Magic-angle effect in magnetic resonance imaging of articular cartilage: a review

Deciphering adiabatic rotating frame relaxometry in biological tissues

PURPOSE

This work aims to unravel the intricacies of adiabatic rotating frame relaxometry in biological tissues.

THEORY AND METHODS

The classical formalisms of dipolar relaxationR 1 ρ $$ {R}_{1\rho } $$ andR 2 ρ $$ {R}_{2\rho } $$ were systematically analyzed for water molecules reorienting on "fast" and "slow" timescales. These two timescales are, respectively, responsible for the absence and presence ofR 1 ρ $$ {R}_{1\rho } $$ dispersion. A time-averagedR 1 ρ $$ {R}_{1\rho } $$ orR 2 ρ $$ {R}_{2\rho } $$ over an adiabatic pulse duration was recast into a sum ofR 1 $$ {R}_1 $$ andR 2 $$ {R}_2 $$ , but with different weightings. These weightings depend on the specific modulations of adiabatic pulse waveforms. In this context, stretched hyperbolic secant (HSn $$ HSn $$ ) pulses were characterized. Previously publishedH S 1 $$ HS1 $$ R 1 ρ $$ {R}_{1\rho } $$ , continuous-wave (CW)R 1 ρ $$ {R}_{1\rho } $$ , andR 1 $$ {R}_1 $$ measures from 12 agarose phantoms were used to validate the theoretical predictions. A similar validation was also performed on previously publishedHSn $$ HSn $$ R 1 ρ $$ {R}_{1\rho } $$ (n $$ n $$ =1, 4, 8) andHS 1 $$ HS1 $$ R 2 ρ $$ {R}_{2\rho } $$ from bovine cartilage specimens.

RESULTS

Longitudinal relaxation weighting decreases forHSn $$ HSn $$ pulses asn $$ n $$ increases. Predicted CWR 1 ρ cal $$ {R}_{1\rho}^{cal} $$ values from agarose phantoms align well with the measured CWR 1 ρ exp $$ {R}_{1\rho}^{exp} $$ values, as indicated by a linear regression function:R 1 ρ cal = 1.04 * R 1 ρ exp - 1.96 $$ {R}_{1\rho}^{cal}={1.04}^{\ast }{R}_{1\rho}^{exp}-1.96 $$ . The predicted adiabaticR 1 ρ $$ {R}_{1\rho } $$ andR 2 ρ $$ {R}_{2\rho } $$ from cartilage specimens are consistent with those previously measured, as quantified by:R 1 ρ , 2 ρ cal = 1.10 * R 1 ρ , 2 ρ exp - 0.41 $$ {R}_{1\rho, 2\rho}^{cal}={1.10}^{\ast }{R}_{1\rho, 2\rho}^{exp}-0.41 $$ .

CONCLUSION

This work has theoretically and experimentally demonstrated that adiabaticR 1 ρ $$ {R}_{1\rho } $$ andR 2 ρ $$ {R}_{2\rho } $$ can be recast into a sum ofR 1 $$ {R}_1 $$ andR 2 $$ {R}_2 $$ , with varying weightings. Therefore, any suggestions that adiabatic rotating frame relaxometry in biological tissues could provide more information than the standardR 1 $$ {R}_1 $$ andR 2 $$ {R}_2 $$ warrant closer scrutiny.

Quantifying Tendon Degeneration Using Magic Angle Insensitive Ultra-Short Echo Time Magnetization Transfer: A Phantom Study in Bovine Tendons

OBJECTIVES

The aim of this study was to qualitatively and quantitatively assess changes in bovine flexor tendons before and after collagen degradation and at different angles in relation to the static B 0 field using 3-dimensional ultra-short echo time (UTE) magnetization transfer (MT) imaging within a clinically feasible acquisition time.

MATERIALS AND METHODS

Eight bovine flexor tendons were examined at 3 T magnetic resonance imaging including 3-dimensional UTE MT and UTE T2* research application sequences (acquired within 4:04 and 6:38 minutes, respectively) before and after enzyme-induced degradation. The tendons were divided into 2 groups: group 1 (controls) treated with phosphate-buffered saline and group 2 treated with collagenase I to induce collagen degeneration. Magnetic resonance imaging was repeated at 0, 27, 55, and 90 degrees to the B 0 field. To calculate quantitative tissue properties, all tendons were semiautomatically segmented, and changes in quantitative UTE T2* and UTE MT ratios (MTRs) were compared at different angles and between groups. In addition to descriptive statistics, the coefficient of variation was calculated to compare UTE MT and UTE T2* imaging.

RESULTS

Ultra-short echo time MTR showed a significantly lower coefficient of variation compared with UTE T2* values, indicating a more robust imaging method (UTE MTR 9.64%-11.25%, UTE T2* 18.81%-24.06%, P < 0.001). Both methods showed good performance in detecting degenerated tendons using histopathology as reference standard, with UTE MT imaging having a better area under the curve than UTE T2* mapping (0.918 vs 0.865). Falsely high UTE T2* values were detected at the 55 degrees acquisition angle, whereas UTE MTR values were robust, that is, insensitive to the MAE.

CONCLUSIONS

Ultra-short echo time MT imaging is a reliable method for quantifying tendon degeneration that is robust to the MAE and can be acquired in a clinically reasonable time.

Clinical evaluation of 3D high-resolution isotropic knee MRI using Multi-Interleaved X-prepared TSE with inTUitive RElaxometry (MIXTURE) for simultaneous morphology and T2 mapping

PURPOSE

Quantitative MRI techniques such as T2 mapping are useful in comprehensive evaluation of various pathologies of the knee joint yet require separate scans to conventional morphological measurements and long acquisition times. The recently introduced 3D MIXTURE (Multi-Interleaved X-prepared Turbo-Spin Echo with Intuitive Relaxometry) technique can obtain simultaneous morphologic and quantitative information of the knee joint. To compare MIXTURE with conventional methods and to identify differences in morphological and quantitative information.

METHODS

Phantom studies were conducted, and in vivo human scans were performed (20 patients) presented with knee arthralgia. MIXTURE is based on 3D TSE without and with T2 preparation modules in an interleaved manner for both morphology with PDW and fat suppressed T2W imaging as well as quantitative T2 mapping within one single scan. Image quality and lesion depiction were visually assessed and compared between MIXTURE and conventional 2D TSE by two experienced radiologists. Contrast-to-noise ratio was used to assess the adjacent tissue contrast in a quantitative way for both obtained PDW and fat suppressed T2W images. Quantitative T2 values were measured in phantom and from in vivo knee cartilage.

RESULTS

The overall diagnostic confidence and contrast-to-noise ratio were deemed comparable between MIXTURE and 2D TSE. While the chosen T2 preparation modules for MIXTURE rendered consistent T2 values comparing to the current standard, measured cartilage T2 values ranged from 26.1 to 50.7 ms, with significant difference between the lesion and normal areas (p < 0.05).

CONCLUSIONS

MIXTURE can help to provide high-resolution information for both anatomical and pathological assessment.

Validation of compositional MRI from a histological standpoint: Advantages of three-dimensional T1ρ mapping for quantitative evaluation of articular cartilage

PURPOSE

We aimed to investigate the relationship between quantitative evaluation by compositional MRI, including T1ρ, and histological and macroscopic assessments, to verify the validity of compositional MRI, and examine the relationship between compositional MRI evaluation reconstructed in three dimensions (3D) and histological and visual assessments.

METHOD

Twenty-seven patients with knee osteoarthritis underwent T1ρ and T2 magnetic resonance imaging (MRI). Histological and gross tissue evaluations were performed on the excised bone sections of total knee arthroplasty. Semi-quantitative histological evaluation of tissue changes were assessed by measuring the optical density of digitally captured safranin O-stained and Collagen type II antibody-stained paraffin sections. Macroscopic cartilage severity was determined on a 5-grade scale (G0-G5). T1ρ and T2 values (3D and 2D), and their correlation with each of these parameters were investigated.

RESULTS

3D T1 ρ is negatively correlated with histological evaluations and positively correlated with visual assessments. Only 3D T1ρ values correlated with histological quantitative evaluation (Safranin-O staining; r = -0.53, P = 0.014, Collagen type II antibody staining; r = -0.60, P = 0.019). 2D T1ρ and 3D, 2D T2 values did not correlate with histological evaluation results. Macroscopic cartilage severity grade correlated with all T1ρ and T2 values (3D T1ρ; r = 0.61, P < 0.001, 2D T1ρ; r = 0.52, P < 0.001, 3D T2; r = 0.33, P = 0.045, 2D T2; r = 0.41, P = 0.01).

CONCLUSIONS

3D T1ρ mapping reflects the changes in the molecular structure of the cartilage matrix that occur in arthropathic changes and may be an effective tool for detecting cartilage degeneration.

A feasibility study of in vivo quantitative ultra-short echo time-MRI for detecting early cartilage degeneration

OBJECTIVES

To explore the feasibility of Ultra-short echo time (UTE) - MRI quantitative imaging in detecting early cartilage degeneration in vivo and underlying pathological and biochemical basis.

METHODS

Twenty volunteers with osteoarthritis (OA) planning for total knee arthroplasty (TKA) were prospectively recruited. UTE-MRI sequences and conventional sequences were performed preoperatively. Regions of interests (ROIs) were manually drawn on the tibial plateau and lateral femoral condyle images to calculate MRI values. Cartilage samples were collected during TKA according to the preset positions corresponding to MR images. Pathological and biochemical components of the corresponding ROI, including histological grading, glycosaminoglycan (GAG) content, collagen integrity, and water content were obtained.

RESULTS

91 ROIs from volunteers of 7 males (age range: 68 to 78 years; 74 ± 3 years) and 13 females (age range: 57 to 79 years; 67 ± 6 years) were evaluated. UTE-MTR (r = -0.619, p < 0.001), UTE-AdiabT1ρ (r = 0.568, p < 0.001), and UTE-T2* values (r = -0.495, p < 0.001) showed higher correlation with Mankin scores than T2 (r = 0.287, p = 0.006) and T1ρ (r = 0.435, p < 0.001) values. Of them, UTE-MTR had the highest diagnostic performance (AUC = 0.824, p < 0.001). UTE-MTR, UTE-AdiabT1ρ and UTE-T2* value was mainly related to collagen structural integrity, PG content and water content, respectively (r = 0.536, -0.652, -0.518, p < 0.001, respectively).

CONCLUSION

UTE-MRI have shown greater in vivo diagnostic value for early cartilage degeneration compared to conventional T2 and T1ρ values. Of them, UTE-MTR has the highest diagnostic efficiency. UTE-MTR, UTE-AdiabT1ρ, and UTE-T2* value mainly reflect different aspects of cartilage degeneration--integrity of collagen structure, PG content, and water content, respectively.

