Imaging biomarker with T1ρ and T2 mappings in osteoarthritis - in vivo human articular cartilage study

Predictive markers for head and neck cancer treatment response: T1rho imaging in nasopharyngeal carcinoma

OBJECTIVES

To investigate the potential of T1rho, a new quantitative imaging sequence for cancer, for pre and early intra-treatment prediction of treatment response in nasopharyngeal carcinoma (NPC) and compare the results with those of diffusion-weighted imaging (DWI).

MATERIALS AND METHODS

T1rho and DWI imaging of primary NPCs were performed pre- and early intra-treatment in 41 prospectively recruited patients. The mean preT1rho, preADC, intraT1rho, intraADC, and % changes in T1rho (ΔT1rho%) and ADC (ΔADC%) were compared between residual and non-residual groups based on biopsy in all patients after chemoradiotherapy (CRT) with (n = 29) or without (n = 12) induction chemotherapy (IC), and between responders and non-responders to IC in the subgroup who received IC, using Mann-Whitney U-test. A p-value of < 0.05 indicated statistical significance.

RESULTS

Significant early intra-treatment changes in mean T1rho (p = 0.049) and mean ADC (p < 0.01) were detected (using paired t-test), most showing a decrease in T1rho (63.4%) and an increase in ADC (95.1%). Responders to IC (n = 17), compared to non-responders (n = 12), showed higher preT1rho (64.0 ms vs 66.5 ms) and a greater decrease in ΔT1rho% (- 7.5% vs 1.3%) (p < 0.05). The non-residual group after CRT (n = 35), compared to the residual group (n = 6), showed higher intraADC (0.96 vs 1.09 × 10-3 mm2/s) and greater increase in ΔADC% (11.7% vs 27.0%) (p = 0.02).

CONCLUSION

Early intra-treatment changes are detectable on T1rho and show potential to predict tumour shrinkage after IC. T1rho may be complementary to DWI, which, unlike T1rho, did not predict response to IC but did predict non-residual disease after CRT.

CLINICAL RELEVANCE STATEMENT

T1rho has the potential to complement DWI in the prediction of treatment response. Unlike DWI, it predicted shrinkage of the primary NPC after IC but not residual disease after CRT.

KEY POINTS

Changes in T1rho were detected early during cancer treatment for NPC. Pre-treatment and early intra-treatment change in T1rho predicted response to IC, but not residual disease after CRT. T1rho can be used to complement DWI with DWI predicting residual disease after CRT.

Baseline-to-loaded changes in regional tibial cartilage thickness, T1ρ and T2: Utilization of an MRI compatible loading device

The objective of the study was to evaluate tibial cartilage thickness (TCT), T1ρ and T2 values within both loaded and baseline configurations in a cadaveric knee model using a 3D bone based tibial coordinate system. Ten intact cadaveric knees were mounted into an magnetic resonance imaging (MRI) compatible loading device. Morphologic and quantitative MRI (qMRI) images were acquired with the knee in a baseline configuration and after application of 50% body weight. The morphologic images were evaluated for cartilage degeneration using a modified Noyes scoring system. A 3D bone-based tibial coordinate system was utilized to evaluate regional changes of tibial T1ρ, T2, and cartilage thickness values among regions covered and uncovered by the meniscus. Inter-regional differences in medial and lateral MRI outcomes were found between loaded and baseline configurations. Cartilage regions covered by the meniscus demonstrated disparate qMRI and TCT results as compared to cartilage regions not covered by the meniscus. The regions covered by meniscus experienced a ~3.5%, ~0.5%, and ~5.5% reduction of T1ρ (p < 0.05, medial and lateral compartments), T2 and TCT, respectively, in both compartments while regions not covered by the meniscus experienced larger reductions of ~10%, ~2%, and ~10.5% reduction of T1ρ (p < 0.05, medial and lateral compartments), T2 and TCT (p < 0.05, lateral compartment only), respectively, in both compartments. T1ρ and T2 decreases following application of 50% body weight load were substantially larger in the tibial regions with modified Noyes grade 3 (n = 2) compared to either healthy regions (n = 85, p < 0.0.003) or regions with modified Noyes grade 2 (n = 13, p < 0.004). Interregional differences in MRI outcomes reflect variations in structure and function, and largely followed a pattern in cartilage regions that were covered or not covered by the meniscus. Results of the current study suggest that ΔT1ρ and ΔT2 values may be sensitive to superficial fissuring, more than baseline or loaded T1ρ or T2 values, or TCT alone, however future studies with additional specimens, with greater variability in OA grade distribution, may further emphasize the current findings.

Insights into the Age Dependency of Compositional MR Biomarkers Quantifying the Health Status of Cartilage in Metacarpophalangeal Joints

(1) Background: We aim to investigate age-related changes in cartilage structure and composition in the metacarpophalangeal (MCP) joints using magnetic resonance (MR) biomarkers. (2) Methods: The cartilage tissue of 90 MCP joints from 30 volunteers without any signs of destruction or inflammation was examined using T1, T2, and T1ρ compositional MR imaging techniques on a 3 Tesla clinical scanner and correlated with age. (3) Results: The T1ρ and T2 relaxation times showed a significant correlation with age (T1ρ: Kendall-τ-b = 0.3, p < 0.001; T2: Kendall-τ-b = 0.2, p = 0.01). No significant correlation was observed for T1 as a function of age (T1: Kendall-τ-b = 0.12, p = 0.13). (4) Conclusions: Our data show an increase in T1ρ and T2 relaxation times with age. We hypothesize that this increase is due to age-related changes in cartilage structure and composition. In future examinations of cartilage using compositional MRI, especially T1ρ and T2 techniques, e.g., in patients with osteoarthritis or rheumatoid arthritis, the age of the patients should be taken into account.

Quantitative T2 mapping monitoring the maturation of engineered elastic cartilage in a rabbit model

BACKGROUND

Cartilage tissue engineering provides a promising approach to reconstruct craniofacial defects, and a noninvasive method is needed to assess its effectiveness. Although magnetic resonance imaging (MRI) has been used to evaluate articular cartilage in vivo, few studies focused on its feasibility in monitoring engineered elastic cartilage (EC).

METHODS

Auricular cartilage, silk fibroin (SF) scaffold, and EC consisting of rabbit auricular chondrocytes and SF scaffold were transplanted subcutaneously into the rabbit back. In eight weeks after transplantation, grafts were imaged by MRI using PROSET, PDW VISTA SPAIR, 3D T2 VISTA, 2D MIXED T2 Multislice, and SAG TE multiecho sequences, followed by histological examination and biochemical analysis. Statistical analyses were performed to identify the association between T2 values and biochemical indicator values of EC.

RESULTS

In vivo imaging shows that 2D MIXED T2 Multislice sequence (T2 mapping) clearly distinguished the native cartilage, engineered cartilage and fibrous tissue. T2 values showed high correlations with cartilage-specific biochemical parameters at different time points, especially the elastic cartilage specific protein elastin (ELN, r= -0.939, P < 0.001).

CONCLUSION

Quantitative T2 mapping can effectively detect the in vivo maturity of engineered elastic cartilage after subcutaneously transplantation. This study would promote the clinical application of MRI T2 mapping in monitoring engineered elastic cartilage in the repair of craniofacial defects.

Quantitatively relating magnetic resonance T1 and T2 to glycosaminoglycan and collagen concentrations mediated by penetrated contrast agents and biomacromolecule-bound water

Magnetic resonance imaging (MRI) is a promising non-invasive method to assess cartilage regeneration based on the quantitative relationship between MRI features and concentrations of the major components in the extracellular matrix (ECM). To this end, in vitro experiments are performed to investigate the relationship and reveal the underlying mechanism. A series of collagen (COL) and glycosaminoglycan (GAG) solutions at different concentrations are prepared, and T₁ and T₂ relaxation times are measured with or without a contrast agent (Gd-DTPA^2-) by MRI. Fourier transform infrared spectrometry is also used to measure the contents of biomacromolecule-bound water and other water, allowing theoretical derivation of the relationship between biomacromolecules and the resulting T₂ values. It has been revealed that the MRI signal in the biomacromolecule aqueous systems is mainly influenced by the protons in hydrogens of biomacromolecule-bound water, which we divide into inner-bound water and outer-bound water. We have also found that COL results in higher sensitivity of bound water than GAG in T₂ mapping. Owing to the charge effect, GAG regulates the penetration of the contrast agent during dialysis and has a more significant effect on T₁ values than COL. Considering that COL and GAG are the most abundant biomacromolecules in the cartilage, this study is particularly useful for the real-time MRI-guided assessment of cartilage regeneration. A clinical case is reported as an in vivo demonstration, which is consistent with our in vitro results. The established quantitative relation plays a critical academic role in establishing an international standard ISO/TS24560-1:2022 'Clinical evaluation of regenerative knee articular cartilage using delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) and T₂ mapping' drafted by us and approved by International Standard Organization.

