Cryogenic contrast-enhanced microCT enables nondestructive 3D quantitative histopathology of soft biological tissues

Beneath the perforators: Unravelling fascia lata intrinsic vascular architecture using microfocus X-ray computed tomography

INTRODUCTION

The fascia lata (FL), a dense connective tissue enveloping the deep structures of the thigh, has served as an avascular scaffold for decades in reconstructive surgeries, but never as a standalone vascularized flap, because its vasculature is only described by perforating vessels coming from the lateral circumflex femoral artery without specific intrinsic vasculature. However, the demand for vascularized tissue replacements requires a thorough understanding of this inherent vascularization. Based on the anterolateral thigh (ALT) flap knowledge, this study explores the detailed quantitative vascular architecture of the FL, from the perspective of using it as a standalone vascularized flap.

MATERIAL & METHODS

High-resolution microfocus X-ray computed tomography (microCT) of Angiofil-latex injected flaps allowed us to study the specific fascial distribution of perforators. Dissections of 11 fresh-frozen lower limbs identified the main perforating arterioles. The intrinsic vascular network within the FL tissue was then analyzed using microCT.

RESULTS

The study confirmed an average of 2.5 ± 0.5 main perforating trunks giving rise to 5.6 ± 2.9 perforating arterioles per thigh. Notably, microCT revealed a distinct intrinsic vascular network within the FL tissue, with tiny arterioles of 55.39 ± 28.47 µm radius and a volumetric density of 33,347,960 ± 23,243,879 µm³ /mm². This intrinsic vasculature exhibited a high density of bifurcations (branching nodes=1.36 ± 2.26/mm²), demonstrating its potential use as a vascularized flap.

DISCUSSION

This study unveils the intrinsic vascularization of the FL, supporting its utility as a mega-thin vascularized flap in reconstructive surgery. Based on this vascular carrier, these findings also open new applications for tissue engineering and personalized medicine, toward an improvement of surgical outcomes and patient recovery.

MicroCT and contrast-enhanced microCT to study the in vivo degradation behavior and biocompatibility of candidate metallic intravascular stent materials

Biodegradable intravascular stents offer a promising alternative to permanent stents for treating atherosclerosis-related artery narrowing by potentially avoiding long-term complications. Identifying materials that degrade harmlessly and uniformly at a suitable rate is crucial. This study evaluated an advanced zinc alloy (Zn-Ag-Cu-Mn-Zr) alongside pure iron and pure zinc, using a simplified stent model of metallic wires implanted in the rat aorta. Assessments were made at 7, 24, and 84 days post-implantation using X-ray microfocus computed tomography (microCT) and contrast-enhanced microCT (CECT). For CECT, a contrast agent was chosen to provide optimal soft tissue contrast and minimal interaction with the wires. This combination of imaging techniques allowed us to evaluate degradation behavior, compare volume loss in various locations (outside the arterial lumen, inside the lumen, and encapsulated by neointima), compute degradation rates, and evaluate neointima tissue formation. Results showed that zinc and its alloy degrade less uniformly than iron, which demonstrates uniform surface degradation. The zinc alloy had a higher initial volume loss than the other materials but showed little increase over time. Neointima formation was similar for zinc and the zinc alloy, while iron provoked less tissue formation than both zinc and the reference cobalt-chromium alloy. Additionally, unlike cobalt-chromium and zinc, iron wires did not achieve consistent tissue encapsulation along their entire length, which may impair their performance. Mild inflammation was noted around zinc-based implants. Combining microCT and CECT provided 3D information on degradation uniformity, degradation products, and neointima morphometrics, highlighting the power of these imaging techniques to evaluate implant materials in a highly accurate way compared to previous 2D methods. STATEMENT OF SIGNIFICANCE: Biodegradable intravascular stents offer a promising solution to long-term complications associated with permanent stents by gradually dissolving in the body. To evaluate a novel zinc alloy (Zn-Ag-Cu-Mn-Zr) with improved mechanical properties, microstructure, and biocompatibility, we compared it to pure iron and zinc. We used advanced 3D imaging techniques, i.e., microCT and contrast-enhanced microCT, to assess the degradation behavior and the tissue response in a rat aorta model. The zinc alloy demonstrated promising properties despite less uniform degradation and mild inflammation compared to iron. Our findings highlight the superiority of 3D imaging over previously used 2D techniques in evaluating stent materials, offering critical insights into degradation processes and biocompatibility. These highly accurate measurements provide crucial information for developing improved biodegradable implants.