CRITICAL RELEVANCE STATEMENT

Ultra-short echo time (UTE)-MRI has the potential to be a novel image biomarkers for detecting early cartilage degeneration in vivo and was correlated with biochemical changes of early cartilage degeneration.

KEY POINTS

Conventional MR may miss some early cartilage changes due to relatively long echo times. Ultra-short echo time (UTE)-MRI showed the ability in identifying early cartilage degeneration in vivo. UTE-MT, UTE-AdiabT1ρ, and UTE-T2* mapping mainly reflect different aspects of cartilage degeneration.

Study of the collagen tissue nanostructure by analyzing the echo decay obtained using the MRI technique

The multicomponent relaxation observed in nuclear magnetic resonance experiments in biological tissues makes it difficult to establish a correlation between specific relaxation times and tissue structural parameters. The analysis of a nanostructure (the characteristic size of 10-1000 nm) is usually based on formulas for relaxation times which depend on structural parameters at the atomic or molecular levels in the size range of 0.1-5 nm. We have recently developed an analysis method in which relaxation times' anisotropy in a sample is explicitly related to its structure of nanocavities containing a liquid or gas. However, the method is based on the analysis of experimental data on the anisotropy of relaxation times obtained by using the standard NMR technique and rotating the sample relative to a magnetic field and requires a series of experiments. In the present study, to address this challenge, we develop a new method of analysis of a multi-exponential magnetic resonance signal that does not require determining relaxation times and eliminates the sample rotation and the necessity of a series of experiments. Using the magnetic resonance imaging (MRI) technique, the total signal from the whole sample was obtained as a sum of the signals (echo decays) from all voxels. In contrast to previous research, the volumes of nanocavities and their angular distribution can be obtained by analyzing a single total signal for the entire cartilage. In addition, within the framework of this approach, it is possible to identify the reason for the multicomponent nature of relaxation. The proposed method for analyzing a single multi-exponential signal (transverse relaxation) was implemented on cartilage. Using the signal, three anatomical zones of cartilage were studied, revealing significant structural differences between them. The proposed method not only avoids the need for sample rotation but also enables repeated application of layer-by-layer magnetic resonance imaging with micron resolution. The study results allow us to suggest that water molecules contributing to the echo decay are more likely located in nanocavities formed by the fibrillar structure rather than inside the fibrils.

Assessment of articular cartilage degradation in response to an impact injury using µMRI

PURPOSE

Degradation of articular cartilage (AC) due to injury to the knee joint may initiate post-traumatic osteoarthritis (PTOA). Failure to diagnose the onset of the disease at an early stage makes the cure ineffective for PTOA. This study investigated the consequences of a mechanical injury to the knee in a rabbit model using microscopic magnetic resonance imaging (µMRI) at high resolution.

MATERIALS AND METHODS

A mechanical injury was induced to the knee joints of 12 rabbits. Cartilage blocks were extracted from the non-impacted and impacted knee joints after 2 and 14 weeks post-impact. The specimens were studied using µMRI T2 relaxation and inductively coupled plasma analysis to determine the early degradation of the articular cartilage.

RESULTS

The data established a connection between T2 relaxation time and the early progression of knee PTOA after an impact injury. T2 values were found to be higher in the impacted cartilage at both 2 and 14 weeks, in particular, T2-55° values in the impacted samples displayed a significant rise of 6.93% after 2 weeks and 20.02% after 14 weeks. Lower glycosaminoglycan measurement and higher water content in the impacted cartilage confirmed the µMRI results.

CONCLUSIONS

This µMRI T2 study was able to detect cartilage damage in the impacted knees. In addition, greater degradation in the affected knees at 14 weeks than at 2 weeks indicated the progressive nature of cartilage deterioration over time. The µMRI results were in accord with the biochemical analysis, indicating the detection of early structural damage in the cartilage.

Multicomponents of spin-spin relaxation, anisotropy of the echo decay, and nanoporous sample structure

We have experimentally and theoretically investigated multicomponent 1H nuclear magnetic resonance (NMR) echo decays in a-Si:H films containing anisotropic nanopores, in which randomly moving hydrogen molecules are entrapped. The experimental results are interpreted within the framework of the previously developed theory, in which a nanoporous material is represented as a set of nanopores containing liquid or gas, and the relaxation rate is determined by the dipole-dipole spin interaction, considering the restricted motion of molecules inside the pores. Previously, such characteristics of a nanostructure as the average volume of pores and their orientation distribution were determined from the angular dependences of the spin-spin and spin-lattice relaxation times. We propose a new approach to the analysis of the NMR signal, the main advantage of which is the possibility of obtaining nanostructure parameters from a single decay of the echo signal. In this case, there is no need to analyze the anisotropy of the relaxation time T 2 , the determination of which is a rather complicated problem in multicomponent decays. Despite multicomponent signals, the fitting parameter associated with the size and shape of nanopores is determined quite accurately. This made it possible to determine the size and shape of nanopores in a-Si:H films, herewith our estimates are in good agreement with the results obtained by other methods. The fitting of the decays also provides information about the nanostructure of the sample, such as the standard deviations of the angular distribution of pores and the polar and azimuthal angles of the average direction of the pore axes relative to the sample axis, with reasonable accuracy. The approach makes it possible to quantitatively determine the parameters of the non-spherical nanoporous structure from NMR data in a non-destructive manner.

Ultrashort echo time magnetization transfer imaging of knee cartilage and meniscus after long-distance running

OBJECTIVE

To assess the detection of changes in knee cartilage and meniscus of amateur marathon runners before and after long-distance running using a 3D ultrashort echo time MRI sequence with magnetization transfer preparation (UTE-MT).

METHODS

We recruited 23 amateur marathon runners (46 knees) in this prospective cohort study. MRI scans using UTE-MT and UTE-T2* sequences were performed pre-race, 2 days post-race, and 4 weeks post-race. UTE-MT ratio (UTE-MTR) and UTE-T2* were measured for knee cartilage (eight subregions) and meniscus (four subregions). The sequence reproducibility and inter-rater reliability were also investigated.

RESULTS

Both the UTE-MTR and UTE-T2* measurements showed good reproducibility and inter-rater reliability. For most subregions of cartilage and meniscus, the UTE-MTR values decreased 2 days post-race and increased after 4 weeks of rest. Conversely, the UTE-T2* values increased 2 days post-race and decreased after 4 weeks. The UTE-MTR values in lateral tibial plateau, central medial femoral condyle, and medial tibial plateau showed a significant decrease at 2 days post-race compared to the other two time points (p < 0.05). By comparison, no significant UTE-T2* changes were found for any cartilage subregions. For meniscus, the UTE-MTR values in medial posterior horn and lateral posterior horn regions at 2 days post-race were significantly lower than those at pre-race and 4 weeks post-race (p < 0.05). By comparison, only the UTE-T2* values in medial posterior horn showed a significant difference.

CONCLUSIONS

UTE-MTR is a promising method for the detection of dynamic changes in knee cartilage and meniscus after long-distance running.

KEY POINTS

• Long-distance running causes changes in the knee cartilage and meniscus. • UTE-MT monitors dynamic changes of knee cartilage and meniscal non-invasively. • UTE-MT is superior to UTE-T2* in monitoring dynamic changes in knee cartilage and meniscus.

Arthroscopic surgery for symptomatic discoid lateral meniscus improves meniscal status assessed by magnetic resonance imaging T2 mapping

INTRODUCTION

Discoid lateral meniscus (DLM) is an anatomic knee variant associated with increased tears and degeneration. This study aimed to quantify meniscal status with magnetic resonance imaging (MRI) T2 mapping before and after arthroscopic reshaping surgery for DLM.

MATERIALS AND METHODS

We retrospectively reviewed the records of patients undergoing arthroscopic reshaping surgery for symptomatic DLM with ≥ 2-year follow-up. MRI T2 mapping was performed preoperatively and at 12 and 24 months postoperatively. T2 relaxation times of the anterior and posterior horns of both menisci and of the adjacent cartilage were assessed.

RESULTS

Thirty-six knees from 32 patients were included. The mean age at surgery was 13.7 years (range 7-24), and the mean follow-up duration was 31.0 months. Saucerization alone was performed on five knees and saucerization with repair on 31 knees. Preoperatively, the T2 relaxation time of the anterior horn of the lateral meniscus was significantly longer than that of the medial meniscus (P < 0.01). T2 relaxation time significantly decreased at 12 and 24 months postoperatively (P < 0.01). Assessments of the posterior horn were comparable. The T2 relaxation time was significantly longer in the tear versus non-tear side at each time point (P < 0.01). There were significant correlations between the T2 relaxation time of the meniscus and that of the corresponding area of the lateral femoral condyle cartilage (anterior horn: r = 0.504, P = 0.002; posterior horn: r = 0.365, P = 0.029).

CONCLUSIONS

The T2 relaxation time of symptomatic DLM was significantly longer than that of the medial meniscus preoperatively, and it decreased 24 months after arthroscopic reshaping surgery. The meniscal T2 relaxation time of the tear side was significantly longer than that of the non-tear side. There were significant correlations between the cartilage and meniscal T2 relaxation times at 24 months after surgery.

Multiscale Label-Free Imaging of Fibrillar Collagen in the Tumor Microenvironment

With recent advances in cancer therapeutics, there is a great need for improved imaging methods for characterizing cancer onset and progression in a quantitative and actionable way. Collagen, the most abundant extracellular matrix protein in the tumor microenvironment (and the body in general), plays a multifaceted role, both hindering and promoting cancer invasion and progression. Collagen deposition can defend the tumor with immunosuppressive effects, while aligned collagen fiber structures can enable tumor cell migration, aiding invasion and metastasis. Given the complex role of collagen fiber organization and topology, imaging has been a tool of choice to characterize these changes on multiple spatial scales, from the organ and tumor scale to cellular and subcellular level. Macroscale density already aids in the detection and diagnosis of solid cancers, but progress is being made to integrate finer microscale features into the process. Here we review imaging modalities ranging from optical methods of second harmonic generation (SHG), polarized light microscopy (PLM), and optical coherence tomography (OCT) to the medical imaging approaches of ultrasound and magnetic resonance imaging (MRI). These methods have enabled scientists and clinicians to better understand the impact collagen structure has on the tumor environment, at both the bulk scale (density) and microscale (fibrillar structure) levels. We focus on imaging methods with the potential to both examine the collagen structure in as natural a state as possible and still be clinically amenable, with an emphasis on label-free strategies, exploiting intrinsic optical properties of collagen fibers.