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.

A Comprehensive Framework to Evaluate the Effects of Anterior Cruciate Ligament Injury and Reconstruction on Graft and Cartilage Status through the Analysis of MRI T2 Relaxation Time and Knee Laxity: A Pilot Study

BACKGROUND

Anterior cruciate ligament (ACL) tear represents a common orthopedic traumatic issue that often leads to an early development of osteoarthritis. To improve the diagnostic and prognostic techniques involved in the assessment of the joint after the trauma and during the healing process, the present work proposes a multi-parametric approach that aims to investigate the relationship between joint function and soft tissue status before and after ACL reconstruction.

METHODS

Thirteen consecutive patients who underwent ACL reconstruction were preliminarily enrolled in this study. Joint laxity assessment as well as magnetic resonance imaging with T2 mapping were performed in the pre-operative stage, at four and 18 months after surgery to acquire objective information to correlate knee function and soft tissue condition.

RESULTS

Correlations were found between graft and cartilage T2 signal, suggesting an interplay between these tissues within the knee joint. Moreover, graft maturation resulted in being connected to joint laxity, as underlined by the correlation between the graft T2 signal and the temporal evolution of knee function.

CONCLUSIONS

This preliminary study represents a step forward in assessing the effects of ACL graft maturation on knee biomechanics, and vice versa. The presented integrated framework underlines the possibility to quantitatively assess the impact of ACL reconstruction on trauma recovery and cartilage homeostasis. Moreover, the reported findings-despite the preliminary nature of the clinical impacts-evidence the possibility of monitoring the surgery outcomes using a multi-parametric prognostic investigation tool.

The Response of Hip Joint Cartilage to Exercise in Children: An MRI Study Using T2-Mapping

OBJECTIVE

The aim of this study was to determine the effects of activity and cam morphology on cartilage composition during adolescence and investigate the development of cartilage composition with age.

DESIGN

Cross-sectional observational cohort study of individuals from football club academies and an age-matched control population, aged 9 to 18 years. Assessments included questionnaires and T2-mapping of hips. Primary imaging outcome measures were T2 relaxation time of acetabular and femoral cartilage, average alpha angle, and lateral epiphyseal extension.

RESULTS

The cohort consisted of 109 elite male footballers, 49 male controls, and 51 female controls. Elite male footballers had an acetabular cartilage T2 value 4.85 ms greater than male controls (P < 0.001). A significant positive correlation existed between Physical Activity Questionnaire Score and acetabular cartilage T2 value (coefficient 1.07, P < 0.001) and femoral cartilage T2 value (coefficient 0.66, P = 0.032). Individuals with a closed physis had an acetabular cartilage T2 value 7.86 ms less than individuals with an open physis. Acetabular cartilage T2 values decreased with age in elite footballers. No correlation existed between alpha angle and anterosuperior acetabular cartilage T2 value and no difference in T2 value existed between individuals with and without cam morphology.

CONCLUSIONS

This study demonstrates that high activity levels may significantly affect acetabular cartilage composition during adolescence, but cam morphology may not detrimentally affect cartilage composition until after adolescence.

Histological Analysis of Cartilage Defects Repaired with an Autologous Human Stem Cell Construct 48 Weeks Postimplantation Reveals Structural Details Not Detected by T2-Mapping MRI

OBJECTIVE

The aim of this study was to elucidate the efficacy of T2-mapping MRI and correlation with histology for the evaluation of tissue repair quality following the first-in-human implantation of an autologous tissue engineered construct.

DESIGN

We directly compared the results of T2-mapping MRI of cartilage repair tissue with the histology of a biopsy specimen from the corresponding area at 48 weeks postoperatively in 5 patients who underwent the implantation of a scaffold-free tissue-engineered construct generated from autologous synovial mesenchymal stem cells to repair an isolated cartilage lesion. T2 values and histological scores were compared at each of 2 layers of equally divided halves of the repair tissue (upper and lower zones).

RESULTS

Histology showed that the repair tissue in the upper zone was dominated by fibrous tissue and the ratio of hyaline-like matrix increased with the depth of the repair tissue. There were significant differences between upper and lower zones in histological scores. Conversely, there were no detectable statistically significant differences in T2 value detected among zones of the repair tissue, but zonal differences were detected in corresponding healthy cartilage. Accordingly, there were no correlations detected between histological scores and T2 values for each repair cartilage zone.

CONCLUSION

Discrepancies in the findings between T2 mapping and histology suggest that T2 mapping was limited in ability to detect details in the architecture and composition of the repair cartilage.

Tibiofemoral articular cartilage composition differs based on serum biochemical profiles following anterior cruciate ligament reconstruction

OBJECTIVE

Biochemical joint changes contribute to posttraumatic osteoarthritis (PTOA) development following anterior cruciate ligament reconstruction (ACLR). The purpose of this longitudinal cohort study was to compare tibiofemoral cartilage composition between ACLR patients with different serum biochemical profiles. We hypothesized that profiles of increased inflammation (monocyte chemoattractant protein-1 [MCP-1]), type-II collagen turnover (type-II collagen breakdown [C2C]:synthesis [CPII]), matrix degradation (matrix metalloproteinase-3 [MMP-3] and cartilage oligomeric matrix protein [COMP]) preoperatively to 6-months post-ACLR would be associated with greater tibiofemoral cartilage T1ρ relaxation times 12-months post-ACLR.

DESIGN

Serum was collected from 24 patients (46% female, 22.1 ± 4.2 years old, 24.0 ± 2.6 kg/m2 body mass index [BMI]) preoperatively (6.4 ± 3.6 days post injury) and 6-months post-ACLR. T1ρ Magnetic Resonance Imaging (MRI) was collected for medial and lateral tibiofemoral articular cartilage at 12-months post-ACLR. A k-means cluster analysis was used to identify profiles based on biomarker changes over time and T1ρ relaxation times were compared between cluster groups controlling for sex, age, BMI, concomitant injury (either meniscal or chondral pathology), and Marx Score.

RESULTS

One cluster exhibited increases in MCP-1 and COMP while the other demonstrated decreases in MCP-1 and COMP preoperatively to 6-months post-ACLR. The cluster group with increases in MCP-1 and COMP demonstrated greater lateral tibial (adjusted mean difference = 3.88, 95% confidence intervals [1.97-5.78]) and femoral (adjusted mean difference = 12.71, 95% confidence intervals [0.41-23.81]) T1ρ relaxation times.

CONCLUSION

Profiles of increased serum levels of inflammation and matrix degradation markers preoperatively to 6-months post-ACLR are associated with MRI changes consistent with lesser lateral tibiofemoral cartilage proteoglycan density 12-months post-ACLR.

Compositional MRI of the Hip: Reproducibility, Effect of Joint Unloading, and Comparison of T2 Relaxometry with Delayed Gadolinium-Enhanced Magnetic Resonance Imaging of Cartilage

OBJECTIVE

Our aim was to compare T2 with delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) in the hip and assess the reproducibility and effect of joint unloading on T2 mapping.

DESIGN

Ten individuals at high risk of developing hip osteoarthritis (SibKids) underwent contemporaneous T2 mapping and dGEMRIC in the hip (10 hips). Twelve healthy volunteers underwent T2 mapping of both hips (24 hips) at time points 25, 35, 45, and 55 minutes post offloading. Acetabular and femoral cartilage was manually segmented into regions of interest. The relationship between T2 and dGEMRIC values from anatomically corresponding regions of interests was quantified using Pearson's correlation. The reproducibility of image analysis for T2 and dGEMRIC, and reproducibility of image acquisition for T2, was quantified using the intraclass correlation coefficient (ICC), root mean square coefficient of variance (RMSCoV), smallest detectable difference (SDD), and Bland-Altman plots. The paired t test was used to determine if difference existed in T2 values at different unloading times.

RESULTS

T2 values correlated most strongly with dGEMRIC values in diseased cartilage (r = -0.61, P = <0.001). T2 image analysis (segmentation) reproducibility was ICC = 0.96 to 0.98, RMSCoV = 3.5% to 5.2%, and SDD = 2.2 to 3.5 ms. T2 values at 25 minutes unloading were not significantly different to longer unloading times (P = 0.132). SDD for T2 image acquisition reproducibility was 7.1 to 7.4 ms.

CONCLUSIONS

T2 values in the hip correlate well with dGEMRIC in areas of cartilage damage. T2 shows high reproducibility and values do not change beyond 25 minutes of joint unloading.

