Contrast-enhanced CT using a cationic contrast agent enables non-destructive assessment of the biochemical and biomechanical properties of mouse tibial plateau cartilage

Iodinated gadolinium-gold nanomaterial as a multimodal contrast agent for cartilage tissue imaging

Cartilage damage, a common cause of osteoarthritis, requires medical imaging for accurate diagnosis of pathological changes. However, current instruments can acquire limited imaging information due to sensitivity and resolution issues. Therefore, multimodal imaging is considered an alternative strategy to provide valuable images and analyzes from different perspectives. Among all biomaterials, gold nanomaterials not only exhibit outstanding benefits as drug carriers, in vitro diagnostics, and radiosensitizers, but are also widely used as contrast agents, particularly for tumors. However, their potential for imaging cartilage damage is rarely discussed. In this study, we developed a versatile iodinated gadolinium-gold nanomaterial, AuNC@BSA-Gd-I, and its radiolabeled derivative, AuNC@BSA-Gd-131I, for cartilage detection. With its small size, negative charge, and multimodal capacities, the probe can penetrate damaged cartilage and be detected or visualized by computed tomography, MRI, IVIS, and gamma counter. Additionally, the multimodal imaging potential of AuNC@BSA-Gd-I was compared to current multifunctional gold nanomaterials containing similar components, including anionic AuNC@BSA, AuNC@BSA-I, and AuNC@BSA-Gd as well as cationic AuNC@CBSA. Due to their high atomic numbers and fluorescent emission, AuNC@BSA nanomaterials could provide fundamental multifunctionality for imaging. By further modifying AuNC@BSA with additional imaging materials, their application could be extended to various types of medical imaging instruments. Nonetheless, our findings showed that each of the current nanomaterials exhibited excellent abilities for imaging cartilage with their predominant imaging modalities, but their versatility was not comparable to that of AuNC@BSA-Gd-I. Thus, AuNC@BSA-Gd-I could be served as a valuable tool in multimodal imaging strategies for cartilage assessment.

Triple contrast computed tomography reveals site-specific biomechanical differences in the human knee joint-A proof of concept study

Cartilage and synovial fluid are challenging to observe separately in native computed tomography (CT). We report the use of triple contrast agent (bismuth nanoparticles [BiNPs], CA4+, and gadoteridol) to image and segment cartilage in cadaveric knee joints with a clinical CT scanner. We hypothesize that BiNPs will remain in synovial fluid while the CA4+ and gadoteridol will diffuse into cartilage, allowing (1) segmentation of cartilage, and (2) evaluation of cartilage biomechanical properties based on contrast agent concentrations. To investigate these hypotheses, triple contrast agent was injected into both knee joints of a cadaver (N = 1), imaged with a clinical CT at multiple timepoints during the contrast agent diffusion. Knee joints were extracted, imaged with micro-CT (µCT), and biomechanical properties of the cartilage surface were determined by stress-relaxation mapping. Cartilage was segmented and contrast agent concentrations (CA4+ and gadoteridol) were compared with the biomechanical properties at multiple locations (n = 185). Spearman's correlation between cartilage thickness from clinical CT and reference µCT images verifies successful and reliable segmentation. CA4+ concentration is significantly higher in femoral than in tibial cartilage at 60 min and further timepoints, which corresponds to the higher Young's modulus observed in femoral cartilage. In this pilot study, we show that (1) large BiNPs do not diffuse into cartilage, facilitating straightforward segmentation of human knee joint cartilage in a clinical setting, and (2) CA4+ concentration in cartilage reflects the biomechanical differences between femoral and tibial cartilage. Thus, the triple contrast agent CT shows potential in cartilage morphology and condition estimation in clinical CT.

Evaluation of a lanthanide nanoparticle-based contrast agent for microcomputed tomography of porous channels in subchondral bone

Osteoarthritis (OA) is a chronic joint disease that causes disability and pain. The osteochondral interface is a gradient tissue region that plays a significant role in maintaining joint health. It has been shown that during OA, increased neoangiogenesis creates porous channels at the osteochondral interface allowing the transport of molecules related to OA. Importantly, the connection between these porous channels and the early stages of OA development is still not fully understood. Microcomputed tomography (microCT) offers the ability to image the porous channels at the osteochondral interface, however, a contrast agent is necessary to delineate the different X-ray attenuations of the tissues. In this study BaYbF₅ -SiO₂ nanoparticles are synthesized and optimized as a microCT contrast agent to obtain an appropriate contrast attenuation for subsequent segmentation of structures of interest, that is, porous channels, and mouse subchondral bone. For this purpose, BaYbF₅ nanoparticles were synthesized and coated with a biocompatible silica shell (SiO₂ ). The optimized BaYbF₅ -SiO₂ 27 nm nanoparticles exhibited the highest average microCT attenuation among the biocompatible nanoparticles tested. The BaYbF₅ -SiO₂ 27 nm nanoparticles increased the mean X-ray attenuation of structures of interest, for example, porous channel models and mouse subchondral bone. The BaYbF₅ -SiO₂ contrast attenuation was steady after diffusion into mouse subchondral bone. In this study, we obtained for the first time, the average microCT attenuation of the BaYbF₅ -SiO₂ nanoparticles into porous channel models and mouse subchondral bone. In conclusion, BaYbF₅ -SiO₂ nanoparticles are a potential contrast agent for imaging porous channels at the osteochondral interface using microCT.

Contrast-enhanced micro-computed tomography of compartment and time-dependent changes in femoral cartilage and subchondral plate in a murine model of osteoarthritis

A lack of understanding of the mechanisms underlying osteoarthritis (OA) progression limits the development of effective long-term treatments. Quantitatively tracking spatiotemporal patterns of cartilage and bone degeneration is critical for assessment of more appropriately targeted OA therapies. In this study, we use contrast-enhanced micro-computed tomography (μCT) to establish a timeline of subchondral plate (SCP) and cartilage changes in the murine femur after destabilization of the medial meniscus (DMM). We performed DMM or sham surgery in 10-12-week-old male C57Bl/6J mice. Femora were imaged using μCT after 0, 2, 4, or 8 weeks. Cartilage-optimized scans were performed after immersion in contrast agent CA4+. Bone mineral density distribution (BMDD), cartilage attenuation, SCP, and cartilage thickness and volume were measured, including lateral and medial femoral condyle and patellar groove compartments. As early as 2 weeks post-DMM, cartilage thickness significantly increased and cartilage attenuation, SCP volume, and BMDD mean significantly decreased. Trends in cartilage and SCP metrics within each joint compartment reflected those seen in global measurements, and both BMDD and SCP thickness were consistently greater in the lateral and medial condyles than the patellar groove. Sham surgery also resulted in significant changes to SCP and cartilage metrics, highlighting a potential limitation of using surgical models to study tissue morphology or composition changes during OA progression. Contrast-enhanced μCT analysis is an effective tool to monitor changes in morphology and composition of cartilage, and when combined with bone-optimized μCT, can be used to assess the progression of degenerative changes after joint injury.