Magic angle effect on diffusion tensor imaging in ligament and brain

PURPOSE

To evaluate the magic angle effect on diffusion tensor imaging (DTI) measurements in rat ligaments and mouse brains.

METHODS

Three rat knee joints and three mouse brains were scanned at 9.4 T using a modified 3D diffusion-weighted spin echo pulse sequence with the isotropic spatial resolution of 45 μm. The b value was 1000 s/mm2 for rat knee and 4000 s/mm2 for mouse brain. DTI model was used to investigate the quantitative metrics at different orientations with respect to the main magnetic field. The collagen fiber structure of the ligament was validated with polarized light microscopy (PLM) imaging.

RESULTS

The signal intensity, signal-to-noise ratio (SNR), and DTI metrics in the ligament were strongly dependent on the collagen fiber orientation with respect to the main magnetic field from both simulation and actual MRI scans. The variation of fractional anisotropy (FA) was about ~32%, and the variation of mean diffusivity (MD) was ~11%. These findings were further validated with the numerical simulation at different SNRs (~10.0 to 86.0). Compared to the ligament, the DTI metrics showed little orientation dependence in mouse brains.

CONCLUSION

Magic angle effect plays an important role in DTI measurements in the highly ordered collagen-rich tissues, while MD showed less orientation dependence than FA.

Structural differences between immature and mature articular cartilage of rabbits by microscopic MRI and polarized light microscopy

This study aimed to determine the structural features between immature and mature articular cartilage from the humeral and femoral joints of rabbits. Specimens of articular cartilage (n = 6 for immature tissue, n = 6 for mature tissue) that were still attached to the underlying bone from a humerus (shoulder joint) or femur (knee joint) were imaged using microscopic MRI (µMRI) and polarized light microscopy (PLM). Quantitative µMRI data with a pixel resolution of 11.7-13.2 µm revealed a number of differences between the immature and mature cartilage, including total thickness, and T2 and T1ρ relaxation values. Quantitative PLM data with a pixel resolution of 0.25-1 µm confirmed the µMRI results and revealed additional differences in cellular features between the tissues. The mature cartilage had a clearly defined tidemark, which was absent in the immature tissue. The ability to differentiate specific maturation-related cartilage characteristics could be beneficial to translational studies of degenerative diseases such as osteoarthritis.

The relation between the biochemical composition of knee articular cartilage and quantitative MRI: a systematic review and meta-analysis

OBJECTIVE

Early and non-invasive detection of osteoarthritis (OA) is required to enable early treatment and monitoring of interventions. Some of the earliest signs of OA are the change in proteoglycan and collagen composition. The aim of this study is to establish the relations between quantitative magnetic resonance imaging (MRI) and biochemical concentration and organization in knee articular cartilage.

METHODS

A preregistered systematic literature review was performed using the databases PubMed and Embase. Papers were included if quantitative MRI and a biochemical assay or polarized light microscopy (PLM) was performed on knee articular cartilage, and a quantified correlation was described. The extracted correlations were pooled using a random effects model.

RESULTS

21 papers were identified. The strongest pooled correlation was found for delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) vs proteoglycan concentration (r = 0.59). T1ρ relaxation times are inversely correlated to proteoglycan concentration (r = -0.54). A weak correlation between T2 relaxation times and proteoglycans was found (r = -0.38). No correlation between T2 relaxation time and collagen concentration was found (r = -0.02). A heterogeneous set of correlations between T2 relaxation times and PLM were identified, including strong correlations to anisotropy.

CONCLUSION

DGEMRIC measures are significantly correlated to proteoglycan concentration. The needed contrast agent is however a disadvantage; the T1ρ sequence was found as a non-invasive alternative. Remarkably, no correlation was found between T2 relaxation times and collagen concentration. T2 relaxation times is related to organization, rather than concentration of collagen fibers.

PROSPERO ID

CRD42020168337.

Patterns of Intervertebral Disk Alteration in Asymptomatic Elite Rowers: A T2* MRI Mapping Study

Background:

Repetitive loading of the back puts elite rowers at risk for acute and chronic back injuries.

Hypothesis:

That asymptomatic elite rowers would demonstrate characteristic intervertebral disk (IVD) alterations on T2* magnetic resonance imaging (MRI) mapping compared with asymptomatic nonrowers.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

This study included 20 asymptomatic elite rowers (mean age, 23.4 ± 3.03 years; 9 women, 11 men) studied at 2 different times, once before (t₁) and once after (t₂) the competition phase. MRI including T2* mapping was performed on a 3-T scanner. The authors derived normative T2* data from a previous study on 40 asymptomatic volunteers (20 men, 20 women) who were not competitive rowers; based on complete T2* data sets, 37 controls were included. T2* values were compared between groups in 4 lumbar IVDs, and midsagittal T2* values were compared in 5 zones: anterior annulus fibrosus (AF), anterior nucleus pulposus (NP), central NP, posterior NP, and posterior AF. The Pfirrmann grade was used for morphological assessment of disk degeneration. Statistical analysis was conducted using the Mann-Whitney U test, Wilcoxon matched-pairs test, and Spearman rank correlation coefficient.

Results:

Lower T2* values were noted in the rower group compared with the controls (37.08 ± 33.63 vs 45.59 ± 35.73 ms, respectively; P < .001). The intersegmental comparison revealed lower mean T2* values among rowers (P ≤ .027 for all). The interzonal comparison indicated significantly lower mean T2* values for the rowers in all zones except for the anterior NP (P ≤ .008 for all). Lower mean T2* values were observed for the rowers at t₁ versus t₂ (39.25 ± 36.19 vs 43.97 ± 38.67 ms, respectively; P = .008). The authors noted a higher level of IVD damage according to Pfirrmann assessment in the rower cohort (P < .001); the Pfirrmann grade distributions of rowers versus controls, respectively, were as follows: 51.3% versus 73.7% (grade 1), 20.5% versus 19.5% (grade 2), 21.8% versus 6.8% (grade 3), 5.1% versus 0% (grade 4), and 1.3% versus 0% (grade 5). The authors also noted a correlation between low T2* and high Pfirrmann grade at t₁ (r =–0.48; P < .001) and t₂ (r =–0.71; P < .001).

Conclusion:

The cohort of elite rowers revealed more degenerative IVD changes compared with controls. The T2* values suggest that repetitive loading of the spine has demonstrable short-term and possibly permanent effects on the lumbar IVD.

Dipolar Relaxation of Water Protons in the Vicinity of a Collagen-like Peptide

Quantitative magnetic resonance imaging is one of the few available methods for noninvasive diagnosis of degenerative changes in articular cartilage. The clinical use of the imaging data is limited by the lack of a clear association between structural changes at the molecular level and the measured magnetic relaxation times. In anisotropic, collagen-containing tissues, such as articular cartilage, the orientation dependency of nuclear magnetic relaxation can obscure the content of the images. Conversely, if the molecular origin of the phenomenon would be better understood, it would provide opportunities for diagnostics as well as treatment planning of degenerative changes in these tissues. We study the magnitude and orientation dependence of the nuclear magnetic relaxation due to dipole–dipole coupling of water protons in anisotropic, collagenous structures. The water–collagen interactions are modeled with molecular dynamics simulations of a small collagen-like peptide dissolved in water. We find that in the vicinity of the collagen-like peptide, the dipolar relaxation of water hydrogen nuclei is anisotropic, which can result in orientation-dependent relaxation times if the water remains close to the peptide. However, the orientation-dependency of the relaxation is different from the commonly observed magic-angle phenomenon in articular cartilage MRI.

Location-Specific Study of Young Rabbit Femoral Cartilage by Quantitative µMRI and Polarized Light Microscopy

OBJECTIVE

Microscopic magnetic resonance imaging (µMRI) and polarized light microscopy (PLM) are used to characterize the structural variations at different anatomical locations of femoral cartilage in young rabbits (12-14 weeks old).

DESIGN

Four intact knees were imaged by µMRI at 86 µm resolution. Three small cartilage-bone specimens were harvested from each of 2 femoral medial condyles and imaged by quantitative µMRI (T2 anisotropy) at 9.75 µm resolution (N = 6). These specimens, as well as the other 2 intact femoral condyles, were used for histology and imaged by quantitative PLM (retardation and angle) at 0.25 µm to 4 µm resolutions.

RESULTS

Quantitative MRI relaxation data and PLM fibril data revealed collaboratively distinct topographical variations in both cartilage thickness and its collagen organization in the juvenile joint. Cartilage characteristics from the central location have a 3-zone arcade-like fibril structure and a distinct magic angle effect, commonly seen in mature articular cartilage, while cartilage at the anterior location lacks these characteristics. Overall, the lowest retardation values and isotropic T2 values have been found in the distal femur (trochlear ridge), with predominant parallel fibers with respect to the articular surface. Central cartilage is the thickest (~550 µm), approximately twice as thick as the anterior and posterior locations.

CONCLUSION

Distinctly different characteristics of tissue properties were found in cartilage at different topographical locations on femoral condyle in rabbits. Knowledge of location-specific structural differences in the collagen network over the joint surface can improve the understanding of local mechanobiology and provide insights to tissue engineering and degradation repairs.

AI MSK clinical applications: cartilage and osteoarthritis

The advancements of artificial intelligence (AI) for osteoarthritis (OA) applications have been rapid in recent years, particularly innovations of deep learning for image classification, lesion detection, cartilage segmentation, and prediction modeling of future knee OA development. This review article focuses on AI applications in OA research, first describing machine learning (ML) techniques and workflow, followed by how these algorithms are used for OA classification tasks through imaging and non-imaging-based ML models. Deep learning applications for OA research, including analysis of both radiographs for automatic detection of OA severity, and MR images for detection of cartilage/meniscus lesions and cartilage segmentation for automatic T₂ quantification will be described. In addition, information on ML models that identify individuals at high risk of OA development will be provided. The future vision of machine learning applications in imaging of OA and cartilage hinges on implementation of AI for optimizing imaging protocols, quantitative assessment of cartilage, and automated analysis of disease burden yielding a faster and more efficient workflow for a radiologist with a higher level of reproducibility and precision. It may also provide risk assessment tools for individual patients, which is an integral part of precision medicine.

Machine learning to predict incident radiographic knee osteoarthritis over 8 Years using combined MR imaging features, demographics, and clinical factors: data from the Osteoarthritis Initiative

OBJECTIVE

To develop a machine learning-based prediction model for incident radiographic osteoarthritis (OA) of the knee over 8 years using MRI-based cartilage biochemical composition and knee joint structure, demographics, and clinical predictors including muscle strength and symptoms.