Muscle strength gains after strengthening exercise explained by reductions in serum inflammation in women with knee osteoarthritis

Background Individuals with knee osteoarthritis have elevated circulating inflammatory markers and altered cartilage properties but it is unclear if these features adapt to exercise. We aimed to determine (1) whether inflammatory markers, cartilage transverse relaxation time and thickness mediate the effect of body mass index (BMI) on quadriceps strength at baseline; and (2) whether these changes explain variance in quadriceps strength improvements after 12 weeks of exercise in women with knee osteoarthritis. Methods This secondary analysis (17 women with clinical knee osteoarthritis) of a randomized control trial compared supervised group interventions, 3 times/week for 12 weeks (36 sessions): (a) weight-bearing progressive resistive quadriceps exercise or (b) attention control. (1) From baseline, separate linear regressions were conducted with strength (Nm/kg) as the dependent, BMI as the predictor, and c-reactive protein, tumor necrosis factor, interleukin-6, cartilage transverse relaxation time or thickness as potential mediators. (2) Multiple linear regression analyses were completed with 12-week strength change (post-pre) as the dependent, change in serum inflammatory markers and cartilage measurements as predictors, and age, BMI and adherence as covariates. Findings (1) At baseline, there was no mediation. (2) A decrease in each of interleukin-6 (β = -0.104 (95% confidence intervals: -0.172, -0.036), R² = 0.51, P < 0.007) and tumor necrosis factor (β = -0.024 (-0.038, -0.009), R² = 0.54, P < 0.005) was associated with strength gains. Interpretation At baseline, inflammatory markers and cartilage measurements do not act as mediators of BMI on quadriceps strength. After 12 weeks of exercise, reduced interleukin-6 and tumor necrosis factor were associated with increased quadriceps strength in women with knee osteoarthritis.

No pressure, no diamonds? - Static vs. dynamic compressive in-situ loading to evaluate human articular cartilage functionality by functional MRI

Biomechanical Magnetic Resonance Imaging (MRI) of articular cartilage, i.e. its imaging under loading, is a promising diagnostic tool to assess the tissue's functionality in health and disease. This study aimed to assess the response to static and dynamic loading of histologically intact cartilage samples by functional MRI and pressure-controlled in-situ loading. To this end, 47 cartilage samples were obtained from the medial femoral condyles of total knee arthroplasties (from 24 patients), prepared to standard thickness, and placed in a standard knee joint in a pressure-controlled whole knee-joint compressive loading device. Cartilage samples' responses to static (i.e. constant), dynamic (i.e. alternating), and no loading, i.e. free-swelling conditions, were assessed before (δ₀), and after 30 min (δ₁) and 60 min (δ₂) of loading using serial T1ρ maps acquired on a 3.0T clinical MRI scanner (Achieva, Philips). Alongside texture features, relative changes in T1ρ (Δ₁, Δ₂) were determined for the upper and lower sample halves and the entire sample, analyzed using appropriate statistical tests, and referenced to histological (Mankin scoring) and biomechanical reference measures (tangent stiffness). Histological, biomechanical, and T1ρ sample characteristics at δ₀ were relatively homogenous in all samples. In response to loading, relative increases in T1ρ were strong and significant after dynamic loading (Δ₁ = 10.3 ± 17.0%, Δ₂ = 21.6 ± 21.8%, p = 0.002), while relative increases in T1ρ after static loading and in controls were moderate and not significant. Generally, texture features did not demonstrate clear loading-related associations underlying the spatial relationships of T1ρ. When realizing the clinical translation, this in-situ study suggests that serial T1ρ mapping is best combined with dynamic loading to assess cartilage functionality in humans based on advanced MRI techniques.

Is T2 mapping reliable in evaluation of native and repair cartilage tissue of the knee?

PURPOSE

To evaluate the effect of imaging plane and experience of observers on the reliability of T2 mapping of native and repair cartilage tissue of the knee.

METHODS

Fifteen consecutive patients from two randomised controlled trials (RCTs) were included in this cross-sectional study. Patients with an isolated knee cartilage lesion were randomised to receive either debridement or microfracture (RCT 1) or debridement or autologous chondrocyte implantation (RCT 2). T2 mapping was performed in coronal and sagittal planes two years postoperatively. A musculoskeletal radiologist, a resident of radiology and two orthopaedic surgeons measured the T2 values independently. Intraclass Correlation Coefficient (ICC) with 95% Confidence Intervals was used to calculate the inter- and intraobserver agreement.

RESULTS

Mean age for the patients was 36.8 ± 11 years, 8 (53%) were men. The overall interobserver agreement varied from poor to good with ICCs in the range of 0.27- 0.76 for native cartilage and 0.00 - 0.90 for repair tissue. The lowest agreement was achieved for evaluations of repair cartilage tissue. The estimated ICCs suggested higher inter- and intraobserver agreement for radiologists. On medial femoral condyles, T2 values were higher for native cartilage on coronal images (p < 0.001) and for repair tissue on sagittal images (p < 0.001).

CONCLUSIONS

The reliability of T2 mapping of articular cartilage is influenced by the imaging plane and the experience of the observers. This influence may be more profound for repair cartilage tissue. This is important to consider when using T2 mapping to measure outcomes after cartilage repair surgery.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02637505 and NCT02636881 , registered December 2015.

LEVEL OF EVIDENCE

II, based on prospective data from two RCTs.

Longitudinal T2 Mapping and Texture Feature Analysis in the Detection and Monitoring of Experimental Post-Traumatic Cartilage Degeneration

Background: Traumatic cartilage injuries predispose articulating joints to focal cartilage defects and, eventually, posttraumatic osteoarthritis. Current clinical-standard imaging modalities such as morphologic MRI fail to reliably detect cartilage trauma and to monitor associated posttraumatic degenerative changes with oftentimes severe prognostic implications. Quantitative MRI techniques such as T2 mapping are promising in detecting and monitoring such changes yet lack sufficient validation in controlled basic research contexts. Material and Methods: 35 macroscopically intact cartilage samples obtained from total joint replacements were exposed to standardized injurious impaction with low (0.49 J, n = 14) or high (0.98 J, n = 14) energy levels and imaged before and immediately, 24 h, and 72 h after impaction by T2 mapping. Contrast, homogeneity, energy, and variance were quantified as features of texture on each T2 map. Unimpacted controls (n = 7) and histologic assessment served as reference. Results: As a function of impaction energy and time, absolute T2 values, contrast, and variance were significantly increased, while homogeneity and energy were significantly decreased. Conclusion: T2 mapping and texture feature analysis are sensitive diagnostic means to detect and monitor traumatic impaction injuries of cartilage and associated posttraumatic degenerative changes and may be used to assess cartilage after trauma to identify “cartilage at risk”.

Identifying the imaging correlates of cartilage functionality based on quantitative MRI mapping - The collagenase exposure model

Cartilage functionality is determined by tissue structure and composition. If altered, cartilage is predisposed to premature degeneration. This pathomimetical study of early osteoarthritis evaluated the dose-dependant effects of collagenase-induced collagen disintegration and proteoglycan depletion on cartilage functionality as assessed by serial T1, T1ρ, T2, and T2* mapping under loading. 30 human femoral osteochondral samples underwent imaging on a clinical 3.0 T MRI scanner (Achieva, Philips) in the unloaded reference configuration (δ₀) and under pressure-controlled quasi-static indentation loading to 15.1 N (δ₁) and to 28.6 N (δ₂). Imaging was performed before and after exposure to low (LC, 0.5 mg/mL; n = 10) or high concentration (HC, 1.5 mg/mL; n = 10) of collagenase. Untreated samples served as controls (n = 10). Loading responses were determined for the entire sample and the directly loaded (i.e. sub-pistonal) and bilaterally adjacent (i.e. peri‑pistonal) regions, referenced histologically, quantified as relative changes, and analysed using adequate parametric and non-parametric statistical tests. Dose-dependant surface disintegration and tissue loss were reflected by distinctly different pre- and post-exposure response-to-loading patterns. While T1 generally decreased with loading, regardless of collagenase exposure, T1ρ increased significantly after HC exposure (p = 0.008). Loading-induced decreases in T2 were significant after LC exposure (p = 0.006), while changes in T2* were ambiguous. In conclusion, aberrant loading-induced changes in T2 and T1ρ reflect moderate and severe matrix changes, respectively, and indicate the close interrelatedness of matrix changes and functionality in cartilage.

