T₁ρ MRI of human musculoskeletal system

Imaging of osteoarthritis-recent research developments and future perspective

In osteoarthritis research, imaging plays an important role in clinical trials and epidemiological observational studies. In this narrative review article, we will describe recent developments in imaging of osteoarthritis in the research arena, mainly focusing on literature evidence published within the past 3 years (2014-2017). We will primarily focus on MRI including advanced imaging techniques that are not currently commonly used in routine clinical practice, although radiography, ultrasound and nuclear medicine (radiotracer) imaging will also be discussed. Research efforts to uncover the disease process of OA as well as to discover a disease modifying OA drug continue. MRI continues to play a large role in these endeavors, while compositional MRI techniques will increasingly become important due to their ability to assess "premorphologic" biochemical changes of articular cartilage and other tissues in and around joints. Radiography remain the primary imaging modality for defining inclusion/exclusion criteria as well as an outcome measure in OA clinical trials, despite known limitations for visualization of OA features. Compositional MRI techniques show promise for predicting structural and clinical outcomes in OA research. Ultrasound can be a useful adjunct to radiography and MRI particularly for evaluation of hand OA. Newer imaging techniques such as hybrid PET/MRI may have a potential but require further research and validation.

The influences of walking, running and stair activity on knee articular cartilage: Quantitative MRI using T1 rho and T2 mapping

OBJECTIVE

To explore the different influences of walking, running and stair activity on knee articular cartilage with T1 rho and T2 mapping sequences.

MATERIALS AND METHODS

MRI (3.0-T) scans of the right knee were performed in twenty-three young healthy adults immediately after 30 minutes of rest, walking, running and stair activity respectively. Articular cartilage was quantitatively assessed based on T1 rho and T2 relaxation times. Analysis of variance for random block design data, bonferroni test and paired samples t tests were performed to estimate the different influences of physiological activities on articular cartilage.

RESULTS

T1 rho and T2 values had reductions after physiological activities in all regions of articular cartilage. T1 rho and T2 values were decreased more after running than walking. T1 rho and T2 values were decreased more after stair activity than running, except for femoral cartilage. The superficial layer of patella cartilage had higher reduction rates than the deep layer. The T1 rho and T2 values of articular cartilage were reduced in the following order: patellofemoral cartilage> medial tibiofemoral cartilage> lateral tibiofemoral cartilage. Patellofemoral cartilage experienced reductions in the following order: lateral part> middle part> medial part. Tibiofemoral cartilage had reductions in the following order: posterior part> middle part> anterior part.

CONCLUSIONS

T1 rho and T2 mapping sequences can quantitatively reflect the different influences of physiological activities on knee articular cartilage. Fluid shifts, collagen fiber deformation, spatial heterogeneity, inherent differences in material properties and tissue stiffness have close relationship with cartilage loading characteristics.

Bi-component T1ρ and T2 Relaxation Mapping of Skeletal Muscle In-Vivo

The goal of this paper was to evaluate the possibility of bi-component T1ρ and T2 relaxation mapping of human skeletal muscle at 3 T in clinically feasible scan times. T1ρ- and T2-weighted images of calf muscle were acquired using a modified 3D-SPGR sequence on a standard 3 T clinical MRI scanner. The mono- and biexponential models were fitted pixel-wise to the series of T1ρ and T2 weighted images. The biexponential decay of T1ρ and T2 relaxations was detected in ~30% and ~40% of the pixels across all volunteers, respectively. Monoexponential and bi-exponential short and long T1ρ relaxation times were estimated to be 26.9 ms, 4.6 ms (fraction 22%) and 33.2 ms (fraction: 78%), respectively. Similarly, the mono- and bi-exponential short and long T2 relaxation times were 24.7 ms, 4.2 ms (fraction 15%) and 30.4 ms (fraction 85%) respectively. The experiments had good repeatability with RMSCV < 15% and ICC > 60%. This approach could potentially be used in exercise intervention studies or in studies of inflammatory myopathies or muscle fibrosis, permitting greater sensitivity and specificity via measurement of different water compartments and their fractions.

