Cross-relaxation imaging of human articular cartilage (original) (raw)
Related papers
2013
A number of experimental issues in the measurement of multi-component T 2 and T 1q relaxations in native and enzymatically digested articular cartilage were investigated by microscopic MRI (lMRI). The issues included the bath solutions (physiological saline and phosphate buffered saline (PBS)), the imaging resolution (35-140 lm), the specimen orientations (0°and 55°), and the strength of spin-lock frequencies (0.5-2 kHz) in the T 1q experiments. In addition to cartilage, the samples of agar gel and doped water solution were also used in the investigation. Two imaging sequences were used: CPMG-SE and MSME. All raw data were analyzed by the non-negative least square (NNLS) method. The MSME sequence was shown to result in the observation of multi-component T 2 , even in the gel and liquid samples, demonstrating the artificial uncleanness of this sequence in the multi-component measurements. The soaking of cartilage in PBS reduced the observable T 2 components to one at both 0°and 55°, suggesting the effect of phosphate ions on proton exchange between different pools of water molecules. The cartilage orientation with respect to the external magnetic field and the spin-lock strengths in the T 1q experiment both affected the quantification of the multi-component relaxation. The transitions between a mono-component and multi-components in cartilage under various experimental conditions call for the extra caution in interpreting the relaxation results.
Cross-Relaxation Imaging of Human Patellar Cartilage In-Vivo at 3.0T
Objective To compare quantitative magnetization transfer (qMT) parameters of patellar cartilage measured using cross relaxation imaging (CRI) in asymptomatic volunteers and patients with osteoarthritis. Design The study was performed with Institutional Review Board approval and with all subjects signing informed consent. CRI of the knee joint was performed at 3.0T on 20 asymptomatic volunteers and 11 patients with osteoarthritis. The fraction of macromolecular bound protons (f), the exchange rate constant between macromolecular bound protons and free water protons (k), and the T2 relaxation time of macromolecular bound protons (T2 B) of patellar cartilage were measured. Mann-Whitney-Wilcoxon rank-sum tests were used to compare qMT parameters between asymptomatic volunteers and patients with osteoarthritis. Results Average f, k, and T2B of patellar cartilage was 12.46%, 7.22 s−1, and 6.49 μs respectively for asymptomatic volunteers and 12.80%, 6.13 s−1, and 6.80 μs respectively for patients with osteoarthritis. There were statistically significant differences between groups of subjects for k (p<0.01) and T2 B (p<0.0001) but not f (p=0.38) of patellar cartilage. Conclusion Patients with osteoarthritis had significantly lower k and significantly higher T2B of patellar cartilage than asymptomatic volunteers which suggests that qMT parameters can detect changes in the macromolecular matrix of degenerative cartilage.
MRI rotating frame relaxation measurements for articular cartilage assessment
Magnetic Resonance Imaging, 2013
In the present work we introduced two MRI rotating frame relaxation methods, namely adiabatic T 1ρ and Relaxation Along a Fictitious Field (RAFF), along with an inversion-prepared Magnetization Transfer (MT) protocol for assessment of articular cartilage. Given the inherent sensitivity of rotating frame relaxation methods to slow molecular motions that are relevant in cartilage, we hypothesized that adiabatic T 1ρ and RAFF would have higher sensitivity to articular cartilage degradation as compared to laboratory frame T 2 and MT. To test this hypothesis, a proteoglycan depletion model was used. Relaxation time measurements were performed at 0 and 48 hours in ten bovine patellar specimens, 5 of which were treated with trypsin and 5 untreated controls were stored under identical conditions in isotonic saline for 48 hours. Relaxation times measured at 48 hours were longer than those measured at 0 hours in both groups. The changes in T 2 and MT relaxation times after 48 hours were approximately 3 times larger in the trypsin treated specimens as compared to the untreated group, whereas increases of adiabatic T 1ρ and RAFF were 4 to 5 fold larger. Overall, these findings demonstrate a higher sensitivity of adiabatic T 1ρ and RAFF to the trypsin-induced changes in bovine patellar cartilage as compared to the commonly used T 2 and MT. Since adiabatic T 1ρ and RAFF are advantageous for human applications as compared to standard continuous-wave T 1ρ methods, adiabatic T 1ρ and RAFF are promising tools for assessing cartilage degradation in clinical settings.
