Abstract
To investigate the potential of quantitative susceptibility mapping (QSM) and T2* relaxation time mapping to determine mechanical and structural properties of articular cartilage via univariate and multivariate analysis. Samples were obtained from a cartilage repair study, in which surgically induced full-thickness chondral defects in the stifle joints of seven Shetland ponies caused post-traumatic osteoarthritis (14 samples). Control samples were collected from non-operated joints of three animals (6 samples). Magnetic resonance imaging (MRI) was performed at 9.4T, using a 3-D multi-echo gradient echo sequence. Biomechanical testing, digital densitometry (DD) and polarized light microscopy (PLM) were utilized as reference methods. To compare MRI parameters with reference parameters (equilibrium and dynamic moduli, proteoglycan content, collagen fiber angle and -anisotropy), depth-wise profiles of MRI parameters were acquired at the biomechanical testing locations. Partial least squares regression (PLSR) and Spearman's rank correlation were utilized in data analysis. PLSR indicated a moderate-to-strong correlation (ρ=0.49-0.66) and a moderate correlation (ρ=0.41-0.55) between the reference values and T2* relaxation time and QSM profiles, respectively (excluding superficial-only results). PLSR correlations were noticeably higher than direct correlations between bulk MRI and reference parameters. 3-D parametric surface maps revealed spatial variations in the MRI parameters between experimental and control groups. Quantitative parameters from 3-D multi-echo gradient echo MRI can be utilized to predict the properties of articular cartilage. With PLSR, especially the T2* relaxation time profile appeared to correlate with the properties of cartilage. Furthermore, the results suggest that degeneration affects the QSM-contrast in the cartilage. However, this change in contrast is not easy to quantify.
Highlights
Osteoarthritis (OA) is a progressive disease that leads to restricted mobility and severe joint pain[1,2]
To overcome the limitations set by desired imaging time and resolution, we propose the use of quantitative susceptibility and T2* relaxation time mapping (QSM and T2*, respectively) that are measurable using standard multi-echo gradient echo sequences
The collagen fiber angles in the radial zone of the experimental group were lower than in the control group and the difference between groups was highest at the locations nearby the lesions (Figs. 3 and 4), except for the proximal regions, for which no significant differences in fiber angle were observed
Summary
Osteoarthritis (OA) is a progressive disease that leads to restricted mobility and severe joint pain[1,2]. Mostly preliminary studies with limited data sets on QSM of articular cartilage have been reported.14e16 Wei et al showed that susceptibility of articular cartilage displays orientational anisotropy and that the susceptibility has depth-wise varying contrast in articular cartilage.[14] In another study, Wei et al utilized the anisotropy of susceptibility to perform collagen fiber orientation tracking using susceptibility tensor imaging.[15,17] Nyka€nen et al showed that proteoglycan loss did not affect the susceptibility in ex vivo cartilage.[16] The same study revealed that anisotropy of QSM was seemingly different from the anisotropy of T2* relaxation, which has been linked to the structural anisotropy of the collagen network in cartilage.[16,18] in a recent in vivo study, Wei et al have shown that the decrease of depth-wise variation in the susceptibility is linked to osteoarthritis in vivo.[19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