Biexponential T1ρ relaxation mapping of human knee cartilage in vivo at 3 T

The purpose of this study was to demonstrate the feasibility of biexponential T_1ρ relaxation mapping of human knee cartilage in vivo. A three-dimensional, customized, turbo-flash sequence was used to acquire T_1ρ -weighted images from healthy volunteers employing a standard 3-T MRI clinical scanner. A series of T_1ρ -weighted images was fitted using monoexponential and biexponential models with two- and four-parametric non-linear approaches, respectively. Non-parametric Kruskal-Wallis and Mann-Whitney U-statistical tests were used to evaluate the regional relaxation and gender differences, respectively, with a level of significance of P = 0.05. Biexponential relaxations were detected in the cartilage of all volunteers. The short and long relaxation components of T_1ρ were estimated to be 6.9 and 51.0 ms, respectively. Similarly, the fractions of short and long T_1ρ were 37.6% and 62.4%, respectively. The monoexponential relaxation of T_1ρ was 32.6 ms. The experiments showed good repeatability with a coefficient of variation (CV) of less than 20%. A biexponential relaxation model showed a better fit than a monoexponential model to the T_1ρ relaxation decay in knee cartilage. Biexponential T_1ρ components could potentially be used to increase the specificity to detect early osteoarthritis by the measurement of different water compartments and their fractions.

Surgical Correction of Cam Deformity in Association with Femoroacetabular Impingement and Its Impact on the Degenerative Process within the Hip Joint

BACKGROUND

Cam morphology in association with femoroacetabular impingement (FAI) is a recognized cause of hip pain and cartilage damage and proposed as a leading cause of arthritis. The purpose of this study was to analyze the functional and biomechanical effects of the surgical correction of the cam deformity on the degenerative process associated with FAI.

METHODS

Ten male patients with a mean age of 34.3 years (range, 23.1 to 46.5 years) and a mean body mass index (and standard deviation) of 26.66 ± 4.79 kg/m underwent corrective surgery for cam deformity in association with FAI. Each patient underwent a computed tomography (CT) scan to assess acetabular bone mineral density (BMD), high-resolution T1ρ magnetic resonance imaging (MRI) of the hips to assess proteoglycan content, and squatting motion analysis as well as completed self-administered functional questionnaires (Hip disability and Osteoarthritis Outcome Score [HOOS]) both preoperatively and 2 years postoperatively.

RESULTS

At a mean follow-up of 24.5 months, improvements in functional scores and squat performance were seen. Regarding the zone of impingement in the anterosuperior quadrant of the acetabular rim, the mean change in BMD at the time of follow-up was -31.8 mg/cc (95% confidence interval [CI], -11 to -53 mg/cc) (p = 0.008), representing a 5% decrease in BMD. The anterosuperior quadrant also demonstrated a significant decrease in T1ρ values, reflecting a stabilization of the cartilage degeneration. Significant correlations were noted between changes in clinical functional scores and changes in T1ρ values (r = -0.86; p = 0.003) as well as between the BMD and maximum vertical force (r = 0.878; p = 0.021).

CONCLUSIONS

Surgical correction of a cam deformity in patients with symptomatic FAI not only improved clinical function but was also associated with decreases in T1ρ values and BMD. These findings are the first, to our knowledge, to show that alteration of the hip biomechanics through surgical intervention improves the overall health of the hip joint.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Ultrasonographic assessment of medial femoral cartilage deformation acutely following walking and running

OBJECTIVE

To determine the magnitude of medial femoral cartilage deformation using ultrasonography (US) following walking and running in healthy individuals.

DESIGN

Twenty-five healthy participants with no history of osteoarthritis or knee injury volunteered for this study. Medial femoral cartilage thickness was assessed using US before and after three separate 30-min loading conditions: (1) walking at a self-selected speed, (2) running at a self-selected speed, and (3) sitting on a treatment table (i.e., control). Cartilage deformation was calculated as the percent change score from pre to post loading in each loading condition. The magnitude of cartilage deformation was compared between the three loading conditions.