Magnetic Resonance in Medicine, 2003
Proteoglycan (PG) loss and disruption of the collagen framework in cartilage are early events associated with osteoarthritis (OA). The feasibility of in vivo high-resolution MRI assessments probing both macromolecules was explored in articular cartilage of the rabbit knee. One-millimeter thick coronal images were obtained at 3 T with a 97 ؋ 97 m 2 pixel size. A 22% decrease in the magnetization transfer (MT) exchange rate along with an ϳ2-fold greater Gd(DTPA) 2-induced decrease in T 1 relaxation time were measured in response to papain injection 1 day prior to the MRI session, indicative of an alteration of collagen integrity and PG depletion, respectively. A two-point method was tested as an alternative to the more time-consuming multipoint method typically used to measure T 1 changes. Kinetics of Gd(DTPA) 2uptake were observed with a 10-min time resolution. The diffusive transport of Gd(DTPA) 2was characterized by a T 1 decrease ϳ2-fold faster in papain-treated knees. These data suggest that kinetics of tracer diffusion may be used as an informative marker of PG loss, in addition to the amplitude of T 1 variations. When applied to a relevant OA model, the combination of MT and Gd(DTPA) 2-MRI may help in identifying new active compounds during efficacy studies on cartilage protection.
Magnetic Resonance in Medicine, 1994
Spatially resolved maps of proton self-diffusion coefficients (C)) and relaxation times (TI and T2) were obtained on cartilage-bone plug samples and on excised disks of canine cartilage at a transverse resolution of 30 pm, using microscopic magnetic resonance imaging (micro-MRI). Results are compared for excised disks of cartilage and intact cartilage-bone pllugs. Correlations between the absolute water concentration, the self-diffusion coefficient and the TI relaxation are reported. The diffusion coefficient is not a linear function of water concentration. The thickness of the disks is 600 pm, compared with the ca. 900 pm observed for the cartilage-bone plugs, presumably due to the absence of the interfacial or tidemark layer of interdigitated cartilage and bone in the former samples. Our results suggest that excised disks of ciirtilage are excellent models for the articular surface and the first 500 or so microns of tissue. The molecular parameters of spin-spin and spin-lattice relaxation times, as well as the water self-diffusion coefficient, are virtually identical in the two types of samples. However, the cartilage-bone plugs have the additional feature of permitting the study of the tidemark region, a region that likely plays a major role in the transmission oi mechanical force.
Cartilage MRI T2 Relaxation Time Mapping: Overview and Applications
Seminars in Musculoskeletal Radiology, 2004
The sensitivity of magnetic resonance imaging to biochemical and biophysical changes in the extracellular matrix of articular cartilage give it the potential to noninvasively detect the earliest changes of cartilage damage. The transverse relaxation time (T2) of cartilage has been shown to be a sensitive parameter for evaluation of early degeneration in articular cartilage, particularly changes in water and collagen content and tissue anisotropy. Although initial application has been in microimaging of small cartilage explants, in vivo techniques have been developed for cartilage T2 mapping of human joints. In addition to potential application in development of new pharmaceuticals and surgical techniques for preserving cartilage, in vivo cartilage T2 mapping can improve understanding of arthritis, cartilage aging, and response of cartilage to exercise.
2016
In Vitro NMR Study of Magnetization Exchange at Low Field and Proteoglycan Depletion at High Field in Articular Cartilage Magnetization exchange between different spin reservoirs, or spin groups, in cartilage tissue is an important aspect of the use of Magnetic Resonance Imaging (MRI) in the early detection of osteoarthritis (OA). A low field (Larmor frequency of 30 MHz) NMR study of relaxation times in bovine articular cartilage was undertaken with the aim of elucidating details about magnetization exchange in this tissue. A key element of successful multi-site exchange modeling is the availability of a sufficient number of apparent relaxation parameters to model the intrinsic multi-site exchange scenario. Two-Dimensional (2D) time domain NMR spin-lattice relaxation experiments in the laboratory frame (T 1 experiments) and the rotating frame (T 1ρ experiments) were performed in articular cartilage, which allows for effective extraction of relaxation parameters from the composite NMR response from the heterogeneous cartilage tissue. 2D inversion recovery T 1 experiments using non-selective excitation and monitor pulses as well as selective excitation and non-selective monitor pulses were used. The 2D relaxation results for each of the above experiments were then analysed for exchange by comparing the experimentally observed parameters to the apparent parameters, calculated from a set of intrinsic parameters, which were adjusted until a reasonable match was realized. In this multi-experiment approach the exchange results from one experiment can be used to corroborate the exchange results from another experiment.