Cryo-X-Ray Phase Contrast Imaging Enables Combined 3D Structural Quantification and Nucleic Acid Analysis of Myocardial Biopsies

Snap-frozen biopsies serve as a valuable clinical resource of archival material for disease research, as they enable a comprehensive array of downstream analyses to be performed, including extraction and sequencing of nucleic acids. Obtaining three-dimensional (3D) structural information before multi-omics is more challenging but can potentially allow for better characterization of tissues and targeting of clinically relevant cells. Conventional histological techniques are limited in this regard due to their destructive nature and the reconstruction artifacts produced by sectioning, dehydration, and chemical processing. These limitations are particularly notable in soft tissues such as the heart. In this study, the feasibility of using synchrotron-based cryo-X-ray phase contrast imaging (cryo-X-PCI) of snap-frozen myocardial biopsies is assessed and 3D structure tensor analysis of aggregated myocytes, followed by nucleic acid (DNA and RNA) extraction and analysis. It is shown that optimal sample preparation is the key driver for successful structural and nucleic acid preservation which is unaffected by the process of cryo-X-PCI. It is proposed that cryo-X-PCI has clinical value for 3D tissue analysis of cardiac and potentially non-cardiac soft tissue biopsies before nucleic acid investigation.

2D and 3D microstructural analysis of the iliotibial tract

The fascial system has gained recognition for its integral role in connecting skin, superficial and deep fasciae, and underlying muscles. However, consensus on its microstructure depending on its topography remains elusive as well as its implications in clinical practices, such as reconstructive surgery and physiotherapy techniques. This study focuses on the iliotibial tract (ITT) implicated in the iliotibial band syndrome. The goal is to describe microstructural characteristics using classical 2D histology and cryogenic contrast-enhanced microcomputed tomography (cryo-CECT) such as the total thickness, number of layers, layer thickness, fibre orientation and tortuosity, according to the specific topography. The total thickness of the ITT varied across topographic regions, with the superior part being on average thicker but non-significantly different from the other regions. The inferior part showed heterogeneity, with the anterior region (AI) being the thinnest and the posterior one (PI) the thickest. The ITT exhibited 1-3 layers, with no significant differences among regions. Most commonly, it consisted of two layers, except for the antero-superior (AS) and antero-middle (AM) regions, which sometimes had only one layer. The posterior regions frequently had 2 or 3 layers, with the PI region having the highest mean (2.7 layers). The intermediate layer was the thickest one, varying from the AI region (0.368 mm ± 0.114) to the PI region (0.640 mm ± 0.305). The superficial layer showed regional variability, with the AS region being the thinnest. The deep layer appeared thinner than the superficial one. Fibre orientation analysis indicated that the intermediate layer mainly consisted of oblique longitudinal fibres, orientated downward and forward, while the superficial and deep layers had transversal or oblique transversal fibres. Cryo-CECT 3D observations confirmed these findings, revealing distinct orientations for different layers. Fibre tortuosity exhibited differences based on orientation. Transversal fibres (>65°) were significantly less tortuous than longitudinal fibres (<25°) and oblique intermediate fibres (25°-65°), aligning with 3D plot observations. This quantitative study highlights various microstructural characteristics of the ITT, offering insights into its regional variations. The analysis accuracy is increased due to the novel technology of cryo-CECT which emerges as a valuable tool for precise assessment of 3D fibre orientation and tortuosity. These findings contribute to a deeper understanding of the ITT structure, useful in clinical practices, such as reconstructive surgery and physiotherapy, and future research endeavours.

