Search

Objectives: This article provides an overview of the initial clinical results of musculoskeletal studies performed at 7 Tesla, with special focus on sodium imaging, new techniques such as chemical exchange saturation transfer (CEST) and T2* imaging, and multinuclear MR spectroscopy., Methods: Sodium imaging was clinically used at 7 T in the evaluation of patients after cartilage repair procedures because it enables the GAG content to be monitored over time. Sodium imaging and T2* mapping allow insights into the ultra-structural composition of the Achilles tendon and help detect early disease. Chemical exchange saturation transfer was, for the first time, successfully applied in the clinical set-up at 7 T in patients after cartilage repair surgery. The potential of phosphorus MR spectroscopy in muscle was demonstrated in a comparison study between 3 and 7 T, with higher spectral resolution and significantly shorter data acquisition times at 7 T., Results: These initial clinical studies demonstrate the potential of ultra-high field MR at 7 T, with the advantage of significantly improved sensitivity for other nuclei, such as (23)Na (sodium) and (31)P (phosphorus)., Conclusions: The application of non-proton imaging and spectroscopy provides new insights into normal and abnormal physiology of musculoskeletal tissues, particularly cartilage, tendons, and muscles., Key Points: • 7 T magnetic resonance provides significantly improved sensitivity for ( 23 ) Na and ( 31 ) P. • Initial clinical studies have now demonstrated ultra-high field MR operating at 7 T. • 7 T provides new insights into normal and abnormal physiology of musculoskeletal tissues.

Objectives: The aim of this study was to assess the texture of repair tissue and tissue adjacent to the repair site after matrix-associated chondrocyte transplantation (MACT) of the knee using gray-level co-occurrence matrix (GLCM) texture analysis of T2 quantitative maps. Methods: Twenty patients derived from the MRI sub-study of multicenter, single-arm phase III study underwent examination on a 3 T MR scanner, including a T2 mapping sequence 12 and 24 months after MACT. Changes between the time points in mean T2 values and 20 GLCM features were assessed for repair tissue, adjacent tissue, and reference cartilage. Differences in T2 values and selected GLCM features between the three cartilage sites at two time points were analyzed using linear mixed-effect models. Results: A significant decrease in T2 values after MACT, between time points, was observed only in repair cartilage (p < 0.001). Models showed significant differences in GLCM features between repair tissue and reference cartilage, namely, autocorrelation (p < 0.001), correlation (p = 0.015), homogeneity (p = 0.002), contrast (p < 0.001), and difference entropy (p = 0.047). The effect of time was significant in a majority of models with regard to GLCM features (except autocorrelation) (p ≤ 0.001). Values in repair and adjacent tissue became similar to reference tissue over time. Conclusions: GLCM is a useful add-on to T2 mapping in the evaluation of knee cartilage after MACT by increasing the sensitivity to changes in cartilage structure. The results suggest that cartilage tissue adjacent to the repair site heals along with the cartilage implant. Key Points: • GLCM is a useful add-on to T2mapping in the evaluation of knee cartilage after MACT by increasing the sensitivity to changes in cartilage structure. • Repair and adjacent tissue became similar to reference tissue over time. • The results suggest that cartilage tissue adjacent to the repair site heals along with the cartilage implant. [ABSTRACT FROM AUTHOR]

Sodium magnetic resonance imaging (23Na‐MRI) is a highly promising imaging modality that offers the possibility to noninvasively quantify sodium content in the tissue, one of the most relevant parameters for biochemical investigations. Despite its great potential, due to the intrinsically low signal‐to‐noise ratio (SNR) of sodium imaging generated by low in vivo sodium concentrations, low gyromagnetic ratio, and substantially shorter relaxation times than for proton (1H) imaging, 23Na‐MRI is extremely challenging. In this article, we aim to provide a comprehensive overview of the literature that has been published in the last 10–15 years and which has demonstrated different technical designs for a range of 23Na‐MRI methods applicable for disease diagnoses and treatment efficacy evaluations. Currently, a wider use of 3.0T and 7.0T systems provide imaging with the expected increase in SNR and, consequently, an increased image resolution and a reduced scanning time. A great interest in translational research has enlarged the field of sodium MRI applications to almost all parts of the body: articular cartilage tendons, spine, heart, breast, muscle, kidney, and brain, etc., and several pathological conditions, such as tumors, neurological and degenerative diseases, and others. The quantitative parameter, tissue sodium concentration, which reflects changes in intracellular sodium concentration, extracellular sodium concentration, and intra–/extracellular volume fractions is becoming acknowledged as a reliable biomarker. Although the great potential of this technique is evident, there must be steady technical development for 23Na‐MRI to become a standard imaging tool. The future role of sodium imaging is not to be considered as an alternative to 1H MRI, but to provide early, diagnostically valuable information about altered metabolism or tissue function associated with disease genesis and progression. Level of Evidence: 1 Technical Efficacy Stage: 1 [ABSTRACT FROM AUTHOR]

Objectives: The aim was to systematically compare T2 relaxation times of the knee and ankle cartilage within subjects at 7T.Methods: Ten healthy volunteers were examined by 7 Tesla MR using a three-dimensional triple-echo steady state sequence (3D-TESS). The differences between seven cartilage compartments (patella, femur, proximal tibia, and distal tibia and talus in both medial and lateral facet) were analyzed by ANOVA.Results: The results showed statistically significantly higher T2 (mean ± standard deviation, in milliseconds) values in patellar (25.8 ± 1.2) and femoral (24.9 ± 1.3) cartilage compared to the tibial (19.2 ± 1) and talar (18.1 ± 0.6 ms) cartilage. The cartilages of the medial and lateral facet in the ankle joint were not significantly different (p>0.05).Conclusions: This is the first study to systematically compare within-subject T2 values in the knee and ankle non-invasively, in vivo. Our results are in agreement with the previous findings demonstrating different biochemical and biomechanical properties between the knee and ankle cartilage. [ABSTRACT FROM AUTHOR]