A microCT imaging protocol for reproducible and efficient quantitative morphometric analysis (QMA) of joint structures of the in situ mouse tibio-femoral joint

Micro-computed tomography (microCT) offers a three-dimensional (3D), high-resolution technique for the visualisation and analysis of bone microstructure. Using contrast-enhanced microCT, this capability has been expanded in recent studies to include cartilage morphometry and whole joint measures, known together as quantitative morphometric analysis (QMA). However, one of the main challenges in quantitative analysis of joint images is sensitivity to joint pose and alignment, which may influence measures related to both joint space and joint biomechanics. Thus, this study proposes a novel microCT imaging protocol for reproducible and efficient QMA of in situ mouse tibio-femoral joint. This work consists of two parts: an in situ diffusion kinetics study for a known cationic iodinated contrast agent (CA4+) for QMA of the cartilage, and a joint positioning and image processing workflow for whole joint QMA. In the diffusion kinetics study, 8 mice were injected at both of their tibio-femoral joints with distinct CA4+ concentrations and diffusion times. The mice were scanned at different time points after injection, and evaluated using attenuation and cartilage QMA measures. Results show that cartilage segmentation and QMA could be performed for CA4+ solution at a concentration of 48 mg/ml, and that reliable measurement and quantification of cartilage were achieved after 5 min of diffusion following contrast agent injection. We established the joint positioning and image processing workflow by developing a novel positioning device to control joint pose during scanning, and a spherical harmonics-based image processing workflow to ensure consistent alignment during image processing. Both legs of seven mice were scanned 10 times, 5 prior to receiving CA4+ and 5 after, and evaluated using whole joint QMA parameters. Joint QMA evaluation of the workflow showed excellent reproducibility; intraclass correlation coefficients ranged from 0.794 to 0.930, confirming that the imaging protocol enables reproducible and efficient QMA of joint structures in preclinical models, and that contrast agent injection did not cause significant alteration to the measured parameters.

Computed Tomography of Cartilage: An Exploration of Novel Cationic Bismuth Contrast Agent

Accurate diagnosis of minor cartilage injuries with delayed contrast-enhanced computed tomography (CECT) is challenging as poor diffusion and toxicity issues limit the usage of common CT contrast agents. Hence, the design of safe contrast agents with physiochemical properties suitable for fast, deep cartilage imaging is imminent. Herein, a novel cationic bismuth contrast agent (Bi-DOTAPXD) based on dodecane tetraacetic acid (DOTA) was synthesized and examined for CECT of cartilage. The complex was designed to improve diagnosis by utilising a net-positive charge for enhanced permeability through cartilage, inherent low-toxicity and high X-ray attenuation of bismuth. Osteochondral plugs (n = 12), excised from visually intact porcine articular cartilage were immersed in Bi-DOTAPXD (8 mg/mL) and Gd-DOTAPXD (10 mg/mL) contrast agents and scanned with a high-resolution microcomputed tomography scanner at multiple time-points. The mean Bi-DOTAPXD and Gd-DOTAPXD partitions at 45-min time-point were 85.7 ± 35.1 and 69.8 ± 30.2%, and the partitions correlated with the histopathological analysis of cartilage proteoglycan (PG) content (r) at 0.657 and 0.632, respectively. The time diffusion constants (τ) for Bi-DOTAPXD and Gd-DOTA were 121 and 159 min, respectively. Diffusion Bi-DOTAPXD and Gd-DOTAPXD reflected inter-sample variation in cartilage PG content. Cationic Bi-DOTAPXD may have the potential as a CT agent for the diagnosis of cartilage.

A Cationic Contrast Agent in X-ray Imaging of Articular Cartilage: Pre-Clinical Evaluation of Diffusion and Attenuation Properties

The aim of this study was the preliminary assessment of a new cationic contrast agent, the CA4+, via the analysis of spatial distribution in cartilage of ex vivo bovine samples, at micrometer and millimeter scale. Osteochondral plugs (n = 18) extracted from bovine stifle joints (n = 2) were immersed in CA4+ solution up to 26 h. Planar images were acquired at different time points, using a microCT apparatus. The CA4+ distribution in cartilage and saturation time were evaluated. Tibial plates from bovine stifle joints (n = 3) were imaged with CT, before and after 24 h-CA4+ bath immersion, at different concentrations. Afterward, potential CA4+ washout from cartilage was investigated. From microCT acquisitions, the CA4+ distribution differentiated into three distinct layers inside the cartilage, reflecting the spatial distribution of proteoglycans. After 24 h of diffusion, the iodine concentration reached in cartilage was approximately seven times that of the CA4+ bath. The resulting saturation time was 1.9 ± 0.9 h and 2.6 ± 2.9 h for femoral and tibial samples, respectively. Analysis of clinical CT acquisitions confirmed overall contrast enhancement of cartilage after 24 h immersion, observed for each CA4+ concentration. Distinct contrast enhancement was reached in different cartilage regions, depending on tissue’s local features. Incomplete but remarkable washout of cartilage was observed. CA4+ significantly improved cartilage visualization and its qualitative analysis.

Contrast solution properties and scan parameters influence the apparent diffusivity of computed tomography contrast agents in articular cartilage

The inability to detect early degenerative changes to the articular cartilage surface that commonly precede bulk osteoarthritic degradation is an obstacle to early disease detection for research or clinical diagnosis. Leveraging a known artefact that blurs tissue boundaries in clinical arthrograms, contrast agent (CA) diffusivity can be derived from computed tomography arthrography (CTa) scans. We combined experimental and computational approaches to study protocol variations that may alter the CTa-derived apparent diffusivity. In experimental studies on bovine cartilage explants, we examined how CA dilution and transport direction (absorption versus desorption) influence the apparent diffusivity of untreated and enzymatically digested cartilage. Using multiphysics simulations, we examined mechanisms underlying experimental observations and the effects of image resolution, scan interval and early scan termination. The apparent diffusivity during absorption decreased with increasing CA concentration by an amount similar to the increase induced by tissue digestion. Models indicated that osmotically-induced fluid efflux strongly contributed to the concentration effect. Simulated changes to spatial resolution, scan spacing and total scan time all influenced the apparent diffusivity, indicating the importance of consistent protocols. With careful control of imaging protocols and interpretations guided by transport models, CTa-derived diffusivity offers promise as a biomarker for early degenerative changes.

Contrast-Enhanced Micro-Computed Tomography for 3D Visualization and Quantification of Glycosaminoglycans in Different Cartilage Types

OBJECTIVE

To compare CA4+-enhanced micro-computed tomography (microCT) of bovine articular, meniscal, nasal, and auricular cartilage, each of which possesses a different extracellular matrix (ECM) composition and structure.

DESIGN

The diffusion kinetics of CA4+ in different native cartilage types were assessed over 20 hours. The feasibility of CA4+-enhanced microCT to visualize and quantify glycosaminoglycans (GAGs) in these different tissues was tested using safranin-O staining and 1,9-dimethylmethylene blue assay.

RESULTS

The diffusion kinetics of CA4+ in auricular cartilage are significantly slower compared with all other cartilage types. Total GAG content per volume correlates to microCT attenuation with an R² value of 0.79 for all cartilage types. Three-dimensional contrast-enhanced microCT images of spatial GAG distribution reflect safranin-O staining and highlight the differences in ECM structure, with heterogeneous regions with higher GAG concentrations highlighted by the contrast agent.

CONCLUSIONS

CA4+-enhanced microCT enables assessment of 3-dimensiona distribution and GAG content in different types of cartilage and has promise as an ex vivo diagnostic technique to monitor matrix development in different tissues over time as well as tissue-engineered constructs.