DESIGN

Individuals (n = 1,044) with baseline Kellgren Lawrence (KL) grade 0-1 in the right knee from the Osteoarthritis Initiative database were analyzed. 3T MRI at baseline was used to quantify knee cartilage T₂, and Whole-Organ Magnetic Resonance Imaging Scores (WORMS) were obtained for cartilage, meniscus, and bone marrow. The outcome was set as true if a subject developed KL grade 2-4 OA in the right knee over 8 years (n = 183) and false if the subject remained at KL 0-1 over 8 years (n = 861). We developed and compared three models: Model 1: 112 predictors based on OA risk factors; Model 2: top ten predictors based on feature importance score from Model 1 and clinical relevance; Model 3: Model 2 without the imaging predictors. We compared the models using the area under the ROC curve derived from hold-out data.

RESULTS

The 10-predictor model (Model 2, that includes cartilage and meniscus WORMS scores and cartilage T₂) had a slightly lower AUC (0.772) compared to the model with 112 predictors (Model 1: AUC = 0.792, p = 0.739); and had a significantly higher AUC compared to the model without MR imaging predictors (Model 3, AUC = 0.669, p = 0.011).

CONCLUSIONS

A 10-predictor model including MRI parameters coupled with demographics, symptoms, muscle, and physical activity scores provides good prediction of incident radiographic OA over 8 years.

Structural Morphology of Rabbit Patella and Suprapatella Cartilage by Microscopic MRI and Polarized Light Microscopy

OBJECTIVE

In order to appreciate the roles articular cartilage of sesamoid bones and sesamoid fibrocartilage play in anatomy and pathology, the articular cartilage of the patella (n = 4) and suprapatella (n = 4) (a sesamoid fibrocartilage) of 12 to 14 weeks old New Zealand rabbits were studied qualitatively and quantitatively.

DESIGN/METHOD

The intact knee joints and block specimens from the joints were imaged using microscopic magnetic resonance imaging (µMRI) at a 97.6-µm pixel resolution for the former and 19.5-µm resolution for the latter. Histological sections were made out of the µMRI-imaged specimens, which were imaged using polarized light microscopy (PLM) at 0.25-, 1-, and 4-µm pixel resolutions.

RESULTS

The patella cartilage varied in thickness across the medial to lateral ends of the sesamoid bone with the central medial aspect slightly thicker than the lateral aspect. The suprapatella fibrocartilage decreased proximally away from the knee joint. Quantitative results of patellar cartilage showed strong dependence of fiber orientation with the tissue depth. Three histological zones can be clearly observed, which are similar to articular cartilage from other large animals. The sesamoid fibrocartilage has one thin surface layer (10 µm thick) of parallel-arranged structured fibers followed immediately by the majority of random fibers in bulk tissue. T2 relaxation time anisotropy was observed in the patellar cartilage but not in the bulk fibrocartilage.

CONCLUSION

Given the different functions of these 2 different types of cartilages in joint motion, these quantitative results will be beneficial to future studies of joint diseases using rabbits as the animal model.

Review of Quantitative Knee Articular Cartilage MR Imaging

Osteoarthritis (OA) is one of the most prevalent disorders in today’s society, resulting in significant socio-economic costs and morbidity. MRI is widely used as a non-invasive imaging tool for OA of the knee. However, conventional knee MRI has limitations to detect subtle early cartilage degeneration before morphological changes are visually apparent. Novel MRI pulse sequences for cartilage assessment have recently received increased attention due to newly developed compositional MRI techniques, including: T2 mapping, T1rho mapping, delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), sodium MRI, diffusion-weighted imaging (DWI)/ diffusion tensor imaging (DTI), ultrashort TE (uTE), and glycosaminoglycan specific chemical exchange saturation transfer (gagCEST) imaging. In this article, we will first review these quantitative assessments. Then, we will discuss the variations of quantitative values of knee articular cartilage with cartilage layer (depth)- and angle (regional)-dependent approaches. Multiple MRI sequence techniques can discern qualitative differences in knee cartilage. Normal articular hyaline cartilage has a zonal variation in T2 relaxation times with increasing T2 values from the subchondral bone to the articular surface. T1rho values were also higher in the superficial layer than in the deep layer in most locations in the medial and lateral femoral condyles, including the weight-bearing portion. Magic angle effect on T2 mapping is clearly observed in the both medial and lateral femoral condyles, especially within the deep layers. One of the limitations for clinical use of these compositional assessments is a long scan time. Recent new approaches with compressed sensing (CS) and MR fingerprinting (MRF) have potential to provide accurate and fast quantitative cartilage assessments.

Low-field and variable-field NMR relaxation studies of H2O and D2O molecular dynamics in articular cartilage

Osteoarthritis (OA) as the main degenerative disease of articular cartilage in joints is accompanied by structural and compositional changes in the tissue. Degeneration is a consequence of a reduction of the amount of macromolecules, the so-called proteoglycans, and of a corresponding increase in water content, both leading to structural weakening of cartilage. NMR investigations of cartilage generally address only the relaxation properties of water. In this study, two-dimensional (T1-T2) measurements of bovine articular cartilage samples were carried out for different stages of hydration, complemented by molecular exchange with D2O and treatment by trypsin which simulates degeneration by OA. Two signal components were identified in all measurements, characterized by very different T2 which suggests liquid-like and solid-like dynamics. These measurements allow the quantification of separate hydrogen components and their assignment to defined physical pools which had been discussed repeatedly in the literature, i.e. bulk-like water and a combination of protein hydrogens and strongly bound water. The first determination of 2H relaxation dispersion in comparison to 1H dispersion suggests intramolecular interactions as the dominating source for the pronounced magnetic field dependence of the longitudinal relaxation time T1.

Macromolecular fraction (MMF) from 3D ultrashort echo time cones magnetization transfer (3D UTE-Cones-MT) imaging predicts meniscal degeneration and knee osteoarthritis

OBJECTIVE

Meniscal degeneration is strongly associated with osteoarthritis (OA). We aimed to evaluate a 3D ultrashort-echo-time Cones magnetization transfer (UTE-Cones-MT) sequence for quantification of macromolecular fraction (MMF) and MT ratio (MTR) in menisci of healthy volunteers and patients with different degrees of OA.

METHODS

Patients with mild OA (n = 19; 37-86 years; 10 males) or advanced OA (n = 12; 52-88 years; 4 males) and healthy volunteers (n = 17; 20-49 years; 7 males) were scanned with T2-FSE and UTE-Cones-MT sequences at 3T. Morphological assessment was performed using meniscal whole-organ magnetic resonance imaging score (WORMS). MMF and MTR were calculated for menisci, and correlated with age and meniscal WORMS scores. The diagnostic efficiency was performed by using receiver operating characteristic (ROC) curve and the area under the curve (AUC) analyses.

RESULTS

Decreased MMF and MTR were observed in menisci of patients with mild or advanced OA compared with healthy subjects, and in menisci with tears (Grade 2-4) compared with normal menisci (Grade 0). Significant negative correlations were observed between MMF (r = -0.769, P < 0.01), MTR (r = -0.320, P < 0.01), and meniscal WORMS score. There was a mild negative correlation between MMF (r = -0.438, P < 0.01), MTR (r = -0.289, P < 0.01), and age. The AUC values of MMF and MTR in the four horns of meniscus and the posterior horn medial meniscus for differentiating OA patients from healthy volunteers were 0.762 and 0.699, and 0.835 and 0.883, respectively.

CONCLUSION

The 3D UTE-Cones-MT biomarkers of MTR and especially MMF can detect compositional changes in meniscus and differentiate healthy subjects from patients with mild or advanced knee OA.

Deuterium double quantum-filtered NMR studies of peripheral and optic nerves

OBJECTIVE

Characterization of the nerve components by deuterium double quantum-filtered magnetization transfer (DQF-MT) NMR.

METHODS

Nerves were equilibrated in deuterated saline and ²H single-pulse and ²H DQF-MT NMR spectra were measured, enabling the separation of the different water compartments, according to their quadrupolar splittings.

RESULTS

Rat sciatic and brachial nerves and porcine optic nerve immersed in deuterated saline yielded ²H DQF spectra composed of three pairs of quadrupolar-split signals assigned to the water in the collagenous compartments and the myelin bilayer and one narrow signal assigned to the axonal water. Stretching of the nerves, application of osmotic stress and incubation in collagenase did not affect the quadrupolar splitting of the myelin water. The signals of myelin and axonal water were shown to decay during Wallerian degeneration and to rise during maturation. The chemical exchange between the myelin and the intra-axonal water was measured for optic nerve during maturation. The quadrupolar splitting of the signal of myelin water was not sensitive to its orientation relative to the magnetic field. This resembles liquid crystalline behavior, but leaves its mechanism open for interpretation.

CONCLUSIONS

²H DQF-MT NMR characterizes the different components of nerves, the water exchange between them and their changes during processes such as nerve maturation and Wallerian degeneration.

Characterization of anisotropic T2W signals from human knee femoral cartilage: The magic angle effect on a spherical surface

The aim of the current study was to propose a generalized magic angle effect (gMAE) function for characterizing anisotropic T2W signals of human knee femoral cartilage with a spherical surface in clinical studies. A gMAE model function f(α, ε) was formulated for an orientation-dependent (ε) transverse T₂ (i.e., 1/R₂ ) relaxation in cartilage assuming an axially symmetric distribution (α) of collagen fibers. T2W sagittal images were acquired on an adult volunteer's healthy knee at 3 T, and ROI-based average signals S(ε) were extracted from angularly and radially segmented femoral cartilage. Compared with the standard MAE (sMAE) functions in the deep (DZ, α = 0°) and in the superficial (SZ, α = 90°) zones, a general form of R₂ orientation-dependent function f(α, ε) was fitted to S(ε), including an isotropic R₂ contribution (internal reference [REF]). Goodness of fit was evaluated by root-mean-square deviations (RMSDs). An F-test and a paired t-test were respectively used to assess significant differences between the observed variances and means, with statistical significance set to p less than .05. As a symmetric orientation-dependence function with a varying dynamic range, the proposed gMAE model outperformed the previous sMAE functions manifested by significantly reduced RMSDs in the DZ (0.239 ± 0.122 vs. 0.267 ± 0.097, p = .014) and in the SZ (0.183 ± 0.081 vs. 0.254 ± 0.085, p < .001). The fitted average angle α (38.5 ± 34.6° vs. 45.1 ± 30.1°, p < .43) and REF (5.092 ± 0.369 vs. 5.305 ± 0.440, p < .001) were smaller in the DZ than those in SZ, in good agreement with the reported collagen fibril microstructural configurations and the nonbound water contribution to R₂ in articular cartilage. In conclusion, a general form of the magic angle effect function was proposed and demonstrated for better characterizing anisotropic T2W signals from human knee femoral cartilage at 3 T in clinical studies.

