Abstract: INTRODUCTION: The goal of this in vitro validation study was to investigate the feasibility of biochemical MRI techniques, such as sodium imaging, T(2) mapping, fast imaging with steady state precession (FISP), and reversed FISP (PSIF), as potential markers for collagen, glycosaminoglycan and water content in the Achilles tendon. MATERIALS AND METHODS: Five fresh cadaver ankles acquired from a local anatomy department were used in the study. To acquire a sodium signal from the Achilles tendon, a 3D-gradient-echo sequence, optimized for sodium imaging, was used with TE=7.71ms and TR=17ms. The T(2) relaxation times were obtained using a multi-echo, spin-echo technique with a repetition time (TR) of 1200ms and six echo times. A 3D, partially balanced, steady-state gradient echo pulse sequence was used to acquire FISP and PSIF images, with TR/TE=6.96/2.46ms. MRI parameters were correlated with each other, as well as with histologically assessed glycosaminoglycan and water content in cadaver Achilles tendons. RESULTS: The highest relevant Pearson correlation coefficient was found between sodium SNR and glycosaminoglycan content (r=0.71, p=0.007). Relatively high correlation was found between the PSIF signal and T(2) values (r=0.51, p=0.036), and between the FISP signal and T(2) values (r=0.56, p=0.047). Other correlations were found to be below the moderate level. CONCLUSION: This study demonstrated the feasibility of progressive biochemical MRI methods for the imaging of the AT. A GAG-specific, contrast-free method (sodium imaging), as well as collagen- and water-sensitive methods (T(2) mapping, FISP, PSIF), may be used in fast-relaxing tissues, such as tendons, in reasonable scan times.
Abstract: Purpose: To evaluate the feasibility of sodium 7-T magnetic resonance (MR) imaging in repaired tissue and native cartilage of patients after matrix-associated autologous chondrocyte transplantation (MACT) and compare results with delayed gadolinium-enhanced MR imaging of cartilage (dGEMRIC) at 3 T. xD;Materials and Methods: Ethical approval was provided by the local ethics committee; written informed consent was obtained from all patients. Six women and six men (mean age, 32.8 year +/- 8.2 [standard deviation] and 32.3 years +/- 12.7, respectively) were included. Mean time between MACT and MR was 56 months +/- 28. A variable three-dimensional (3D) gradient-echo (GRE) dual-flip-angle technique was used for T1 mapping before and after contrast agent administration at 3 T. All patients were also examined at 7 T (mean delay, 70.5 days +/- 80.1). A sodium 23-only transmit-receive knee coil was used with the 3D GRE sequence. A statistical analysis of variance and Pearson correlation were applied. xD;Results: Mean signal-to-noise ratio (SNR) was 24 in native cartilage and was 16 in transplants (P<.001). Mean sodium signal intensities normalized with the reference sample were 174 +/- 53 and 267 +/- 42 for repaired tissue in the cartilage transplant and healthy cartilage, respectively (P<.001). Mean postcontrast T1 values were 510 msec +/- 195 and 756 msec +/- 188 for repaired tissue and healthy cartilage, respectively (P=.005). Mean score of MR observation of cartilage repair tissue was 75 +/- 14. Association between postcontrast T1 and normalized sodium signal values showed a high Pearson correlation coefficient (R) of 0.706 (P=.001). A high correlation of R = 0.836 (P=.001) was found between ratios of normalized sodium values and ratios of T1 postcontrast values. xD;Conclusion: With the modified 3D GRE sequence at 7 T, a sufficiently high SNR in sodium images was achieved, allowing for differentiation of repaired tissue from native cartilage after MACT. A strong correlation was found between sodium imaging and dGEMRIC in patients after MACT. (C) RSNA, 2010
Abstract: Purpose/Introduction: The aim of this study was to determine the T(1) relaxivities (r(1)) of 8 gadolinium (Gd)-based MR contrast agents in human blood plasma at 7 Tesla, compared with 3 Tesla. xD;Subjects and Methods: Eight commercially available Gd-based MR contrast agents were diluted in human blood plasma to concentrations of 0, 0.25, 0.5, 1, and 2 mmol/L. In vitro measurements were performed at 37 degrees C, on a 7 Tesla and on a 3 Tesla whole-body magnetic resonance imaging scanner. For the determination of T(1) relaxation times, Inversion Recovery Sequences with inversion times from 0 to 3500 ms were used. The relaxivities were calculated. xD;Results: The r(1) relaxivities of all agents, diluted in human blood plasma at body temperature, were lower at 7 Tesla than at 3 Tesla. The values at 3 Tesla were comparable to those published earlier. Notably, in some agents, a minor negative correlation of r(1) with a concentration of up to 2 mmol/L could be observed. This was most pronounced in the agents with the highest protein-binding capacity. xD;Discussion/Conclusion: At 7 Tesla, the in vitro r(1) relaxivities of Gd-based contrast agents in human blood plasma are lower than those at 3 Tesla. This work may serve as a basis for the application of Gd-based MR contrast agents at 7 Tesla. Further studies are required to optimize the contrast agent dose in vivo.