Synchrotron X-ray imaging of soft biological tissues - principles, applications and future prospects

Synchrotron-based tomographic phase-contrast X-ray imaging (SRµCT or SRnCT) is a versatile isotropic three-dimensional imaging technique that can be used to study biological samples spanning from single cells to human-sized specimens. SRµCT and SRnCT take advantage of the highly brilliant and coherent X-rays produced by a synchrotron light source. This enables fast data acquisition and enhanced image contrast for soft biological samples owing to the exploitation of phase contrast. In this Review, we provide an overview of the basics behind the technique, discuss its applications for biologists and provide an outlook on the future of this emerging technique for biology. We introduce the latest advances in the field, such as whole human organs imaged with micron resolution, using X-rays as a tool for virtual histology and resolving neuronal connections in the brain.

A single Angiofil-latex injection for both radiological and anatomical assessment of arterial territories in the limbs

INTRODUCTION

Postmortem evaluation of the human vascular system has a long history, with advancements ranging from dissections to modern imaging techniques like computed tomography (CT scan). This study designs a novel combination of Angiofil, a liquid radiopaque polymer, and latex, a flexible cast material, for cadaveric vascular analysis.

MATERIAL & METHODS

The aim was to synergize the advantages of both components, providing accurate radiological images and optimal dissection conditions. Three arterial territories (lateral circumflex femoral artery, profunda brachii artery, and radial artery) were injected and assessed through CT scans and dissections.

RESULTS

The Angiofil-latex mixture allowed successful visualization of the vascular networks, offering a simple, reproducible, and non-toxic approach. Quantitative assessments of the three territories, including diameters and lengths, showed comparable results between CT scan and dissection.

DISCUSSION

The technique precision and versatility make it an accessible and valuable tool for anatomical studies, potentially extending its application to MRI analyses. Overall, the Angiofil-latex combination presents a cost-effective solution for researchers, offering enhanced visibility and detailed anatomical insights for various applications, including anatomical variation studies.

Bioimaging of sense organs and the central nervous system in extant fishes and reptiles in situ: A review

Bioimaging is changing the field of sensory biology, especially for taxa that are lesser-known, rare, and logistically difficult to source. When integrated with traditional neurobiological approaches, developing an archival, digital repository of morphological images can offer the opportunity to improve our understanding of whole neural systems without the issues of surgical intervention and negate the risk of damage and artefactual interpretation. This review focuses on current approaches to bioimaging the peripheral (sense organs) and central (brain) nervous systems in extant fishes (cartilaginous and bony) and non-avian reptiles in situ. Magnetic resonance imaging (MRI), micro-computed tomography (μCT), both super-resolution track density imaging and diffusion tensor-based imaging, and a range of other new technological advances are presented, together with novel approaches in optimizing both contrast and resolution, for developing detailed neuroanatomical atlases and enhancing comparative analyses of museum specimens. For MRI, tissue preparation, including choice of fixative, impacts tissue MR responses, where both resolving power and signal-to-noise ratio improve as field strength increases. Time in fixative, concentration of contrast agent, and duration of immersion in the contrast agent can also significantly affect relaxation times, and thus image quality. For μCT, the use of contrast-enhancing stains (iodine-, non-iodine-, or nanoparticle-based) is critical, where the type of fixative used, and the concentration of stain and duration of staining time often require species-specific optimization. Advanced reconstruction algorithms to reduce noise and artifacts and post-processing techniques, such as deconvolution and filtering, are now being used to improve image quality and resolution.

Exploring contrast-enhancing staining agents for studying adipose tissue through contrast-enhanced computed tomography