Influence of fixation on CA4+ contrast enhanced microCT of articular cartilage and subsequent feasibility for histological evaluation

CA4+ is a novel cationic iodinated contrast agent utilized for contrast-enhanced microCT (CECT). In this study, we compared CA4+ CECT for cartilage quantification of unfixed and neutral buffered formalin (NBF)-fixed rabbit distal femur cartilage after 8-, 24- and 30-hours of contrast agent diffusion. The stability of CA4+ binding to cartilage after PBS soak and decalcification was also investigated by CECT. We further assessed the feasibility of cartilage histology and immunohistochemistry after CA4+ CECT. Contrast-enhanced CA4+ labeled unfixed and NBF-fixed cartilage tissues facilitate articular cartilage quantification and accurate morphological assessment. The NBF fixed tissues demonstrate higher cartilage intensity and imaging characteristics distinct from subchondral bone than unfixed tissues while maintaining stable binding even after decalcification with 10% EDTA. The unfixed tissues labeled with CA4+, after CECT imaging and decalcification, are amenable to H&E, Alcian blue, and Safranin O staining, as well as Col2 immunohistochemistry. In contrast, only H&E and Alcian blue staining can be accomplished with CA4+ labeled NBF fixed cartilage, and CA4+ labeling interferes with downstream immunohistochemistry and Safranin O staining, likely due to its positive charge. In conclusion, CA4+ CECT of NBF fixed tissues provides high quality microCT cartilage images and allows for convenient quantification along with feasible downstream H&E and Alcian blue staining after decalcification. CA4+ CECT of unfixed tissues enables researchers to obtain both quantitative microCT as well as cartilage histology and immunohistochemistry data from one set of animals in a cost-, time-, and labor-efficient manner.

Cationic contrast-enhanced computed tomography distinguishes between reparative, degenerative, and healthy equine articular cartilage

Cationic contrast-enhanced computed tomography (CECT) is a quantitative imaging technique that characterizes articular cartilage, though its efficacy in differentiating repair tissue from other disease states is undetermined. We hypothesized that cationic CECT attenuation will distinguish between reparative, degenerative, and healthy equine articular cartilage and will reflect biochemical, mechanical, and histologic properties. Chondral defects were created in vivo on equine femoropatellar joint surfaces. Within defects, calcified cartilage was retained (Repair 1) or removed (Repair 2). At sacrifice, plugs were collected from within defects, and at locations bordering (adjacent site) and remote to defects along with site-matched controls. Articular cartilage was analyzed via CECT using CA4+ to assess glycosaminoglycan (GAG) content, compressive modulus (E _eq ), and International Cartilage Repair Society (ICRS) II histologic score. Comparisons of variables were made between sites using mixed model analysis and between variables with correlations. Cationic CECT attenuation was significantly lower in Repair 1 (1478 ± 333 Hounsfield units [HUs]), Repair 2 (1229 ± 191 HUs), and adjacent (2139 ± 336 HUs) sites when compared with site-matched controls (2587 ± 298, 2505 ± 184, and 2563 ± 538 HUs, respectively; all p < .0001). Cationic CECT attenuation was significantly higher at remote sites (2928 ± 420 HUs) compared with Repair 1, Repair 2, and adjacent sites (all p < .0001). Cationic CECT attenuation correlated with ICRS II score (r = .79), GAG (r = .76), and E _eq (r = .71; all p < .0001). Cationic CECT distinguishes between reparative, degenerative, and healthy articular cartilage and highly correlates with biochemical, mechanical, and histological tissue properties.

Effects of human articular cartilage constituents on simultaneous diffusion of cationic and nonionic contrast agents

Contrast-enhanced computed tomography is an emerging diagnostic technique for osteoarthritis. However, the effects of increased water content, as well as decreased collagen and proteoglycan concentrations due to cartilage degeneration, on the diffusion of cationic and nonionic agents, are not fully understood. We hypothesize that for a cationic agent, these variations increase the diffusion rate while decreasing partition, whereas, for a nonionic agent, these changes increase both the rate of diffusion and partition. Thus, we examine the diffusion of cationic and nonionic contrast agents within degraded tissue in time- and depth-dependent manners. Osteochondral plugs (N = 15, d = 8 mm) were extracted from human cadaver knee joints, immersed in a mixture of cationic CA4+ and nonionic gadoteridol contrast agents, and imaged at multiple time-points, using the dual-contrast method. Water content, and collagen and proteoglycan concentrations were determined using lyophilization, infrared spectroscopy, and digital densitometry, respectively. Superficial to mid (0%-60% depth) cartilage CA4+ partitions correlated with water content (R < -0.521, P < .05), whereas in deeper (40%-100%) cartilage, CA4+ correlated only with proteoglycans (R > 0.671, P < .01). Gadoteridol partition correlated inversely with collagen concentration (0%-100%, R < -0.514, P < .05). Cartilage degeneration substantially increased the time for CA4+ compared with healthy tissue (248 ± 171 vs 175 ± 95 minute) to reach the bone-cartilage interface, whereas for gadoteridol the time (111 ± 63 vs 179 ± 163 minute) decreased. The work clarifies the diffusion mechanisms of two different contrast agents and presents depth and time-dependent effects resulting from articular cartilage constituents. The results will inform the development of new contrast agents and optimal timing between agent administration and joint imaging.

Quantitative Evaluation of Equine Articular Cartilage Using Cationic Contrast-Enhanced Computed Tomography

OBJECTIVE

To investigate the diffusion trajectory of a cationic contrast medium (CA4+) into equine articular cartilage, and to assess normal and degenerative equine articular cartilage using cationic contrast-enhanced computed tomography (CECT).

DESIGN

In the first experiment (Exp1), equine osteochondral specimens were serially imaged with cationic CECT to establish the diffusion time constant and time to reach equilibrium in healthy articular cartilage. In a separate experiment (Exp2), articular cartilage defects were created on the femoral trochlea (defect joint) in a juvenile horse, while the opposite joint was a sham-operated control. After 7 weeks, osteochondral biopsies were collected throughout the articular surfaces of both joints. Biopsies were analyzed for cationic CECT attenuation, glycosaminoglycan (GAG) content, mechanical stiffness (Eeq), and histology. Imaging, biochemical and mechanical data were compared between defect and control joints.

RESULTS

Exp1: The mean diffusion time constant was longer for medial condyle cartilage (3.05 ± 0.1 hours) than lateral condyle cartilage (1.54 ± 0.3 hours, P = 0.04). Exp2: Cationic CECT attenuation was lower in the defect joint than the control joint (P = 0.005) and also varied by anatomic location (P = 0.045). Mean cationic CECT attenuation from the lateral trochlear ridge was lower in the defect joint than in the control joint (2223 ± 329 HU and 2667 ± 540 HU, respectively; P = 0.02). Cationic CECT attenuation was strongly correlated with both GAG (ρ = 0.79, P < 0.0001) and Eeq (ρ = 0.61, P < 0.0001).

CONCLUSIONS

The equilibration time of CA4+ into equine articular cartilage is affected by tissue volume. Quantitative cationic CECT imaging reflects the biochemical, biomechanical and histological state of normal and degenerative equine articular cartilage.

