Optical polarization tractography revealed significant fiber disarray in skeletal muscles of a mouse model for Duchenne muscular dystrophy

Non-destructive Characterization of Skeletal Muscle Extracellular Matrix Morphology by Combining Optical Coherence Tomography (OCT) Imaging with Tissue Clearing

Histology is an essential step to visualize and analyze the microstructure of any biological tissue; however, histological processing is often irreversible, and histological samples are unable to be imaged or tested further. In this work, a novel non-destructive protocol is proposed for morphological analysis of skeletal muscles, combining Optical Coherence Tomography (OCT) imaging with Tissue Clearing. Imaging combining OCT and Propylene Glycol (PG) as a tissue-clearing agent, was performed on rat tail and extensor digitorum longus (EDL) muscle. The results show that the extracellular matrix morphology of skeletal muscles, including muscular fibers and the whole microstructure architecture were clearly identified. PG improved OCT imaging as measured by image quality metric Contrast Per Pixel CPP (increases by 3.9%), Naturalness Image Quality Evaluator NIQE (decreases by 23%), and Volume of Interest VOI size (higher for CPP and lower for NIQE values). The tendon microstructure was observed with less precision, as collagen fibers could not be clearly detected. The reversibility of the optical effects of the PG on the immersed tissue (in a Phosphate-Buffered Saline solution) was studied comparing native and rehydrated OCT image acquisition from a single EDL sample. Optical properties and microstructure visibility (CPP and NIQE) have been recovered to 99% of the native sample values. Moreover, clearing process caused shrinkage of the tissue recovered to 86% of the original width. Future work will aim to employ the proposed experimental protocol to identify the local mechanical properties of biological tissues.

High-resolution polarization-sensitive optical coherence tomography for zebrafish muscle imaging

Zebrafish are an important animal model, whose structure and function information can be used to study development, pathologic changes and genetic mutations. However, limited by the penetration depth, the available optical methods are difficult to image the whole-body zebrafish in juvenile and adult stages. Based on a home-made high-resolution polarization-sensitive optical coherence tomography (PS-OCT) system, we finished in vivo volumetric imaging for zebrafish, and various muscles can be clearly discerned by scanning from dorsal, ventral, and lateral directions. Besides structure information, polarization properties extracted from PS-OCT images provide abundant function information to distinguish different muscles. Furthermore, we found local retardation and local optic axis of zebrafish muscle are related to their composition and fiber orientation. We think high-resolution PS-OCT will be a promising tool in studying myopathy models of zebrafish.

Temporal dynamics of muscle optical properties during degeneration and regeneration in a canine muscle xenograft model

We studied time-dependent changes in muscle optical properties during degeneration and regeneration using polarization-sensitive optical coherence tomography (PSOCT). Excised canine muscle transplants in a xenograft mouse model were imaged ex vivo from 3- to 112-day post-transplantation. PSOCT images were quantified to evaluate post-transplantation changes of three optical/structural properties: attenuation, birefringence and fiber alignment. The birefringence and fiber alignment decreased after transplantation until 20∼30-day and recovered thereafter. The attenuation coefficient showed a reversed trend over the same period of time. These results suggest that optical properties could be used for monitoring skeletal muscle degeneration and regeneration.

High-resolution 3D tractography of fibrous tissue based on polarization-sensitive optical coherence tomography

Fibrous tissues play important roles in many parts of the body. Their highly organized directional structure is essential in achieving their normal biomechanical and physiological functions. Disruption of the typical fiber organization in these tissues is often linked to pathological changes and disease progression. Tractography is a specialized imaging method that can reveal the detailed fiber architecture. Here, we review recent developments in high-resolution optical tractography using Jones matrix polarization-sensitive optical coherence tomography. We also illustrate the use of this new tractography technology for visualizing depth-resolved, three-dimensional fibrous structures and quantifying tissue damages in several major fibrous tissues.

Polarized reflectance from articular cartilage depends upon superficial zone collagen network microstructure

Polarized reflectance from articular cartilage involves light scattering dependent on surface features, sub-surface optical properties, and collagen birefringence. To understand how surface roughness, zonal collagen microstructure, and chondrocyte organization contribute to polarized reflectance signals, experiments were conducted on bovine cartilage explants and osteochondral cores to compare polarized reflectance texture with split lines and relate these signals to cartilage zonal features and chondrocyte distribution. Texture parameter sensitivity to articular surface damage was determined from polarized reflectance maps and optimized to detect surface damage. Results indicate that polarized reflectance texture predominantly derives from the superficial zone collagen network, while the parameter average value also depends on surface roughness and total cartilage thickness.

