Transport of Iodine Is Different in Cartilage and Meniscus

Spatial and temporal evaluation of iodine uptake and radiodensity in meniscus tissue using contrast-enhanced micro-CT

Rationale and objective

The visualization of soft tissues, like the meniscus, through X-ray micro-computed tomography (micro-CT), requires the use of contrast agents (CAs). While other studies have investigated CA diffusion in fibrocartilagineous tissues, this work aimed to optimize iodine staining protocols for meniscal tissue that improve their visualization by micro-CT. Specific objectives included evaluating the diffusion of CAs within meniscal samples over time, assessing volume changes due to staining, and identifying the iodine ions absorbed by the tissue.

Materials and methods

Water-based and PBS-based Lugol solutions (KI3) were used to stain sheep and pig menisci for 24 days. Samples were scanned using micro-CT at different time points (0, 1, 4, 8, 12, 16, 20, and 24 days) to monitor CA diffusion and volume changes. Micro-CT provided three-dimensional (3D) visualization of iodine distribution and quantification of volume changes and radiodensity in the menisci. Additionally, UV-visible spectroscopy (UV-vis) analyses were performed to determine the uptake of iodine ions by the meniscus.

Results

Results indicated volumetric shrinkage and increased radiodensity within the first days of staining, with diffusion primarily occurring from the periphery of the meniscus. UV-visible spectroscopy identified two iodide ions in the CA solution (I- and I3 -) and revealed a preferential absorption of the triiodide ion (I3 -).

Conclusion

This study demonstrated the utility of iodine-based CAs and micro-CT technique for visualizing and investigating the spatial and temporal iodine diffusion within the meniscal tissue of sheep and pigs. The findings of this study have important implications for using iodine-based CAs in imaging analyses of the meniscus and offer potentially valuable insights into the diffusion patterns of iodine in fibrocartilagineous tissues.

Global research hotspots and trends of iodinated contrast agents in medical imaging: a bibliometric and visualization analysis

Objective

This study employs bibliometric methods to explore the global research dynamics of iodine contrast agents in medical imaging. Through the visualization of knowledge maps, it presents research progress and reveals the research directions, hotspots, trends, and frontiers in this field.

Methods

Using Web of Science Core Collection database, CiteSpace and VOSviewer were employed to conduct a visual analysis of the global application of iodine contrast agents in medical imaging over the past four decades. The analysis focused on annual publication volume, collaboration networks, citation characteristics, and keywords.

Results

A total of 3,775 studies on the application of iodine contrast agents in medical imaging were included. The earliest paper was published in 1977, with a slight increase in publications from 1991 to 2004, followed by a significant rise after 2005. The United States emerged as the leading country in publication volume. Harvard University was identified as a globally influential institution with 126 publications. Although a large author collaboration cluster and several smaller ones were formed, most collaborations between authors were relatively weak, with no high-density integrated academic network yet established. Pietsch Hubertus was the most prolific author, while Bae KT was the most highly co-cited author. The most highly cited journal was Radiology, with 2,384 citations. Co-occurrence analysis revealed that the top three keywords by frequency were "agent," "CT," and "image quality." Keyword clustering analysis showed that the top three clusters were "gadolinium," "gold nanoparticles," and "image quality." The timeline analysis indicated that clusters such as "gadolinium," "gold nanoparticles," "image quality," and "material decomposition" exhibited strong temporal continuity, while the keyword with the highest burst value was "digital subtraction angiography" (19.38). Burst term trend analysis suggested that recent research has been focusing on areas like "deep learning," "risk," "radiation dosage," and "iodine quantification."

Conclusion

This study is the first to systematically reveal the global trends, hotspots, frontiers, and development dynamics of iodine contrast agents in medical imaging through the use of CiteSpace and VOSviewer. It provides a novel perspective for understanding the role of iodine contrast agents in imaging and offers valuable insights for advancing global research in medical imaging.