Real-Time Quantification of Cartilage Degeneration by GAG-Targeted Cationic Nanoparticles for Efficient Therapeutic Monitoring in Living Mice

One of the characterizations of degenerative cartilage disease is the progressive loss of glycosaminoglycans (GAGs). The real-time imaging method to quantify GAGs is of great significance for the biochemical analysis of cartilage and diagnosis and therapeutic monitoring of cartilage degeneration in vivo. To this end, a cationic photoacoustic (PA) contrast agent, poly-l-lysine melanin nanoparticles (PLL-MNPs), specifically targeting anionic GAGs was developed in this study to investigate whether it can image cartilage degeneration. PLL-MNP assessed GAG depletion by Chondroitinase ABC in vitro rat cartilage and intact ex vivo mouse knee joint. A papain-induced cartilage degenerative mice model was used for in vivo photoacoustic imaging (PAI). Oral cartilage supplement glucosamine sulfate was intragastrically administered for mice cartilage repair and the therapeutic efficacy was monitored by PLL-MNP-enhanced PAI. Histologic findings were used to further confirm PAI results. In vitro results revealed that the PLL-MNPs not only had a high binding ability with GAGs but also sensitively monitored GAG content changes by PAI. The PA signal was gradually weakened along with the depletion of GAGs in cartilage. Particularly, PLL-MNPs depicted the cartilage structure and the distribution of GAGs was demonstrated in PA images in ex vivo joints. Compared with the normal joint, a lower signal intensity was detected from degenerative joint at 3 weeks after papain injection, suggesting an early diagnosis of cartilage lesion by PLL-MNPs. Importantly, this PA-enhanced nanoprobe was suitable for monitoring in vivo efficacy of glucosamine sulfate, which effectively blocked cartilage degradation in a high dose manner. In vivo imaging findings correlated well with histological examinations. PLL-MNPs provided sensitive visualization of cartilage degeneration and promising monitoring of therapeutic response in living subjects.

Accelerating functional gene discovery in osteoarthritis

Osteoarthritis causes debilitating pain and disability, resulting in a considerable socioeconomic burden, yet no drugs are available that prevent disease onset or progression. Here, we develop, validate and use rapid-throughput imaging techniques to identify abnormal joint phenotypes in randomly selected mutant mice generated by the International Knockout Mouse Consortium. We identify 14 genes with functional involvement in osteoarthritis pathogenesis, including the homeobox gene Pitx1, and functionally characterize 6 candidate human osteoarthritis genes in mouse models. We demonstrate sensitivity of the methods by identifying age-related degenerative joint damage in wild-type mice. Finally, we phenotype previously generated mutant mice with an osteoarthritis-associated polymorphism in the Dio2 gene by CRISPR/Cas9 genome editing and demonstrate a protective role in disease onset with public health implications. We hope this expanding resource of mutant mice will accelerate functional gene discovery in osteoarthritis and offer drug discovery opportunities for this common, incapacitating chronic disease.

Challenges and opportunities for small volumes delivery into the skin

Each individual's skin has its own features, such as strength, elasticity, or permeability to drugs, which limits the effectiveness of one-size-fits-all approaches typically found in medical treatments. Therefore, understanding the transport mechanisms of substances across the skin is instrumental for the development of novel minimal invasive transdermal therapies. However, the large difference between transport timescales and length scales of disparate molecules needed for medical therapies makes it difficult to address fundamental questions. Thus, this lack of fundamental knowledge has limited the efficacy of bioengineering equipment and medical treatments. In this article, we provide an overview of the most important microfluidics-related transport phenomena through the skin and versatile tools to study them. Moreover, we provide a summary of challenges and opportunities faced by advanced transdermal delivery methods, such as needle-free jet injectors, microneedles, and tattooing, which could pave the way to the implementation of better therapies and new methods.

Topology of microfractures in osteonecrotic femoral heads at μCT and histology

AIM

To assess the topology of bone and cartilage microfractures in osteonecrotic femoral heads.

METHOD

Sixteen resected human femoral heads with collapsed osteonecrosis (ON, n = 11) or osteoarthritis (OA, n = 5) were imaged at μCT with 12 μ nominal resolution. Forty-seven histological sections and μCT reformats with (n = 30) or without (8 from ON and 9 from OA femoral heads) osteonecrotic lesions were obtained and divided in 2 × 2 mm segments by a superposed grid. A radiologist and a pathologist separately assessed the presence of bone and cartilage microfractures in each segment on μCT and histological images, respectively. We determined the frequency and distribution of segments with bone microfractures according to a zonal distribution. Matrix analysis was performed by using Matlab to calculate the connectivity index and long/short axis ratios of clustered segments with microfractures.

RESULTS

Segments with bone microfractures but not with cartilage microfractures were found more frequently in ON than in OA femoral heads. In the 38 matched μCT and histological images from ON femoral heads, 86%/82% of segments with cortical microfracture, 91%/96% of segments with trabecular microfractures involved ON lesions at μCT/histology. At histology, 83% of segments with cartilage microfractures involved ON lesions. In the 30 paired μCT and histological images containing necrotic lesions, the frequency of segments with trabecular microfractures in the superficial layers (55% at μCT/51% at histology) was statistically significantly higher than in the deep layer (25% P < 0.0001/35%; P = 0.0006). Clustered segments with cortical/trabecular microfractures, exclusively found in osteonecrotic lesions, had a connectivity index >2.0/20.0 and mean long/short axis ratio > 2.35/2.2, respectively.

CONCLUSION

Segments with bone microfractures predominate in necrotic lesions. Segments with trabecular microfractures form elongated clusters near the femoral head surface.

The emerging landscape of nanotheranostic-based diagnosis and therapy for osteoarthritis

Osteoarthritis (OA) is a common degenerative disease involving numerous joint tissues and cells, with a growing rate in prevalence that ultimately results in a negative social impact. Early diagnosis, OA progression monitoring and effective treatment are of significant importance in halting OA process. However, traditional imaging techniques lack sensitivity and specificity, which lead to a delay in timely clinical intervention. Additionally, current treatments only slow the progression of OA but have not meet the largely medical need for disease-modifying therapy. In order to overcome the above-mentioned problems and improve clinical efficacy, nanotheranostics has been proposed on OA remedy, which has confirmed success in animal models. In this review, different imaging targets-based nanoprobe for early and timely OA diagnosis is first discussed. Second, therapeutic strategies delivered by nanosystem are summarized as much as possible. Their advantages and the potential for clinical translation are detailed discussed. Third, nanomedicine simultaneously combined with the imaging for OA treatment is introduced. Nanotheranostics dynamically tracked the OA treatment outcomes to timely and individually adjust therapy. Finally, future prospects and challenges of nanotechnology-based OA diagnosis, imaging and treatment are concluded and predicted. It is believed that nanoprobe and nanomedicine will become prospective in OA therapeutic revolution.

Contrast-enhanced micro-computed tomography of articular cartilage morphology with ioversol and iomeprol

Non-ionic, low-osmolar contrast agents (CAs) used for computed tomography, such as Optiray (ioversol) and Iomeron (iomeprol), are associated with the reduced risk of adverse reactions and toxicity in comparison with ionic CAs, such as Hexabrix. Hexabrix has previously been used for imaging articular cartilage but has been commercially discontinued. This study aimed to evaluate the efficacy of Optiray and Iomeron as alternatives for visualisation of articular cartilage in small animal joints using contrast-enhanced micro-computed tomography (CECT). For this purpose, mouse femora were immersed in different concentrations (20%-50%) of Optiray 350 or Iomeron 350 for periods of time starting at five minutes. The femoral condyles were scanned ex vivo using CECT, and regions of articular cartilage manually contoured to calculate mean attenuation at each time point and concentration. For both CAs, a 30% CA concentration produced a mean cartilage attenuation optimally distinct from both bone and background signal, whilst 5-min immersion times were sufficient for equilibration of CA absorption. Additionally, plugs of bovine articular cartilage were digested by chondroitinase ABC to produce a spectrum of glycosaminoglycan (GAG) content. These samples were immersed in CA and assessed for any correlation between mean attenuation and GAG content. No significant correlation was found between attenuation and cartilage GAG content for either CAs. In conclusion, Optiray and Iomeron enable high-resolution morphological assessment of articular cartilage in small animals using CECT; however, they are not indicative of GAG content.