Contrast-enhanced computed tomography offers a nondestructive approach to studying adipose tissue in 3D. Several contrast-enhancing staining agents (CESAs) have been explored, whereof osmium tetroxide (OsO4) is the most popular nowadays. However, due to the toxicity and volatility of the conventional OsO4, alternative CESAs with similar staining properties were desired. Hf-WD 1:2 POM and Hexabrix have proven effective for structural analysis of adipocytes using contrast-enhanced computed tomography but fail to provide chemical information. This study introduces isotonic Lugol's iodine (IL) as an alternative CESA for adipose tissue analysis, comparing its staining potential with Hf-WD 1:2 POM and Hexabrix in murine caudal vertebrae and bovine muscle tissue strips. Single and sequential staining protocols were compared to assess the maximization of information extraction from each sample. The study investigated interactions, distribution, and reactivity of iodine species towards biomolecules using simplified model systems and assesses the potential of the CESA to provide chemical information. (Bio)chemical analyses on whole tissues revealed that differences in adipocyte gray values post-IL staining were associated with chemical distinctions between bovine muscle tissue and murine caudal vertebrae. More specific, a difference in the degree of unsaturation of fatty acids was identified as a likely contributor, though not the sole determinant of gray value differences. This research sheds light on the potential of IL as a CESA, offering both structural and chemical insights into adipose tissue composition.

Analysis of 3D pathology samples using weakly supervised AI

Human tissue, which is inherently three-dimensional (3D), is traditionally examined through standard-of-care histopathology as limited two-dimensional (2D) cross-sections that can insufficiently represent the tissue due to sampling bias. To holistically characterize histomorphology, 3D imaging modalities have been developed, but clinical translation is hampered by complex manual evaluation and lack of computational platforms to distill clinical insights from large, high-resolution datasets. We present TriPath, a deep-learning platform for processing tissue volumes and efficiently predicting clinical outcomes based on 3D morphological features. Recurrence risk-stratification models were trained on prostate cancer specimens imaged with open-top light-sheet microscopy or microcomputed tomography. By comprehensively capturing 3D morphologies, 3D volume-based prognostication achieves superior performance to traditional 2D slice-based approaches, including clinical/histopathological baselines from six certified genitourinary pathologists. Incorporating greater tissue volume improves prognostic performance and mitigates risk prediction variability from sampling bias, further emphasizing the value of capturing larger extents of heterogeneous morphology.

X-Ray-Based 3D Histopathology of the Kidney Using Cryogenic Contrast-Enhanced MicroCT

The kidney's microstructure, which comprises a highly convoluted tubular and vascular network, can only be partially revealed using classical 2D histology. Considering that the kidney's microstructure is closely related to its function and is often affected by pathologies, there is a need for powerful and high-resolution 3D imaging techniques to visualize the microstructure. Here, we present how cryogenic contrast-enhanced microCT (cryo-CECT) allowed 3D visualization of glomeruli, tubuli, and vasculature. By comparing different contrast-enhancing staining agents and freezing protocols, we found that the preferred sample preparation protocol was the combination of staining with 1:2 hafnium(IV)-substituted Wells-Dawson polyoxometalate and freezing by submersion in isopentane at -78°C. This optimized protocol showed to be highly sensitive, allowing to detect small pathology-induced microstructural changes in a mouse model of mild trauma-related acute kidney injury after thorax trauma and hemorrhagic shock. In summary, we demonstrated that cryo-CECT is an effective 3D histopathological tool that allows to enhance our understanding of kidney tissue microstructure and their related function.

Collagen molecular organization preservation in human fascia lata and periosteum after tissue engineering

Large bone defect regeneration remains a major challenge for orthopedic surgeons. Tissue engineering approaches are therefore emerging in order to overcome this limitation. However, these processes can alter some of essential native tissue properties such as intermolecular crosslinks of collagen triple helices, which are known for their essential role in tissue structure and function. We assessed the persistence of extracellular matrix (ECM) properties in human fascia lata (HFL) and periosteum (HP) after tissue engineering processes such as decellularization and sterilization. Harvested from cadaveric donors (N = 3), samples from each HFL and HP were decellularized following five different chemical protocols with and without detergents (D1-D4 and D5, respectively). D1 to D4 consisted of different combinations of Triton, Sodium dodecyl sulfate and Deoxyribonuclease, while D5 is routinely used in the institutional tissue bank. Decellularized HFL tissues were further gamma-irradiated (minimum 25 kGy) in order to study the impact of sterilization on the ECM. Polarized light microscopy (PLM) was used to estimate the thickness and density of collagen fibers. Tissue hydration and content of hydroxyproline, enzymatic crosslinks, and non-enzymatic crosslinks (pentosidine) were semi-quantified with Raman spectroscopy. ELISA was also used to analyze the maintenance of the decorin (DCN), an important small leucine rich proteoglycan for fibrillogenesis. Among the decellularization protocols, detergent-free treatments tended to further disorganize HFL samples, as more thin fibers (+53.7%) and less thick ones (-32.6%) were recorded, as well as less collagen enzymatic crosslinks (-25.2%, p = 0.19) and a significant decrease of DCN (p = 0.036). GAG content was significantly reduced in both tissue types after all decellularization protocols. On the other hand, HP samples were more sensitive to the D1 detergent-based treatments, with more disrupted collagen organization and greater, though not significant loss of enzymatic crosslinks (-37.4%, p = 0.137). Irradiation of D5 HFL samples, led to a further and significant loss in the content of enzymatic crosslinks (-29.4%, p = 0.037) than what was observed with the decellularization process. Overall, the results suggest that the decellularization processes did not significantly alter the matrix. However, the addition of a gamma-irradiation is deleterious to the collagen structural integrity of the tissue.