Serum cartilage oligomeric matrix protein is correlated with quantitative magnetic resonance imaging and arthroscopic cartilage findings in anterior cruciate ligament deficient knees without osteoarthritic changes

INTRODUCTION/OBJECTIVES

To investigate the association between serum biomarker [cartilage oligomeric matrix protein (COMP) and matrix metalloproteinase-3 (MMP-3)] levels and clinical, magnetic resonance imaging (MRI), and arthroscopic findings in anterior cruciate ligament (ACL)-deficient knees without osteoarthritic changes on radiographs.

METHOD

Patients with ACL injury of Kellgren-Lawrence grade 0 or 1 were enrolled. Serum COMP and MMP-3 levels were measured preoperatively. Correlations of serum biomarker levels with age, body mass index (BMI), duration from time of injury, Tegner activity scale (TAS) score, Lysholm knee score, International Knee Documentation Committee score, KT-1000 arthrometer measurements, whole-organ MRI score (WORMS), MRI T2 relaxation time, and arthroscopic International Cartilage Research Society (ICRS) grade were assessed by calculating Spearman correlation coefficients. Associations between intraoperative findings (cartilage, meniscus) and serum biomarker levels were determined using the Mann-Whitney U test. Multiple regression analysis was performed to investigate the correlations between serum biomarker levels and MRI and arthroscopic findings.

RESULTS

Ninety-eight patients with a mean age of 23.7 years were enrolled. Higher serum COMP level was correlated with older age and higher BMI, TAS score, serum MMP-3 level, WORMS, and T2 relaxation times (medial femur, medial tibia). Multivariate analysis showed that the serum COMP level was independently associated with WORMS and ICRS grade.

CONCLUSIONS

The serum COMP level was correlated with age, BMI, TAS score, and MMP-3 level in ACL-deficient knees and was independently correlated with WORMS and ICRS grade. Thus, the serum COMP level can help detect cartilage degeneration even in patients without radiographic osteoarthritic changes. Key Points • Serum COMP correlated with WORMS and ICRS grade in ACL deficient knee. • The serum COMP level could help in detecting cartilage degeneration, even in patients with no radiographic osteoarthritic changes.

Change in Susceptibility Values in Knee Cartilage After Marathon Running Measured Using Quantitative Susceptibility Mapping

BACKGROUND

Quantitative susceptibility mapping (QSM) has been used to study the magnetic susceptibility properties of collagen fibers in articular cartilage; however, it is unclear whether QSM is sensitive to changes due to degradation caused by long-distance running. It is clinically important to understand the link between long-distance running and microstructural changes in knee cartilage.

PURPOSE

To investigate the ability of QSM to assess microstructural changes within cartilage after repetitive loading.

STUDY TYPE

Prospective.

POPULATION

Thirteen recreational, male long-distance runners.

FIELD STRENGTH/SEQUENCE

Three-dimensional gradient recalled echo acquired at 3 T.

ASSESSMENT

Magnetic resonance imaging (MRI) and 3D kinematics (translations and rotations during treadmill walking and running) of the knee joint were collected before and after marathon running. The compartments for analysis included the patella, trochlea, and subregions of femoral and tibial cartilage. Changes in regional susceptibility and cartilage thickness were calculated after marathon running. A susceptibility profile was obtained by fitting susceptibility as a function of the normalized depth of cartilage from the superficial to deep layers.

STATISTICAL TESTS

Paired t-test or Wilcoxon signed-rank test, 95% confidence interval (CI) of the depth-wise susceptibility profile, Pearson correlation or Spearman correlation.

RESULTS

There was a statistically significant increase in susceptibility value in the weight-bearing region of central medial femoral cartilage (cMF-c) after marathon running (pre-marathon: -0.0219 ± 0.0151 ppm, post-marathon: -0.0070 ± 0.0213 ppm, P < 0.05), while the cartilage thickness did not show significant changes in any regions (P-value range: 0.068-0.963). Significant susceptibility elevations occurred in the middle and deep layers of cMF-c (95% CIs did not overlap). A trend toward a positive correlation was found between the changes in susceptibility value in cMF-c and proximal-distal translation of the knee joint during walking (r = 0.55, P = 0.101) and running (r = 0.57, P = 0.089).

DATA CONCLUSION

Localized magnetic susceptibility alterations were observed within knee cartilage in the weight-bearing area after repetitive loading without any morphologic changes.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 2.

What Is the Correlation Among dGEMRIC, T1p, and T2* Quantitative MRI Cartilage Mapping Techniques in Developmental Hip Dysplasia?

BACKGROUND

Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) is a validated technique for evaluating cartilage health in developmental dysplasia of the hip (DDH), which can be a helpful prognosticator for the response to surgical treatments. dGEMRIC requires intravenous injection of gadolinium contrast, however, which adds time, expense, and possible adverse reactions to the imaging procedure. Newer MRI cartilage mapping techniques such as T1 rho (ρ) and T2* have been performed in the hip without the need for any contrast, although it is unknown whether they are equivalent to dGEMRIC.

QUESTION/PURPOSE

In this study, our purpose was to determine the correlation between the relaxation values of three cartilage mapping techniques, dGEMRIC, T1ρ, and T2*, in patients with DDH.

METHODS

Fifteen patients with DDH (three male, 12 female; mean age 29 ± 9 years) scheduled for periacetabular osteotomy underwent preoperative dGEMRIC, T1ρ, and T2* MRI at 3T with quantitative cartilage mapping. The outcomes of dGEMRIC, T1ρ, and T2* mapping were calculated for three regions of interest (ROI) to analyze the weightbearing cartilage of the hip: global ROI, anterior and posterior ROI, and further subdivided into medial, intermediate, and lateral to generate six smaller ROIs. The correlation between the respective relaxation time values was evaluated using the Spearman correlation coefficient (rS) for each ROI, categorized as negligible, weak, moderate, strong, or very strong. The relaxation values within the subdivided ROIs were compared for each of the three cartilage mapping techniques using the Kruskal-Wallis test.

RESULTS

There was a moderate correlation of T1ρ and T2* relaxation values with dGEMRIC relaxation values. For the global ROI, there was a moderate correlation between dGEMRIC and T2* (moderate; rS = 0.63; p = 0.01). For the anterior ROI, a moderate or strong correlation was found between dGEMRIC and both T1ρ and T2*: dGEMRIC and T1ρ (strong; rS = -0.71; p = 0.003) and dGEMRIC and T2* (moderate; rS = 0.69; p = 0.004). There were no correlations for the posterior ROI. The mean dGEMRIC, T1ρ, and T2* relaxation values were not different between the anterior and posterior ROIs nor between the subdivided six ROIs.

CONCLUSION

Quantitative T1ρ and T2* cartilage mapping demonstrated a moderate correlation with dGEMRIC, anteriorly and globally, respectively. However, the clinical relevance of such a correlation remains unclear. Further research investigating the correlation of these two noncontrast techniques with clinical function and outcome scores is needed before broad implementation in the preoperative investigation of DDH.

LEVEL OF EVIDENCE

Level II, diagnostic study.

Quantitative 3D Ultrashort Echo Time Magnetization Transfer Imaging for Evaluation of Knee Cartilage Degeneration In Vivo

BACKGROUND

Recent studies suggest that macromolecular fraction (MMF) derived from three-dimensional ultrashort echo time magnetization transfer (UTE-MT) imaging is insensitive to the magic angle effect. However, its clinical use in osteoarthritis (OA) remains to be investigated.

PURPOSE

To investigate the feasibility of 3D UTE-MT-derived MMF in differentiating normal from degenerated cartilage.

STUDY TYPE

Prospective.

SUBJECTS

Sixty-two participants (54.8 ± 16.7 years, 30 females) with and without OA, plus two healthy volunteers (mean age 35.0 years) for reproducibility test.

FIELD STRENGTH/SEQUENCE

3 T/UTE-MT sequence.

ASSESSMENT

A 3D UTE-MT sequence was employed to calculate MMF based on a two-pool model. Kellgren-Lawrence (KL) grade and Whole-Organ Magnetic Resonance Imaging Score (WORMS) were evaluated by three experienced musculoskeletal radiologists. KL grade was condensed into three groups: KL0, KL1-2, and KL3-4. WORMS was regrouped based on extent of lesion (extent group) and depth of lesion (depth group), respectively. The performance of MMF at evaluating the degeneration of cartilage was assessed via Spearman's correlation coefficient and the area under the curve (AUC) calculated according to the receiver-operating characteristic curve.

STATISTICAL TESTS

After normality check, one-way analysis of variance was used to evaluate the performance. Tukey-Kramer test was performed for post hoc testing.

RESULTS

MMF showed significant negative correlations with KL grade (r = -0.53, P < 0.05) and WORMS (r = -0.49, P < 0.05). Significantly lower MMFs were found in subjects with greater KL grade (11.8 ± 0.8% for KL0; 10.9 ± 0.9% for KL1-2; 10.6 ± 1.1% for KL3-4; P < 0.05) and in cartilage with greater extent (12.1 ± 1.6% for normal cartilage; 10.9 ± 1.6% for regional lesions; 9.6 ± 1.7% for diffuse lesions; P < 0.05) and depth (12.1 ± 1.6% for normal cartilage; 10.6 ± 1.6% for partial-thickness lesions; 8.8 ± 1.7% for full-thickness lesions; P < 0.05) of lesions. AUC values of MMF for doubtful-minimal OA (KL1-2) and mild cartilage degradation (WORMS1-2) were 0.8 and 0.7, respectively.

DATA CONCLUSION

This study highlights the clinical potential of MMF in the detection of early OA.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 2.

Orientation anisotropy of quantitative MRI parameters in degenerated human articular cartilage

Quantitative magnetic resonance (MR) relaxation parameters demonstrate varying sensitivity to the orientation of the ordered tissues in the magnetic field. In this study, the orientation dependence of multiple relaxation parameters was assessed in cadaveric human cartilage with varying degree of natural degeneration, and compared with biomechanical testing, histological scoring, and quantitative histology. Twelve patellar cartilage samples were imaged at 9.4 T MRI with multiple relaxation parameters, including T₁ , T₂ , CW - T_1ρ , and adiabatic T_1ρ , at three different orientations with respect to the main magnetic field. Anisotropy of the relaxation parameters was quantified, and the results were compared with the reference measurements and between samples of different histological Osteoarthritis Research Society International (OARSI) grades. T₂ and CW - T_1ρ at 400 Hz spin-lock demonstrated the clearest anisotropy patterns. Radial zone anisotropy for T₂ was significantly higher for samples with OARSI grade 2 than for grade 4. The proteoglycan content (measured as optical density) correlated with the radial zone MRI orientation anisotropy for T₂ (r = 0.818) and CW - T_1ρ with 400 Hz spin-lock (r = 0.650). Orientation anisotropy of MRI parameters altered with progressing cartilage degeneration. This is associated with differences in the integrity of the collagen fiber network, but it also seems to be related to the proteoglycan content of the cartilage. Samples with advanced OA had great variation in all biomechanical and histological properties and exhibited more variation in MRI orientation anisotropy than the less degenerated samples. Understanding the background of relaxation anisotropy on a molecular level would help to develop new MRI contrasts and improve the application of previously established quantitative relaxation contrasts.