Tracking Osteoarthritis Progress through Cationic Nanoprobe-Enhanced Photoacoustic Imaging of Cartilage

A major obstacle in osteoarthritis (OA) theranostics is the lack of a timely and accurate monitoring method. It is hypothesized that the loss of anionic glycosaminoglycans (GAGs) in articular cartilage reflects the progression of OA. Thus, this study investigated the feasibility of photoacoustic imaging (PAI) applied for monitoring the in vivo course of OA progression via GAG-targeted cationic nanoprobes. The nanoprobes were synthesized through electrostatic attraction between poly-l-Lysine and melanin (PLL-MNPs). Cartilage explants with different concentrations of GAGs incubated with PLL-MNPs to test the relationship between GAGs content and PA signal intensity. GAG activity was then evaluated in vivo in destabilization of the medial meniscus (DMM) surgically-induced mouse model. To track OA progression over time, mice were imaged consistently for 10 weeks after OA-inducing surgery. X-ray was used to verify the superiority of PAI in detecting OA. The correlation between PAI data and histologic results was also analyzed. In vitro study demonstrated the ability of PLL-MNPs in sensitively detecting different GAGs concentrations. In vivo PAI exhibited significantly lower signal intensity from OA knees compared to normal knees. More importantly, PA signal intensity showed serial reduction over the course of OA, while X-ray showed visible joint destruction until 6 weeks. A decrease in GAGs content was confirmed by histologic examinations; moreover, histologic findings were well correlated with PAI results. Therefore, using cationic nanoprobe-enhanced PAI to detect the changes in GAG contents provides sensitive and consistent visualization of OA development. This approach will further facilitate OA theranostics and clinical translation. STATEMENT OF SIGNIFICANCE: The study of in vivo monitoring osteoarthritis (OA) is of high significance to tracking the trajectory of OA development and therapeutic monitoring. Here, we developed a cartilage-targeted cationic nanoprobe, poly-l-Lysine-melanin nanoparticles (PLL-MNPs), enhancing photoacoustic imaging (PAI) to monitor the progression of OA. The in vitro study demonstrated the ability of PLL-MNPs to detect different concentrations of GAGs with high sensitivity. We found that the contents of GAGs in vivo steadily decreased from the development of OA initial-stage to the end-point of our investigation via PAI; it reflected the course of OA in living subjects with high sensitivity. These results allow for further development in various aspects of OA research. It has potential for clinical translation and has a great impact on personalized medicine.

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.

Contrast enhanced computed tomography for real-time quantification of glycosaminoglycans in cartilage tissue engineered constructs

Tissue engineering and regenerative medicine are two therapeutic strategies to treat, and to potentially cure, diseases affecting cartilaginous tissues, such as osteoarthritis and cartilage defects. Insights into the processes occurring during regeneration are essential to steer and inform development of the envisaged regenerative strategy, however tools are needed for longitudinal and quantitative monitoring of cartilage matrix components. In this study, we introduce a contrast-enhanced computed tomography (CECT)-based method using a cationic iodinated contrast agent (CA4+) for longitudinal quantification of glycosaminoglycans (GAG) in cartilage-engineered constructs. CA4+ concentration and scanning protocols were first optimized to ensure no cytotoxicity and a facile procedure with minimal radiation dose. Chondrocyte and mesenchymal stem cell pellets, containing different GAG content were generated and exposed to CA4+. The CA4+ content in the pellets, as determined by micro computed tomography, was plotted against GAG content, as measured by 1,9-dimethylmethylene blue analysis, and showed a high linear correlation. The established equation was used for longitudinal measurements of GAG content over 28 days of pellet culture. Importantly, this method did not adversely affect cell viability or chondrogenesis. Additionally, the CA4+ distribution accurately matched safranin-O staining on histological sections. Hence, we show proof-of-concept for the application of CECT, utilizing a positively charged contrast agent, for longitudinal and quantitative imaging of GAG distribution in cartilage tissue-engineered constructs. STATEMENT OF SIGNIFICANCE: Tissue engineering and regenerative medicine are promising therapeutic strategies for different joint pathologies such as cartilage defects or osteoarthritis. Currently, in vitro assessment on the quality and composition of the engineered cartilage mainly relies on destructive methods. Therefore, there is a need for the development of techniques that allow for longitudinal and quantitative imaging and monitoring of cartilage-engineered constructs. This work harnesses the electrostatic interactions between the negatively-charged glycosaminoglycans (GAGs) and a positively-charged contrast agent for longitudinal and non-destructive quantification of GAGs, providing valuable insight on GAG development and distribution in cartilage engineered constructs. Such technique can advance the development of regenerative strategies, not only by allowing continuous monitoring but also by serving as a pre-implantation screening tool.

Non-Destructive Spectroscopic Assessment of High and Low Weight Bearing Articular Cartilage Correlates with Mechanical Properties

OBJECTIVE

Autologous articular cartilage (AC) harvested for repair procedures of high weight bearing (HWB) regions of the femoral condyles is typically obtained from low weight bearing (LWB) regions, in part due to the lack of non-destructive techniques for cartilage composition assessment. Here, we demonstrate that infrared fiber optic spectroscopy can be used to non-destructively evaluate variations in compositional and mechanical properties of AC across LWB and HWB regions.

DESIGN

AC plugs (N = 72) were harvested from the patellofemoral groove of juvenile bovine stifle joints, a LWB region, and femoral condyles, a HWB region. Near-infrared (NIR) and mid-infrared (MIR) fiber optic spectra were collected from plugs, and indentation tests were performed to determine the short-term and equilibrium moduli, followed by gravimetric water and biochemical analysis.

RESULTS

LWB tissues had a significantly greater amount of water determined by NIR and gravimetric assay. The moduli generally increased in tissues from the patellofemoral groove to the condyles, with HWB condyle cartilage having significantly higher moduli. A greater amount of proteoglycan content was also found in HWB tissues, but no differences in collagen content. In addition, NIR-determined water correlated with short-term modulus and proteoglycan content (R = -0.40 and -0.31, respectively), and a multivariate model with NIR data was able to predict short-term modulus within 15% error.

CONCLUSIONS

The properties of tissues from LWB regions differ from HWB tissues and can be determined non-destructively by infrared fiber optic spectroscopy. Clinicians may be able to use this modality to assess AC prior to harvesting osteochondral grafts for focal defect repair.

Evaluation of equine articular cartilage degeneration after mechanical impact injury using cationic contrast-enhanced computed tomography

OBJECTIVE

Cationic agent contrast-enhanced computed tomography (cationic CECT) characterizes articular cartilage ex vivo, however, its capacity to detect post-traumatic injury is unknown. The study objectives were to correlate cationic CECT attenuation with biochemical, mechanical and histological properties of cartilage and morphologic computed tomography (CT) measures of bone, and to determine the ability of cationic CECT to distinguish subtly damaged from normal cartilage in an in vivo equine model.

DESIGN

Mechanical impact injury was initiated in equine femoropatellar joints in vivo to establish subtle cartilage degeneration with site-matched controls. Cationic CECT was performed in vivo (clinical) and postmortem (microCT). Articular cartilage was characterized by glycosaminoglycan (GAG) content, biochemical moduli and histological scores. Bone was characterized by volume density (BV/TV) and trabecular number (Tb.N.), thickness (Tb.Th.) and spacing (Tb.Sp.).