Multimodal experimental studies of the passive mechanical behavior of human aortas: Current approaches and future directions

Cardiovascular diseases are the leading cause of death worldwide and include, among others, critical conditions of the aortic wall. Importantly, such critical conditions require effective diagnosis and treatment, which are not yet accurate enough. However, they could be significantly strengthened with predictive material models of the aortic wall. In particular, such predictive models could support surgical decisions, preoperative planning, and estimation of postoperative tissue remodeling. However, developing a predictive model requires experimental data showing both structural parameters and mechanical behavior. Such experimental data can be obtained using multimodal experiments. This review therefore discusses the current approaches to multimodal experiments. Importantly, the strength of the aortic wall is determined primarily by its passive components, i.e., mainly collagen, elastin, and proteoglycans. Therefore, this review focuses on multimodal experiments that relate the passive mechanical behavior of the human aortic wall to the structure and organization of its passive components. In particular, the multimodal experiments are classified according to the expected results. Multiple examples are provided for each experimental class and summarized with highlighted advantages and disadvantages of the method. Finally, future directions of multimodal experiments are envisioned and evaluated. STATEMENT OF SIGNIFICANCE: Multimodal experiments are innovative approaches that have gained interest very quickly, but also recently. This review presents therefore a first clear summary of groundbreaking research in the field of multimodal experiments. The benefits and limitations of various types of multimodal experiments are thoroughly discussed, and a comprehensive overview of possible results is provided. Although this review focuses on multimodal experiments performed on human aortic tissues, the methods used and described are not limited to human aortic tissues but can be extended to other soft materials.

Full-field strain distribution in hierarchical electrospun nanofibrous poly-L(lactic) acid/collagen scaffolds for tendon and ligament regeneration: A multiscale study

Regeneration of injured tendons and ligaments (T/L) is a worldwide need. In this study electrospun hierarchical scaffolds made of a poly-L (lactic) acid/collagen blend were developed reproducing all the multiscale levels of aggregation of these tissues. Scanning electron microscopy, microCT and tensile mechanical tests were carried out, including a multiscale digital volume correlation analysis to measure the full-field strain distribution of electrospun structures. The principal strains (εp1 and εp3) described the pattern of strains caused by the nanofibers rearrangement, while the deviatoric strains (εD) revealed the related internal sliding of nanofibers and bundles. The results of this study confirmed the biomimicry of such electrospun hierarchical scaffolds, paving the way to further tissue engineering and clinical applications.