RESULTS

There was no difference in baseline cartilage thickness between the three sessions (F_1,24 = 0.18, P = 0.68). Cartilage deformation was different between the loading conditions (F_1,24 = 47.54, P < 0.001). The walking (%Δ = -6.7, t₂₄ = 6.90, P < 0.001, d = -1.92) and running (%Δ = -8.9, t₂₄ = 8.14, P < 0.001, d = -1.85) conditions resulted in greater cartilage deformation when compared to the control condition (%Δ = +3.4). There was no difference in cartilage deformation between the running and walking conditions (t₂₄ = 1.10, P = 0.28, d = 0.33). US measured medial femoral cartilage thickness demonstrated reliability and precision within a single session (ICC_2,k = 0.966, SEM = 0.07 mm) and between additional sessions separated by seven (ICC_2,k = 0.964, SEM = 0.08 mm) and 16 days (ICC_2,k = 0.919, SEM = 0.11 mm).

CONCLUSIONS

US demonstrated to be a reliable and sensitive imaging modality at quantifying medial femoral cartilage deformation in healthy individuals. Both walking and running conditions created greater cartilage deformation when compared to the control conditions, but no difference was observed between the walking and running conditions.

Biexponential T2 relaxation estimation of human knee cartilage in vivo at 3T

PURPOSE

To evaluate biexponential T₂ relaxation mapping of human knee cartilage in vivo in clinically feasible scan times.

MATERIALS AND METHODS

T₂ -weighted magnetic resonance (MR) images were acquired from eight healthy volunteers using a standard 3T clinical scanner. A 3D Turbo-Flash sequence was modified to enable T₂ -weighted imaging with different echo times. Series of T₂ -weighted images were fitted using mono- and biexponential models with two- and four-parametric nonlinear approaches, respectively.

RESULTS

Biexponential relaxation of T₂ was detected in the knee cartilage in five regions of interest in all eight healthy volunteers. Short/long relaxation components of T₂ were estimated to be 8.27 ± 0.68 / 45.35 ± 3.79 msec with corresponding fractions of 41.3 ± 1.1% / 58.6 ± 4.6%, respectively. The monoexponential relaxation of T₂ was measured to be 26.9 ± 2.27 msec. The experiments showed good repeatability with coefficient of variation root mean square (CV_rms ) < 18% in all regions. The only difference in gender was observed in medial tibial cartilage, where the biexponential T₂ in female volunteers was significantly higher compared to male volunteers (P = 0.014). Significant differences were observed in T₂ relaxation between different regions on interest.

CONCLUSION

Biexponential relaxation of T₂ was observed in the human knee cartilage in vivo. The short and long components are thought to be related to the tightly bound and loosely bound macromolecular water compartments. These preliminary results of biexponential T₂ analysis could potentially be used to increase the specificity for detection of early osteoarthritis by measuring different water compartments and their fractions.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:809-819.

A non-contrast CMR index for assessing myocardial fibrosis

PURPOSE

Safe, sensitive, and non-invasive imaging methods to assess the presence, extent, and turnover of myocardial fibrosis are needed for early stratification of risk in patients who might develop heart failure after myocardial infarction. We describe a non-contrast cardiac magnetic resonance (CMR) approach for sensitive detection of myocardial fibrosis using a canine model of myocardial infarction and reperfusion.

METHODS

Seven dogs had coronary thrombotic occlusion of the left anterior descending coronary arteries followed by fibrinolytic reperfusion. CMR studies were performed at 7days after reperfusion. A CMR spin-locking T₁ρ mapping sequence was used to acquire T₁ρ dispersion data with spin-lock frequencies of 0 and 511Hz. A fibrosis index map was derived on a pixel-by-pixel basis. CMR native T₁ mapping, first-pass myocardial perfusion imaging, and post-contrast late gadolinium enhancement imaging were also performed for assessing myocardial ischemia and fibrosis. Hearts were dissected after CMR for histopathological staining and two myocardial tissue segments from the septal regions of adjacent left ventricular slices were qualitatively assessed to grade the extent of myocardial fibrosis.