RESULTS

Cationic CECT attenuation (microCT) of cartilage correlated with GAG (r = 0.74, P < 0.0001), compressive modulus (E_eq) (r = 0.79, P < 0.0001) and safranin-O histological score (r = -0.66, P < 0.0001) of cartilage, and correlated with BV/TV (r = 0.37, P = 0.0005), Tb.N. (r = 0.39, P = 0.0003), Tb.Th. (r = 0.28, P = 0.0095) and Tb.Sp. (r = -0.44, P < 0.0001) of bone. Mean [95% CI] cationic CECT attenuation at the impact site (2215 [1987, 2443] Hounsfield Units [HUs]) was lower than site-matched controls (2836 [2490, 3182] HUs, P = 0.036). Clinical cationic CECT attenuation correlated with GAG (r = 0.23, P = 0.049), E_eq (r = 0.26, P = 0.025) and safranin-O histology score (r = -0.32, P = 0.0046).

CONCLUSIONS

Cationic CECT (microCT) reflects articular cartilage properties enabling segregation of subtly degenerated from healthy tissue and also reflects bone morphometric properties on CT. Cationic CECT is capable of characterizing articular cartilage in clinical scanners.

In Vivo Tracking of Tissue Engineered Constructs

To date, the fields of biomaterials science and tissue engineering have shown great promise in creating bioartificial tissues and organs for use in a variety of regenerative medicine applications. With the emergence of new technologies such as additive biomanufacturing and 3D bioprinting, increasingly complex tissue constructs are being fabricated to fulfill the desired patient-specific requirements. Fundamental to the further advancement of this field is the design and development of imaging modalities that can enable visualization of the bioengineered constructs following implantation, at adequate spatial and temporal resolution and high penetration depths. These in vivo tracking techniques should introduce minimum toxicity, disruption, and destruction to treated tissues, while generating clinically relevant signal-to-noise ratios. This article reviews the imaging techniques that are currently being adopted in both research and clinical studies to track tissue engineering scaffolds in vivo, with special attention to 3D bioprinted tissue constructs.

Contrast-Enhanced MicroCT for Virtual 3D Anatomical Pathology of Biological Tissues: A Literature Review

To date, the combination of histological sectioning, staining, and microscopic assessment of the 2D sections is still the golden standard for structural and compositional analysis of biological tissues. X-ray microfocus computed tomography (microCT) is an emerging 3D imaging technique with high potential for 3D structural analysis of biological tissues with a complex and heterogeneous 3D structure, such as the trabecular bone. However, its use has been mostly limited to mineralized tissues because of the inherently low X-ray absorption of soft tissues. To achieve sufficient X-ray attenuation, chemical compounds containing high atomic number elements that bind to soft tissues have been recently adopted as contrast agents (CAs) for contrast-enhanced microCT (CE-CT); this novel technique is very promising for quantitative "virtual" 3D anatomical pathology of both mineralized and soft biological tissues. In this paper, we provided a review of the advances in CE-CT since the very first reports on the technology to date. Perfusion CAs for in vivo imaging have not been discussed, as the focus of this review was on CAs that bind to the tissue of interest and that are, thus, used for ex vivo imaging of biological tissues. As CE-CT has mostly been applied for the characterization of musculoskeletal tissues, we have put specific emphasis on these tissues. Advantages and limitations of multiple CAs for different musculoskeletal tissues have been highlighted, and their reproducibility has been discussed. Additionally, the advantages of the "full" 3D CE-CT information have been pinpointed, and its importance for more detailed structural, spatial, and functional characterization of the tissues of interest has been shown. Finally, the remaining challenges that are still hampering a broader adoption of CE-CT have been highlighted, and suggestions have been made to move the field of CE-CT imaging one step further towards a standard accepted tool for quantitative virtual 3D anatomical pathology.

Assessment of healthy trapeziometacarpal cartilage properties using indentation testing and contrast-enhanced computed tomography

BACKGROUND

The trapeziometacarpal joint is a common site for osteoarthritis development in the hand. When osteoarthritis is present, it results in significant functional disabilities due to the broad range of activities performed by this joint. However, our understanding of osteoarthritis initiation and progression at this joint is limited because of the current lack of knowledge regarding the properties and structure of the corresponding cartilage layers. The objective of this study is to assess the morphological and mechanical properties of trapeziometacarpal cartilage via the combination of indentation testing and contrast-enhanced computed tomography. Such research may lead to the development of medical imaging-based approaches to measure cartilage properties in vivo.

METHODS

Intact first metacarpals and trapezia were extracted from 16 fresh-frozen human cadaver hands. For each specimen, load-displacement behavior was measured at 9 testing sites using a standardized indentation testing device to calculate the normal force and Young's modulus of the cartilage sub-regions. The specimens were then immersed in CA4+ contrast agent solution for 48 h and subsequently scanned with a resolution of 41 μm in a HR-pQCT scanner to measure cartilage thickness and attenuation. Finally, correlations between compressive Young's modulus and contrast-enhanced computed tomography attenuation of the cartilage were assessed.

FINDINGS

No significant difference was found in cartilage thickness between the trapezium and first metacarpal, but the comparison between articular regions showed thinner cartilage around the volar aspect of both the first metacarpal and the trapezium. The first metacarpal cartilage was stiffer than the trapezial cartilage. A significant positive correlation was observed between Young's modulus and mean contrast-enhanced CT attenuations in superficial and full-depth cartilage in both the first metacarpal and the trapezium cartilage.

INTERPRETATION

The quantitative measurements of trapeziometacarpal thickness and stiffness as well as a correlation between Young's modulus and contrast-enhanced computed tomography attenuation provides a method for the non-destructive in vivo assessment of cartilage properties, a greater understanding of thumb cartilage behavior, and a dataset for the development of more accurate computer models.

Contrast-enhanced computed tomography (CECT) attenuation is associated with stiffness of intact knee cartilage

Contrast-enhanced computed tomography (CECT) using charged contrast-agents enables quantification of cartilage glycosaminoglycan content. Since glycosaminoglycan content is a key determinant of cartilage compressive stiffness, CECT measurements have the potential to non-invasively assess cartilage stiffness. The objective of this study was to determine whether CECT attenuation, using a cationic contrast-agent (CA4+), correlates with the stiffness of intact cartilage. Six fresh femoral and six fresh tibial compartments with intact cartilage were obtained from patients undergoing total knee replacement surgery. The instantaneous stiffness was determined for 25-50 points on the surface of each compartment using an established indentation technique. The samples were then immersed in CA4+ solution for 48 h, scanned in a micro-CT scanner, and the average CECT attenuation at each indentation site was found for the superficial cartilage. A significant (p < 0.01) and positive correlation was observed between stiffness and CECT attenuation for sites from each individual cartilage surface, with correlation coefficients ranging from r = 0.37-0.57 and r = 0.48-0.69 (p < 0.01) for the tibia and femur, respectively. When data for each type of cartilage surface were pooled together, the correlation coefficients were r = 0.73 for femoral condyle data points and r = 0.49 for tibial plateau data points. CECT provided a map of cartilage stiffness across each surface, which allows regions of low stiffness to be identified. These findings support continued evaluation and development of quantitative imaging techniques to assess the functional properties of cartilage. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2641-2647, 2018.