T2 analysis of the entire osteoarthritis initiative dataset

While substantial work has been done to understand the relationships between cartilage T₂ relaxation times and osteoarthritis (OA), diagnostic and prognostic abilities of T₂ on a large population yet need to be established. Using 3921 manually annotated 2D multi-slice multi-echo spin-echo magnetic resonance imaging volume, a segmentation model for automatic knee cartilage segmentation was built and evaluated. The optimized model was then used to calculate T₂ values on the entire osteoarthritis initiative (OAI) dataset composed of longitudinal acquisitions of 4796 unique patients, 25 729 magnetic resonance imaging studies in total. Cross-sectional relationships between T₂ values, OA risk factors, radiographic OA, and pain were analyzed in the entire OAI dataset. The performance of T₂ values in predicting the future incidence of radiographic OA as well as total knee replacement (TKR) were also explored. Automatic T₂ values were comparable with manual ones. Significant associations between T₂ relaxation times and demographic and clinical variables were found. Subjects in the highest 25% quartile of tibio-femoral T₂ values had a five times higher risk of radiographic OA incidence 2 years later. Elevation of medial femur T₂ values was significantly associated with TKR after 5 years (coeff = 0.10; P = .036; CI = [0.01,0.20]). Our investigation reinforces the predictive value of T₂ for future incidence OA and TKR. The inclusion of T₂ averages from the automatic segmentation model improved several evaluation metrics when compared to only using demographic and clinical variables.

Associations Between Vitamins C and D Intake and Cartilage Composition and Knee Joint Morphology Over 4 Years: Data From the Osteoarthritis Initiative

OBJECTIVE

To determine the cross-sectional and longitudinal associations of vitamin C and D intake with magnetic resonance imaging (MRI) measures of cartilage composition (T2) and joint structure (cartilage, meniscus, and bone marrow) using data from the Osteoarthritis Initiative (OAI) cohort.

METHODS

A total of 1,785 subjects with radiographic Kellgren/Lawrence knee grades 0-3 in the right knee were selected from the OAI database. Vitamins C and vitamin D intake (diet, supplements, and total) were assessed using the Block Brief 2000 Food Frequency Questionnaire at baseline. The MRI analysis protocol included 3T cartilage T2 quantification and semiquantitative joint morphology gradings (Whole-Organ Magnetic Resonance Imaging Score [WORMS]) at baseline and 4 years. Linear regression was used to assess the association between standardized baseline vitamin intake and both baseline WORMS scores and standardized cartilage T2 values.

RESULTS

Higher vitamin C intake was associated with lower average cartilage T2 values, medial tibia T2 values, and medial tibia WORMS scores (standardized coefficient range -0.07 to -0.05, P < 0.05). Higher vitamin D intake was associated with a lower cartilage WORMS sum score and medial femur WORMS score (standardized coefficient range -0.24 to -0.09, P < 0.05). Consistent use of vitamin D supplements of 400 IU at least once a week over 4 years was associated with significantly less worsening of cartilage, meniscus, and bone marrow abnormalities (odds ratio range 0.40-0.56, P < 0.05).

CONCLUSION

Supplementation with vitamin D over 4 years was associated with significantly less progression of knee joint abnormalities. Given the observational nature of this study, future longitudinal randomized controlled trials of vitamin D supplementation are warranted.

A mobile MRI field study of the biochemical cartilage reaction of the knee joint during a 4,486 km transcontinental multistage ultra-marathon using T2* mapping

Nearly nothing is known about the consequences of ultra-long-distance running on knee cartilage. In this mobile MRI field study, we analysed the biochemical effects of a 4,486 km transcontinental multistage ultra-marathon on femorotibial joint (FTJ) cartilage. Serial MRI data were acquired from 22 subjects (20 male, 18 finisher) using a 1.5 T MR scanner mounted on a 38-ton trailer, travelling with the participants of the TransEurope FootRace (TEFR) day by day over 64 stages. The statistical analyses focused on intrachondral T2* behaviour during the course of the TEFR as the main outcome variable of interest. T2* mapping (sagittal FLASH T2* weighted gradient echo) is a validated and highly accurate method for quantitative compositional cartilage analysis of specific weightbearing areas of the FTJ. T2* mapping is sensitive to changes in the equilibrium of free intrachondral water, which depends on the content and orientation of collagen and the proteoglycan content in the extracellular cartilage matrix. Within the first 1,100 km, a significant running load-induced T2* increase occurred in all joint regions: 44.0% femoral-lateral, 42.9% tibial-lateral, 34.9% femoral-medial, and 25.1% tibial-medial. Osteochondral lesions showed no relevant changes or new occurrence during the TEFR. The reasons for stopping the race were not associated with knee problems. As no further T2* elevation was found in the second half of the TEFR but a decreasing T2* trend (recovery) was observed after the 3,500 km run, we assume that no further softening of the cartilage occurs with ongoing running burden over ultra-long distances extending 4,500 km. Instead, we assume the ability of the FTJ cartilage matrix to reorganize and adapt to the load.

Assessment of Meniscal Healing Status by Magnetic Resonance Imaging T2 Mapping After Meniscal Repair

BACKGROUND

Although the sensitivity and specificity of magnetic resonance imaging (MRI) for the diagnosis of primary meniscal tears are high, these values are lower for the assessment of healing status of repaired menisci.

PURPOSE

To compare the accuracy of MRI T2 mapping and conventional MRI in assessing meniscal healing after repair.

STUDY DESIGN

Cohort study (diagnosis); Level of evidence, 2.

METHODS

Patients who underwent meniscal repair with concurrent anterior cruciate ligament reconstruction between 2012 and 2016 and had a follow-up second-look arthroscopy were enrolled. The patients were divided into healed and incompletely/not healed groups based on the second-look arthroscopy findings. For the repaired menisci, the following were compared between the groups, (1) Stoller and Crues classification on conventional MRI with a proton density-weighted fat-saturated sequence and (2) the remaining colored meniscal tear line on T2 mapping coincident with the high signal line showing the primary tear on conventional MRI were compared. The change of T2 relaxation time (ΔT2) of the colored meniscal tear line pre- to postoperatively was compared between the groups. The mean T2 relaxation time of the whole area of the postoperative meniscus at each slice was also compared with that of control menisci to assess the whole quality of the repaired meniscus.

RESULTS

A total of 26 menisci from 24 knees were assessed (16 healed menisci, 10 incompletely/not healed menisci). According to the Crues classification on conventional MRI, 8 of 16 healed menisci and 3 of 10 incompletely/not healed menisci improved from grade 3 to 2, with there being no significant difference between the groups (P = .43). However, the colored meniscal tear line remained in only 3 of the 16 healed menisci as compared with 9 of the 10 incompletely/not healed menisci, and the presence of this colored line allowed differentiation between healed menisci and incompletely/not healed menisci (sensitivity, 81.3%; specificity, 90.0%; odds ratio, 39.0; P = .001). The mean (SD) ΔT2 was -31.1 ± 3.2 and -19.9 ± 4.4 ms in the healed and incompletely/not healed groups, respectively (P < .001). Receiver operating characteristic curve analysis showed a cutoff ΔT2 value of -22.3 ms for separation of meniscal healing (P < .001). The T2 relaxation times of the whole area of the repaired menisci were 31.7 ± 3.4 and 32.8 ± 3.8 ms in the healed and incompletely/unhealed groups, respectively (P = .69), with these values being significantly longer than the 26.9 ± 2.2 ms in the controls (P < .001).

CONCLUSION

MRI T2 mapping allowed the differentiation of healing status after meniscal repair, with high sensitivity and specificity as compared with conventional MRI.

T1- and T2*-Mapping for Assessment of Tendon Tissue Biophysical Properties: A Phantom MRI Study

OBJECTIVES

The aim of this study was to quantitatively assess changes in collagen structure using MR T1- and T2*-mapping in a novel controlled ex vivo tendon model setup.

MATERIALS AND METHODS

Twenty-four cadaveric bovine flexor tendons underwent MRI at 3 T before and after chemical modifications, representing mechanical degeneration and augmentation. Collagen degradation (COL), augmenting collagen fiber cross-linking (CXL), and a control (phosphate-buffered saline [PBS]) were examined in experimental groups, using histopathology as standard of reference. Variable echo-time and variable-flip angle gradient-echo sequences were used for T2*- and T1-mapping, respectively. Standard T1- and T2-weighted spin-echo sequences were acquired for visual assessment of tendon texture. Tendons were assessed subsequently for their biomechanical properties and compared with quantitative MRI analysis.

RESULTS

T1- and T2*-mapping was feasible and repeatable for untreated (mean, 545 milliseconds, 2.0 milliseconds) and treated tendons. Mean T1 and T2* values of COL, CXL, and PBS tendons were 1459, 934, and 1017 milliseconds, and 5.5, 3.6, and 2.5 milliseconds, respectively. T2* values were significantly different between enzymatically degraded tendons, cross-linked tendons, and controls, and were significantly correlated with mechanical tendon properties (r = -0.74, P < 0.01). T1 values and visual assessment could not differentiate CXL from PBS tendons. Photo-spectroscopy showed increased autofluorescence of cross-linked tendons, whereas histopathology verified degenerative lesions of enzymatically degraded tendons.

CONCLUSIONS

T2*-mapping has the potential to detect and quantify subtle changes in tendon collagen structure not visible on conventional clinical MRI. Tendon T2* values might serve as a biomarker for biochemical alterations associated with tendon pathology.

An order parameter without magic angle effect (OPTIMA) derived from R 1 ρ dispersion in ordered tissue

PURPOSE

MR R₂ imaging of ordered tissue exhibits the magic angle effect, potentially masking subtle pathological changes in cartilage. This work aimed to develop an orientation-independent order parameter (S) exclusively sensitive to collagen degeneration.

METHODS

A theory was developed based on R 1 ρ dispersion coupled with a simplified molecular motion model in which anisotropic R 2 a ( θ ) became directly proportional to correlation time τ b θ and S could be derived. This new parameter was validated with ex vivo R 1 ρ dispersion reported on orientated (n = 4), enzymatically depleted bovine cartilage (n = 6), and osteoarthritic human knee specimens (n = 14) at 9.4 Tesla, which was further demonstrated on 1 healthy human knee in vivo at 3 Tesla.