A serial multiparametric quantitative magnetic resonance imaging study to assess proteoglycan depletion of human articular cartilage and its effects on functionality

Water, collagen, and proteoglycans determine articular cartilage functionality. If altered, susceptibility to premature degeneration is increased. This study investigated the effects of enzymatic proteoglycan depletion on cartilage functionality as assessed by advanced Magnetic Resonance Imaging (MRI) techniques under standardized loading. Lateral femoral condylar cartilage-bone samples from patients undergoing knee replacement (n = 29) were serially imaged by Proton Density-weighted and T1, T1ρ, T2, and T2* mapping sequences on a clinical 3.0 T MRI scanner (Achieva, Philips). Using pressure-controlled indentation loading, samples were imaged unloaded and quasi-statically loaded to 15.1 N and 28.6 N, and both before and after exposure to low-concentrated (LT, 0.1 mg/mL, n = 10) or high-concentrated trypsin (HT, 1.0 mg/mL, n = 10). Controls were not treated (n = 9). Responses to loading were assessed for the entire sample and regionally, i.e. sub- and peri-pistonally, and zonally, i.e. upper and lower sample halves. Trypsin effects were quantified as relative changes (Δ), analysed using appropriate statistical tests, and referenced histologically. Histological proteoglycan depletion was reflected by significant sub-pistonal decreases in T1 (p = 0.003) and T2 (p = 0.008) after HT exposure. Loading-induced changes in T1ρ and T2* were not related. In conclusion, proteoglycan depletion alters cartilage functionality and may be assessed using serial T1 and T2 mapping under loading.

Human articular cartilage mechanosensitivity is related to histological degeneration - a functional MRI study

OBJECTIVE

To investigate changes in response to sequential pressure-controlled loading and unloading in human articular cartilage of variable histological degeneration using serial T1ρ mapping.

METHOD

We obtained 42 cartilage samples of variable degeneration from the medial femoral condyles of 42 patients undergoing total knee replacement. Samples were placed in a standardized artificial knee joint within an MRI-compatible whole knee-joint compressive loading device and imaged before (δ₀), during (δ_ld1, δ_ld2, δ_ld3, δ_ld4, δ_ld5) and after (δ_rl1, δ_rl2, δ_rl3, δ_rl4, δ_rl5) pressure-controlled loading to 0.663 ± 0.021 kN (94% body weight) using serial T1ρ mapping (spin-lock multigradient echo sequence; 3.0T MRI system [Achieva, Philips]). Reference assessment included histology (Mankin scoring) and conventional biomechanics (Tangent stiffness). We dichotomized sample into intact (n = 21) and degenerative (n = 21) based on histology and analyzed data using Mann Whitney, Kruskal Wallis, one-way ANOVA tests and Spearman's correlation, respectively.

RESULTS

At δ₀, we found no significant differences between intact and degenerative samples, while the response-to-loading patterns were distinctly different. In intact samples, T1ρ increases were consistent and non-significant, while in degenerative samples, T1ρ increases were significantly higher (P = 0.004, δ0 vs δld1, δ0 vs δld3), yet undulating and variable. With unloading, T1ρ increases subsided, yet were persistently elevated beyond δ0.

CONCLUSION

Cartilage mechanosensitivity is related to histological degeneration and assessable by serial T1ρ mapping. Unloaded, T1ρ characteristics are not significantly different in intact vs degenerative cartilage, while load bearing is organized in intact cartilage and disorganized in degenerative cartilage.

Comparison of T1 Mapping and T1rho Values with Conventional Diffusion-weighted Imaging to Assess Fibrosis in a Rat Model of Unilateral Ureteral Obstruction

RATIONALE AND OBJECTIVES

The aim of this study was to investigate the potential of magnetic resonance imaging (MRI) T1 mapping and T1 relaxation time in the rotating frame (T1rho) for assessment of renal fibrosis in a rat model of unilateral ureteral obstruction (UUO).

MATERIALS AND METHODS

UUO was created in 36 rats. Six rats were scanned at each of the six time points (on days 0, 1, 3, 5, 10, and 15 after UUO). The contralateral kidneys were examined as controls. Hematoxylin-eosin, Masson's trichrome, and alpha-smooth muscle actin (α-SMA) antibody staining assays were performed. MRI data obtained with a 3.0T scanner were analyzed with α-SMA expression and Masson's staining.

RESULTS

The T1 relaxation times and T1rho values increased, and the mean apparent diffusion coefficient (ADC) values decreased with time after UUO. Simple regression analysis indicated that the mean ADCs, T1 relaxation times, and T1rho values had strong correlations with the α-SMA expression levels (R² = 0.34, R² = 0.66, R² = 0.71, respectively; P< .001) and positive Masson's staining (R² = 0.38, R² = 0.67, R² = 0.65, respectively; P< .001).

CONCLUSIONS

The T1 mapping and T1rho parameters had better correlations with α-SMA expression and Masson's staining than ADC values.

Prediction of Lumbar Disk Herniation and Clinical Outcome Using Quantitative Magnetic Resonance Imaging: A 5-Year Follow-Up Study

OBJECTIVES

The aim of this study was to assess the predictive value of T2 mapping at baseline with regard to the development of disk herniation and clinical outcome at a 5-year follow-up in patients with low back pain.

MATERIALS AND METHODS

Twenty-five symptomatic patients (13 male; mean age, 44.0 years; range, 24-64 years at baseline) were examined at 3 T magnetic resonance imaging, with a 5-year follow-up. Region of interest analysis was performed on 125 lumbar intervertebral disks on 2 central sagittal T2 maps. Absolute T2 relaxation times and a T2 value ratio of the posterior annulus fibrosus as a percentage of the nucleus pulposus (NPAF) were evaluated for each disk. All disks were graded morphologically using the Pfirrmann score. Roland-Morris Disability Questionnaires (RMDQ) and a visual analogue scale (VAS) were assessed for each patient at follow-up as a clinical end point and compared with diagnosed lumbar disk herniation. Statistical analysis was conducted by a biomedical statistician.

RESULTS

Using the baseline NPAF ratio, follow-up development of herniation was predicted with an area under the curve (AUC) of 0.893 in a receiver operating characteristic curve. The same was done using the baseline nucleus pulposus T2, resulting in an AUC of 0.901. Baseline and follow-up NPAF, as well as baseline and follow-up nucleus pulposus T2, differed significantly (P < 0.001) between disks with no herniation, disks with herniation at baseline, and disks with new herniation at follow-up. Difference was still significant (all P < 0.001), when only testing for difference in degenerated discs with Pfirrmann score III to V. Calculating sensitivity and specificity for herniation prediction only in discs with Pfirmann III to V using a receiver operating characteristic, AUC was 0.844 with baseline herniations excluded.The lowest baseline nucleus pulposus T2 per patient correlated significantly with follow-up RMDQ (r = -0.517; P = 0.008) and VAS (r = -0.494; P = 0.012). The highest baseline NPAF correlated significantly with RMDQ (r = 0.462; P = 0.020), but not VAS (r = 0.279; P = 0.177).

CONCLUSIONS

Quantitative T2 mapping may serve as a clinically feasible, noninvasive imaging biomarker that can indicate disks at risk for herniation and correlates with clinical outcome and subjective patient burden in a representative cohort of patients with low back pain.

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.

Progression of Post-Traumatic Osteoarthritis in rat meniscectomy models: Comprehensive monitoring using MRI

Knee injury often triggers post-traumatic osteoarthritis (PTOA) that affects articular cartilage (AC), subchondral bone, meniscus and the synovial membrane. The available treatments for PTOA are largely ineffective due to late diagnosis past the “treatment window”. This study aimed to develop a detailed understanding of the time line of the progression of PTOA in murine models through longitudinal observation of the femorotibial joint from the onset of the disease to the advanced stage. Quantitative magnetic resonance microimaging (µMRI) and histology were used to evaluate PTOA-associated changes in the knee joints of rats subjected to knee meniscectomy. Systematic longitudinal changes in the articular cartilage thickness, cartilage T₂ and the T₂ of epiphysis within medial condyles of the tibia were all found to be associated with the development of PTOA in the animals. The following pathogenesis cascade was found to precede advanced PTOA: meniscal injury → AC swelling → subchondral bone remodelling → proteoglycan depletion → free water influx → cartilage erosion. Importantly, the imaging protocol used was entirely MRI-based. This protocol is potentially suitable for whole-knee longitudinal, non-invasive assessment of the development of OA. The results of this work will inform the improvement of the imaging methods for early diagnosis of PTOA.

Non-invasive T1ρ mapping of the human cartilage response to loading and unloading

OBJECTIVE

To define the physiological response to sequential loading and unloading in histologically intact human articular cartilage using serial T1ρ mapping, as T1ρ is considered to indicate the tissue's macromolecular content.