Optical Coherence Elastography as a Tool for Studying Deformations in Biomaterials: Spatially-Resolved Osmotic Strain Dynamics in Cartilaginous Samples

This paper presents a recently developed variant of phase-resolved Optical Coherence Elastography (OCE) enabling non-contact visualization of transient local strains of various origins in biological tissues and other materials. In this work, we demonstrate the possibilities of this new technique for studying dynamics of osmotically-induced strains in cartilaginous tissue impregnated with optical clearing agents (OCA). For poroelastic water-containing biological tissues, application of non-isotonic OCAs, various contrast additives, as well as drug solutions administration, may excite transient spatially-inhomogeneous strain fields of high magnitude in the tissue bulk, initiating mechanical and structural alterations. The range of the strain reliably observed by OCE varied from ±10-3 to ±0.4 for diluted and pure glycerol, correspondingly. The OCE-technique used made it possible to reveal previously inaccessible details of the complex spatio-temporal evolution of alternating-sign osmotic strains at the initial stages of agent diffusion. Qualitatively different effects produced by particular hydrophilic OCAs, such as glycerol and iohexol, are discussed, as well as concentration-dependent differences. Overall, the work demonstrates the unique abilities of the new OCE-modality in providing a deeper insight in real-time kinetics of osmotically-induced strains relevant to a broad range of biomedical applications.

Three-Dimensional Printing Strategies for Irregularly Shaped Cartilage Tissue Engineering: Current State and Challenges

Although there have been remarkable advances in cartilage tissue engineering, construction of irregularly shaped cartilage, including auricular, nasal, tracheal, and meniscus cartilages, remains challenging because of the difficulty in reproducing its precise structure and specific function. Among the advanced fabrication methods, three-dimensional (3D) printing technology offers great potential for achieving shape imitation and bionic performance in cartilage tissue engineering. This review discusses requirements for 3D printing of various irregularly shaped cartilage tissues, as well as selection of appropriate printing materials and seed cells. Current advances in 3D printing of irregularly shaped cartilage are also highlighted. Finally, developments in various types of cartilage tissue are described. This review is intended to provide guidance for future research in tissue engineering of irregularly shaped cartilage.

EFFECTS OF SOLUTE SIZE AND TISSUE COMPOSITION ON MOLECULAR AND MACROMOLECULAR DIFFUSIVITY IN HUMAN KNEE CARTILAGE

Objective

Articular cartilage is an avascular tissue. Accordingly, diffusivity represents a fundamental transport mechanism for nutrients and other molecular signals regulating its cell metabolism and maintenance of the extracellular matrix. Understanding how solutes spread into articular cartilage is crucial to elucidating its pathologies, and to designing treatments for repair and restoration of its extracellular matrix. As in other connective tissues, diffusivity in articular cartilage may vary depending both its composition and the specific diffusing solute. Hence, this study investigated the roles of solute size and tissue composition on molecular diffusion in knee articular cartilage.

Design

FRAP tests were conducted to measure diffusivity of five molecular probes, with size ranging from ~332Da to 70,000Da, in human knee articular cartilage. The measured diffusion coefficients were related to molecular size, as well as water and glycosaminoglycan (GAG) content of femoral and tibial condyle cartilage.

Results

Diffusivity was affected by molecular size, with the magnitude of the diffusion coefficients decreasing as the Stokes radius of the probe increased. The values of diffusion coefficients in tibial and femoral samples were not significantly different from one another, despite the fact that tibial samples exhibited significantly higher water content and lower GAG content of the femoral specimens. Water content did not affect diffusivity. In contrast, diffusivities of large molecules were sensitive to GAG content.

