Diffusion of ionic and non-ionic contrast agents in articular cartilage with increased cross-linking--contribution of steric and electrostatic effects

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.

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.

Intermolecular interactions play a role in the distribution and transport of charged contrast agents in a cartilage model

The transport and distribution of charged molecules in polyelectrolyte solutions are of both fundamental and practical importance. A practical example, which is the specific subject addressed in the present paper, is the transport and distribution of charged species into cartilage. The charged species could be a contrast agent or a drug molecule involved in diagnosis or treatment of the widespread degenerative disease osteoarthritis, which leads to degradation of articular cartilage. Associated scientific issues include the rate of transport and the equilibrium concentrations of the charged species in the cartilage and the synovial fluid. To address these questions, we present results from magnetic resonance micro-imaging experiments on a model system of articular cartilage. The experiments yield temporally and spatially resolved data on the transport of a negatively charged contrast agent (charge = -2), used in medical examinations of cartilage, into a polyelectrolyte solution, which is designed to capture the electrostatic interactions in cartilage. Also presented is a theoretical analysis of the transport where the relevant differential equations are solved using finite element techniques as well as treated with approximate analytical expressions. In the analysis, non-ideal effects are included in the treatment of the mobile species in the system. This is made possible by using results from previous Monte Carlo simulations. The results demonstrate the importance of taking non-idealities into account when data from measurements of transport of charged solutes in a system with fixed charges from biological polyelectrolytes are analyzed.

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.

Aging does not change the compressive stiffness of mandibular condylar cartilage in horses

OBJECTIVE

Aging can cause an increase in the stiffness of hyaline cartilage as a consequence of increased protein crosslinks. By induction of crosslinking, a reduction in the diffusion of solutions into the hyaline cartilage has been observed. However, there is a lack of knowledge about the effects of aging on the biophysical and biochemical properties of the temporomandibular joint (TMJ) cartilage. Hence, the aim of this study was to examine the biophysical properties (thickness, stiffness, and diffusion) of the TMJ condylar cartilage of horses of different ages and their correlation with biochemical parameters.

MATERIALS AND METHODS

We measured the compressive stiffness of the condyles, after which the diffusion of two contrast agents into cartilage was measured using Contrast Enhanced Computed Tomography technique. Furthermore, the content of water, collagen, GAG, and pentosidine was analyzed.

RESULTS

Contrary to our expectations, the stiffness of the cartilage did not change with age (modulus remained around 0.7 MPa). The diffusion of the negatively charged contrast agent (Hexabrix) also did not alter. However, the diffusion of the uncharged contrast agent (Visipaque) decreased with aging. The flux was negatively correlated with the amount of collagen and crosslink level which increased with aging. Pentosidine, collagen, and GAG were positively correlated with age whereas thickness and water content showed negative correlations.

CONCLUSION

Our data demonstrated that aging was not necessarily reflected in the biophysical properties of TMJ condylar cartilage. The combination of the changes happening due to aging resulted in different diffusive properties, depending on the nature of the solution.

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.

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.

Mechanical stiffness of TMJ condylar cartilage increases after artificial aging by ribose

OBJECTIVE

Aging is accompanied by a series of changes in mature tissues that influence their properties and functions. Collagen, as one of the main extracellular components of cartilage, becomes highly crosslinked during aging. In this study, the aim was to examine whether a correlation exists between collagen crosslinking induced by artificial aging and mechanical properties of the temporomandibular joint (TMJ) condyle. To evaluate this hypothesis, collagen crosslinks were induced using ribose incubation.

METHODS

Porcine TMJ condyles were incubated for 7 days with different concentrations of ribose. The compressive modulus and stiffness ratio (incubated versus control) was determined after loading. Glycosaminoglycan and collagen content, and the number of crosslinks were analyzed. Tissue structure was visualized by microscopy using different staining methods.

RESULTS

Concomitant with an increasing concentration of ribose, an increase of collagen crosslinks was found. The number of crosslinks increased almost 50 fold after incubation with the highest concentration of ribose. Simultaneously, the stiffness ratio of the samples showed a significant increase after incubation with the ribose. Pearson correlation analyses showed a significant positive correlation between the overall stiffness ratio and the crosslink level; the higher the number of crosslinks the higher the stiffness.