METHOD

18 macroscopically intact cartilage-bone samples were obtained from the central lateral femoral condyles of 18 patients undergoing total knee replacement. Serial T1ρ mapping was performed on a clinical 3.0-T MRI system using a modified prostate coil. Spin-lock multiple gradient-echo sequences prior to, during and after standardized indentation loading (displacement controlled, strain 20%) were used to obtain seven serial T1ρ maps: unloaded (δ₀), quasi-statically loaded (indentation₁-indentation₃) and under subsequent relaxation (relaxation₁-relaxation₃). After manual segmentation, zonal and regional regions-of-interest were defined. ROI-specific relative changes were calculated and statistically assessed using paired t-tests. Histological (Mankin classification) and biomechanical (unconfined compression) evaluations served as references.

RESULTS

All samples were histologically and biomechanically grossly intact (Mankin sum: 1.8 ± 1.2; Young's Modulus: 0.7 ± 0.4 MPa). Upon loading, T1ρ consistently increased throughout the entire sample thickness, primarily subpistonally (indentation₁ [M ± SD]: 9.5 ± 7.8% [sub-pistonal area, SPA] vs 4.2 ± 5.8% [peri-pistonal area, PPA]; P < 0.001). T1ρ further increased with ongoing loading (indentation₃: 14.1 ± 8.1 [SPA] vs 7.7 ± 5.9% [PPA]; P < 0.001). Even upon unloading (i.e., relaxation), T1ρ persistently increased in time.

CONCLUSION

Serial T1ρ-mapping reveals distinct and complex zonal and regional changes in articular cartilage as a function of loading and unloading. Thereby, longitudinal adaptive processes in hyaline cartilage become evident, which may be used for the tissue's non-invasive functional characterization by T1ρ.

EULAR recommendations for the use of imaging in the clinical management of peripheral joint osteoarthritis

The increased information provided by modern imaging has led to its more extensive use. Our aim was to develop evidence-based recommendations for the use of imaging in the clinical management of the most common arthropathy, osteoarthritis (OA). A task force (including rheumatologists, radiologists, methodologists, primary care doctors and patients) from nine countries defined 10 questions on the role of imaging in OA to support a systematic literature review (SLR). Joints of interest were the knee, hip, hand and foot; imaging modalities included conventional radiography (CR), MRI, ultrasonography, CT and nuclear medicine. PubMed and EMBASE were searched. The evidence was presented to the task force who subsequently developed the recommendations. The strength of agreement for each recommendation was assessed. 17 011 references were identified from which 390 studies were included in the SLR. Seven recommendations were produced, covering the lack of need for diagnostic imaging in patients with typical symptoms; the role of imaging in differential diagnosis; the lack of benefit in monitoring when no therapeutic modification is related, though consideration is required when unexpected clinical deterioration occurs; CR as the first-choice imaging modality; consideration of how to correctly acquire images and the role of imaging in guiding local injections. Recommendations for future research were also developed based on gaps in evidence, such as the use of imaging in identifying therapeutic targets, and demonstrating the added value of imaging. These evidence-based recommendations and related research agenda provide the basis for sensible use of imaging in routine clinical assessment of people with OA.

Cluster analysis of quantitative MRI T2 and T1ρ relaxation times of cartilage identifies differences between healthy and ACL-injured individuals at 3T

PURPOSE

To identify focal lesions of elevated MRI T₂ and T_1ρ relaxation times in articular cartilage of an ACL-injured group using a novel cluster analysis technique.

MATERIALS AND METHODS

Eighteen ACL-injured patients underwent 3T MRI T₂ and T_1ρ relaxometry at baseline, 6 months and 1 year and six healthy volunteers at baseline, 1 day and 1 year. Clusters of contiguous pixels above or below T₂ and T_1ρ intensity and area thresholds were identified on a projection map of the 3D femoral cartilage surface. The total area of femoral cartilage plate covered by clusters (%CA) was split into areas above (%CA+) and below (%CA-) the thresholds and the differences in %CA(+ or -) over time in the ACL-injured group were determined using the Wilcoxon signed rank test.

RESULTS

%CA+ was greater in the ACL-injured patients than the healthy volunteers at 6 months and 1 year with average %CA+ of 5.2 ± 4.0% (p = 0.0054) and 6.6 ± 3.7% (p = 0.0041) for T₂ and 6.2 ± 7.1% (p = 0.063) and 8.2 ± 6.9% (p = 0.042) for T_1ρ, respectively. %CA- at 6 months and 1 year was 3.0 ± 1.8% (p > 0.1) and 5.9 ± 5.0% (p > 0.1) for T₂ and 4.4 ± 4.9% (p > 0.1) and 4.5 ± 4.6% (p > 0.1) for T_1ρ, respectively.

CONCLUSION

With the proposed cluster analysis technique, we have quantified cartilage lesion coverage and demonstrated that the ACL-injured group had greater areas of elevated T₂ and T_1ρ relaxation times as compared to healthy volunteers.

Predictive Value of 3-T Magnetic Resonance Imaging in Diagnosing Grade 3 and 4 Chondral Lesions in the Hip

PURPOSE

To assess the diagnostic capability and predictive value of 3-T magnetic resonance imaging (MRI) in detecting grade 3 and 4 cartilage lesions in the hip.

METHODS

From August 2010 to April 2015, patients who underwent 3-T MRI and hip arthroscopy were included in the study. Data were prospectively collected and retrospectively reviewed. A radiologist prospectively documented MRI findings, and the surgeon documented cartilage damage at arthroscopy using the Outerbridge grading system. Arthroscopy was considered the diagnostic gold standard. This study was approved by the institutional review board.

RESULTS

The study group comprised 606 patients, with 354 men (58%) and 252 women (42%). The mean patient age was 34 years (range, 18 to 71 years). For femoral head defects, the sensitivity was 61% (95% confidence interval [CI], 53% to 68%), specificity was 58% (95% CI, 55% to 62%), positive predictive value was 29% (95% CI, 25% to 33%), and negative predictive value was 84% (95% CI, 81% to 87%). For chondral defects of the acetabulum, the sensitivity was 80% (95% CI, 75% to 84%), specificity was 41% (95% CI, 38% to 44%), positive predictive value was 42% (95% CI, 39% to 45%), and negative predictive value was 79% (95% CI, 74% to 84%).

CONCLUSIONS

The results of this study showed that 3-T MRI had sensitivity, as well as specificity, for identifying chondral defects that is similar to what has been previously reported. MRI showed increased sensitivity when identifying acetabular defects compared with femoral head defects. With a low positive predictive value, MRI may be most useful in ruling out cartilage lesions.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Is T1ρ Mapping an Alternative to Delayed Gadolinium-enhanced MR Imaging of Cartilage in the Assessment of Sulphated Glycosaminoglycan Content in Human Osteoarthritic Knees? An in Vivo Validation Study

PURPOSE

To determine if T1ρ mapping can be used as an alternative to delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) in the quantification of cartilage biochemical composition in vivo in human knees with osteoarthritis.

MATERIALS AND METHODS

This study was approved by the institutional review board. Written informed consent was obtained from all participants. Twelve patients with knee osteoarthritis underwent dGEMRIC and T1ρ mapping at 3.0 T before undergoing total knee replacement. Outcomes of dGEMRIC and T1ρ mapping were calculated in six cartilage regions of interest. Femoral and tibial cartilages were harvested during total knee replacement. Cartilage sulphated glycosaminoglycan (sGAG) and collagen content were assessed with dimethylmethylene blue and hydroxyproline assays, respectively. A four-dimensional multivariate mixed-effects model was used to simultaneously assess the correlation between outcomes of dGEMRIC and T1ρ mapping and the sGAG and collagen content of the articular cartilage.

RESULTS

T1 relaxation times at dGEMRIC showed strong correlation with cartilage sGAG content (r = 0.73; 95% credibility interval [CI] = 0.60, 0.83) and weak correlation with cartilage collagen content (r = 0.40; 95% CI: 0.18, 0.58). T1ρ relaxation times did not correlate with cartilage sGAG content (r = 0.04; 95% CI: -0.21, 0.28) or collagen content (r = -0.05; 95% CI = -0.31, 0.20).

CONCLUSION

dGEMRIC can help accurately measure cartilage sGAG content in vivo in patients with knee osteoarthritis, whereas T1ρ mapping does not appear suitable for this purpose. Although the technique is not completely sGAG specific and requires a contrast agent, dGEMRIC is a validated and robust method for quantifying cartilage sGAG content in human osteoarthritis subjects in clinical research.

T1rho mapping of entire femoral cartilage using depth- and angle-dependent analysis

Objectives

To create and evaluate normalized T1rho profiles of the entire femoral cartilage in healthy subjects with three-dimensional (3D) angle- and depth-dependent analysis.

Methods

T1rho images of the knee from 20 healthy volunteers were acquired on a 3.0-T unit. Cartilage segmentation of the entire femur was performed slice-by-slice by a board-certified radiologist. The T1rho depth/angle-dependent profile was investigated by partitioning cartilage into superficial and deep layers, and angular segmentation in increments of 4° over the length of segmented cartilage. Average T1rho values were calculated with normalized T1rho profiles. Surface maps and 3D graphs were created.