Studying Osteoarthritis Pathogenesis in Mice

With the increasing availability and complexity of mouse models of disease, either spontaneous or induced, there is a concomitant increase in their use in the analysis of pathogenesis. Among such diseases is osteoarthritis, a debilitating disease with few treatment options. While advances in our understanding of the pathogenesis of osteoarthritis has advanced through clinical investigations and genome-wide association studies, there is still a large gap in our knowledge, hindering advances in therapy. Patient samples are available ex vivo, but these are generally in the very late stages of disease. However, with mice, we are able to induce disease at a defined time and track the progression in vivo and ex vivo, from inception to end stage, to delineate the processes involved in disease development. © 2018 by John Wiley & Sons, Inc.

Method for Segmentation of Knee Articular Cartilages Based on Contrast-Enhanced CT Images

Segmentation of contrast-enhanced computed tomography (CECT) images enables quantitative evaluation of morphology of articular cartilage as well as the significance of the lesions. Unfortunately, automatic segmentation methods for CECT images are currently lacking. Here, we introduce a semiautomated technique to segment articular cartilage from in vivo CECT images of human knee. The segmented cartilage geometries of nine knee joints, imaged using a clinical CT-scanner with an intra-articular contrast agent, were compared with manual segmentations from CT and magnetic resonance (MR) images. The Dice similarity coefficients (DSCs) between semiautomatic and manual CT segmentations were 0.79-0.83 and sensitivity and specificity values were also high (0.76-0.86). When comparing semiautomatic and manual CT segmentations, mean cartilage thicknesses agreed well (intraclass correlation coefficient = 0.85-0.93); the difference in thickness (mean ± SD) was 0.27 ± 0.03 mm. Differences in DSC, when MR segmentations were compared with manual and semiautomated CT segmentations, were statistically insignificant. Similarly, differences in volume were not statistically significant between manual and semiautomatic CT segmentations. Semiautomation decreased the segmentation time from 450 ± 190 to 42 ± 10 min per joint. The results reveal that the proposed technique is fast and reliable for segmentation of cartilage. Importantly, this is the first study presenting semiautomated segmentation of cartilage from CECT images of human knee joint with minimal user interaction.

Cationic poly-l-lysine-encapsulated melanin nanoparticles as efficient photoacoustic agents targeting to glycosaminoglycans for the early diagnosis of articular cartilage degeneration in osteoarthritis

Cartilage degeneration is the hallmark of osteoarthritis (OA) and its early diagnosis is essential for effective cartilage repair. However, until now, there was still a lack of imaging modalities that can accurately detect and evaluate cartilage degeneration in its early stage. Herein, we introduce endogenous melanin nanoparticles (MNPs) encapsulated by poly-l-lysine (PLL) as positively charged contrast agents for the accurate photoacoustic (PA) imaging of cartilage degeneration through its strong electrostatic interaction with anionic glycosaminoglycans (GAGs) in the cartilage. PLL-MNPs presented high PA intensity, photostability and biocompatibility. In vitro PAI studies showed that PLL-MNPs with a zeta potential of +32.5 ± 9.3 mV had more cartilage uptake and longer retention time than anionic MNPs, and generated a positive relationship with the GAG content in the cartilage. After administration via intra-articular injection in living mouse models, PLL-MNPs exhibited about a two-fold stronger PA signal in a normal joint (with high GAG content) than an OA joint (with low GAG content). Furthermore, the obtained PAI results provided accurate information of the GAG content distribution in the OA knee joint. Consequently, by detecting and analyzing the changes of the GAG content in OA cartilage using PAI, we can clearly distinguish early OA from late OA and monitor the therapeutic efficacy in OA after drug treatment. All PAI results were examined histologically.

Nondestructive, indirect assessment of the biomechanical properties of the rat intervertebral disc using contrast-enhanced μCT

Mechanical characterization of the intervertebral disc involves labor-intensive and destructive experimental methodology. Contrast-enhanced micro-computed tomography is a nondestructive imaging modality for high-resolution visualization and glycosaminoglycan quantification of cartilaginous tissues. The purpose of this study was to determine whether anionic and cationic contrast-enhanced micro-computed tomography of the intervertebral disc can be used to indirectly assess disc mechanical properties in an ex vivo model of disc degeneration. L3/L4 motion segments were dissected from female Lewis rats. To deplete glycosaminoglycan, samples were treated with 0 U/ml (Control) or 5 U/ml papain. Contrast-enhanced micro-computed tomography was performed following incubation in 40% Hexabrix (anionic) or 30 mg I/ml CA⁴⁺ (cationic) for 24 h (n = 10/contrast agent/digestion group). Motion segments underwent cyclic mechanical testing to determine compressive and tensile modulus, stiffness, and hysteresis. Glycosaminoglycan content was determined using the dimethylmethylene blue assay. Correlations between glycosaminoglycan content, contrast-enhanced micro-computed tomography attenuation, and mechanical properties were assessed via the Pearson correlation. The predictive accuracy of attenuation on compressive properties was assessed via repeated random sub-sampling cross validation. Papain digestion produced significant decreases in glycosaminoglycan content and corresponding differences in attenuation and mechanical properties. Attenuation correlated significantly to glycosaminoglycan content and to all compressive mechanical properties using both Hexabrix and CA⁴⁺ . Predictive linear regression models demonstrated a predictive accuracy of attenuation on compressive modulus and stiffness of 79.8-86.0%. Contrast-enhanced micro-computed tomography was highly predictive of compressive mechanical properties in an ex vivo simulation of disc degeneration and may represent an effective modality for indirectly assessing disc compressive properties. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2030-2038, 2018.

Effect of intra-articular administration of superparamagnetic iron oxide nanoparticles (SPIONs) for MRI assessment of the cartilage barrier in a large animal model

Early diagnosis of cartilage disease at a time when changes are limited to depletion of extracellular matrix components represents an important diagnostic target to reduce patient morbidity. This report is to present proof of concept for nanoparticle dependent cartilage barrier imaging in a large animal model including the use of clinical magnetic resonance imaging (MRI). Conditioned (following matrix depletion) and unconditioned porcine metacarpophalangeal cartilage was evaluated on the basis of fluorophore conjugated 30 nm and 80 nm spherical gold nanoparticle permeation and multiphoton laser scanning and bright field microscopy after autometallographic particle enhancement. Consequently, conditioned and unconditioned joints underwent MRI pre- and post-injection with 12 nm superparamagnetic iron oxide nanoparticles (SPIONs) to evaluate particle permeation in the context of matrix depletion and use of a clinical 1.5 Tesla MRI scanner. To gauge the potential pro-inflammatory effect of intra-articular nanoparticle delivery co-cultures of equine synovium and cartilage tissue were exposed to an escalating dose of SPIONs and IL-6, IL-10, IFN-γ and PGE₂ were assessed in culture media. The chemotactic potential of growth media samples was subsequently assessed in transwell migration assays on isolated equine neutrophils. Results demonstrate an increase in MRI signal following conditioning of porcine joints which suggests that nanoparticle dependent compositional cartilage imaging is feasible. Tissue culture and neutrophil migration assays highlight a dose dependent inflammatory response following SPION exposure which at the imaging dose investigated was not different from controls. The preliminary safety and imaging data support the continued investigation of nanoparticle dependent compositional cartilage imaging. To our knowledge, this is the first report in using SPIONs as intra-articular MRI contrast agent for studying cartilage barrier function, which could potentially lead to a new diagnostic technique for early detection of cartilage disease.