RESULTS

Histopathology of 14 myocardial tissue segments from septal regions was graded as grade 1 (fibrosis area, <20% of a low power field, n=9), grade 2 (fibrosis area, 20-50% of field, n=4), or grade 3 (fibrosis area, >50% of field, n=1). A dramatic difference in fibrosis index (183%, P<0.001) was observed by CMR from grade 1 to 2, whereas differences were much smaller for T₁ρ (9%, P=0.14), native T₁ (5.5%, P=0.12), and perfusion (-21%, P=0.05).

CONCLUSION

A non-contrast CMR index based on T₁ρ dispersion contrast was shown in preliminary studies to detect and correlate with the extent of myocardial fibrosis identified histopathologically. A non-contrast approach may have important implications for managing cardiac patients with heart failure, particularly in the presence of impaired renal function.

Principal component analysis-T1ρ voxel based relaxometry of the articular cartilage: a comparison of biochemical patterns in osteoarthritis and anterior cruciate ligament subjects

BACKGROUND

Quantitative MR, including T_1ρ mapping, has been extensively used to probe early biochemical changes in knee articular cartilage of subjects with osteoarthritis (OA) and others at risk for cartilage degeneration, such as those with anterior cruciate ligament (ACL) injury and reconstruction. However, limited studies have been performed aimed to assess the spatial location and patterns of T_1ρ. In this study we used a novel voxel-based relaxometry (VBR) technique coupled with principal component analysis (PCA) to extract relevant features so as to describe regional patterns and to investigate their similarities and differences in T_1ρ maps in subjects with OA and subjects six months after ACL reconstruction (ACLR).

METHODS

T_1ρ quantitative MRI images were collected for 180 subjects from two separate cohorts. The OA cohort included 93 osteoarthritic patients and 25 age-matched controls. The ACLR-6M cohort included 52 patients with unilateral ACL tears who were imaged 6 months after ACL reconstruction, and 10 age-matched controls. Non-rigid registration on a single template and local Z-score conversion were adopted for T_1ρ spatial and intensity normalization of all the images in the dataset. PCA was used as a data dimensionality reduction to obtain a description of all subjects in a 10-dimensional feature space. Logistic linear regression was used to identify distinctive features of OA and ACL subjects.

RESULTS

Global prolongation of the Z-score was observed in both OA and ACL subjects compared to controls [higher values in 1^st principal component (PC1); P=0.01]. In addition, relaxation time differences between superficial and deep cartilage layers of the lateral tibia and trochlea were observed to be significant distinctive features between OA and ACL subjects. OA subjects demonstrated similar values between the two cartilage layers [higher value in 2^nd principal component (PC2); P=0.008], while ACL reconstructed subjects showed T_1ρ prolongation specifically in the cartilage superficial layer (lower values in PC2; P<0.0001). T_1ρ elevation located outside of the weight-bearing area, located in the posterior and anterior aspects of the lateral femoral compartment, was also observed to be a key feature in distinguishing OA subjects from controls [higher value in 6^th principal component (PC6); P=0.007].

CONCLUSIONS

This study is the first example of T_1ρ local/regional pattern analysis and data-driven feature extraction in knees with cartilage degeneration. Our results revealed similarities and differences between OA and ACL relaxation patterns that could be potentially useful to better understand the pathogenesis of post-traumatic cartilage degeneration and the identification of imaging biomarkers for the early stratification of subjects at risk for developing post-traumatic OA.

Ex vivo quantitative multiparametric MRI mapping of human meniscus degeneration

OBJECTIVES

To evaluate the diagnostic performance of T1, T1ρ, T2, T2*, and UTE-T2* (ultrashort-echo time-enhanced T2*) mapping in the refined graduation of human meniscus degeneration with histology serving as standard-of-reference.

MATERIALS AND METHODS

This IRB-approved intra-individual comparative ex vivo study was performed on 24 lateral meniscus body samples obtained from 24 patients undergoing total knee replacement. Samples were assessed on a 3.0-T MRI scanner using inversion-recovery (T1), spin-lock multi-gradient-echo (T1ρ), multi-spin-echo (T2) and multi-gradient-echo (T2* and UTE-T2*) sequences to determine relaxation times of quantitative MRI (qMRI) parameters. Relaxation times were calculated on the respective maps, averaged to the entire meniscus and to its zones. Histologically, samples were analyzed on a four-point score according to Williams (0-III). QMRI results and Williams (sub)scores were correlated using Spearman's ρ, while Williams grade-dependent differences were assessed using Kruskal-Wallis and Dunn's tests. Sensitivities and specificities in the detection of intact (Williams grade [WG]-0) and severely degenerate meniscus (WG-II-III) were calculated.

