Seven tesla knee MRI T2*-mapping detects intrasubstance meniscus degeneration in patients with posterior root tears.

Background: Medial meniscus root tears often lead to knee osteoarthritis. The extent of meniscal tissue changes beyond the localized root tear is unknown. Purpose: To evaluate if 7 Tesla 3D T2*-mapping can detect intrasubstance meniscal degeneration in patients with arthroscopically verified medial meniscus posterior root tears (MMPRTs), and assess if tissue changes extend beyond the immediate site of the posterior root tear detected on surface examination by arthroscopy. Methods: In this prospective study we acquired 7 T knee MRIs from patients with MMPRTs and asymptomatic controls. Using a linear mixed model, we compared T2* values between patients and controls, and across different meniscal regions. Patients underwent arthroscopic assessment before MMPRT repair. Changes in pain levels before and after repair were calculated using Knee Injury & Osteoarthritis Outcome Score (KOOS). Pain changes and meniscal extrusion were correlated with T2* using Pearson correlation (r). Results: Twenty patients (mean age 53 ± 8; 16 females) demonstrated significantly higher T2* values across the medial meniscus (anterior horn, posterior body and posterior horn: all P < .001; anterior body: P = .007), and lateral meniscus anterior (P = .024) and posterior (P < .001) horns when compared to the corresponding regions in ten matched controls (mean age 53 ± 12; 8 females). Elevated T2* values were inversely correlated with the change in pain levels before and after repair. All patients had medial meniscal extrusion of ≥2 mm. Arthroscopy did not reveal surface abnormalities in 70% of patients (14 out of 20). Conclusions: Elevated T2* values across both medial and lateral menisci indicate that degenerative changes in patients with MMPRTs extend beyond the immediate vicinity of the posterior root tear. This suggests more widespread meniscal degeneration, often undetected by surface examinations in arthroscopy.

Quantitative MRI methods for the assessment of structure, composition, and function of musculoskeletal tissues in basic research and preclinical applications.

Osteoarthritis (OA) is a disabling chronic disease involving the gradual degradation of joint structures causing pain and dysfunction. Magnetic resonance imaging (MRI) has been widely used as a non-invasive tool for assessing OA-related changes. While anatomical MRI is limited to the morphological assessment of the joint structures, quantitative MRI (qMRI) allows for the measurement of biophysical properties of the tissues at the molecular level. Quantitative MRI techniques have been employed to characterize tissues' structural integrity, biochemical content, and mechanical properties. Their applications extend to studying degenerative alterations, early OA detection, and evaluating therapeutic intervention. This article is a review of qMRI techniques for musculoskeletal tissue evaluation, with a particular emphasis on articular cartilage. The goal is to describe the underlying mechanism and primary limitations of the qMRI parameters, their association with the tissue physiological properties and their potential in detecting tissue degeneration leading to the development of OA with a primary focus on basic and preclinical research studies. Additionally, the review highlights some clinical applications of qMRI, discussing the role of texture-based radiomics and machine learning in advancing OA research.

Assessing post-traumatic changes in cartilage using T1ρ dispersion parameters.

Degeneration of cartilage can be studied non-invasively with quantitative MRI. A promising parameter for detecting early osteoarthritis in articular cartilage is T1ρ, which can be tuned via the amplitude of the spin-lock pulse. By measuring T1ρ at several spin-lock amplitudes, the dispersion of T1ρ is obtained. The aim of this study is to find out if the dispersion contains diagnostically relevant information complementary to a T1ρ measurement at a single spin-lock amplitude. To this end, five differently acquired dispersion parameters are utilized; A, B, τc, T1ρ/T2, and R2 - R1ρ. An open dataset of an equine model of post-traumatic cartilage was utilized to assess the T1ρ dispersion parameters for the evaluation of cartilage degeneration. Firstly, the parameters were compared for their sensitivity in detecting degenerative changes. Secondly, the relationship of the dispersion parameters to histological and biomechanical reference parameters was studied. Parameters A, T1ρ/T2, and R2 - R1ρ were found to be sensitive to lesion-induced changes in the cartilage within sample. Strong correlations of several dispersion parameters with optical density, as well as with collagen fibril angle were found. Most of the dispersion parameters correlated strongly with individual T1ρ values. The results suggest that dispersion parameters can in some cases provide a more accurate description of the biochemical composition of cartilage as compared to conventional MRI parameters. However, in most cases the information given by the dispersion parameters is more of a refinement than complementary to conventional quantitative MRI.

