well-suited for structural reconstructions and measurements. Good images of the osseous spiral lamina, spiral ligament, scala tympani, scala vestibuli, and nerve bundles were obtained. The vestibular (Reissner's) membrane was easily identified in the mustached bat and it appears to bulge into the scala vestibuli. The visibility of this structure suggests that MR microscopy would be well-suited for studies of endolymphatic hydrops.

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Cited by (34)

Visualization of Reissner membrane and the spiral ganglion in human fetal cochlea by micro-computed tomography
2009, American Journal of Otolaryngology - Head and Neck Medicine and Surgery
Citation Excerpt :
We consider that the fact that the organ of Corti is not observed in Figs. 2 and 3 is due to the above factors. Henson et al [4] succeeded in obtaining images of Reissner membrane of mustached bat at 25 × 25 × 25 μm voxel size with a 7.1-T MRI microscope with a total scanning time of 58 hours. They found the thickness of Reissner membrane measured by an optical microscope to be 1.5 to 5.4 μm.
Although visualization of fine structures in the cochlea such as Reissner membrane (vestibular membrane) is important for elucidation of the mechanism and the establishment of therapy for inner ear diseases, they cannot be visualized by even the most advanced high-resolution medical computed tomography (CT) and magnetic resonance imaging. Visualization of Reissner membrane in dissected animals by micro-magnetic resonance imaging has been reported, but bone could not be visualized. We attempted to visualize human fetal Reissner membrane and the spiral ganglion by micro-focus x-ray CT (μ-CT), which has a spatial resolution several hundred times greater than the conventional medical CT.
Serial tomograms of a dissected pyramis, including the cochlea of human fetuses (stillborn specimens), were obtained by μ-CT, and 3-dimensional reconstruction was performed by a volume-rendering method.
Clear tomograms (theoretical spatial resolution, 12.2 × 12.2 μm; slice thickness 77.5 μm) and 3-dimensional reconstructed images (theoretical spatial resolution, 6.8 × 6.8 μm; slice thickness, 40.0 μm) of Reissner membrane and the spiral ganglion with a bony labyrinth (cochlear bone) were successfully obtained for the first time. The thickness of Reissner membrane obtained by the tomogram was 12 μm, which corresponds to the optical macroscopic value from resin-embedded histologic sections.
This study showed that μ-CT enables us to visualize the internal fine structure of the human cochlea. As the success rate of the visualization of Reissner membrane is not high, it is necessary to improve the image quality and contrast resolution of μ-CT to enable stable visualization of fine structures. The development of imaging equipment such as μ-CT for medical use should play an important role in the elucidation of the mechanism and the establishment of therapy for inner ear diseases.
Imaging the intact guinea pig tympanic bulla by orthogonal-plane fluorescence optical sectioning microscopy
2002, Hearing Research
Orthogonal-plane fluorescence optical sectioning (OPFOS) microscopy was developed for the purpose of making quantitative measurements of the intact mammalian cochlea and to facilitate 3D reconstructions of complex features. A new version of this imaging apparatus was built with a specimen chamber designed to accommodate samples as large as the intact guinea pig bulla. This method left the cochlear connections with the vestibular system and with the ossicles of the middle ear undisturbed, providing views within the cochlea with no breaches of its structural integrity. Since the features within the bulla were not physically touched during the preparation process, the risk of damage was minimized, and were imaged in relatively pristine condition with spatial resolution to 16 μm. A description of the imaging method and specimen preparation procedure is presented, as are images of features from the cochlea, ossicles, and vestibular system.
Quantitative anatomy of the round window and cochlear aqueduct in guinea pigs
2001, Hearing Research
In order to analyze the entry of solutes through the round window membrane, a quantitative description of round window anatomy in relationship to scala tympani is required. High-resolution magnetic resonance microscopy was used to visualize the fluid spaces and tissues of the inner ear in three dimensions in isolated, fixed specimens from guinea pigs. Each specimen was represented as consecutive serial slices, with a voxel size of approximately 25 μm³. The round window membrane, and its relationship to the terminal portion of scala tympani in the basal turn, was quantified in six specimens. In each image slice, the round window membrane and scala tympani were identified and segmented. The total surface area of the round window membrane averaged 1.18 mm² (S.D. 0.08, n=6). The length and variation of cross-sectional area as a function of distance for the cochlear aqueduct was determined in five specimens. The cochlear aqueduct was shown to enter scala tympani at the medial limit of the round window membrane, which corresponded to a distance of approximately 1 mm from the end of the scala when measured along its mid-point. These data are of value in simulating drug and other solute movements in the cochlear fluids and have been incorporated into a public-domain simulation program available at http://oto.wustl.edu/cochlea/.
Anatomical and functional imaging of the auditory cortex in awake mustached bats using magnetic resonance technology
1999, Brain Research Protocols
The auditory cortex of mustached bats, Pteronotus parnellii, has been studied extensively using neuroanatomical tract-tracing and electrophysiological techniques to elucidate the functional organization and neural mechanisms important for auditory processing. While these techniques have identified several cortical maps involved in processing auditory information, there has been no direct observation of the dynamics of simultaneous activation of several discrete areas. We applied magnetic resonance (MR) imaging techniques for visualizing brain structures in awake bats using a 7-Tesla magnet system; we also investigated functional MR imaging by measuring changes in stimulus-correlated blood oxygenation levels to detect cortical areas exhibiting evoked neural activity. High resolution (100 μm) anatomical images were successfully acquired without any motion artifacts. It was possible to reconstruct the whole brain image and analyze brain surface structures with three dimensional (3D) MR imaging data. These data provide detailed morphometric measurements that will allow localization of stimulus specific neural activity patterns using modified functional magnetic-resonance-imaging (fMRI) protocols. Motion artifacts is the primary disadvantage of using awake bats; our study shows that fMRI of a bat's brain is feasible and may prove to be an important advancement for a further understanding of auditory processing in this species.
Themes: Sensory systems, Neural basis of behavior.