This work deals with hip joint cartilage segmentation, which is an important task in joint diseases diagnosis. Since the manual segmentation commonly used nowadays, is a tedious and lengthy task, this work brings a new idea into its automation and simplification of the medical expert work. The proposed method is an interactive algorithm for hip joint cartilage segmentation, and hence it requires some user interaction, which is common and usually desired in medical image processing. The first step of the method is a selection of several points in several slices lying inside the cartilage. The purpose is a rough delimitation of the cartilage area. This delimitation is based on the assumption that the femoral head has approximately circular shape. The cartilage is then segmented using the combination of Graph Cut segmentation and K-means clustering techniques. The algorithm was tested on 3D isotropic True-FISP volumes of patients with femoroacetabular impingement and the results were evaluated by commonly used Dice Similarity Coefficient (0.62). The results of the segmentation will be prospectively used for the segmentation of quantitative MR maps (T1 and T2) in femoro-acetabular impingement (FAI) investigation. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to compare 3T and 7T signal-to-noise and contrast-to noise ratios of clinical sequences for imaging of the ankles with optimized sequences and dedicated coils. Ten healthy volunteers were examined consecutively on both systems with three clinical sequences: (1) 3D gradient-echo, T1-weighted; (2) 2D fast spin-echo, PD-weighted; and (3) 2D spin-echo, T1-weighted. SNR was calculated for six regions: cartilage; bone; muscle; synovial fluid; Achilles tendon; and Kager''s fat-pad. CNR was obtained for cartilage/bone, cartilage/fluid, cartilage/muscle, and muscle/fat-pad, and compared by a one-way ANOVA test for repeated measures. Mean SNR significantly increased at 7T compared to 3T for 3D GRE, and 2D TSE was 60.9% and 86.7%, respectively. In contrast, an average SNR decrease of almost 25% was observed in the 2D SE sequence. A CNR increase was observed in 2D TSE images, and in most 3D GRE images. There was a substantial benefit from ultra high-field MR imaging of ankles with routine clinical sequences at 7T compared to 3T. Higher SNR and CNR at ultra-high field MR scanners may be useful in clinical practice for ankle imaging. However, carefully optimized protocols and dedicated extremity coils are necessary to obtain optimal results. [Copyright &y& Elsevier]

Abstract: The objective of this study was to evaluate the correlations between MR parameters and the biomechanical properties of naturally degenerated human articular cartilage. Human cartilage explants from the femoral condyles of patients who underwent total knee replacement were evaluated on a micro-imaging system at 3T. To quantify glycosaminoglycan (GAG) content, delayed gadolinium-enhanced MRI of the cartilage (dGEMRIC) was used. T 2 maps were created by using multi-echo, multi-slice spin echo sequences with six echoes: 15, 30, 45, 60, 75, and 90ms. Data for apparent diffusion constant (ADC) maps were obtained from pulsed gradient spin echo (PGSE) sequences with five b-values: 10.472, 220.0, 627.0, 452.8, 724.5, and 957.7. MR parameters were correlated with mechanical parameters (instantaneous (I) and equilibrium (Eq) modulus and relaxation time (τ)), and the OA stage of each cartilage specimen was determined by histological evaluation of hematoxylin–eosin stained slices. For some parameters, a high correlation was found: the correlation of T 1Gd vs Eq (r =0.8095), T 1Gd vs I/Eq (r =−0.8441) and T 1Gd vs τ (r =0.8469). The correlation of T 2 and ADC with selected biomechanical parameters was not statistically significant. In conclusion, GAG content measured by dGEMRIC is highly related to the selected biomechanical properties of naturally degenerated articular cartilage. In contrast, T 2 and ADC were unable to estimate these properties. The results of the study imply that some MR parameters can non-invasively predict the biomechanical properties of degenerated articular cartilage. [Copyright &y& Elsevier]

Magnetic resonance (MR) transverse relaxation time (T 2 ) mapping has been frequently used to evaluate collagen content and its organization. In this study, MR T 2 mapping, using the multi-slice, multi-echo Carr–Purcell–Meiboom–Gill technique, was performed in volunteers and patients after matrix-associated autologous chondrocyte transplantation (MACT) under unloading and loading conditions with an MR-compatible compression device. In the volunteer study, a statistically significant decrease in the cartilage MR T 2 values was observed during the loading phase when compared to the initial load-free measurement. During the recovery period, a statistically significant increase in the T 2 values was found in the central superficial layer ( p =0.001), the central deep layer ( p =0.005), the posterior deep layer ( p =0.001), and in the tibia superficial layer ( p =0.01) when compared to measurements under loading. In patients after MACT, during unloading or loading conditions, statistically significant changes in T 2 values were observed in the transplant deep zone ( p =0.005), in the posterior deep zone ( p =0.004), and in the tibia superficial zone ( p =0.012). The results of this study show that MR T 2 mapping under loading conditions may provide additional information about cartilage repair tissue composition and organization during the postoperative follow-up, and may help to evaluate the efficacy of cartilage-repair surgery techniques. [ABSTRACT FROM AUTHOR]