Composite of bacterial cellulose and gelatin: A versatile biocompatible scaffold for tissue engineering

Synthesis of 0.4 ± 0.03 g/L per day of pure and porous bacterial cellulose (BC) scaffolds (scaffBC) and BC scaffolds modified with gelatin (scaffBC/Gel) was carried out using the Medusomyces gisevii Sa-28 bacterial strain. FT-IR spectroscopy and X-ray diffraction analysis showed that the scaffolds largely consist of crystalline cellulose I (Iα, Iß). Heating of BC with gelatin to 60 °C with subsequent lyophilization led to its modification by adsorption and binding of low-molecular fractions of gelatin and the formation of small pores between the fibers, which increased the biocompatibility and solubility of BC. The solubility of scaffBC and scaffBC/Gel was 20.8 % and 44.4 %, respectively, which enhances degradation in vivo. Light microscopy, scanning electron microscopy, and microcomputed tomography showed a uniform distribution of pores with a diameter of 100-500 μm. The chicken chorioallantoic membrane (CAM) model and subcutaneous implantation in rats confirmed low immunogenicity and intense formation of collagen fibers in both scaffolds and active germination of new blood vessels in scaffBC and scaffBC/Gel. The proliferative cellular activity of fibroblasts confirmed the safety of scaffolds. Taken together, the results obtained show that scaffBC/Gel can be used for the engineering of hard and soft tissues, which opens opportunities for further research.

Col1A-2 Mutation in Osteogenesis Imperfecta Mice Contributes to Long Bone Fragility by Modifying Cell-Matrix Organization

Osteogenesis imperfecta (OI) is a rare congenital bone dysplasia generally caused by a mutation of one of the type I collagen genes and characterized by low bone mass, numerous fractures, and bone deformities. The collagen organization and osteocyte lacuna arrangement were investigated in the long bones of 17-week-old wildtype (WT, n = 17) and osteogenesis imperfecta mice (OIM, n = 16) that is a validated model of severe human OI in order to assess their possible role in bone fragility. Fractures were counted after in vivo scanning at weeks 5, 11, and 17. Humerus, femur, and tibia diaphyses from both groups were analyzed ex vivo with pQCT, polarized and ordinary light histology, and Nano-CT. The fractures observed in the OIM were more numerous in the humerus and femur than in the tibia, whereas the quantitative bone parameters were altered in different ways among these bones. Collagen fiber organization appeared disrupted, with a lower birefringence in OIM than WT bones, whereas the osteocyte lacunae were more numerous, more spherical, and not aligned in a lamellar pattern. These modifications, which are typical of immature and less mechanically competent bone, attest to the reciprocal alteration of collagen matrix and osteocyte lacuna organization in the OIM, thereby contributing to bone fragility.

Effects of Heliotropium indicum L. on Uterine Involution and Its Underlying Mechanisms: an in vivo and in vitro Study

OBJECTIVE

To investigate the effect of Heliotropium indicum L. (H. indicum L.) on uterine involution and its underlying mechanisms in both in vivo and in vitro study.

METHODS

For in vivo studies, postpartum rats were randomly divided into 2 groups (n=24 for each): control group and treated group which were orally and daily administered with ethanolic extract of H. indicum L. (250 mg/kg body weight) until day 5 of postpartum. Uteri were collected for analysis of weight, cross-sectional area, collagen cross-sectional area, and collagen content on postpartum day 1, 3, and 5 (n=8 for each) from both groups. Blood samples were collected for hepatotoxicity and 17β-estradiol (E2) measurement. For in vitro studies, the extract effects on uterine contraction at half maximum effective concentration of 2.50 mg/mL were studied in organ bath system for at least 20 min.

RESULTS

Uterine parameters were significantly decreased after treated with extract of H. indicum L. (P<0.05). H. indicum L. extract significantly accelerated the reduction of those parameters and significantly decreased E2 (P<0.05). The extract facilitated uterine involution with no hepatotoxicity. H. indicum L. extract significantly stimulated uterine contraction (P<0.05) and synergized with oxytocin, prostaglandin and its precursor, linoleic acid. By investigating the different sequencing of the extract with the additional stimulants (added before or after), the two showed antagonistic effects, but still showed potentiated force when compared with control (without the stimulants).

CONCLUSIONS

The underlying mechanisms by which H. indicum L. facilitated uterine involution might be due to reducing E2 which induces collagenase activity, leading to decreases in uterine weight and size and stimulating uterine contraction. Our study provides new findings for future drug development for facilitating uterine involution with H. indicum L.