CONCLUSION

The present model, in which ribose was used to mimic certain aspects of age-related changes, can be employed as an in vitro model to study age-related mechanical changes in the TMJ condyle.

Infrared microspectroscopic determination of collagen cross-links in articular cartilage

Collagen forms an organized network in articular cartilage to give tensile stiffness to the tissue. Due to its long half-life, collagen is susceptible to cross-links caused by advanced glycation end-products. The current standard method for determination of cross-link concentrations in tissues is the destructive high-performance liquid chromatography (HPLC). The aim of this study was to analyze the cross-link concentrations nondestructively from standard unstained histological articular cartilage sections by using Fourier transform infrared (FTIR) microspectroscopy. Half of the bovine articular cartilage samples ( n = 27 ) were treated with threose to increase the collagen cross-linking while the other half ( n = 27 ) served as a control group. Partial least squares (PLS) regression with variable selection algorithms was used to predict the cross-link concentrations from the measured average FTIR spectra of the samples, and HPLC was used as the reference method for cross-link concentrations. The correlation coefficients between the PLS regression models and the biochemical reference values were r = 0.84 ( p < 0.001 ), r = 0.87 ( p < 0.001 ) and r = 0.92 ( p < 0.001 ) for hydroxylysyl pyridinoline (HP), lysyl pyridinoline (LP), and pentosidine (Pent) cross-links, respectively. The study demonstrated that FTIR microspectroscopy is a feasible method for investigating cross-link concentrations in articular cartilage.

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.

Effect of collagen cross-linking on quantitative MRI parameters of articular cartilage

OBJECTIVE

To investigate the sensitivity of quantitative magnetic resonance imaging (MRI) parameters to increase of collagen cross-linking in articular cartilage, a factor possibly contributing to the aging-related development of osteoarthritis (OA). The issue has not been widely studied although collagen cross-links may significantly affect the evaluation of cartilage imaging outcome.

DESIGN

Osteochondral samples (n = 14) were prepared from seven bovine patellae. To induce cross-linking, seven samples were incubated in threose while the other seven served as non-treated controls. The specimens were scanned at 9.4 T for T1, T1Gd (dGEMRIC), T2, adiabatic and continuous wave (CW) T1ρ, adiabatic T2ρ and T1sat relaxation times. Specimens from adjacent tissue were identically treated and used for reference to determine biomechanical properties, collagen, proteoglycan and cross-link contents, fixed charge density (FCD), collagen fibril anisotropy and water concentration of cartilage.

RESULTS

In the threose-treated sample group, cross-links (pentosidine, lysyl pyridinoline (LP)), FCD and equilibrium modulus were significantly (P < 0.05) higher as compared to the non-treated group. Threose treatment resulted in significantly greater T1Gd relaxation time constant (+26%, P < 0.05), although proteoglycan content was not altered. Adiabatic and CW-T1ρ were also significantly increased (+16%, +28%, P < 0.05) while pre-contrast T1 was significantly decreased (-10%, P < 0.05) in the threose group. T2, T2ρ and T1sat did not change significantly.

CONCLUSION

Threose treatment induced collagen cross-linking and changes in the properties of articular cartilage, which were detected by T1, T1Gd and T1ρ relaxation time constants. Cross-linking should be considered especially when interpreting the outcome of contrast-enhanced MRI in aging populations.