Results

T1rho profiles have regional and depth variations, with no significant magic angle effect. Average T1rho values in the superficial layer of the femoral cartilage were higher than those in the deep layer in most locations (p < 0.05). T1rho values in the deep layer of the weight-bearing portions of the medial and lateral condyles were lower than those of the corresponding non-weight-bearing portions (p < 0.05). Surface maps and 3D graphs demonstrated that cartilage T1rho values were not homogeneous over the entire femur.

Conclusions

Normalized T1rho profiles from the entire femoral cartilage will be useful for diagnosing local or early T1rho abnormalities and osteoarthritis in clinical applications.

Key Points

• T1rho profiles are not homogeneous over the entire femur.

• There is angle- and depth-dependent variation in T1rho profiles.

• There is no influence of magic angle effect on T1rho profiles.

• Maps/graphs might be useful if several difficulties are solved.

Improved differentiation between knees with cartilage lesions and controls using 7T relaxation time mapping

Background/Objective

T1_ρ and T2 relaxation mapping in knee cartilage have been used extensively at 3 Tesla (T) as markers for proteoglycan and collagen, respectively. The objective of this study was to evaluate the feasibility of T1_ρ and T2 imaging of knee cartilage at 7T in comparison to 3T and to evaluate the ability of T1_ρ and T2 to determine differences between normal and osteoarthritis (OA) patients.

Materials and methods

Twenty patients, seven healthy patients (Kellgren–Lawrence = 0), and 13 patients with signs of radiographic OA (Kellgren–Lawrence > 0) were scanned at 3T and 7T. The knee cartilage was segmented into six compartments and the T1_ρ and T2 values were fit using a two-parameter model. Additionally, patients were stratified by the presence of cartilage lesions using the modified Whole Organ Magnetic Resonance Imaging Score classification of the knee. One-way analysis of variance was used to compare the healthy and OA groups at 3T and 7T. The specific absorption ratio was kept under Food and Drug Administration limits during all scans.

Results

T1_ρ and T2 values at 3T and 7T were significantly higher in the lateral femoral condyle and patella in patients with OA. However, more regions were significant or approached significance at 7T compared with 3T, with the differences between healthy and OA patients also larger at 7T. The signal to noise ratio across all cartilage and meniscus compartments was 60% higher on average at 7T compared to 3T.

Conclusion

T1_ρ imaging at 7T has been established as a viable imaging method for the differentiation of degenerated cartilage despite previous concerns over specific absorption rate and imaging time. The potential increased sensitivity of T1_ρ and T2 imaging at 7T may be useful for future studies in the development of OA.

Comparison of T1ρ and T2* Relaxation Mapping in Patients with Different Grades of Disc Degeneration at 3T MR

BACKGROUND

T1ρ and T2* relaxation times are capable of providing information about early biochemical changes in intervertebral disk degeneration (IVDD). The purpose of this study was to assess and compare T1ρ and T2* mapping in IVDD with reference to Pfirrmann grade.

MATERIAL AND METHODS

Lumbar sagittal T2-weighted, T1ρ and T2* relaxation MRI were performed at 3.0T in 42 subjects covering discs L1-L2 to L5-S1. All the discs were morphologically assessed according to the Pfirrmann grade. Regions of interest (ROIs) were drawn over the T1ρ and T2*mappings, including nucleus pulposus (NP) and annulus fibrosus (AF). Wilcoxon signed rank test, Kruskal-Wallis test, and Spearman rank correlation were performed.

RESULTS

The difference in T1ρ and T2* values between NP and AF were highly significant (P<0.001). The trends of decreasing T1ρ and T2* values of both NP and AF with increasing Pfirrmann grades was significant (P<0.01), particularly between Pfirrmann grade II and III (P<0.001), whereas T2* mapping was additionally able to detect changes in the AF between Pfirrmann grade I and II (P<0.05). Pfirrmann grades were inversely significantly correlated with both T1ρ and T2* values in the NP (r=-0.69, P<0.001; r=-0.56, P<0.001) and AF (r=-0.45, P<0.001; r=-0.26, P<0.001).

CONCLUSIONS

The process of IVDD can be detected by T1ρ and T2* mapping, particularly at early stage, and both methodologies displayed roughly comparable performance.

Articular Cartilage of the Human Knee Joint: In Vivo Multicomponent T2 Analysis at 3.0 T

PURPOSE

To compare multicomponent T2 parameters of the articular cartilage of the knee joint measured by using multicomponent driven equilibrium single-shot observation of T1 and T2 (mcDESPOT) in asymptomatic volunteers and patients with osteoarthritis.

MATERIALS AND METHODS

This prospective study was performed with institutional review board approval and with written informed consent from all subjects. The mcDESPOT sequence was performed in the knee joint of 13 asymptomatic volunteers and 14 patients with osteoarthritis of the knee. Single-component T2 (T2(Single)), T2 of the fast-relaxing water component (T2F) and of the slow-relaxing water component (T2S), and the fraction of the fast-relaxing water component (F(F)) of cartilage were measured. Wilcoxon rank-sum tests and multivariate linear regression models were used to compare mcDESPOT parameters between volunteers and patients with osteoarthritis. Receiver operating characteristic analysis was used to assess diagnostic performance with mcDESPOT parameters for distinguishing morphologically normal cartilage from morphologically degenerative cartilage identified at magnetic resonance imaging in eight cartilage subsections of the knee joint.

RESULTS

Higher cartilage T2(Single) (P < .001), lower cartilage F(F) (P < .001), and similar cartilage T2F (P = .079) and T2S (P = .124) values were seen in patients with osteoarthritis compared with those in asymptomatic volunteers. Differences in T2(Single) and F(F) remained significant (P < .05) after consideration of age differences between groups of subjects. Diagnostic performance was higher with F(F) than with T2(Single) for distinguishing between normal and degenerative cartilage (P < .05), with greater areas under the curve at receiver operating characteristic analysis.

CONCLUSION

Patients with osteoarthritis of the knee had significantly higher cartilage T2(Single) and significantly lower cartilage F(F) than did asymptomatic volunteers, and receiver operating characteristic analysis results suggested that F(F) may allow greater diagnostic performance than that with T2(Single) for distinguishing between normal and degenerative cartilage.

Imaging strategies for assessing cartilage composition in osteoarthritis

Efforts to reduce the ever-increasing rates of osteoarthritis (OA) in the developed world require the ability to non-invasively detect the degradation of joint tissues before advanced damage has occurred. This is particularly relevant for damage to articular cartilage because this soft tissue lacks the capacity to repair itself following major damage and is essential to proper joint function. While conventional magnetic resonance imaging (MRI) provides sufficient contrast to visualize articular cartilage morphology, more advanced imaging strategies are necessary for understanding the underlying biochemical composition of cartilage that begins to break down in the earliest stages of OA. This review discusses the biochemical basis and the advantages and disadvantages associated with each of these techniques. Recent implementations for these techniques are touched upon, and future considerations for improving the research and clinical power of these imaging technologies are also discussed.

Classification of histologically scored human knee osteochondral plugs by quantitative analysis of magnetic resonance images at 3T

This work evaluates the ability of quantitative MRI to discriminate between normal and pathological human osteochondral plugs characterized by the Osteoarthritis Research Society International (OARSI) histological system. Normal and osteoarthritic human osteochondral plugs were scored using the OARSI histological system and imaged at 3 T using MRI sequences producing T1 and T2 contrast and measuring T1, T2, and T2* relaxation times, magnetization transfer, and diffusion. The classification accuracies of quantitative MRI parameters and corresponding weighted image intensities were evaluated. Classification models based on the Mahalanobis distance metric for each MRI measurement were trained and validated using leave-one-out cross-validation with plugs grouped according to OARSI histological grade and score. MRI measurements used for classification were performed using a region-of-interest analysis which included superficial, deep, and full-thickness cartilage. The best classifiers based on OARSI grade and score were T1- and T2-weighted image intensities, which yielded accuracies of 0.68 and 0.75, respectively. Classification accuracies using OARSI score-based group membership were generally higher when compared with grade-based group membership. MRI-based classification--either using quantitative MRI parameters or weighted image intensities--is able to detect early osteoarthritic tissue changes as classified by the OARSI histological system. These findings suggest the benefit of incorporating quantitative MRI acquisitions in a comprehensive clinical evaluation of OA.

Evaluation of the relationship between T1ρ and T2 values and patella cartilage degeneration in patients of the same age group

OBJECTIVE

The aim of this study was to investigate the association between the T1ρ and T2 values and the progression of cartilage degeneration in patients of the same age group.

