MRI heterogeneity of articular cartilage in strong magnetic fields: Dependence on proteoglycan content

Abstract

Articular cartilage is a thin heterogeneous tissue (typical thickness of less than 2 mm) composed of collagen, proteoglycan, and water that coats skeletal joint surfaces. Its physical and chemical integrity are essential for maintaining normal joint articulation. MR imaging techniques are being developed to visualize articular cartilage for the purpose of assessing changes in its structure that occur with age and the onset of joint disease. Emerging high-field MR systems (greater than 4 T) have a higher signal-to-noise ratio, which can be used to improve the spatial resolution for imaging articular cartilage beyond that available in most clinical systems. In this study, we examined the effect of changing the proteoglycan content of articular cartilage on high-resolution (40 ϫ 40 ϫ 100 m) T1-and T2-weighted images acquired at 11.74 T (500 MHz for protons). Susceptibility artifacts were observed near the cartilage-bone interface that were verified by separating the cartilage from the bone. MR image heterogeneity of articular cartilage was observed as a function of depth and in the transverse directions of the sample. Enzymatic depletion of cartilage proteoglycan demonstrated that the MR image heterogeneity is due in part to variation of the proteoglycan content in different regions of the cartilage. The apparent diffusion coefficient (ADC) was measured as a function of depth in the cartilage. The ADC varied from the subchondral bone to the articular surface for both normal and digested cartilage. In addition, the ADC increased by 20% after 6 hours of enzymatic digestion of proteoglycan. These results suggest a role for high-field MRI of articular cartilage in the management and staging of osteoarthritis and other joint diseases.

Spatially-resolved nanometer-scale measurement of cartilage extracellular matrix mobility

“…In this study, the 2D SAXS pattern illustrated in Fig. 1A is elliptical rather than circular, indicating the cartilage structure is heterogeneous, which aligns with previous literature [19]. While the cartilage structure is heterogeneous, dynamic trends in both the horizontal and vertical masked data were the same; therefore, horizontally masked data were analyzed in data below (Fig 1B).…”

Histological and Radiological Assessment of Endogenously Generated Repair Tissue In Vivo Following a Chondral Harvest

“…However, MR signal can also be influenced by the extracellular matrix organization, in addition to absolute differences in water or proteoglycans. 44 Certainly, there was no notable difference in proteoglycan content as observed metachromatically in biopsies obtained from the joints with different MRI intensities for the repair tissue. In addition, as also seen with repair tissue following procedures such as ACI, the repair tissue as assessed via its microscopic morphology was variable between/within the samples, highlighting a similar level of unpredictability for the quality of natural repair achieved.…”