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Contrast diffusion into articular cartilage detected with CTa correlates with sGAG content and to a lesser extent with structural composition of cartilage ECM. CTa may be clinically applicable to quantitatively measure the quality of articular cartilage.

).q RSNA, 2015 Purpose:To determine if T1r mapping can be used as an alternative to delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) in the quantification of cartilage biochemical composition in vivo in human knees with osteoarthritis. Materials and Methods:This study was approved by the institutional review board. Written informed consent was obtained from all participants. Twelve patients with knee osteoarthritis underwent dGEMRIC and T1r mapping at 3.0 T before undergoing total knee replacement. Outcomes of dGEMRIC and T1r mapping were calculated in six cartilage regions of interest. Femoral and tibial cartilages were harvested during total knee replacement. Cartilage sulphated glycosaminoglycan (sGAG) and collagen content were assessed with dimethylmethylene blue and hydroxyproline assays, respectively. A four-dimensional multivariate mixed-effects model was used to simultaneously assess the correlation between outcomes of dGEMRIC and T1r mapping and the sGAG and collagen content of the articular cartilage. Results:T1 relaxation times at dGEMRIC showed strong correlation with cartilage sGAG content (r = 0.73; 95% credibility in- Conclusion:dGEMRIC can help accurately measure cartilage sGAG content in vivo in patients with knee osteoarthritis, whereas T1r mapping does not appear suitable for this purpose. Although the technique is not completely sGAG specific and requires a contrast agent, dGEMRIC is a validated and robust method for quantifying cartilage sGAG content in human osteoarthritis subjects in clinical research.q RSNA, 2015

ObjectivesTo evaluate the effect of automated registration in delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) of the knee on the occurrence of movement artefacts on the T1 map and the reproducibility of region-of-interest (ROI)-based measurements.MethodsEleven patients with early-stage knee osteoarthritis and ten healthy controls underwent dGEMRIC twice at 3 T. Controls underwent unenhanced imaging. ROIs were manually drawn on the femoral and tibial cartilage. T1 calculation was performed with and without registration of the T1-weighted images. Automated three-dimensional rigid registration was performed on the femur and tibia cartilage separately. Registration quality was evaluated using the square root Cramér–Rao lower bound (CRLBσ). Additionally, the reproducibility of dGEMRIC was assessed by comparing automated registration with manual slice-matching.ResultsAutomated registration of the T1-weighted images improved the T1 maps as the 90% percentile of the CRLBσ was significantly (P < 0.05) reduced with a median reduction of 55.8 ms (patients) and 112.9 ms (controls). Manual matching and automated registration of the re-imaged T1 map gave comparable intraclass correlation coefficients of respectively 0.89/0.90 (patients) and 0.85/0.85 (controls).ConclusionsRegistration in dGEMRIC reduces movement artefacts on T1 maps and provides a good alternative to manual slice-matching in longitudinal studies.Key Points• Quantitative MRI is increasingly used for biomedical assessment of knee articular cartilage• Image registration leads to more accurate quantification of cartilage quality and damage• Movement artefacts in delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) are reduced• Automated image registration successfully aligns baseline and follow-up dGEMRIC examinations• Reproducibility of dGEMRIC with registration is similar to that using manual slice-matching