"Of Mice and Measures": A Project to Improve How We Advance Duchenne Muscular Dystrophy Therapies to the Clinic

A new line of dystrophic mdx mice on the DBA/2J (D2) background has emerged as a candidate to study the efficacy of therapeutic approaches for Duchenne muscular dystrophy (DMD). These mice harbor genetic polymorphisms that appear to increase the severity of the dystropathology, with disease modifiers that also occur in DMD patients, making them attractive for efficacy studies and drug development. This workshop aimed at collecting and consolidating available data on the pathological features and the natural history of these new D2/mdx mice, for comparison with classic mdx mice and controls, and to identify gaps in information and their potential value. The overall aim is to establish guidance on how to best use the D2/mdx mouse model in preclinical studies.

Robust reconstruction of local optic axis orientation with fiber-based polarization-sensitive optical coherence tomography

It is challenging to recover local optic axis orientation from samples probed with fiber-based polarization-sensitive optical coherence tomography (PS-OCT). In addition to the effect of preceding tissue layers, the transmission through fiber and system elements, and imperfect system alignment, need to be compensated. Here, we present a method to retrieve the required correction factors from measurements with depth-multiplexed PS-OCT, which accurately measures the full Jones matrix. The correction considers both retardation and diattenuation and is applied in the wavenumber domain, preserving the axial resolution of the system. The robustness of the method is validated by measuring a birefringence phantom with a misaligned system. Imaging ex-vivo lamb trachea and human bronchus demonstrates the utility of reconstructing the local optic axis orientation to assess smooth muscle, which is expected to be useful in the assessment of airway smooth muscle thickness in asthma, amongst other fiber-based applications.

Whole-body clearing, staining and screening of calcium deposits in the mdx mouse model of Duchenne muscular dystrophy

Background

Duchenne muscular dystrophy (DMD) is a fatal, X-linked genetic disorder. Although DMD is the most common form of muscular dystrophy, only two FDA-approved drugs were developed to delay its progression. In order to assess therapies for treating DMD, several murine models have recently been introduced. As the wide variety of murine models enlighten mechanisms underlying DMD pathology, the question on how to monitor the progression of the disease within the entire musculoskeletal system still remains to be answered. One considerable approach to monitor such progression is histological evaluation of calcium deposits within muscle biopsies. Although accurate, histology is limited to small tissue area and cannot be utilized to evaluate systemic progression of DMD. Therefore, we aimed to develop a methodology suitable for rapid and high-resolution screening of calcium deposits within the entire murine organism.

Methods

Procedures were performed on adult male C57BL/10-mdx and adult male C57BL mice. Animals were sacrificed, perfused, paraformaldehyde-fixed, and subjected to whole-body clearing using optimized perfusion-based CUBIC protocol. Next, cleared organisms were stained with alizarin red S to visualize calcium deposits and subjected to imaging.

Results

Study revealed presence of calcium deposits within degenerated muscles of the entire C57BL/10-mdx mouse organism. Calcified deposits were observed within skeletal muscles of the forelimb, diaphragm, lumbar region, pelvic region, and hindlimb. Calcified deposits found in quadriceps femoris, triceps brachii, and spinalis pars lumborum were characterized. Analysis of cumulative frequency distribution showed different distribution characteristics of calcified deposits in quadriceps femoris muscle in comparison to triceps brachii and spinalis pars lumborum muscles (p < 0.001) and quadriceps femoris vs spinalis pars lumborum (p < 0.001). Differences between the number of calcified deposits in selected muscles, their volume, and average volume were statistically significant.

Conclusions

In aggregate, we present new methodology to monitor calcium deposits in situ in the mouse model of Duchenne muscular dystrophy. Sample imaging with the presented setup is feasible and applicable for whole-organ/body imaging. Accompanied by the development of custom-made LSFM apparatus, it allows targeted and precise characterization of calcium deposits in cleared muscles. Hence, presented approach might be broadly utilized to monitor degree to which muscles of the entire organism are affected by the necrosis and how is it altered by the treatment or physical activity of the animal. We believe that this would be a valuable tool for studying organs alternations in a wide group of animal models of muscle dystrophy and bone-oriented diseases.

Electronic supplementary material

The online version of this article (10.1186/s13395-018-0168-8) contains supplementary material, which is available to authorized users.