Internal and interfacial microstructure characterization of ice droplets on surfaces by X-ray computed tomography

HYPOTHESIS

Characterizing the microstructure of an ice/surface interface and its effect on the icephobic behavior of surfaces remains a significant challenge. Introducing X-ray Computed Tomography (XCT) can provide unprecedented insights into the internal (porosity) and interfacial structures, i.e. wetting regime, between (super)hydrophobic surfaces and ice by visualizing these optically inaccessible regions.

EXPERIMENTS

Frozen droplets with controlled volume were deposited on top of metallic and polymeric substrates with different levels of wettability. Different modes of XCT (3D and 4D) were utilized to obtain information on the internal and interfacial structure of the ice/surface system. The results were supplemented by conventional surface analysis techniques, including optical profilometry and contact angle measurements.

FINDINGS

Using XCT on ice/surface systems, the 3D and 4D (imaging with temporal resolution) structural information can be visualized. From these datasets, qualitative and quantitative results were obtained, not only for characterizing the interface but also for analyzing the entire droplet/surface system, e.g., measurement of porosity size, shape, and location. These results highlight the potential of XCT in the characterization of both droplets and substrates and proves that the technique can aid to develop hydrophobic surfaces for use as icephobic materials.

3D histopathology of stenotic aortic valve cusps using ex vivo microfocus computed tomography

Background

Calcific aortic stenosis (AS) is the most prevalent heart valve disease in developed countries. The aortic valve cusps progressively thicken and the valve does not open fully due to the presence of calcifications. In vivo imaging, usually used for diagnosis, does not allow the visualization of the microstructural changes associated with AS.

Methods

Ex vivo high-resolution microfocus computed tomography (microCT) was used to quantitatively describe the microstructure of calcified aortic valve cusps in full 3D. As case study in our work, this quantitative analysis was applied to normal-flow low-gradient severe AS (NF-LG-SAS), for which the medical prognostic is still highly debated in the current literature, and high-gradient severe AS (HG-SAS).

Results

The volume proportion of calcification, the size and number of calcified particles and their density composition was quantified. A new size-based classification considering small-sized particles that are not detected with in vivo imaging was defined for macro-, meso- and microscale calcifications. Volume and thickness of aortic valve cusps, including the complete thickness distribution, were also determined. Moreover, changes in the cusp soft tissues were also visualized with microCT and confirmed by scanning electron microscopy images of the same sample. NF-LG-SAS cusps contained lower relative amount of calcifications than HG-SAS. Moreover, the number and size of calcified objects and the volume and thickness of the cusps were also lower in NF-LG-SAS cusps than in HG-SAS.

Conclusions

The application of high-resolution ex vivo microCT to stenotic aortic valve cusps provided a quantitative description of the general structure of the cusps and of the calcifications present in the cusp soft tissues. This detailed description could help in the future to better understand the mechanisms of AS.

Anatomically and mechanically accurate scala tympani model for electrode insertion studies

The risk of insertion trauma in cochlear implantation is determined by the interplay between individual cochlear anatomy and electrode insertion mechanics. Whereas patient anatomy cannot be changed, new surgical techniques, devices for cochlear monitoring, drugs, and electrode array designs are continuously being developed and tested, to optimize the insertion mechanics and prevent trauma. Preclinical testing of these developments is a crucial step in feasibility testing and optimization for clinical application. Human cadaveric specimens allow for the best simulation of an intraoperative setting. However, their availability is limited and it is not possible to conduct repeated, controlled experiments on the same sample. A variety of artificial cochlear models have been developed for electrode insertion studies, but none of them were both anatomically and mechanically representative for surgical insertion into an individual cochlea. In this study, we developed anatomically representative models of the scala tympani for surgical insertion through the round window, based on microCT images of individual human cochleae. The models were produced in transparent material using commonly-available 3D printing technology at a desired scale. The anatomical and mechanical accuracy of the produced models was validated by comparison with human cadaveric cochleae. Mechanical evaluation was performed by recording insertion forces, counting the number of inserted electrodes and grading tactile feedback during manual insertion of a straight electrode by experienced cochlear implant surgeons. Our results demonstrated that the developed models were highly representative for the anatomy of the original cochleae and for the insertion mechanics in human cadaveric cochleae. The individual anatomy of the produced models had a significant impact on the insertion mechanics. The described models have a promising potential to accelerate preclinical development and testing of atraumatic insertion techniques, reducing the need for human cadaveric material. In addition, realistic models of the cochlea can be used for surgical training and preoperative planning of patient-tailored cochlear implantation surgery.

