Quantitative susceptibility mapping of articular cartilage: Ex vivo findings at multiple orientations and following different degradation treatments

Abstract

PurposeWe investigated the feasibility of quantitative susceptibility mapping (QSM) for assessing degradation of articular cartilage by measuring ex vivo bovine cartilage samples subjected to different degradative treatments. Specimens were scanned at several orientations to study if degradation affects the susceptibility anisotropy. T2*‐mapping, histological stainings, and polarized light microscopy were used as reference methods. Additionally, simulations of susceptibility in layered geometry were performed.MethodsSamples (n = 9) were harvested from the patellae of skeletally mature bovines. Three specimens served as controls, and the rest were artificially degraded. MRI was performed at 9.4T using a 3D gradient echo sequence. QSM and T2* images and depth profiles through the centers of the samples were compared with each other and the histological findings. A planar isotropic model with depth‐wise susceptibility variation was used in the simulations.ResultsA strong diamagnetic contrast was seen in the deep and calcified layers of cartilage, while T2* maps reflected the typical trilaminar structure of the collagen network. Anisotropy of susceptibility in cartilage was observed and was found to differ from the T2* anisotropy. Slight changes were observed in QSM and T2* following the degradative treatments. In simulations, anisotropy was observed.ConclusionsThe results suggest that QSM is not sensitive to cartilage proteoglycan content, but shows sensitivity to the amount of calcification and to the integrity of the collagen network, providing potential for assessing osteoarthritis. The simulations suggested that the anisotropy of susceptibility might be partially explained by the layered geometry of susceptibility in cartilage.

Diffusion tensor imaging and arterial tissue: establishing the influence of arterial tissue microstructure on fractional anisotropy, mean diffusivity and tractography

“…Despite the idealised ex vivo experimental set up, the work presented here highlights the promise for DTI metrics to yield valuable insight into arterial microstructure which could ultimately provide novel insight into diseased tissue morphologies. For example, recent in vivo studies have used quantitative susceptibility mapping to investigate gross morphological features [69][70][71] and inflammation 72 in atherosclerotic plaques, but this approach also has potential to provide markers of tissue microstructure and integrity 73 . Ideally, a combination of methods which allow for the full characterisation of the microstructure within the vessel wall would provide the insight needed to better inform the risk of atherosclerotic plaque rupture.…”

Quantitative susceptibility mapping of articular cartilage in patients with osteoarthritis at 3T

“…A previous study investigated the feasibility of QSM and ‐mapping for assessing degradation of articular cartilage by measuring ex vivo bovine cartilage samples subjected to different degradative treatments . They found that the susceptibility anisotropy of the cartilage differed from the anisotropy.…”

“…24 Other techniques such as polarized light microscopy can also be used to detect the collagen fibril orientation of knee cartilage. 34 QSM is valuable in assessing early OA, as it provides specific information on the distribution and content of collagen fibrils in cartilage. 34 We are currently investigating the ability of QSM to study the susceptibility changes of knee in aging in a large cohort, as these changes are potentially important to initiate early treatment, monitor disease progression, and follow-up of operative cartilage repair.…”

Evaluation of the Suitability of Miniature Pigs as an Animal Model of Juvenile Osteochondritis Dissecans

“…The 3D GRE datasets acquired at 9.4 T MRI were processed for quantitative susceptibility mapping (QSM) to visualize the vascular structures in the cartilage canals using an approach similar to that previously described . The QSM processing consisted of first manually creating a mask for the articular‐epiphyseal cartilage complex (AECC) using ITK‐SNAP (http://www.itksnap.org).…”

“…The 3D GRE datasets acquired at 9.4 T MRI were processed for quantitative susceptibility mapping (QSM) to visualize the vascular structures in the cartilage canals using an approach similar to that previously described. 15,[17][18][19] The QSM processing consisted of first manually creating a mask for the articular-epiphyseal cartilage complex (AECC) using ITK-SNAP (www.itksnap.org). Subsequently, the field map was calculated from the phase data in the masked region utilizing Laplacian unwrapping (cutoff frequency = 10 −10 ) 20 followed by variable-kernel sophisticated harmonic artifact reduction for phase data (V-SHARP) background field removal (the SHARP threshold was set to 0.5 and kernel radius varied between 2 and 9).…”