Quantitative Imaging Biomarkers of Knee Cartilage Composition

For a long time, radiography and subsequently conventional magnetic resonance imaging (MRI) were used as imaging biomarkers for evaluating cartilage morphological disease state in osteoarthritis (OA). Because research is switching its focus towards disease modification or even prevention to target OA at an early stage, imaging techniques that measure cartilage composition rather than its morphology became of interest. Several MRI and computed tomography (CT) based quantitative imaging biomarkers for cartilage composition were developed. These techniques were advocated to allow a quantitative measure of the sulphated glycosaminoglycan (sGAG) content, an important composite of the cartilage extracellular matrix. The main aims of this thesis is based have been divided between MRI and CT based quantitative imaging biomarkers since their different stage of application in research. MRI has already been applied in human OA research, whereas CT was still to be translated and implemented in clinical research. The first part of this thesis focused on MRI based techniques and aimed at optimization of image post processing, assessing reproducibility, comparison of different MRI sequences and application in clinical OA research. Since accurate image post processing is of utmost importance to generate reliable and robust quantitative MRI outcomes, an imaging post processing tool was developed and described in chapter 2. This tool corrects for intra-sequence patient motion during acquisition of quantitative MR images, by applying image registration reducing errors and incorrect outcomes. This resulted in 6-14% improvement in accuracy of delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) T1 relaxation time. Using image registration, the tool also allows assessment of the same cartilage region throughout multiple MRI acquisitions, which makes analyses less time consuming. Finally, the algorithm also involves a fitting technique which corrects for unreliable quantitative MRI biomarker data by calculating a weighted mean outcome for all voxels in a specific cartilage region based on the inaccuracy of each voxel. Because of these abilities and the fact that this tool could be used in any quantitative MRI biomarker, e.g. T1rho-mapping or T2-mapping, the image post processing tool was used in all chapters in this thesis where MRI based measures were used for cartilage sGAG content. Along with robust image processing tools, the outcomes of the MRI exam itself should also be reproducible in order to be able to apply the particular technique in cross-sectional or longitudinal study designs. Therefore, chapter 3 described a reproducibility study of dGEMRIC acquired at 3 Tesla in early stage knee OA patient. It was shown that dGEMRIC is highly reproducible in terms of results in large cartilage regions, as well as for differentiating between spatial distributions of diverse cartilage quality within a single slice. dGEMRIC can therefore be used as an imaging biomarker in cross-sectional and longitudinal study designs. In addition, a threshold for defining significant changes in dGEMRIC results for longitudinal follow-up was determined. T1rho-mapping has been proposed as a non-contrast-enhanced alternative to dGEMRIC for sGAG quantification in clinical studies. However, no thorough validation has been performed comparing both techniques within the same OA patients using a reference standard for cartilage sGAG. Therefore, in chapter 4 an in vivo comparison and validation study assessing the capability of dGEMRIC and T1rho-mapping was performed. In knee OA patients, dGEMRIC results strongly correlate with cartilage sGAG content, whereas T1rho-mapping did not. Therefore, it appears that T1rho-mapping cannot be regarded as an alternative for dGEMRIC to measure cartilage sGAG content in clinical OA research. It was also shown that resu

Quantitative in vivo CT arthrography of the human osteoarthritic knee to estimate cartilage sulphated glycosaminoglycan content: Correlation with ex-vivo reference standards

Objective: Recently, computed tomography arthrography (CTa) was introduced as quantitative imaging biomarker to estimate cartilage sulphated glycosaminoglycan (sGAG) content in human cadaveric knees. Our aim was to assess the correlation between in vivo CTa in human osteoarthritis (OA) knees and ex vivo reference standards for sGAG and collagen content. Design: In this prospective observational study 11 knee OA patients underwent CTa before total knee replacement (TKR). Cartilage X-ray attenuation was determined in six cartilage regions. Femoral and tibial cartilage specimens harvested during TKR were re-scanned using equilibrium partitioning of an ionic contrast agent with micro-CT (EPIC-μCT), which served as reference standard for sGAG. Next, cartilage sGAG and collagen content were determined using dimethylmethylene blue (DMMB) and hydroxyproline assays. The correlation between CTa X-ray attenuation, EPIC-μCT X-ray attenuation, sGAG content and collagen content was assessed. Results: CTa X-ray attenuation correlated well with EPIC-μCT (r = 0.76, 95% credibility interval (95%CI) 0.64 to 0.85). CTa correlated moderately with the DMMB assay (sGAG content) (r = -0.66, 95%CI -0.87 to -0.49) and to lesser extent with the hydroxyproline assay (collagen content) (r = -0.56, 95%CI -0.70 to -0.36). Conclusions: Outcomes of in vivo CTa in human OA knees correlate well with sGAG content. Outcomes of CTa also slightly correlate with cartilage collagen content. Since outcomes of CTa are mainly sGAG dependent and despite the fact that further validation using hyaline cartilage of other joints with different biochemical composition should be conducted, CTa may be suitable as quantitative imaging biomarker to estimate cartilage sGAG content in future clinical OA research

Quantitative subchondral bone perfusion imaging in knee osteoarthritis using dynamic contrast enhanced MRI