Transport of Iodine Is Different in Cartilage and Meniscus

Contrast enhanced computed tomography (CECT) has been proposed for diagnostics of cartilage and meniscus injuries and degeneration. As both tissues may be imaged simultaneously, CECT could provide a method for comprehensive evaluation of knee joint health. Since the composition and structure of cartilage and meniscus are different, we hypothesize that transport characteristics of anionic contrast agents also differ between the tissues. This would affect interpretation of CECT images and warrants investigation. To clarify this, we aimed to determine the transport kinematics of anionic iodine (q = -1, M = 126.9 g/mol), assumed to not be significantly affected by the steric hindrance, thus providing faster transport than large molecule contrast agents (e.g., ioxaglate). Cylindrical samples (d = 6 mm, h = 2 mm) were prepared from healthy bovine (n = 10) patella and meniscus, immersed in isotonic phosphate-buffered NaI solution (20 mgI/mL), and subsequently imaged with a micro-CT at 20 time points up to 23 h. Subsequently, normalized attenuation and contrast agent flux, as well as water, collagen, and proteoglycan (PG) contents in the tissues were determined. Normalized attenuation at equilibrium was higher (p = 0.005) in meniscus. Contrast agent flux was lower (p = 0.005) in the meniscus at 10 min, but higher (p < 0.05) between 30 and 120 min. In both tissues, contrast agent distribution at equilibrium suggested an inverse agreement with the depth-wise PG distribution. In conclusion, iodine transport into cartilage and meniscus was different, especially between the first 2 hours after the immersion. This is an important finding which should be considered during simultaneous CECT of cartilage and meniscus.

Diffusion of MRI and CT contrast agents in articular cartilage under static compression

Cartilage has a limited capacity for self-repair and focal damage can eventually lead to complete degradation of the tissue. Early diagnosis of degenerative changes in cartilage is therefore essential. Contrast agent-based computed tomography and magnetic resonance imaging provide promising tools for this purpose. However, the common assumption in clinical applications that contrast agents reach steady-state distributions within the tissue has been of questionable validity. Characterization of nonequilibrium diffusion of contrast agents rather than their equilibrium distributions may therefore be more effective for image-based cartilage assessment. Transport of contrast agent through the extracellular matrix of cartilage can be affected by tissue compression due to matrix structural and compositional changes including reduced pore size and fluid content. We therefore investigate the effects of static compression on diffusion of three common contrast agents: sodium iodide, sodium diatrizoate, and gadolinium diethylenetriamine-pentaacid (Gd-DTPA). Results showed that static compression was associated with significant decreases in diffusivities for sodium iodide and Gd-DTPA, with similar (but not significant) trends for sodium diatrizoate. Molecular mass of contrast agents affected diffusivities as the smallest one tested, sodium iodide, showed higher diffusivity than sodium diatrizoate and Gd-DTPA. Compression-associated cartilage matrix alterations such as glycosaminoglycan and fluid contents were found to correspond with variations in contrast agent diffusivities. Although decreased diffusivity was significantly correlated with increasing glycosaminoglycan content for sodium iodide and Gd-DTPA only, diffusivity significantly increased for all contrast agents by increasing fluid fraction. Because compounds based on iodine and gadolinium are commonly used for computed tomography and magnetic resonance imaging, present findings can be valuable for more accurate image-based assessment of variations in cartilage composition associated with focal injuries.

Contrast enhanced imaging of human meniscus using cone beam CT

OBJECTIVE

Meniscal injuries can lead to mechanical overloading of articular cartilage and eventually to knee osteoarthritis. The objective was to evaluate the potential of contrast enhanced computed tomography (CECT) to image contrast agent (CA) diffusion in human menisci with a clinical cone beam CT scanner.

DESIGN

Isolated human menisci (n = 26) were imaged using magnetic resonance imaging (MRI) and CECT in situ. Diffusion of anionic CA into the meniscus was imaged for up to 30 h. The results of CECT were compared with water, collagen and proteoglycan (PG) contents, biomechanical properties, age and histological and MR images of the samples.

RESULTS

Diffusion of CA required over 25 h to reach equilibrium. The CA partition (the CA concentration in the tissue divided by that in the bath) at the 40 min time point correlated significantly with that at the 30 h time point in both lateral (r = 0.706, P = 0.007) and medial (r = 0.669, P = 0.012) menisci. Furthermore, CA partition in meniscus after 30 h of diffusion agreed qualitatively with the distribution of PGs.

CONCLUSION

The cross-sectional distribution of CA was consistent with that reported in a previous μCT study on bovine meniscus. The time required to reach diffusion equilibrium was found impractical for clinical applications. However, based on the present results, shorter delay between injection and imaging (e.g., 40 min) could be feasible in clinical diagnostics of meniscal pathologies.