Conclusions

This study provides new knowledge on the mechanisms of diffusion in articular cartilage. Our findings can be leveraged to further investigate osteoarthritis and to design treatments for cartilage restoration or replacement.

dGEMRIC and CECT Comparison of Cationic and Anionic Contrast Agents in Cadaveric Human Metacarpal Cartilage

Magnetic resonance imaging (MRI) and computed tomography (CT) are widely used to image cartilage and their diagnostic capability is enhanced in the presence of contrast agents. The aim of the study is to directly compare the performance between commercial anionic MRI (Gd(DTPA), Gd2-) and CT (Ioxaglate, Iox1-) contrast agents with novel cationic MRI (Gd(DTPA)Lys2 , Gd4+) and CT (CA4+) contrast agents for assessment of cartilage mechanical and biochemical properties using the ex vivo human osteoarthritis metacarpal cartilage model. First, indentation testing was conducted to obtain the compressive modulus of the human fifth metacarpals. The samples were then immersed in the anionic and cationic contrast agents prior to delayed gadolinium-enhanced MRI of cartilage and CT scanning, respectively. The cartilage glycosaminoglycan (GAG) content and distribution were determined using the 1,9-dimethylmethylene blue assay and Safranin-O histology. Cationic agents significantly accumulate in cartilage compared with anionic agents. Significant positive correlations (p < 0.05) exist between imaging results of cationic agents and GAG content (Gd4+: R2  = 0.43; CA4+: R2  = 0.67) and indentation equilibrium modulus (Gd4+: R2  = 0.48; CA4+: R2  = 0.77). Significant negative correlations are observed between anionic MRI relaxation times, but not contrast-enhanced computed tomography attenuation and cartilage GAG content (Gd2-: R2  = 0.56, p < 0.05; Iox1-: R2  = 0.31, p > 0.05) and indentation equilibrium modulus (Gd2-: R2  = 0.38, p < 0.05; Iox1-: R2  = 0.17, p > 0.05). MRI or CT with cationic contrast agents provides greater sensitivity than their anionic analogs at assessing the biochemical and biomechanical properties of ex vivo human metacarpal cartilage. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:719-725, 2020.

Simultaneous Quantitation of Cationic and Non-ionic Contrast Agents in Articular Cartilage Using Synchrotron MicroCT Imaging

Early diagnosis of acute cartilage injuries enables monitoring of disease progression and improved treatment option planning to prevent post-traumatic osteoarthritis. In contrast-enhanced computed tomography (CECT), the changes in cationic agent diffusion within the tissue reflect cartilage degeneration. The diffusion in degenerated cartilage depends on proteoglycan (PG) content and water content, but each having an opposite effect on diffusion, thus compromising the diagnostic sensitivity. To overcome this limitation, we propose the simultaneous imaging of cationic (sensitive to PG and water contents) and non-ionic (sensitive to water content) agents. In this study, quantitative dual-energy CT (QDECT) imaging of two agents is reported for the first time at clinically feasible imaging time points. Furthermore, this is the first time synchrotron microCT with monochromatic X-rays is employed in cartilage CECT. Imaging was conducted at 1 and 2 h post contrast agent immersion. Intact, PG-depleted, and mechanically injured + PG-depleted cartilage samples (n = 33) were imaged in a mixture of cationic (iodine-based CA4+) and non-ionic (gadolinium-based gadoteridol) agents. Concurrent evaluation of CA4+ and gadoteridol partitions in cartilage is accomplished using QDECT. Subsequent normalization of the CA4+ partition with that of the gadoteridol affords CA4+ attenuations that significantly correlate with PG content – a key marker of OA.

Diffusion of charged and uncharged contrast agents in equine mandibular condylar cartilage is not affected by an increased level of sugar-induced collagen crosslinking

