New Techniques in Articular Cartilage Imaging
Section snippets
Cartilage structure
Hyaline articular cartilage is a viscoelastic substance with strong imaging and biomechanical anisotropy. Articular cartilage has resilience to compression, while transmitting and distributing load, thereby reducing peak stresses on underlying subchondral bone. Joint cartilage also provides a smooth surface and lubrication, permitting the movement of opposing surfaces with minimal friction.1 Chondrocytes comprise less than 10% of the cartilage volume, with water being the most abundant
Morphologic cartilage assessment
Although many pulse sequences are suitable for evaluation of articular cartilage, it is important to remember that traditional MRI protocols, including T1- and heavily T2-weighted images, are not effective in assessing articular cartilage. Acceptable accuracy based on an arthroscopic standard and good interobserver variability has been shown using a moderate echo time fast spin-echo sequence in a study of over 600 articular surfaces and 88 patients, generating a weighted Kappa statistic of
Delayed Gadolinium-Enhanced MRI of Cartilage
The compressive strength of the proteoglycans is understood when one notes that the proteoglycan monomers, with their negatively charged glycosaminoglycans (GAG; chondroitin sulfate or keratin sulfate), radiate from a protein core. These monomers bind to hyaluronic acid to form large aggregates that resist compression due to their highly hydrophilic structure. Strategies that are sensitive to the proteoglycan component of the extracellular matrix may exploit the negative fixed-charge of the GAG
T2 Mapping
One of the strategies to assess the collagen component of articular cartilage is T2 mapping. The collagen fibers within type-1 collagen provide tensile strength due to their high ratio of length to thickness. Both intramolecular and intermolecular cross-linking provide structural rigidity to the collagen fibrils and prevent slipping and sliding between the collagen molecules. This highly ordered structure, when bound with water, provides the important network for maintaining part of the
Linking MRI to cartilage material properties
Additional focus will be placed on linking quantitative MR assessment to material properties. The in vitro study of human patellar cartilage samples by T2 mapping and dGEMRIC measures were made at both 1.5 T and 9.4 T and were then correlated with static and dynamic compressive moduli at 6 discrete anatomic locations.43 It is worth noting that statistically significant linear correlations were observed between T2 mapping and mechanical properties at clinically relevant field strength,
MRI assessment of cartilage repair
MRI provides an essential objective outcome standard to augment the information obtained from validated subjective outcome instruments, such as pain and function scores. Given the limited ability of articular cartilage to undergo primary repair, many surgical procedures have been developed to repair tissue, including marrow stimulation techniques such as microfracture, osteochondral transfer using either autologous or allograft tissue, and tissue engineered techniques, which require a matrix
Summary
Standardized MRI pulse sequences are now readily available and provide an accurate, reproducible assessment of cartilage morphology. 3D modeling techniques enable semiautomated models of the joint surface, which may eventually prove essential in templating before partial or total joint resurfacing. The addition of quantitative MRI techniques provides insights into tissue biochemistry in a noninvasive fashion, and the link to material properties may predict the functional capacity of native and
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T2 mapping of the sacroiliac joints in patients with axial spondyloarthritis
2020, European Journal of RadiologyCitation Excerpt :Over the last years, advancements in MRI technology opened new frontiers in the assessment of joint diseases. Several MRI applications such as delayed Gadolinium-Enhanced MRI of Cartilage (dGEMRIC), T1rho, T2 mapping, diffusion-weighted imaging, and diffusion tensor imaging enable evaluation of cartilage ultrastructure [18,19], potentially detecting early and subtle changes in collagen fibre architecture, local water, and proteoglycan content. T2 mapping is obtained through the measurement of T2 relaxation times of articular cartilage after the acquisition of multiple images of the same slice at multiple echoes [18].
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