RESULTS

Except for T2*, significant increases in qMRI parameters with increasing Williams grades were observed. T1, T1ρ, T2, and UTE-T2* exhibited high sensitivity and variable specificity rates. Significant marked-to-strong correlations were observed for these parameters with each other, with histological WGs and the subscores tissue integrity and cellularity.

CONCLUSIONS

QMRI mapping holds promise in the objective evaluation of human meniscus. Although sufficient discriminatory power of T1, T1ρ, T2, and UTE-T2* was only demonstrated for the histological extremes, these data may aid in the future MRI-based parameterization and quantification of human meniscus degeneration.

Interobserver and Test-Retest Reproducibility of T1ρ and T2 Measurements of Lumbar Intervertebral Discs by 3T Magnetic Resonance Imaging

Objective

To investigate the interobserver and test-retest reproducibility of T1ρ and T2 measurements of lumbar intervertebral discs using 3T magnetic resonance imaging (MRI).

Materials and Methods

This study included a total of 51 volunteers (female, 26; male, 25; mean age, 54 ± 16.3 years) who underwent lumbar spine MRI with a 3.0 T scanner. Amongst these subjects, 40 underwent repeat T1ρ and T2 measurement acquisitions with identical image protocol. Two observers independently performed the region of interest measurements in the nuclei pulposi of the discs from L1–2 through L5–S1 levels. Statistical analysis was performed using intraclass correlation coefficient (ICC) with a two-way random model of absolute agreement. Comparison of the ICC values was done after acquisition of ICC values using Z test. Statistical significance was defined as p value < 0.05.

Results

The ICCs of interobserver reproducibility were 0.951 and 0.672 for T1ρ and T2 mapping, respectively. The ICCs of test-retest reproducibility (40 subjects) for T1ρ and T2 measurements were 0.922 and 0.617 for observer A and 0.914 and 0.628 for observer B, respectively. In the comparison of the aforementioned ICCs, ICCs of interobserver and test-retest reproducibility for T1ρ mapping were significantly higher than T2 mapping (p < 0.001).

Conclusion

The interobserver and test-retest reproducibility of T1ρ mapping were significantly higher than those of T2 mapping for the quantitative assessment of nuclei pulposi of lumbar intervertebral discs.

Evaluating radiocarpal cartilage matrix changes 3-months after anti-TNF treatment for rheumatoid arthritis using MR T1ρ imaging

PURPOSE

To evaluate the feasibility of MR T1ρ in assessing radiocarpal cartilage matrix changes following rheumatoid arthritis (RA) treatment.

MATERIALS AND METHODS

Five healthy controls and nine RA patients were studied: three RA patients with low disease activity that were treated with methotrexate (MTX) alone and six with active disease despite MTX treatment who were additionally treated with certolizumab pegol, an anti-tumor necrosis factor biologic. Wrist 3 Tesla MRI were acquired at baseline and 3-month follow-up. T1ρ were quantified for lunar, radius, and scaphoid cartilage. Reproducibility was evaluated using coefficients of variation (CV). Longitudinal changes were evaluated with t-test and relationships between T1ρ with clinical, MRI, and patient-reported outcomes were evaluated with Spearman's rho.

RESULTS

Scan/re-scan CVs of T1ρ values were all <5%, and intra- and inter-reader CVs were all < 2.0%. Baseline scaphoid T1ρ values were significantly higher in RA patients compared with healthy controls (P = 0.032). Changes in T1ρ (baseline, 3-month) were correlated with EULAR treatment response criteria: -2.26 ± 0.75 ms, 1.08 ± 0.52 ms, and 2.18 ± 0.45 ms for good, moderate, and nonresponders, respectively. Significant correlations were found between changes in global T1ρ values and changes in DAS28-CRP (r_s  = 0.683; P = 0.042), MHQ (r_s  = -0.783; P = 0.013), and HAQ (r_s  = 0.833; P = 0.010).