Human cochlear microstructures at risk of electrode insertion trauma, elucidated in 3D with contrast-enhanced microCT

Cochlear implant restores hearing loss through electrical stimulation of the hearing nerve from within the cochlea. Unfortunately, surgical implantation of this neuroprosthesis often traumatizes delicate intracochlear structures, resulting in loss of residual hearing and compromising hearing in noisy environments and appreciation of music. To avoid cochlear trauma, insertion techniques and devices have to be adjusted to the cochlear microanatomy. However, existing techniques were unable to achieve a representative visualization of the human cochlea: classical histology damages the tissues and lacks 3D perspective; standard microCT fails to resolve the cochlear soft tissues; and previously used X-ray contrast-enhancing staining agents are destructive. In this study, we overcame these limitations by performing contrast-enhanced microCT imaging (CECT) with a novel polyoxometalate staining agent Hf-WD POM. With Hf-WD POM-based CECT, we achieved nondestructive, high-resolution, simultaneous, 3D visualization of the mineralized and soft microstructures in fresh-frozen human cochleae. This enabled quantitative analysis of the true intracochlear dimensions and led to anatomical discoveries, concerning surgically-relevant microstructures: the round window membrane, the Rosenthal's canal and the secondary spiral lamina. Furthermore, we demonstrated that Hf-WD POM-based CECT enables quantitative assessment of these structures as well as their trauma.

Gold nanoparticle-enhanced X-ray microtomography of the rodent reveals region-specific cerebrospinal fluid circulation in the brain

Cerebrospinal fluid (CSF) is essential for the development and function of the central nervous system (CNS). However, the brain and its interstitium have largely been thought of as a single entity through which CSF circulates, and it is not known whether specific cell populations within the CNS preferentially interact with the CSF. Here, we develop a technique for CSF tracking, gold nanoparticle-enhanced X-ray microtomography, to achieve micrometer-scale resolution visualization of CSF circulation patterns during development. Using this method and subsequent histological analysis in rodents, we identify previously uncharacterized CSF pathways from the subarachnoid space (particularly the basal cisterns) that mediate CSF-parenchymal interactions involving 24 functional-anatomic cell groupings in the brain and spinal cord. CSF distribution to these areas is largely restricted to early development and is altered in posthemorrhagic hydrocephalus. Our study also presents particle size-dependent CSF circulation patterns through the CNS including interaction between neurons and small CSF tracers, but not large CSF tracers. These findings have implications for understanding the biological basis of normal brain development and the pathogenesis of a broad range of disease states, including hydrocephalus.

An optically-guided cochlear implant sheath for real-time monitoring of electrode insertion into the human cochlea

In cochlear implant surgery, insertion of perimodiolar electrode arrays into the scala tympani can be complicated by trauma or even accidental translocation of the electrode array within the cochlea. In patients with partial hearing loss, cochlear trauma can not only negatively affect implant performance, but also reduce residual hearing function. These events have been related to suboptimal positioning of the cochlear implant electrode array with respect to critical cochlear walls of the scala tympani (modiolar wall, osseous spiral lamina and basilar membrane). Currently, the position of the electrode array in relation to these walls cannot be assessed during the insertion and the surgeon depends on tactile feedback, which is unreliable and often comes too late. This study presents an image-guided cochlear implant device with an integrated, fiber-optic imaging probe that provides real-time feedback using optical coherence tomography during insertion into the human cochlea. This novel device enables the surgeon to accurately detect and identify the cochlear walls ahead and to adjust the insertion trajectory, avoiding collision and trauma. The functionality of this prototype has been demonstrated in a series of insertion experiments, conducted by experienced cochlear implant surgeons on fresh-frozen human cadaveric cochleae.