Topics: Auditory systems: central anatomy, Auditory systems: central physiology, Neuroethology, Neural plasticity.
Fixation-induced shrinkage of Reissner's membrane and its potential influence on the assessment of endolymph volume
1997, Hearing Research
The quantification of endolymph volume by histological techniques or by magnetic resonance (MR) microscopy requires the inner ear to be first treated with chemical fixatives. If the fixative induces soft-tissue shrinkage, it would tend to return a distended Reissner's membrane towards a straight position, since this membrane is anchored to bone at its medial and lateral edges. The goal of this study was to determine the degree of Reissner's membrane shrinkage induced by different fixation protocols to establish methods which minimize tissue shrinkage. Fragments of fresh Reissner's membrane were dissected from isolated cochleae in an artificial perilymph. Specimens were viewed with an inverted microscope during infusion of fixatives, and changes recorded on video tape. Size changes of the specimen were quantified, usually over a 20 min period. Heidenhain-Susa, a fixative which is widely used in histological studies of hydropic cochleae, caused substantial shrinkage of Reissner's membrane, decreasing the length of specimens by an average of 15.1%. Other fixation procedures induced far less shrinkage. The use of 3X/0 glutaraldehyde in Hanks' balanced salt solution produced a mean length decrease of only 0.3%. The inclusion in the fixation medium of 4.5`/0 mercuric chloride, corresponding to the concentration which is present in Heidenhain-Susa and which acts to increase the contrast of Reissner's membrane in MR microscopy, contributes significantly to specimen shrinkage. We can conclude that the degree of endolymphatic hydrops may be underestimated in specimens fixed with media containing high levels of mercuric chloride.
A VRML-based anatomical visualization tool for medical education
1998, IEEE Transactions on Information Technology in Biomedicine

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Imaging the cochlea by magnetic resonance microscopy

Abstract

J. Magn. Reson.

J. Magn. Reson.

J. Magn. Reson.

J. Magn. Reson.

J. Magn. Reson.

J. Magn. Reson.

Magn. Reson. Imaging

A generalized formulation of diffusion effects in μm resolution nuclear magnetic resonance imaging

Med. Phys.

Nuclear magnetic resonance imaging of a single cell

Nature

Seeing in volume

Pixel

A probe for specimen magnetic resonance microscopy

Investigative Radiology