MATERIALS AND METHODS

Sagittal T1ρ and T2 mapping and three-dimensional (3D) gradient-echo images were obtained from 78 subjects with medial knee osteoarthritis (OA). The degree of patella cartilage degeneration was classified into four groups using MRI-based grading: apparently normal cartilage, mild OA, moderate OA, and severe OA group. We measured the T1ρ and T2 values (ms) in the regions of interest set on the full-thickness patella cartilage. Then, we analyzed the relationship between the T1ρ and T2 values and the degree of patella cartilage degeneration.

RESULTS

There were no significant differences in age among the four groups. Both the T1ρ and T2 values showed a positive correlation with the degree of OA progression (ρ=0.737 and ρ=0.632, respectively). By comparison between the apparently normal cartilage and the mild OA groups, there were significant differences in the T1ρ mapping, but not in the T2 mapping.

CONCLUSIONS

Our study confirmed that T1ρ and T2 mapping can quantitatively evaluate the degree of patella cartilage degeneration in patients within the same age group.

Effects of spin-lock field direction on the quantitative measurement of spin-lattice relaxation time constant in the rotating frame (T1ρ) in a clinical MRI system

PURPOSE

To investigate whether the direction of spin-lock field, either parallel or antiparallel to the rotating magnetization, has any effect on the spin-lock MRI signal and further on the quantitative measurement of T1ρ, in a clinical 3 T MRI system.

METHODS

The effects of inverted spin-lock field direction were investigated by acquiring a series of spin-lock MRI signals for an American College of Radiology MRI phantom, while the spin-lock field direction was switched between the parallel and antiparallel directions. The acquisition was performed for different spin-locking methods (i.e., for the single- and dual-field spin-locking methods) and for different levels of clinically feasible spin-lock field strength, ranging from 100 to 500 Hz, while the spin-lock duration was varied in the range from 0 to 100 ms.

RESULTS

When the spin-lock field was inverted into the antiparallel direction, the rate of MRI signal decay was altered and the T1ρ value, when compared to the value for the parallel field, was clearly different. Different degrees of such direction-dependency were observed for different spin-lock field strengths. In addition, the dependency was much smaller when the parallel and the antiparallel fields are mixed together in the dual-field method.

CONCLUSIONS

The spin-lock field direction could impact the MRI signal and further the T1ρ measurement in a clinical MRI system.

Physical activity and spatial differences in medial knee T1rho and t2 relaxation times in knee osteoarthritis

STUDY DESIGN

Cross-sectional.

OBJECTIVES

To investigate the association between knee loading- related osteoarthritis (OA) risk factors (obesity, malalignment, and physical activity) and medial knee laminar (superficial and deep) T1rho and T2 relaxation times.

BACKGROUND

The interaction of various modifiable loading-related knee risk factors and cartilage health in knee OA is currently not well known.

METHODS

Participants with and without knee OA (n = 151) underwent magnetic resonance imaging at 3 T for superficial and deep cartilage T1rho and T2 magnetic resonance relaxation times in the medial femur (MF) and medial tibia (MT). Other variables included radiographic Kellgren-Lawrence (KL) grade, alignment, pain and symptoms using the Knee injury and Osteoarthritis Outcome Score, and physical activity using the International Physical Activity Questionnaire (IPAQ). Individuals with a KL grade of 4 were excluded. Group differences were calculated using 1-way analysis of variance, adjusting for age and body mass index. Linear regression models were created with age, sex, body mass index, alignment, KL grade, and the IPAQ scores to predict the laminar T1rho and T2 times.

RESULTS

Total IPAQ scores were the only significant predictors among the loading-related variables for superficial MF T1rho (P = .005), deep MT T1rho (P = .026), and superficial MF T2 (P = .049). Additionally, the KL grade predicted the superficial MF T1rho (P = .023) and deep MT T1rho (P = .022).

CONCLUSION

Higher physical activity levels and worse radiographic severity of knee OA, but not obesity or alignment, were associated with worse cartilage composition.

Quantitative magnetic resonance imaging of the articular cartilage of the knee joint

Osteoarthritis is characterized by a decrease in the proteoglycan content and disruption of the highly organized collagen fiber network of articular cartilage. Various quantitative magnetic resonance imaging techniques have been developed for noninvasive assessment of the proteoglycan and collagen components of cartilage. These techniques have been extensively used in clinical practice to detect early cartilage degeneration and in osteoarthritis research studies to monitor disease-related and treatment-related changes in cartilage over time. This article reviews the role of quantitative magnetic resonance imaging in evaluating the composition and ultrastructure of the articular cartilage of the knee joint.

A new CT grading system for hip osteoarthritis

OBJECTIVES

We have developed a new grading system for hip osteoarthritis using clinical computed tomography (CT). This technique was compared with Kellgren and Lawrence (K&L) grading and minimum joint space width (JSW) measurement in digitally reconstructed radiographs (DRRs) from the same CT data. In this paper we evaluate and compare the accuracy and reliability of these measures in the assessment of radiological disease.

DESIGN

CT imaging of hips from 30 female volunteers aged 66 ± 17 years were used in two reproducibility studies, one testing the reliability of the new system, the other testing K&L grading and minimum JSW measurement in DRRs.

RESULTS

Intra- and inter-observer reliability was substantial for CT grading according to weighted kappa (0.74 and 0.75 respectively), while intra- and inter-observer reliability was at worst moderate (0.57) and substantial (0.63) respectively for DRR K&L grading. Bland-Altman analysis showed a systematic difference in minimum JSW measurement of 0.82 mm between reviewers, with a least detectable difference of 1.06 mm. The area under the curve from ROC analysis was 0.91 for our CT composite score.

CONCLUSIONS

CT grading of hip osteoarthritis (categorised as none, developing and established) has substantial reliability. Sensitivity was increased when CT features of osteoarthritis were assigned a composite score (0 = none to 7 = severest) that also performed well as a diagnostic test, but at the cost of reliability. Having established feasibility and reliability for this new CT system, sensitivity testing and validation against clinical measures of hip osteoarthritis will now be performed.

The role of imaging in early hip OA

Hip osteoarthritis (OA) is characterized by cartilage degradation, subchondral bone sclerosis and osteophyte formation. Nowadays, OA is thought to develop via different etiologies that all lead to a similar form of end stage joint degradation. One of these subtypes is related to an abnormal shaped hip joint, like acetabular dysplasia and a cam deformity. These bony abnormalities are highly predictive for development of hip OA, but they are likely to already be present from childhood. This suggests that these deformations induce OA changes in the hip, well before extensive hip degradation becomes present three to four decades later. Accurate detection and successful characterization of these early OA events might lead to better treatment options for hip OA besides nowadays available invasive joint replacement surgery. However, current diagnostic imaging techniques like radiographs or plain magnetic resonance imaging (MRI), are not sensitive enough to detect these subtle early OA changes. Nor are they able to disentangle intertwined and overlapping cascades from different OA subtypes, and neither can they predict OA progression. New and more sensitive imaging techniques might enable us to detect first OA changes on a cellular level, providing us with new opportunities for early intervention. In this respect, shape analysis using radiography, MRI, computed tomography (CT), single photon emission computed tomography (SPECT)/CT, and positron emission tomography (PET) might prove promising techniques and be more suited to detect early pathological changes in the hip joint. A broad application of these techniques might give us more understanding what can be considered physiological adaptation of the hip, or when early OA really starts. With a more clear definition of early OA, more homogenous patient populations can be selected and help with the development of new disease modifying OA interventions.

Imaging following acute knee trauma

Joint injury has been recognized as a potent risk factor for the onset of osteoarthritis. The vast majority of studies using imaging technology for longitudinal assessment of patients following joint injury have focused on the injured knee joint, specifically in patients with anterior cruciate ligament injury and meniscus tears where a high risk for rapid onset of post-traumatic osteoarthritis is well known. Although there are many imaging modalities under constant development, magnetic resonance (MR) imaging is the most important instrument for longitudinal monitoring after joint injury. MR imaging is sensitive for detecting early cartilage degeneration and can evaluate other joint structures including the menisci, bone marrow, tendons, and ligaments which can be sources of pain following acute injury. In this review, focusing on imaging following acute knee trauma, several studies were identified with promising short-term results of osseous and soft tissue changes after joint injury. However, studies connecting these promising short-term results to the development of osteoarthritis were limited which is likely due to the long follow-up periods needed to document the radiographic and clinical onset of the disease. Thus, it is recommended that additional high quality longitudinal studies with extended follow-up periods be performed to further investigate the long-term consequences of the early osseous and soft tissue changes identified on MR imaging after acute knee trauma.