Abstract: Purpose: The region-of-interest (ROI) selection and evaluation is one of the key factors in the successful evaluation of radiological images. However, the presence of noise in images may lead to incorrect diagnosis. The aim of this study was to test the hypothesis that the weighting by error estimation in ROI assessment might significantly improve the validity of the results. xD;Methods: As a model, the data maps of the transverse relaxation time constants (T(2)) from patients who underwent a matrix-associated chondrocyte transplantation procedure on the femoral condyle were analyzed. Artificial noise with a Rician density probability distribution was added to each TE image. ROIs were processed either as a regular arithmetic mean or as a weighted mean, in which weighted coefficients were calculated with regard to fitting error estimates [coefficient of determination (R(2)); root mean squared error (RMSE), mean absolute error (MSE), mean squared error (MAE), and chi-squared error (chi(2))]. xD;Results: The global T(2) values in repair tissue (mean +/- standard deviation, 62 +/- 7 ms; range 51-70 ms) and in healthy cartilage (mean +/- SD, 49 +/- 6 ms; range 40-60 ms) were significantly different (p < 0.001). With a 45% or greater decrease from the original SNR value (corresponding to a noise level of 35% of random value), the statistical significance was lost (P > 0.05); however, the use of the coefficient of determination (R(2)) as a correction factor was able to maintain the p-value of <0.05 up to a 56% decrease from the original SNR value. xD;Conclusions: The results of this study can prospectively be applied in a wide range of radiological imaging techniques in cases when error estimation is possible. Our analysis on MR images with artificially added noise showed that utilization of the correlation of determination (R(2)) as a weighting parameter in ROI evaluation may significantly improve the differentiation between native and transplanted cartilage tissue in noisy images. This could be an added benefit in the non-invasive monitoring of the post-operative status of patients with cartilage transplants if the MR images are not ideal (e.g., lower field strength or lower SNR). (C) 2010 American Association of Physicists in Medicine. [DOI: 10.1118/1.3431995]
Abstract: The aim of this study was to assess the changes in MRI parameters during applied load directly in MR scanner and correlate these changes with biomechanical parameters of human articular cartilage. Cartilage explants from patients who underwent total knee replacement were examined in the micro-imaging system in 3T scanner. Respective MRI parameters (T(1) without- and T(1) with contrast agent as a marker of proteoglycan content, T(2) as a marker of collagen network anisotropy and ADC as a measure of diffusivity) were calculated in pre- and during compression state. Subsequently, these parameters were compared to the biomechanical properties of articular cartilage, instantaneous modulus (I), equilibrium modulus (Eq) and time of tissue relaxation (tau). Significant load-induced changes of T2 and ADC were recorded. High correlation between T1Gd and I (r = 0.6324), and between ADC and Eq (r = -0.4884) was found. Multi-parametric MRI may have great potential in analyzing static and dynamic biomechanical behavior of articular cartilage in early stages of osteoarthritis (OA).
Abstract: The aims of this study were to examine the clinical feasibility and reproducibility of kinematic MR imaging with respect to changes in T (2) in the femoral condyle articular cartilage. We used a flexible knee coil, which allows acquisition of data in different positions from 40A degrees flexion to full extension during MR examinations. The reproducibility of T (2) measurements was evaluated for inter-rater and inter-individual variability and determined as a coefficient of variation (CV) for each volunteer and rater. Three different volunteers were measured twice and regions of interest (ROIs) were selected by three raters at different time points. To prove the clinical feasibility of this method, 20 subjects (10 patients and 10 age- and sex-matched volunteers) were enrolled in the study. Inter-rater variability ranged from 2 to 9 and from 2 to 10% in the deep and superficial zones, respectively. Mean inter-individual variability was 7% for both zones. Different T (2) values were observed in the superficial cartilage zone of patients compared with volunteers. Since repair tissue showed a different behavior in the contact zone compared with healthy cartilage, a possible marker for improved evaluation of repair tissue quality after matrix-associated autologous chondrocyte transplantation (MACT) may be available and may allow biomechanical assessment of cartilage transplants.