Microporous and Mesoporous Materials, 2017
At low magnetic fields, T 1 variation within cartilage represents a robust parameter that is employed to quantify the layered structure in the tissue and is sensitive to factors such as enzymatic degradation, external load, and degeneration such as osteoarthritis. Variable-field relaxometry, on the other hand, provides access to the quadrupolar dips, i.e. enhanced relaxation rates of 1 H particularly at field strengths between 50 and 70 mT, that probe proton-nitrogen interaction and thus the content and local order of macromolecular constituents, namely glycosaminoglycans and collagen. At the same time, an strong overall dispersion of T 1 is observed over the whole accessible range of magnetic fields upward from 0.25 mT. In this study on 20 human cartilage samples, low-field and variable-field techniques were combined for the first time to correlate corresponding NMR parameters and the response to load with the severity of osteoarthritis. The magnitude of the quadrupolar dips, as well as cartilage thickness obtained from profile measurements, is found to correlate with the severity of osteoarthritis. At the same time, a significant correlation was identified for relaxation time variation before and after uniaxial compression at 0.6 MPa, a typical value for forces appearing in the human knee and hip joint. This finding is of importance since the spatial resolution of 50 mm obtained with the single-sided scanner is about one order of magnitude better than the one in clinical high-field or low-field scanners, thus allowing a much more detailed investigation and yet providing constraints for the interpretation of averaged values obtained with whole-body scanners.
New Journal of Physics, 2011
When inverting nuclear magnetic resonance relaxation data in order to obtain quasi-continuous distributions of relaxation times for fluids in porous media, it is common practice to impose a non-negative (NN) constraint on the distributions. While this approach can be useful in reducing the effects of data distortion and/or preventing wild oscillations in the distributions, it may give misleading results in the presence of real negative amplitude components. Here, some examples of valid negative components for articular cartilage and hydrated collagen are given. Articular cartilage is a connective tissue, consisting mainly of collagen, proteoglycans and water, which can be considered, in many aspects, as a porous medium. Separate T1 relaxation data are obtained for low-mobility ('solid') macromolecular 1H and for higher-mobility ('liquid') 1H by the separation of these components in free induction decays, with α denoting the solid/liquid 1H ratio. When quasi-continuous distributions of relaxation times (T1) of the solid and liquid signal components of cartilage or collagen are computed from experimental relaxation data without imposing the usual NN constraint, valid negative peaks may appear. The features of the distributions, in particular negative peaks, and the fact that peaks at longer times for macromolecular and water protons are at essentially the same T1, are interpreted as the result of a magnetization exchange between these two spin pools. For the only-slightly-hydrated collagen samples, with α>1, the exchange leads to small negative peaks at short T1 times for the macromolecular component. However, for the cartilage, with substantial hydration or for a strongly hydrated collagen sample, both with αLt1, the behavior is reversed, with a negative peak for water at short times. The validity of a negative peak may be accepted (dismissed) by a high (low) cost of NN in error of fit. Computed distributions for simulated data using observed signal-to-noise ratios also verify the need for some negative components. Observed relaxation times and signal ratios can be fitted formally by a simple two-site exchange model that gives the exchange times and the uncoupled relaxation times of the liquid and solid components, with significant trends of these parameters with increasing 1H ratio, α. The solid-to-liquid exchange times are found to be in the range from 10 ms to a few tens of ms at all hydration levels. The results may be of interest for the application of magnetization exchange contrast in the imaging of articular cartilage to determine changes associated with pathologies and ageing. Other important porous media exist where exchange phenomena and negative relaxation components cannot be disregarded.