Murine articular cartilage morphology and compositional quantification with high resolution cationic contrast-enhanced μCT

Articular cartilage lines the load-bearing surfaces of long bones and undergoes compositional and structural degeneration during osteoarthritis progression. Contrast enhanced microcomputed tomography (μCT) is being applied to a variety of preclinical models, including the mouse, to map structural and compositional properties in 3-D. The thinness (∼30-50 μm) and high cellularity of mouse articular cartilage presents a significant imaging challenge. Our group previously showed that mouse articular cartilage and proteoglycan (PG) content can be assessed by μCT with the ioxagalate-based contrast agent Hexabrix, but the voxel size used (6 μm) was deemed to be barely adequate. The objective of the present study is to assess the utility of a novel contrast agent, CA4+, to quantify mouse articular cartilage morphology and composition with high resolution μCT imaging (3 μm voxels) and to compare the sensitivity of CA4+ and Hexabrix to detect between-group differences. While both contrast agents are iodine-based, Hexabrix is anionic and CA4+ is cationic so they interact differently with negatively charged PGs. With CA4+, a strong correlation was found between non-calcified articular cartilage thickness measurements made with histology and μCT (R²  = 0.72, p < 0.001). Cartilage degeneration-as assessed by loss in volume, thickness, and PG content-was observed in 34-week-old mice when compared to both 7- and 12-week-old mice. High measurement precision was observed with CA4+, with the coefficient of variation after repositioning and re-imaging samples equaling 2.8%, 4.5%, 7.4% and 5.9% for attenuation, thickness, volume, and PG content, respectively. Use of CA4+ allowed increased sensitivity for assessing PG content compared to Hexabrix, but had no advantage for measurement of cartilage thickness or volume. This improvement in imaging should prove useful in preclinical studies of cartilage degeneration and regeneration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2740-2748, 2017.

Application of novel targeting nanoparticles contrast agent combined with contrast-enhanced computed tomography during screening for early-phase gastric carcinoma

Gastric cancer is one of the most common human tumors worldwide. The biggest bottleneck is a lack of advanced and sensitive protocols for the diagnosis of patients with early-stage gastric cancer. Therefore, more sensitive methods of diagnosing gastric cancer are urgently required to improve survival rates. In this clinical study, contrast-enhanced computed tomography (CECT) with targeting nanoparticles contrast agent (CECT-TNCA) was used to diagnose early-stage gastric cancer. The specific-targeted tyrosine kinase inhibitors of gastric cancer, including platelet-derived growth factor receptor-β, Ret and Kit, were used as TNCAs. A total of 484 patients with suspected gastric cancer were voluntarily recruited to investigate the efficacy of CECT-TNCA in the diagnosis of patients with early-stage gastric cancer. Patients with suspected gastric cancer were subjected CT and CECT-TNCA to detect whether gastric tumors existed. TNCA was orally administered before CT and CECT-TNCA (20 min). Our diagnostic data revealed that CECT-TNCA improved sensitivity and provided a new protocol to diagnose tumors in patients with suspected gastric cancer at the early stage. In addition, imaging using CECT-TNCA enabled the visualization of tiny nodules in the gastric area. CECT-TNCA diagnosed 182 patients with suspected gastric cancer as tumor-free. CECT-TNCA confirmed gastric cancer in 302 patients. Our novel diagnosis indicated significantly (P<0.01) differential signal enhancement in the gastric nodules via CECT-TNCA compared with CT, suggesting higher accuracy and the accumulation of TNCA in tumor nodules in the stomach. Furthermore, survival rates of patients detected by early-diagnosis of CECT-TNCA were significantly higher than the mean five-year survival (P<0.01). In conclusion, our investigations demonstrate that the sensibility and accuracy of CT is improved through combination with liposome-encapsulated nanoparticle contrast agent for the diagnosis of early stage gastric cancer when compared with single CT detection. CECT-TNCA improves the accuracy of CT and diagnostic confidence in assessing mural enhancement in patients with suspected gastric cancer.

Application of autofluorescence robotic histology for quantitative evaluation of the 3-dimensional morphology of murine articular cartilage

Murine models of osteoarthritis (OA) are increasingly important for understating pathogenesis and for testing new therapeutic approaches. Their translational potential is, however, limited by the reduced size of mouse limbs which requires a much higher resolution to evaluate their articular cartilage compared to clinical imaging tools. In experimental models, this tissue has been predominantly assessed by time-consuming histopathology using standardized semi-quantitative scoring systems. This study aimed to develop a novel imaging method for 3-dimensional (3D) histology of mouse articular cartilage, using a robotic system-termed here "3D histocutter"-which automatically sections tissue samples and serially acquires fluorescence microscopy images of each section. Tibiae dissected from C57Bl/6 mice, either naïve or OA-induced by surgical destabilization of the medial meniscus (DMM), were imaged using the 3D histocutter by exploiting tissue autofluorescence. Accuracy of 3D imaging was validated by ex vivo contrast-enhanced micro-CT and sensitivity to lesion detection compared with conventional histology. Reconstructions of tibiae obtained from 3D histocutter serial sections showed an excellent agreement with contrast-enhanced micro-CT reconstructions. Furthermore, osteoarthritic features, including articular cartilage loss and osteophytes, were also visualized. An in-house developed software allowed to automatically evaluate articular cartilage morphology, eliminating the subjectivity associated to semi-quantitative scoring and considerably increasing analysis throughput. The novelty of this methodology is, not only the increased throughput in imaging and evaluating mouse articular cartilage morphology starting from conventionally embedded samples, but also the ability to add the third dimension to conventional histomorphometry which might be useful to improve disease assessment in the model.

Contrast-enhanced μCT of the intervertebral disc: A comparison of anionic and cationic contrast agents for biochemical and morphological characterization

The objective of this study was to quantify and compare the contrast-enhancing properties of the anionic contrast agent ioxaglate/Hexabrix, and cationic contrast agent CA⁴⁺ for biochemical and morphological characterization of the intervertebral disc (IVD) via μCT. Optimal contrast agent concentrations were determined by incubating rat lumbar IVDs in dilutions of Hexabrix-320 (20%, 30%, 40%, and 50%) and CA⁴⁺ (10, 20, 30, and 40 mg I/ml). μCT imaging was performed at 70 kVp, 114 μA, and 250 ms integration time, 12 μm voxel size. The kinetics of contrast enhancement were quantified with cumulative incubations for 0.5, 1, 2, 12, 16, 20, and 24 h using both agents. Agreement in morphological quantification was assessed via serial scans of the same IVDs. Correlation of attenuation to glycosaminoglycan (GAG) content was determined by enzymatic digestion of IVDs, subsequent μCT imaging, and GAG quantification via dimethylmethylene blue assay. Forty percent Hexabrix and 30 mg I/ml CA⁴⁺ were chosen as optimal concentrations. Hexabrix enabled greater delineation of the IVD from surrounding tissues, and CA⁴⁺ had the lowest uptake in surrounding soft tissue. Twenty-four hour incubation was sufficient for >99% equilibration of both agents. A high level of agreement was observed in the quantification of IVD volume (ICC = 0.951, r = 0.997) and height (ICC = 0.947, r = 0.991). Both agents exhibited strong linear correlations between μCT attenuation and GAG content (Hexabrix: r = -0.940; CA⁴⁺ : r = 0.887). Both agents enable biochemical and morphological quantification of the IVD via contrast-enhanced μCT and are effective tools for preclinical characterization. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1067-1075, 2017.

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.