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 3 T. 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 90 ms. 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 (1) and equilibrium (Eq) modulus and relaxation time (tau)), 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 tau (r = 0.8469). The correlation of T(2) and ADC with selected biomechanical parameters was not statistically significant. xD;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. (C) 2009 Published by Elsevier Inc.
Abstract: This contribution describes experiments with image reconstruction from projections based on perspective imaging techniques. Modifications of the basic reconstruction algorithm to eliminate some imperfections following from physical properties of used X-ray detector and applied scanning technique are also mentioned in the paper. The applicability of the parallel beam and fan beam reconstruction methods was compared on the test phantom objects.
Abstract: The purpose of this study was to evaluate changes of several MR parameters (T1, T2 and ADC) before and after compression in human cartilage samples using unique microimaging compression system. Cartilage samples were prepared from joints of 10 patients, who underwent a total knee joint replacement. Study was performed on a Bruker 3T Medspec whole-body scanner (Bruker, Ettlingen, Germany) using BGA-12 micro-gradients with a special designed compression device built for this gradient system. Employing this equipment there is a possibility to reach accuracy of moving the compressive piston of 1/100 mm. T1 mapping was performed by the inversion recovery spin echo pulse sequence, for T2 mapping a multi-echo multi-slice spin echo sequence was used and ADCs were calculated from data collected from pulsed gradient spin echo (PGSE), all before and after compression. Fitting routines were written in IDL using mpcurvefit routine. Equipment for cartilage compression evaluation seems to be feasible for studying influence of static compression on cartilage tissue. Significant changes of T1, T2 and ADC parameters during compression were found. Biochemical imaging provided by multi-parametric MR improves biomechanical studies of articular cartilage.
Abstract: Magnetic Resonance Imaging is powerful tool for the non-invasive evaluation of cartilage repair process. It can be used with advantage for both, in-vitro as well as in-vivo evaluation of articular cartilage. In our study, we focused on the in-vitro evaluation of maturation process of nude-mouse model human articular cartilage maturation. Unique nude-mouse model cartilage samples were prepared from joints of human femoral head after a total joint replacement. Cartilage-bone samples with chondrocyte transplantation grafts were placed under the skin of mouse for 4 and 8 weeks associated with the special immunity treatment for no-immunology reaction of the mouse against human tissue. Study was performed on a Bruker 3T Medspec whole-body scanner (Bruker, Ettlingen, Germany) using BGA-12 micro-gradient system. AM parameter to study was T2 relaxation time constant. T2 mapping was performed using multi-slice multi-echo (MSME) sequence. Fitting routines were written in IDL, using mpcurvefit routine. T2 study of nude-mouse model provided unique information about the maturation of seeded cartilage cells, specifically degree of internal organization and water content in the load-free and motion-free conditions.
Abstract: We measured and imaged. magnetic field distributions of thin layers (2-D objects with negligible thickness) of biological and physical samples, by using nuclear magnetic resonance (NMR). The image represents the magnetic susceptibility distribution in the sample. We used a standard gradient echo imaging method, susceptible to magnetic field homogeneity, for detection. Since the physical and biological samples we investigated do not generate any NMR signal, we used a homogeneous phantom reference-a container filled with water-as a medium. The image acquired by this method is actually a projection of the sample properties onto the homogeneous phantom. The method can be applied in nanotechnology, microelectronics, and especially in the biological and medical sciences.
Abstract: The paper deals with a new method for imaging of very thin layers based on principle of magnetic field deformation measurement using magnetic resonance imager. The transducer consists of a thin vessel filled with CuSO4 solution (homogeneous phantom) placed into the planar RF coil. The measured sample is a physical or biological object preserved by low concentrated magnetic fluid. Magnetic field deformation was measured and imaged using Gradient Echo imaging sequence. The resultant image represents the magnetic susceptibility distribution in the sample. First experiments on physical and biological samples have been performed The method could be applied in nanotechnology, microelectronics and especially in biological and medical sciences for measurement and imaging of samples and dissections properties in connection with environment changes and medical diagnostics.