CONCLUSION

Despite the limited sample size and follow-up time points, there were significant correlations between changes in radiocarpal T1ρ and changes in disease activity as assessed by clinical and patient-reported outcomes. Our findings encourage further research into MR T1ρ assessment of RA disease activity and treatment response.

LEVEL OF EVIDENCE

1 J. MAGN. RESON. IMAGING 2017;45:1514-1522.

Assessment of female ballet dancers' ankles in the en pointe position using high field strength magnetic resonance imaging

BACKGROUND

The en pointe position of the ankle in ballet is extreme. Previously, magnetic resonance imaging (MRI) of ballet dancers' ankles en pointe was confined to a low field, open MR device.

PURPOSE

To develop a reproducible ankle MRI protocol for ballet dancers en pointe and to assess the positions of the key structures in the dancers ankles.

MATERIAL AND METHODS

Six female ballet dancers participated; each was randomly assigned to stand en pointe while one of her feet and ankles was splinted with wooden rods affixed with straps or to begin with the ankle in neutral position. She lay in an MR scanner with the ankle inside a knee coil for en pointe imaging and inside an ankle/foot coil for neutral position imaging. Proton density weighted images with and without fat suppression and 3D water excitation gradient recalled echo images were obtained en pointe and in neutral position in sagittal, axial, and coronal planes. We compared the bones, cartilage, and soft tissues within and between positions.

RESULTS

No difficulties using the protocol were encountered. En pointe the posterior articular surface of the tibial plafond was incongruent with the talar dome and rested on the posterior talus. The posterior edge of the plafond impinged Kager's fat pad. All participants exhibited one or more small ganglion cysts about the ankle and proximal foot, as well as fluid accumulation in the flexor and fibularis tendon sheaths.

CONCLUSION

Our MRI protocol allows assessment of female ballet dancers' ankles in the extreme plantar flexion position in which the dancers perform. We consistently noted incongruence of the talocrural joint and convergence of the tibia, talus, and calcaneus posteriorly. This protocol may be useful for clinicians who evaluate dancers.

New Imaging Methods for Non-invasive Assessment of Mechanical, Structural, and Biochemical Properties of Human Achilles Tendon: A Mini Review

The mechanical properties of tendon play a fundamental role to passively transmit forces from muscle to bone, withstand sudden stretches, and act as a mechanical buffer allowing the muscle to work more efficiently. The use of non-invasive imaging methods for the assessment of human tendon's mechanical, structural, and biochemical properties in vivo is relatively young in sports medicine, clinical practice, and basic science. Non-invasive assessment of the tendon properties may enhance the diagnosis of tendon injury and the characterization of recovery treatments. While ultrasonographic imaging is the most popular tool to assess the tendon's structural and indirectly, mechanical properties, ultrasonographic elastography, and ultra-high field magnetic resonance imaging (UHF MRI) have recently emerged as potentially powerful techniques to explore tendon tissues. This paper highlights some methodological cautions associated with conventional ultrasonography and perspectives for in vivo human Achilles tendon assessment using ultrasonographic elastography and UHF MRI.

Quantitative rotating frame relaxometry methods in MRI

Macromolecular degeneration and biochemical changes in tissue can be quantified using rotating frame relaxometry in MRI. It has been shown in several studies that the rotating frame longitudinal relaxation rate constant (R1ρ ) and the rotating frame transverse relaxation rate constant (R2ρ ) are sensitive biomarkers of phenomena at the cellular level. In this comprehensive review, existing MRI methods for probing the biophysical mechanisms that affect the rotating frame relaxation rates of the tissue (i.e. R1ρ and R2ρ ) are presented. Long acquisition times and high radiofrequency (RF) energy deposition into tissue during the process of spin-locking in rotating frame relaxometry are the major barriers to the establishment of these relaxation contrasts at high magnetic fields. Therefore, clinical applications of R1ρ and R2ρ MRI using on- or off-resonance RF excitation methods remain challenging. Accordingly, this review describes the theoretical and experimental approaches to the design of hard RF pulse cluster- and adiabatic RF pulse-based excitation schemes for accurate and precise measurements of R1ρ and R2ρ . The merits and drawbacks of different MRI acquisition strategies for quantitative relaxation rate measurement in the rotating frame regime are reviewed. In addition, this review summarizes current clinical applications of rotating frame MRI sequences. Copyright © 2016 John Wiley & Sons, Ltd.