RESULTS

τ b θ from orientation-dependent R 1 ρ dispersion revealed a significantly high average correlation (r = 0.89 ± 0.05, P < 0.05) with R 2 a (θ) on cartilage samples and a moderate correlation (r = 0.48, P < 0.001) for the human knee in vivo. The derived S (10^-3 ) significantly decreased in advanced osteoarthritis (1.64 ± 0.03 vs. 2.30 ± 0.11, P < 0.001) and collagen-depleted samples (1.30 ± 0.11 vs. 2.12 ± 0.12, P < 0.001) when compared with early osteoarthritis and the control, respectively.

CONCLUSION

The proposed order parameter could be a potentially useful orientation-independent MR biomarker for collagen alterations in cartilage and other highly structured tissues.

T2* Mapping of the Adult Intervertebral Lumbar Disc: Normative Data and Analysis of Diurnal Effects

In this prospective study, we sought to establish normative data for T2* analysis of lumbar intervertebral discs (IVDs). Further, potential diurnal effects regarding T2* relaxometry of the lower spine were examined. Lumbar IVDs of young, healthy, adult men (n = 20) and women (n = 20; mean age = 24.5 ± 2.9 years) were assessed. Magnetic resonance imaging including T2* mapping was performed on a 3-T scanner. Mid-sagittal T2* values were obtained in five regions: anterior annulus fibrosus (AF), anterior nucleus pulposus (NP), central NP, posterior NP, and posterior AF. Zonal and segmental differences, as well as diurnal variations between the T2* analysis in the morning and the evening and effects of unloading, were analyzed. Discs with signs of degeneration on morphological images or imaging artifacts were excluded. We noted a zonal and segmental T2* distribution with high values in the NP, low T2* values in the AF and a T2* increase towards the caudal NP. We observed no diurnal differences between the mean T2* values in the morning and in the evening (p = 0.748). The effect of unloading the spine was low (maximum T2* difference between four measurements = 13.6 ms; significant difference noted only between the 0 and 15-min measurement). The T2* values obtained in this study will serve as normative values for future T2* measurements. There are no diurnal influences, and we suggest that unloading of the spine has no demonstrable effect after 30 min on the T2* results. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1956-1962, 2019.

Elite Rowers Demonstrate Consistent Patterns of Hip Cartilage Damage Compared With Matched Controls: A T2* Mapping Study

BACKGROUND

Rowing exposes the femoral head and acetabulum to high levels of repetitive abutment motion and axial loading that may put elite athletes at an increased risk for developing early hip osteoarthritis.

QUESTIONS/PURPOSES

Do elite rowers demonstrate characteristic hip cartilage lesions on T2 MRI sequences compared with asymptomatic individuals who do not row?

METHODS

This study included 20 asymptomatic rowers (mean age, 23 ± 3 years; nine females, 11 males) who had a minimum of 5 years of intensive (≥ 12 hours/week) training. The recruiting of the rowers took place from the central German federal rowing base, which has inherent intense training and selection requirements to declare these athletes as "elite rowers." We investigated one hip per study participant. MRI was performed on a 3-T scanner. The protocol included standard sequences, a double-echo steady-state sequence, and a multiecho data image combination sequence with inline T2 calculation (= the decay of transverse magnetization arising from molecular interactions [T2] and inhomogeneities in the magnetic field resulting from tissue susceptibility-induced field distortions and variations in the magnet itself), which detects changes in water content and the disruption of collagen structure. Although extrinsic and intrinsic influences on the T2 values including diurnal effects, MR technic-derived variations, and anatomic-related regional disparities need to be taken into account, low T2 values well below 20 ms indicate cartilage degeneration. Cartilage was morphologically analyzed in the anterior, anterosuperior, superoanterior, superior, superoposterior, posterosuperior, and posterior regions of the hip and graded as follows: Grade 0 = normal; Grade 1 = signal changes; Grade 2 = cartilage abrasion; Grade 3 = cartilage loss. Labrum was classified as follows: Grade 0 = normal; Grade 1 = partial tear; Grade 2 = full-thickness tear; Grade 3 = labrum degeneration. The T2 measurement was done through a region of interest analysis. For reliability assessment, morphologic evaluation and T2 measurement were performed by two observers while one observer repeated his analysis with a time interval > 2 weeks. Intra- and interobserver reliability was determined using κ analysis and intraclass correlation coefficients. Control T2 data were derived from a previous study on 15 hips in 15 asymptomatic volunteers of similar ages (seven males and eight females) who were not competitive rowers with similar MR hardware and imaging sequences.

RESULTS

Compared with the control group of asymptomatic volunteers who were not competitive rowers, we noted a high level of labrum and cartilage degeneration in the cohort of elite rowers. In the group of elite rowers, cartilage degeneration was noted in all hips. Regarding the acetabular cartilage, 271 zones could be evaluated. Of those, 44% (120 of 271) were graded normal, 6% (15 of 271) revealed signal alteration, 45% (122 of 271) demonstrated cartilage abrasion, and 5% (14 of 271) were noted to have full-thickness cartilage loss. Morphologic cartilage degeneration in the femoral head was less frequent. T2 values were lower than the control hips in all zones except for the posterior central acetabular zone (global T2 acetabular: 20 ± 6 ms, range, 9-36 ms, 95% confidence interval [CI], 19-21 ms versus 25 ± 5 ms, range, 14-44 ms, 95% CI, 24-25 ms, p < 0.001; global T2 femoral: 23 ± 7 ms, range, 9-38 ms, 95% CI, 22-24 ms versus 27 ± 5 ms, range, 17-45 ms, 95% CI, 26-28 ms, p < 0.001). The difference in T2 between the two study groups was superior in the peripheral zone of the anterosuperior region (16 ± 3 ms; range, 10-22 ms, 95% CI, 15-18 ms versus 26 ms ± 5 ms, range, 18-38 ms, 95% CI, 24-29 ms, p < 0.001).

CONCLUSIONS

We found signs of hip cartilage degeneration to a much greater degree in elite rowers than in asymptomatic controls. Although causation cannot be inferred, this is concerning, and future investigations including controlled longitudinal studies both on elite and nonelite athletes with sufficient cohort size are warranted to clarify our findings.

LEVEL OF EVIDENCE

Level III, therapeutic study.

A unique anisotropic R2 of collagen degeneration (ARCADE) mapping as an efficient alternative to composite relaxation metric (R2 -R1 ρ ) in human knee cartilage study

PURPOSE

Anisotropic transverse R₂ (1/T₂ ) relaxation of water proton is sensitive to cartilage degenerative changes. The purpose is to develop an efficient method to extract this relaxation metric in clinical studies.

METHODS

Anisotropic R₂ can be measured inefficiently by standard R₂ mapping after removing an isotropic contribution obtained from R_{1 ρ} mapping. In the proposed method, named as a unique anisotropic R₂ of collagen degeneration (ARCADE) mapping, an assumed uniform isotropic R₂ was estimated at magic angle locations in the deep cartilage, and an anisotropic R₂ was thus isolated in a single T2W sagittal image. Five human knees from 4 volunteers were studied with standard R₂ and R_{1 ρ} mappings at 3T, and anisotropic R₂ derived from ARCADE on the T2W (TE = 48.8 ms) image from R₂ mapping was compared with the composite relaxation (R₂ - R_{1 ρ} ) using statistical analysis including Student's t-test and Pearson's correlation coefficient.

RESULTS

Anisotropic R₂ (1/s) from ARCADE was highly positively correlated with but not significantly different from standard R₂ - R_{1 ρ} (1/s) in the segmented deep (r = 0.83 ± 0.06; 8.3 ± 2.9 vs. 7.3 ± 1.9, P = .50) and the superficial (r = 0.82 ± 0.05; 3.5 ± 2.4 vs. 4.5 ± 1.6, P = .39) zones. However, after eliminating systematic errors by the normalization in terms of zonal contrast, anisotropic R₂ was significantly higher (60.2 ± 18.5% vs. 38.4 ± 16.6%, P < .01) than R₂ - R_{1 ρ} as predicted.

CONCLUSION

The proposed anisotropic R₂ mapping could be an efficient alternative to the conventional approach, holding great promise in providing both high-resolution morphological and more sensitive transverse relaxation imaging from a single T2W scan in a clinical setting.

Spin locking in liquid entrapped in nanocavities: Application to study connective tissues

Study of the spin-lattice relaxation in the spin-locking state offers important information about atomic and molecular motions, which cannot be obtained by spin lattice relaxation in strong external magnetic fields. The application of this technique for the investigation of the spin-lattice relaxation in biological samples with fibril structures reveals an anisotropy effect for the relaxation time under spin locking, T_1ρ. To explain the anisotropy of the spin-lattice relaxation under spin-locking in connective tissue a model which represents a tissue by a set of nanocavities containing water is used. The developed model allows us to estimate the correlation time for water molecular motion in articular cartilage, τ_c=30μs and the averaged nanocavity volume, V≃5400nm³. Based on the developed model which represents a connective tissue by a set of nanocavities containing water, a good agreement with the experimental data from an articular cartilage and a tendon was demonstrated. The fitting parameters were obtained for each layer in each region of the articular cartilage. These parameters vary with the known anatomic microstructures of the tissue. Through Gaussian distributions to nanocavity directions, we have calculated the anisotropy of the relaxation time under spin locking T_1ρ for a human Achilles tendon specimen and an articular cartilage. The value of the fitting parameters obtained at matching of calculation to experimental results can be used in future investigations for characterizing the fine fibril structure of biological samples.

Diffusion based MR measurements correlates with age-related changes in human intervertebral disks

BACKGROUND

Understanding the association between MR parameters and age related deterioration in human intervertebral disks forms an important step in the development of clinical diagnostic protocols for disk disease.

METHODS

Ten unfixed thoracic and lumbar cadaver disk joints, age 37-81 years were imaged at 9.4 T using T2 relaxation (CPMG) and ADC (DWI spin echo) MR protocols. For each MR parameter, spatial maps were computed from the axial images, with the AF and NP segmented based on the T2 maps. Linear regression tested for the correlation between mean and variance (COV) of T2 and ADC with age in the disk, nucleus and annulus, and the effect of thoracic vs. lumbar spine on these correlations.