Automatic quantification of microscopic heart damage in a mouse model of Duchenne muscular dystrophy using optical polarization tractography

Quantification of microscopic myocardium damage in a diseased heart is important in studying disease progression and evaluating treatment outcome. However, it is challenging to use traditional histology and existing medical imaging modalities to quantify all microscopic damages in a small animal heart. Here, a method was developed for fast visualization and quantification of focal tissue damage in the mouse heart based on the fiber alignment index of the local myofiber organization obtained in optical polarization tractography (OPT). This method was tested in freshly excised hearts of the mdx4cv mouse, a commonly used mouse model for studying Duchenne cardiomyopathy. The hearts of age-matched C57BL/6 mice were also imaged as the normal controls. The results revealed a significant amount of damage in the mdx4cv hearts. Histology comparisons confirmed the damage identified by OPT. This fast and automatic method may greatly enhance preclinical studies in murine models of heart diseases.

Heart structural remodeling in a mouse model of Duchenne cardiomyopathy revealed using optical polarization tractography [Invited]

We investigated the heart structural remodeling in the mdx4cv mouse model of Duchenne cardiomyopathy using optical polarization tractography. Whole heart tractography was obtained in freshly dissected hearts from six mdx4cv mice. Six hearts from C57BL/6J mice were also imaged as the normal control. The mdx4cv hearts were significantly larger than the control hearts and had significantly higher between-subject variations in myofiber organization. While both strains showed classic cross-helical fiber organization in the left ventricle, the rate of the myocardial fiber orientation change across the heart wall was significantly altered in the right ventricle of the mdx4cv heart.

High resolution imaging of the fibrous microstructure in bovine common carotid artery using optical polarization tractography

The biomechanical properties of artery are primarily determined by the fibrous structures in the vessel wall. Many vascular diseases are associated with alternations in the orientation and alignment of the fibrous structure in the arterial wall. Knowledge on the structural features of the artery wall is crucial to our understanding of the biology of vascular diseases and the development of novel therapies. Optical coherence tomography (OCT) and polarization-sensitive OCT have shown great promise in imaging blood vessels due to their high resolution, fast acquisition, good imaging depth, and large field of view. However, the feasibility of using OCT based methods for imaging fiber orientation and distribution in the arterial wall has not been investigated. Here we show that the optical polarization tractography (OPT), a technology developed from Jones matrix OCT, can reveal the fiber orientation and alignment in the bovine common carotid artery. The fiber orientation and alignment data obtained in OPT provided a robust contrast marker to clearly resolve the intima and media boundary of the carotid artery wall. Optical polarization tractography can visualize fiber orientation and alignment in carotid artery.

Nondestructive imaging of fiber structure in articular cartilage using optical polarization tractography

Collagen fiber orientation plays an important role in determining the structure and function of the articular cartilage. However, there is currently a lack of nondestructive means to image the fiber orientation from the cartilage surface. The purpose of this study is to investigate whether the newly developed optical polarization tractography (OPT) can image fiber structure in articular cartilage. OPT was applied to obtain the depth-dependent fiber orientation in fresh articular cartilage samples obtained from porcine phalanges. For comparison, we also obtained collagen fiber orientation in the superficial zone of the cartilage using the established split-line method. The direction of each split-line was quantified using image processing. The orientation measured in OPT agreed well with those obtained from the split-line method. The correlation analysis of a total of 112 split-lines showed a greater than 0.9 coefficient of determination (R2) between the split-line results and OPT measurements obtained between 40 and 108???m in depth. In addition, the thickness of the superficial layer can also be assessed from the birefringence images obtained in OPT. These results support that OPT provides a nondestructive way to image the collagen fiber structure in articular cartilage. This technology may be valuable for both basic cartilage research and clinical orthopedic applications.

Mapping 3D fiber orientation in tissue using dual-angle optical polarization tractography

Optical polarization tractography (OPT) has recently been applied to map fiber organization in the heart, skeletal muscle, and arterial vessel wall with high resolution. The fiber orientation measured in OPT represents the 2D projected fiber angle in a plane that is perpendicular to the incident light. We report here a dual-angle extension of the OPT technology to measure the actual 3D fiber orientation in tissue. This method was first verified by imaging the murine extensor digitorum muscle placed at various known orientations in space. The accuracy of the method was further studied by analyzing the 3D fiber orientation of the mouse tibialis anterior muscle. Finally we showed that dual-angle OPT successfully revealed the unique 3D "arcade" fiber structure in the bovine articular cartilage.