Quantitative OCT and MRI biomarkers for the differentiation of cartilage degeneration

OBJECTIVE

To evaluate the usefulness of quantitative parameters obtained by optical coherence tomography (OCT) and magnetic resonance imaging (MRI) in the comprehensive assessment of human articular cartilage degeneration.

MATERIALS AND METHODS

Human osteochondral samples of variable degeneration (n = 45) were obtained from total knee replacements and assessed by MRI sequences measuring T1, T1ρ, T2 and T2* relaxivity and by OCT-based quantification of irregularity (OII, optical irregularity index), homogeneity (OHI, optical homogeneity index]) and attenuation (OAI, optical attenuation index]). Samples were also assessed macroscopically (Outerbridge classification) and histologically (Mankin classification) as grade-0 (Mankin scores 0-4)/grade-I (scores 5-8)/grade-II (scores 9-10)/grade-III (score 11-14). After data normalisation, differences between Mankin grades and correlations between imaging parameters were assessed using ANOVA and Tukey's post-hoc test and Spearman's correlation coefficients, respectively. Sensitivities and specificities in the detection of Mankin grade-0 were calculated.

RESULTS

Significant degeneration-related increases were found for T2 and OII and decreases for OAI, while T1, T1ρ, T2* or OHI did not reveal significant changes in relation to degeneration. A number of significant correlations between imaging parameters and histological (sub)scores were found, in particular for T2 and OII. Sensitivities and specificities in the detection of Mankin grade-0 were highest for OHI/T1 and OII/T1ρ, respectively.

CONCLUSION

Quantitative OCT and MRI techniques seem to complement each other in the comprehensive assessment of cartilage degeneration. Sufficiently large structural and compositional changes in the extracellular matrix may thus be parameterized and quantified, while the detection of early degeneration remains challenging.

Validation and optimization of adiabatic T1ρ and T2ρ for quantitative imaging of articular cartilage at 3 T

PURPOSE

The aim of the present work was to validate and optimize adiabatic T_1ρ and T_2ρ mapping for in vivo measurements of articular cartilage at 3 Tesla (T).

METHODS

Phantom and in vivo experiments were systematically performed on a 3T clinical system to evaluate the sequences using hyperbolic secant HS1 and HS4 pulses. R_1ρ and R_2ρ relaxation rates were studied as a function of agarose and chondroitin sulfate concentration and pulse duration. Optimal in vivo protocol was determined by imaging the articular cartilage of two volunteers and varying the sequence parameters, and successively applied in eight additional subjects. Reproducibility was assessed in phantoms and in vivo.

RESULTS

Relaxation rates depended on agarose and chondroitin sulfate concentration. The sequences were able to generate relaxation time maps with pulse lengths of 8 and 6 ms for HS1 and HS4, respectively. In vivo findings were in good agreement with the phantoms. The implemented adiabatic T_1ρ and T_2ρ sequences demonstrated regional variation in relaxation time maps of femorotibial cartilage. Reproducibility in phantoms and in vivo was good to excellent for both adiabatic T_1ρ and T_2ρ .