FINDINGS

In the disk, age negatively correlated with mean ADC (P < 0.001) and positively with COV of ADC (P < 0.001) and T2 (P < 0.05). Age was negatively correlated with mean T2 (P < 0.01), mean ADC (P < 0.001) and positively with COV of ADC (P < 0.001) and T2 (P < 0.05) in the NP and positively correlated with mean T2 (P < 0.05), COV of ADC (P < 0.01) and T2 (P < 0.05) and negatively with mean ADC (P < 0.05) in the AF. Compared to thoracic disks, lumbar disks showed higher mean ADC (P < 0.05), lower mean T2 (P < 0.001) and higher COV of ADC (P < 0.01) and T2 (P < 0.05).

INTERPRETATION

Compared to T2, MR diffusion was a more sensitive measure of age mediated changes in disk tissues. Strong differences in the association of MR parameters with age between the lumbar and thoracic suggest that mechanical environment effects tissue specific MR parameters' association with age.

Maturation-Related Changes in T2 Relaxation Times of Cartilage and Meniscus of the Pediatric Knee Joint at 3 T

OBJECTIVE

The objective of our study was to use a T2 mapping sequence performed at 3 T to investigate changes in the composition and microstructure of the cartilage and menisci of the pediatric knee joint during maturation.

MATERIALS AND METHODS

This retrospective study was performed of MRI examinations of 76 pediatric knees without internal derangement in 72 subjects (29 boys [mean age, 12.5 years] and 43 girls [mean age, 13.0 years]) who were evaluated with a sagittal T2 mapping sequence. T2 relaxation time values were quantitatively measured in eight cartilage subregions and in the medial and lateral menisci. Wilcoxon rank sum and Kruskal-Wallis tests were used to analyze the relationship between cartilage and meniscus T2 relaxation time values and sex and skeletal maturation, respectively. A multivariate linear regression model was used to investigate the independent association between cartilage T2 relaxation time values and age, weight, and body mass index (BMI [weight in kilograms divided by the square of height in meters]).

RESULTS

There were no significant sex differences (p = 0.26-0.91) in T2 relaxation time values for cartilage or meniscus. T2 relaxation time values in each individual cartilage subregion significantly decreased (p < 0.001) with progressive maturation. T2 relaxation time values in the lateral meniscus significantly increased (p = 0.001) with maturation, whereas T2 relaxation time values in the medial meniscus did not significantly change (p = 0.82). There was a significant association (p < 0.001) between cartilage T2 relaxation time values and age independent of weight and BMI, but no significant association between cartilage T2 relaxation time values and weight (p = 0.06) and BMI (p = 0.20) independent of age.

CONCLUSION

Cartilage T2 relaxation time values significantly decreased in all cartilage subregions and meniscus T2 relaxation time values significantly increased in the lateral meniscus during maturation. These changes in T2 relaxation time values reflect age-related changes in tissue composition and microstructure.

Associations between molecular biomarkers and MR-based cartilage composition and knee joint morphology: data from the Osteoarthritis Initiative

OBJECTIVE

The purpose of this study was to assess the associations between serum/urine biomarkers for osteoarthritis and magnetic resonance (MR) imaging measures of cartilage composition and joint structure (cartilage, meniscus, and bone marrow), using MR imaging data from the Osteoarthritis Initiative (OAI).

DESIGN

141 subjects with Kellgren Lawrence (KL) grades 0-3 in the right knee and with available serum/urine biomarker assays were selected from the OAI. Cartilage magnetic resonance imaging (MRI) T2 measurements were performed in the medial femur, lateral femur, medial tibia, lateral tibia, and patella compartments. Compartment-specific knee morphologic grading [whole-organ magnetic resonance imaging score (WORMS)] in the cartilage, meniscus, and bone marrow was also performed. We focused on associations of serum hyaluronan (sHA), serum cartilage oligomeric matrix protein (sCOMP), serum matrix metalloproteinase-3 (sMMP3), and Urine Carboxy-Terminal Telepeptides of Type II Collagen (uCtX-II)) with MRI parameters (T2, WORMS), assessed using partial correlations adjusted for age, gender, body mass index (BMI), KL grade in both knees, and diabetes status.

RESULTS

Higher levels of sHA, sMMP3 and sCOMP were correlated (P < 0.05) with T2 of the lateral femur (r = 0.18 to 0.32) and lateral tibia (r = 0.17 to 0.23), and with average T2 of all knee regions (r = 0.23). uCTXII was correlated with patellar T2 (r = 0.19, P = 0.04). Among the morphologic measures, sHA and sMMP3 was positively correlated (r = 0.17 to 0.21, P < 0.05) with meniscal damage.

CONCLUSIONS

This study suggests weak, but statistically significant, correlations between serum biomarkers of OA (sHA, sCOMP, and sMMP3) and MRI T2 measures of cartilage extra-cellular matrix degeneration.

Matrix changes in articular cartilage in the knee of patients with rheumatoid arthritis after biological therapy: 1-year follow-up evaluation by T2 and T1ρ MRI quantification

AIM

To estimate the morphological changes in the articular cartilage of the knees of patients with rheumatoid arthritis treated with biological disease-modifying anti-rheumatic drugs (bDMARDs).

MATERIALS AND METHODS

Cartilage-specific magnetic resonance imaging (MRI) results, including T2 and T1ρ mapping of the femorotibial joint of 17 patients, were obtained before and 1 year after starting treatment with bDMARDs. Regions of interest were selected on the sagittal images of the cartilage of the medial and lateral femoral condyles (MFC, LFC) and the tibial plateau (MTP, LTP). Cartilage thickness, T2, and T1ρ were measured, and the correlations of their changes were evaluated.

RESULTS

The mean changes in cartilage thickness tended to decrease in all four condyles, and the rate was significant in the MFC. T2 and T1ρ tended to increase, and T2 in the MFC significantly increased. Changes in cartilage thickness after 1 year showed a moderate correlation with the baseline T2 in the MFC as well as changes in T2 in the MTP.

CONCLUSIONS

Decreasing cartilage thickness and matrix changes appeared in the MFC after 1 year of treatment with bDMARDs. Microstructural damage of the cartilage at baseline is a predictor for further cartilage damage in the knee joint, even if treatment with bDMARDs is effective.

Multiparametric MRI and Computational Modelling in the Assessment of Human Articular Cartilage Properties: A Comprehensive Approach

Quantitative magnetic resonance imaging (qMRI) is a promising approach to detect early cartilage degeneration. However, there is no consensus on which cartilage component contributes to the tissue's qMRI signal properties. T1, T1ρ, and T2^⁎ maps of cartilage samples (n = 8) were generated on a clinical 3.0-T MRI system. All samples underwent histological assessment to ensure structural integrity. For cross-referencing, a discretized numerical model capturing distinct compositional and structural tissue properties, that is, fluid fraction (FF), proteoglycan (PG) and collagen (CO) content and collagen fiber orientation (CFO), was implemented. In a pixel-wise and region-specific manner (central versus peripheral region), qMRI parameter values and modelled tissue parameters were correlated and quantified in terms of Spearman's correlation coefficient ρs. Significant correlations were found between modelled compositional parameters and T1 and T2^⁎, in particular in the central region (T1: ρs ≥ 0.7 [FF, CFO], ρs ≤ −0.8 [CO, PG]; T2^⁎: ρs ≥ 0.67 [FF, CFO], ρs ≤ −0.71 [CO, PG]). For T1ρ, correlations were considerably weaker and fewer (0.16 ≤ ρs ≤ −0.15). QMRI parameters are characterized in their biophysical properties and their sensitivity and specificity profiles in a basic scientific context. Although none of these is specific towards any particular cartilage constituent, T1 and T2^⁎ reflect actual tissue compositional features more closely than T1ρ.

Juvenile Osteochondritis Dissecans: Cartilage T2 Mapping of Stable Medial Femoral Condyle Lesions

Purpose To determine whether a T2 mapping sequence could depict early changes in the composition and microstructure of cartilage overlying stable lesions of the medial femoral condyle in patients with juvenile osteochondritis dissecans (JOCD). Materials and Methods This retrospective study analyzed a sagittal T2 mapping sequence performed between September 1, 2015, and March 31, 2017, on 16 patients (10 boys and six girls; median age, 11.5 years) with 18 stable medial femoral condyle JOCD lesions and 18 age-, sex-, and skeletal maturation-matched control participants (11 boys and seven girls; median age, 11.5 years). Cartilage T2 values were quantitatively measured within regions of interest placed around the cartilage within and overlying the JOCD lesion in patients with JOCD and around the cartilage on the weight-bearing medial femoral condyle in patients with JOCD and controls. Wilcoxon signed rank and Wilcoxon rank sum tests were used to compare T2 values. Results T2 values were significantly higher (P < .001) for cartilage within the JOCD lesion than for cartilage overlying the JOCD lesion in patients with JOCD. However, there were no significant differences in T2 values between cartilage overlying the JOCD lesion and cartilage on the weight-bearing medial femoral condyle in patients with JOCD (P = .67) or in T2 values of the cartilage on the weight-bearing medial femoral condyle between patients with JOCD and controls (P = .30). Conclusion There were no significant quantifiable differences in T2 values of cartilage overlying stable JOCD lesions and normal cartilage on the medial femoral condyle, suggesting no substantial changes in cartilage composition and microstructure.

Quantitative mapping of glenohumeral cartilage in asymptomatic subjects using 3 T magnetic resonance imaging

OBJECTIVE

The purpose of this study was to develop quantitative T2 mapping methodology in asymptomatic shoulders for the entire mappable region of the glenohumeral cartilage in the coronal and sagittal planes, to assess the feasibility and limitations of the development of a diagnostic tool for future application in symptomatic patients.

MATERIALS AND METHODS

Twenty-one asymptomatic volunteers underwent sagittal and coronal glenohumeral T2 mapping, as the spherical geometry of the humeral head obviates the need to evaluate the entire glenohumeral cartilage in a single plane. The humeral head cartilage orthogonal to the mapping plane was manually segmented in the sagittal and coronal planes, whereas the glenoid cartilage was segmented in the coronal plane. Cartilage T2 summary statistics were calculated and coverage in each mapping plane was qualitatively assessed.

RESULTS

The mean ± standard deviation of the glenoid cartilage T2 was 38 ± 2 ms. The coronal and sagittal mapping planes captured different regions of the humeral head with some overlap: inferior-medial to superior-lateral versus superior/superior-lateral to anterior-lateral and posterior-lateral respectively. The mean humeral head cartilage T2 in the coronal plane was 41 ± 3 ms, which was significantly different (p < 0.05) from the sagittal plane mean of 34 ± 2 ms.

CONCLUSION

This study measured characteristic glenoid and humeral head cartilage T2 values over the area mappable with two planes. Importantly, this study demonstrated that two-dimensional mapping in a single plane or two combined planes cannot capture the entirety of the semi-spherical humeral head cartilage. This highlights the need for three-dimensional T2 mapping techniques in the shoulder.