Longitudinal 3T MRI T2 * mapping of Juvenile osteochondritis dissecans (JOCD) lesions differentiates operative from non-operative patients-Pilot study.

Juvenile osteochondritis dissecans (JOCD) is an orthopedic joint disorder of children and adolescents that can lead to premature osteoarthritis. Thirteen patients (mean age: 12.3 years, 4 females), 15 JOCD-affected and five contralateral healthy knees, that had a baseline and a follow-up magnetic resonance imaging (MRI) (mean interval of 8.9 months) and were treated nonoperatively during this interval were included. Retrospectively, patients were assigned to operative or nonoperative groups based on their electronic medical records. Volumetric mean T2 * values were calculated within regions of interest (progeny lesion, interface, parent bone) and region matched control bone in healthy contralateral knees and condyles. The normalized percentage difference of T2 * between baseline and follow up MRI in nonoperative patients significantly increased in progeny lesion (-47.8%, p < 0.001), parent bone (-13.9%, p < 0.001), and interface (-32.3%, p = 0.011), whereas the differences in operative patients were nonsignificant and below 11%. In nonoperative patients, the progeny lesion (p < 0.001) and interface T2 * values (p = 0.012) were significantly higher than control bone T2 * at baseline, but not at follow-up (p = 0.219, p = 1.000, respectively). In operative patients, the progeny lesion and interface T2 * values remained significantly elevated compared to the control bone both at baseline (p < 0.001, p < 0.001) and follow-up (p < 0.001, p < 0.001), respectively. Clinical Significance: Longitudinal T2 * mapping differentiated nonhealing from healing JOCD lesions following initial nonoperative treatment, which may assist in prognosis and improve the ability of surgeons to make recommendations regarding operative versus nonoperative treatment.

Machine Learning Prediction of Collagen Fiber Orientation and Proteoglycan Content From Multiparametric Quantitative MRI in Articular Cartilage.

BACKGROUND: Machine learning models trained with multiparametric quantitative MRIs (qMRIs) have the potential to provide valuable information about the structural composition of articular cartilage. PURPOSE: To study the performance and feasibility of machine learning models combined with qMRIs for noninvasive assessment of collagen fiber orientation and proteoglycan content. STUDY TYPE: Retrospective, animal model. ANIMAL MODEL: An open-source single slice MRI dataset obtained from 20 samples of 10 Shetland ponies (seven with surgically induced cartilage lesions followed by treatment and three healthy controls) yielded to 1600 data points, including 10% for test and 90% for train validation. FIELD STRENGTH/SEQUENCE: A 9.4 T MRI scanner/qMRI sequences: T1 , T2 , adiabatic T1ρ and T2ρ , continuous-wave T1ρ and relaxation along a fictitious field (TRAFF ) maps. ASSESSMENT: Five machine learning regression models were developed: random forest (RF), support vector regression (SVR), gradient boosting (GB), multilayer perceptron (MLP), and Gaussian process regression (GPR). A nested cross-validation was used for performance evaluation. For reference, proteoglycan content and collagen fiber orientation were determined by quantitative histology from digital densitometry (DD) and polarized light microscopy (PLM), respectively. STATISTICAL TESTS: Normality was tested using Shapiro-Wilk test, and association between predicted and measured values was evaluated using Spearman's Rho test. A P-value of 0.05 was considered as the limit of statistical significance. RESULTS: Four out of the five models (RF, GB, MLP, and GPR) yielded high accuracy (R2  = 0.68-0.75 for PLM and 0.62-0.66 for DD), and strong significant correlations between the reference measurements and predicted cartilage matrix properties (Spearman's Rho = 0.72-0.88 for PLM and 0.61-0.83 for DD). GPR algorithm had the highest accuracy (R2  = 0.75 and 0.66) and lowest prediction-error (root mean squared [RMSE] = 1.34 and 2.55) for PLM and DD, respectively. DATA CONCLUSION: Multiparametric qMRIs in combination with regression models can determine cartilage compositional and structural features, with higher accuracy for collagen fiber orientation than proteoglycan content. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 2.