Cross-relaxation imaging of human patellar cartilage in vivo at 3.0T

OBJECTIVE

To compare quantitative magnetization transfer (qMT) parameters of patellar cartilage measured using cross-relaxation imaging (CRI) in asymptomatic volunteers and patients with osteoarthritis.

DESIGN

The study was performed with Institutional Review Board approval and with all subjects signing informed consent. CRI of the knee joint was performed at 3.0T on 20 asymptomatic volunteers and 11 patients with osteoarthritis. The fraction of macromolecular bound protons (f), the exchange rate constant between macromolecular bound protons and free water protons (k), and the T2 relaxation time of macromolecular bound protons (T2(B)) of patellar cartilage were measured. Mann-Whitney-Wilcoxon rank-sum tests were used to compare qMT parameters between asymptomatic volunteers and patients with osteoarthritis.

RESULTS

Average f, k, and T2(B) of patellar cartilage was 12.46%, 7.22 s(-1), and 6.49 μs respectively for asymptomatic volunteers and 12.80%, 6.13 s(-1), and 6.80 μs respectively for patients with osteoarthritis. There were statistically significant differences between groups of subjects for k (P < 0.01) and T2(B) (P < 0.0001) but not f (P = 0.38) of patellar cartilage.

CONCLUSION

Patients with osteoarthritis had significantly lower k and significantly higher T2(B) of patellar cartilage than asymptomatic volunteers which suggests that qMT parameters can detect changes in the macromolecular matrix of degenerative cartilage.

Total-body irradiation produces late degenerative joint damage in rats

PURPOSE

Premature musculoskeletal joint failure is a major source of morbidity among childhood cancer survivors. Radiation effects on synovial joint tissues of the skeleton are poorly understood. Our goal was to assess long-term changes in the knee joint from skeletally mature rats that received total-body irradiation while skeletal growth was ongoing.

MATERIALS AND METHODS

14 week-old rats were irradiated with 1, 3 or 7 Gy total-body doses of 18 MV X-rays. At 53 weeks of age, structural and compositional changes in knee joint tissues (articular cartilage, subchondral bone, and trabecular bone) were characterized using 7T MRI, nanocomputed tomography (nanoCT), microcomputed tomography (microCT), and histology.

RESULTS

T2 relaxation times of the articular cartilage were lower after exposure to all doses. Likewise, calcifications were observed in the articular cartilage. Trabecular bone microarchitecture was compromised in the tibial metaphysis at 7 Gy. Mild to moderate cartilage erosion was scored in the 3 and 7 Gy rats.

CONCLUSIONS

Late degenerative changes in articular cartilage and bone were observed after total-body irradiation in adult rats exposed prior to skeletal maturity. 7T MRI, microCT, nanoCT, and histology identified potential prognostic indicators of late radiation-induced joint damage.

Quantitative evaluation in combination with nonquantitative evaluation in early patellar cartilage osteoarthritis at 3.0 T

Purpose

To evaluate quantitative T1 and T2 relaxation times and magnetization transfer ratios (MTRs) in the early diagnosis of patellar cartilage osteoarthritis (OA) and to quantify and possibly refine the current Kellgren-Lawrence score criteria.

Materials and methods

A total of 92 cases of knee joints with 40 normal volunteers and 30 patients with OA were prospectively evaluated. The knee joints with OA were divided into mild and moderate groups according to the Kellgren-Lawrence score criteria. The discriminative analysis method was used to analyze the accuracy of the original grouped cases correctly classified by age, sex, T1 relaxation times, T2 relaxation times, and MTR values. Linear regression analysis was used between T1 relaxation time, T2 relaxation time, and MTR values.

Results

The mean T1 relaxation times decreased with the severity of OA, and a significant difference was only found between the normal and moderate OA groups (P<0.05). The mean T2 relaxation times increased, and significant differences were found between the normal and mild OA groups and the normal and moderate OA groups (P<0.001). The MTR values were 35.8%±4.2%, 36.1%±3.2%, and 35.4%±3.8%, respectively. There were no significant differences between the normal and OA groups. In addition, T1 relaxation times were positively correlated with MTR values (P<0.01). A discriminative analysis using a synthesis of all the influential factors indicated a high accuracy rate (93.9%) for the correct classification of the original grouped cases.

Conclusion

Quantitative T1 and T2 relaxation times were useful in the diagnosis of early OA; T2 relaxation times were more relatively sensitive. The functional usefulness of MTR values may be limited. T1 relaxation times positively correlated with MTR values. Multiple quantitative parameters, combined with some relative nonquantitative clinical parameters and Kellgren-Lawrence scores, may be useful in the early stage of OA and provide better information for clinical treatment and follow-up.

Precision-guided sampling schedules for efficient T1ρ mapping

PURPOSE

To describe, assess, and implement a simple precision estimation framework for optimization of spin-lock time (TSL) sampling schedules for quantitative T1ρ mapping using a mono-exponential signal model.

MATERIALS AND METHODS

A method is described for estimating T1ρ precision, and a cost function based on the precision estimates is evaluated to determine efficient TSL sampling schedules. The validity of the framework was tested by imaging a phantom with various sampling schedules and comparing theoretical and experimental precision values. The method utility was demonstrated with in vivo T1ρ mapping of brain tissue using a similar procedure as the phantom experiment. To assist investigators, optimal sampling schedules are tabulated for various tissue types and an online calculator is implemented.

RESULTS

Theoretical and experimental precision values followed similar trends for both the phantom and in vivo experiments. The mean absolute percentage error (MAPE) of theoretical estimates of T1ρ map signal-to-noise ratio (SNR) was typically 5% in the phantom experiment and 33% in the in vivo demonstration. In both experiments, optimal TSL schedules yielded greater T1ρ map SNR efficiency than typical schedules.

CONCLUSION

The framework can be used to improve the imaging efficiency of T1ρ mapping protocols and to guide selection of imaging parameters.

Longitudinal evaluation of T1ρ and T2 spatial distribution in osteoarthritic and healthy medial knee cartilage

OBJECTIVE

To investigate longitudinal changes in laminar and spatial distribution of knee articular cartilage magnetic resonance imaging (MRI) T1ρ and T2 relaxation times, in individuals with and without medial compartment cartilage defects.

DESIGN

All subjects (at baseline n = 88, >18 years old) underwent 3-Tesla knee MRI at baseline and annually thereafter for 3 years. The MR studies were evaluated for presence of cartilage defects (modified Whole-Organ Magnetic Resonance Imaging Scoring - mWORMS), and quantitative T1ρ and T2 relaxation time maps. Subjects were segregated into those with (mWORMS ≥2) and without (mWORMS ≤1) cartilage lesions at the medial tibia (MT) or medial femur (MF) at each time point. Laminar (bone and articular layer) and spatial (gray level co-occurrence matrix - GLCM) distribution of the T1ρ and T2 relaxation time maps were calculated. Linear regression models (cross-sectional) and Generalized Estimating Equations (GEEs) (longitudinal) were used.

RESULTS

Global T1ρ, global T2 and articular layer T2 relaxation times at the MF, and global and articular layer T2 relaxation times at the MT, were higher in subjects with cartilage lesions compared to those without lesions. At the MT global T1ρ relaxation times were higher at each time point in subjects with lesions. MT T1ρ and T2 became progressively more heterogeneous than control compartments over the course of the study.

CONCLUSION

Spatial distribution of T1ρ and T2 relaxation time maps in medial knee OA using GLCM technique may be a sensitive indicator of cartilage deterioration, in addition to whole-compartment relaxation time data.

Simultaneous acquisition of T1ρ and T2 quantification in knee cartilage: repeatability and diurnal variation

PURPOSE

To develop a robust sequence that combines T1ρ and T2 quantifications and to examine the in vivo repeatability and diurnal variation of T1ρ and T2 quantifications in knee cartilage.

MATERIALS AND METHODS

Six healthy volunteers were scanned in the morning and afternoon on 2 days using a combined T1ρ and T2 quantification sequence developed in this study. Repeatability of T1ρ and T2 quantification was estimated using root-mean-square coefficients-of-variation (RMS-CV). T1ρ and T2 values from morning scans were compared to those from afternoon scans using paired t-tests.

RESULTS

The overall RMS-CV of in vivo T1ρ and T2 quantification was 5.3% and 5.2%, respectively. The RMS-CV of am scans was 4.2% and 5.0% while the RMS-CV of pm scans was 6.0% and 6.3% for T1ρ and T2 , respectively. No significant difference was found between T1ρ or T2 values in the morning and in the afternoon.

CONCLUSION

A sequence that combines T1ρ and T2 quantification with scan time less than 10 minutes and is robust to B0 and B1 inhomogeneity was developed with excellent repeatability. For a cohort with low-level daily activity, although no significant diurnal variation of cartilage MR relaxation times was observed, the afternoon scans had inferior repeatability compared to morning scans.