CONCLUSIONS

The findings indicate that sequences are suitable for quantitative in vivo assessment of articular cartilage at 3 T. Magn Reson Med 77:1265-1275, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

T1ρ magnetic resonance: basic physics principles and applications in knee and intervertebral disc imaging

T1ρ relaxation time provides a new contrast mechanism that differs from T1- and T2-weighted contrast, and is useful to study low-frequency motional processes and chemical exchange in biological tissues. T1ρ imaging can be performed in the forms of T1ρ-weighted image, T1ρ mapping and T1ρ dispersion. T1ρ imaging, particularly at low spin-lock frequency, is sensitive to B0 and B1 inhomogeneity. Various composite spin-lock pulses have been proposed to alleviate the influence of field inhomogeneity so as to reduce the banding-like spin-lock artifacts. T1ρ imaging could be specific absorption rate (SAR) intensive and time consuming. Efforts to address these issues and speed-up data acquisition are being explored to facilitate wider clinical applications. This paper reviews the T1ρ imaging's basic physic principles, as well as its application for cartilage imaging and intervertebral disc imaging. Compared to more established T2 relaxation time, it has been shown that T1ρ provides more sensitive detection of proteoglycan (PG) loss at early stages of cartilage degeneration. T1ρ has also been shown to provide more sensitive evaluation of annulus fibrosis (AF) degeneration of the discs.

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.

Regional Articular Cartilage Abnormalities of the Hip

OBJECTIVE

Imaging of hip cartilage is challenging because of its limited thickness and complex geometry and therefore requires advanced MRI techniques. However, cartilage abnormalities are found in a number of disease entities, and their diagnosis may impact patient management. This article will provide pertinent information about the motivation to image hip cartilage, which imaging techniques to use, and how to analyze cartilage; finally, we will discuss disease entities with regional cartilage lesions, including the typical MRI findings.

CONCLUSION

Because the detection and quantification of regional cartilage abnormalities are critical for guidance of operative and nonoperative management of hip disorders, radiologists should be familiar with imaging and analysis techniques for assessing hip cartilage.

Ultrashort Echo Time T1ρ Is Sensitive to Enzymatic Degeneration of Human Menisci

OBJECTIVE

The aim of the study was to determine whether quantitative ultrashort echo time (UTE) -T1ρ magnetic resonance (MR) measurements are sensitive to proteoglycan degradation in human menisci by trypsin digestion.

METHODS

Conventional and quantitative UTE-T1ρ MR sequences were performed on 4 meniscal samples using a 3T scanner. Magnetic resonance imaging was performed before and after 4, 8, and 12 hours of trypsin solution immersion, inducing proteoglycan loss. One sample was used as a control. Digest solutions were analyzed for glycosaminoglycan (GAG) content. The UTE-T1ρ studies were analyzed for quantitative changes.

RESULTS

Images showed progressive tissue swelling, fiber disorganization, and increase in signal intensity after GAG depletion. The UTE-T1ρ values tended to increase with time after trypsin treatment (P = 0.06). Cumulative GAG loss into the bath showed a trend of increased values for trypsin-treated samples (P = 0.1).

CONCLUSIONS

Ultrashort echo time T1ρ measurements can noninvasively detect and quantify severity of meniscal degeneration, which has been correlated with progression of osteoarthritis.

Magnetic Resonance Imaging of the Hip

Hip pain is common in all age groups, and osteoarthritis of this joint is an increasingly recognized problem particularly in aging populations. One of the primary goals in the diagnostic evaluation in patients with hip pain is to identify and correct pathologies that could progress to osteoarthritis. Magnetic resonance imaging (MRI) has become an important noninvasive method for characterizing hip anatomy and pathology in these patients. Improvements in MRI hardware and techniques have allowed high spatial and contrast resolution imaging to detect subtle abnormalities, such as acetabular labral and articular cartilage injuries, which often contribute to patient symptoms. Newer MRI techniques, such as delayed gadolinium-enhanced MRI of cartilage and T2 mapping, can give insight into the biochemical structure of tissues such as the articular cartilage. In turn, these can allow quantitative assessment and enable imagers to more directly compare the findings of patients at earlier stages of disease. It is important to understand the fundamental principles of various MRI techniques and their limitations to know when these techniques can best be applied. In addition, understanding of normal hip anatomy and common anatomic variants is useful for being able to accurately detect and localize areas of pathology and to prevent misinterpreting normal structures as diseased. The aims of this work were to briefly review normal hip anatomy and common anatomic variants seen on routine MRI examination, to discuss principles often used in high-resolution hip MRI and newer techniques for biochemical evaluation, and to examine several intra-articular pathologic conditions of the hip joint that are of current clinical interest.