Nutrition of articular cartilage relies mainly on diffusion and convection of solutes through the interstitial fluid due to the lack of blood vessels. The diffusion is controlled by two factors: steric hindrance and electrostatic interactions between the solutes and the matrix components. Aging comes with changes in the cartilage structure and composition, which can influence the diffusion. In this study, we treated fibrocartilage of mandibular condyle with ribose to induce an aging-like effect by accumulating collagen crosslinks. The effect of steric hindrance or electrostatic forces on the diffusion was analyzed using either charged (Hexabrix) or uncharged (Visipaque) contrast agents. Osteochondral plugs from young equine mandibular condyles were treated with 500 mM ribose for 7 days. The effect of crosslinking on mechanical properties was then evaluated via dynamic indentation. Thereafter, the samples were exposed to contrast agents and imaged using contrast-enhanced computed tomography (CECT) at 18 different time points up to 48 h to measure their diffusion. Normalized concentration of contrast agents in the cartilage and contrast agent diffusion flux, as well as the content of crosslink level (pentosidine), water, collagen, and glycosaminoglycan (GAG) were determined. Ribose treatment significantly increased the pentosidine level (from 0.01 to 7.6 mmol/mol collagen), which resulted in an increase in tissue stiffness (~1.5 fold). Interestingly, the normalized concentration and diffusion flux did not change after the induction of an increased level of pentosidine either for Hexabrix or Visipaque. The results of this study strongly suggest that sugar-induced collagen crosslinking in TMJ condylar cartilage does not affect the diffusion properties.

Contrast-enhanced CT imaging as a non-destructive tool for ex vivo examination of the biochemical content and structure of the human meniscus

The biochemical and histopathological techniques used to investigate meniscal content and structure are destructive and time-consuming. Therefore, this study evaluated whether contrast-enhanced computed tomography (CECT) attenuation and contrast agent flux using the iodinated contrast agents CA4+ and ioxaglate correlate with the glycosaminoglycan (GAG) content/distribution and water content in human menisci. The optimal ioxaglate and CA4+ contrast agent concentrations for mapping meniscal GAG distribution were qualitatively determined by comparison of CECT color maps with Safranin-O stained histological sections. The associations between CECT attenuation and GAG content, CECT attenuation and water content, and flux and water content at various time points were determined using both contrast agents. Depth-wise analyses were also performed through each of the native surfaces to examine differences in contrast agent diffusion kinetics and equilibrium partitioning. The optimal concentrations for GAG depiction for ioxaglate and CA4+ were ≥80 and 12 mgI/ml, respectively. Using these concentrations, weak to moderate associations were found between ioxaglate attenuation and GAG content at all diffusion time points (1-48 h), while strong and significant associations were observed between CA4+ attenuation and GAG content as early as 7 h (R²  ≥ 0.67), being strongest at the equilibrium time point (48 h, R²  = 0.81). CECT attenuation for both agents did not significantly correlate with water content, but CA4+ flux correlated with water content (R²  = 0.56-0.64). CECT is a promising, non-destructive imaging technique for ex vivo assessment of meniscal GAG concentration and water content compared to traditional biochemical and histopathological methods. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1018-1028, 2017.

Cationic Contrast Agent Diffusion Differs Between Cartilage and Meniscus

Contrast enhanced computed tomography (CECT) is a non-destructive imaging technique used for the assessment of composition and structure of articular cartilage and meniscus. Due to structural and compositional differences between these tissues, diffusion and distribution of contrast agents may differ in cartilage and meniscus. The aim of this study is to determine the diffusion kinematics of a novel iodine based cationic contrast agent (CA(2+)) in cartilage and meniscus. Cylindrical cartilage and meniscus samples (d = 6 mm, h ≈ 2 mm) were harvested from healthy bovine knee joints (n = 10), immersed in isotonic cationic contrast agent (20 mgI/mL), and imaged using a micro-CT scanner at 26 time points up to 48 h. Subsequently, normalized X-ray attenuation and contrast agent diffusion flux, as well as water, collagen and proteoglycan (PG) contents in the tissues were determined. The contrast agent distributions within cartilage and meniscus were different. In addition, the normalized attenuation and diffusion flux were higher (p < 0.05) in cartilage. Based on these results, diffusion kinematics vary between cartilage and meniscus. These tissue specific variations can affect the interpretation of CECT images and should be considered when cartilage and meniscus are assessed simultaneously.