Objective: Subchondral bone changes, characterized by increased bone turnover and vascularity, are believed to stimulate progression and pain in knee osteoarthritis (OA). The objective of this study was to evaluate the bone perfusion in knee OA using quantitative dynamic contrast enhanced MRI (DCE-MRI). Design: Unicompartmental knee OA patients were included and underwent 3 Tesla DCE-MRI and T2-weighted MRI. Quantitative DCE-MRI analysis of Ktrans and Kep, representing perfusion parameters, was performed to evaluate differences between the most and least affected knee compartment. First, DCE-MRI parameter differences between epimetaphyseal and subchondral bone in both femur and tibia were assessed. Second, DCE-MRI parameters in subchondral bone marrow lesions (BMLs) were compared to surrounding subchondral bone without BMLs. Results: Twenty-three patients were analyzed. Median Ktrans and Kep in epimetaphyseal bone were significantly higher (p < 0.05) in the most affected (Ktrans: 0.014; Kep: 0.054 min−1) compared to least affected (Ktrans: 0.010; Kep: 0.016 min−1) compartment. For subchondral bone, DCE-MRI parameters were significantly higher (p < 0.05) in the most affected (Ktrans: 0.019; Kep: 0.091 min−1) compared to least affected (Ktrans: 0.014; Kep: 0.058 min−1) compartment as well. Subchondral BMLs detected on fat-saturated T2-weighted images were present in all patients. Median Ktrans (0.091 vs 0.000 min−1) and Kep (0.258 vs 0.000 min−1) were significantly higher within subchondral BMLs compared to surrounding subchondral bone without BMLs (p < 0.001). Conclusions: Increased perfusion parameters in epimetaphyseal bone, subchondral bone and BMLs are observed in unicompartmental knee OA. BMLs likely account for most of the effect of the higher bone perfusion in knee OA

Has the reporting quality of published randomised controlled trial protocols improved since the SPIRIT statement? A methodological study

OBJECTIVES: To determine the reporting quality of published randomised controlled trial (RCT) protocols before and after the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) statemen

T-2 mapping of the meniscus is a biomarker for early osteoarthritis

Purpose To evaluate in vivo T2 mapping as quantitative, imaging-based biomarker for meniscal degeneration in humans, by studying the correlation between T2 relaxation time and degree of histological degeneration as reference standard. Methods In this prospective validation study, 13 menisci from seven patients with radiographic knee osteoarthritis (median age 67 years, three males) were included. Menisci were obtained during total knee replacement surgery. All patients underwent preoperative magnetic resonance imaging using a 3-T MR scanner which included a T2 mapping pulse sequence with multiple echoes. Histological analysis of the collected menisci was performed using the Pauli score, involving surface integrity, cellularity, matrix organization, and staining intensity. Mean T2 relaxation times were calculated in meniscal regions of interest corresponding with the areas scored histologically, using a multi-slice multi-echo postprocessing algorithm. Correlation between T2 mapping and histology was assessed using a generalized least squares model fit by maximum likelihood. Results The mean T2 relaxation time was 22.4 ± 2.7 ms (range 18.5–27). The median histological score was 10, IQR 7–11 (range 4–13). A strong correlation between T2 relaxation time and histological score was found (rs = 0.84, CI 95% 0.64–0.93). Conclusion In vivo T2 mapping of the human meniscus correlates strongly with histological degeneration, suggesting that T2 mapping enables the detection and quantification of early compositional changes of the meniscus in knee OA

Is T1r mapping an alternative to delayed gadolinium-enhanced mr imaging of cartilage in the assessment of sulphated glycosaminoglycan content in human osteoarthritic knees? an in vivo validation study

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 interval [CI] = 0.60, 0.83) and weak correlation with cartilage collagen content (r = 0.40; 95% CI: 0.18, 0.58). T1r relaxation times did not correlate with cartilage sGAG content (r = 0.04; 95% CI: 20.21, 0.28) or collagen content (r = 20.05; 95% CI = 20.31, 0.20). Conclusion: dGEMRIC can help accurately measure cartilage sGAG content in vivo in patients

Image registration improves human knee cartilage T1 mapping with delayed gadolinium-enhanced MRI of cartilage (dGEMRIC)

Objectives: To 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. Methods: Eleven 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. Results: Automated registration of the T1-weighted images improved the T1 maps as the 90% percentile of the CRLBσwas significantly (P < 0.05) reduced with a median reduction of 55.8ms (patients) and 112

Reproducibility of fluorescent expression from engineered biological constructs in E. coli

We present results of the first large-scale interlaboratory study carried out in synthetic biology, as part of the 2014 and 2015 International Genetically Engineered Machine (iGEM) competitions. Participants at 88 institutions around the world measured fluorescence from three engineered constitutive constructs in E. coli. Few participants were able to measure absolute fluorescence, so data was analyzed in terms of ratios. Precision was strongly related to fluorescent strength, ranging from 1.54-fold standard deviation for the ratio between strong promoters to 5.75-fold for the ratio between the strongest and weakest promoter, and while host strain did not affect expression ratios, choice of instrument did. This result shows that high quantitative precision and reproducibility of results is possible, while at the same time indicating areas needing improved laboratory practices.Peer reviewe