Naturally occurring osteochondrosis latens lesions identified by quantitative and morphological 10.5 T MRI in pigs.

Juvenile osteochondritis dissecans (JOCD) is a pediatric orthopedic disorder that involves the articular-epiphyseal cartilage complex and underlying bone. Clinical disease is often characterized by the presence of radiographically apparent osteochondral flaps and fragments. The existence of early JOCD lesions (osteochondrosis latens [OCL] and osteochondrosis manifesta [OCM]) that precede the development of osteochondral flaps and fragments is also well recognized. However, identification of naturally occurring OCL lesions (confined to cartilage) using noninvasive imaging techniques has not yet been accomplished. We hypothesized that 10.5 T magnetic resonance imaging (MRI) can identify naturally occurring OCL lesions at predilection sites in intact joints of juvenile pigs. Unilateral elbows and knees (stifles) were harvested from three pigs aged 4, 8, and 12 weeks, and scanned in a 10.5 T MRI to obtain morphological 3D DESS images, and quantitative T2 and T1ρ relaxation time maps. Areas with increased T2 and T1ρ relaxation times in the articular-epiphyseal cartilage complex were identified in 1/3 distal femora and 3/3 distal humeri and were considered suspicious for OCL or OCM lesions. Histological assessment confirmed the presence of OCL or OCM lesions at each of these sites and failed to identify additional lesions. Histological findings included necrotic vascular profiles associated with areas of chondronecrosis either confined to the epiphyseal cartilage (OCL, 4- and 8-week-old specimens) or resulting in a delay in endochondral ossification (OCM, 12-week-old specimen). Future studies with clinical MR systems (≤7 T) are needed to determine whether these MRI methods are suitable for the in vivo diagnosis of early JOCD lesions in humans.

Evaluation of lesion and overlying articular cartilage in patients with juvenile osteochondritis dissecans of the knee using quantitative diffusion MRI.

Current clinical MRI of patients with juvenile osteochondritis dissecans (JOCD) is limited by the low reproducibility of lesion instability evaluation and inability to predict which lesions will heal after nonoperative treatment and which will later require surgery. The aim of this study is to verify the ability of apparent diffusion coefficient (ADC) to detect differences in lesion microstructure between different JOCD stages, treatment groups, and healthy, unaffected contralateral knees. Pediatric patients with JOCD received quantitative diffusion MRI between January 2016 and September 2020 in this prospective research study. A disease stage (I-IV) and stability of each JOCD lesion was evaluated. ADCs were calculated in progeny lesion, interface, parent bone, cartilage overlying lesion, control bone, and control cartilage regions. ADC differences were evaluated using linear mixed models with Bonferroni correction. Evaluated were 30 patients (mean age, 13 years; 21 males), with 40 JOCD-affected and 12 healthy knees. Nine patients received surgical treatment after MRI. Negative Spearman rank correlations were found between ADCs and JOCD stage in the progeny lesion (ρ = -0.572; p < 0.001), interface (ρ = -0.324; p = 0.041), and parent bone (ρ = -0.610; p < 0.001), demonstrating the sensitivity of ADC to microstructural differences in lesions at different JOCD stages. We observed a significant increase in the interface ADCs (p = 0.007) between operative (mean [95% CI] = 1.79 [1.56-2.01] × 10-3 mm2 /s) and nonoperative group (1.27 [0.98-1.57] × 10-3 mm2 /s). Quantitative diffusion MRI detects microstructural differences in lesions at different stages of JOCD progression towards healing and reveals differences between patients assigned for operative versus nonoperative treatment.

Evaluation of articular cartilage with quantitative MRI in an equine model of post-traumatic osteoarthritis.

Chondral lesions lead to degenerative changes in the surrounding cartilage tissue, increasing the risk of developing post-traumatic osteoarthritis (PTOA). This study aimed to investigate the feasibility of quantitative magnetic resonance imaging (qMRI) for evaluation of articular cartilage in PTOA. Articular explants containing surgically induced and repaired chondral lesions were obtained from the stifle joints of seven Shetland ponies (14 samples). Three age-matched nonoperated ponies served as controls (six samples). The samples were imaged at 9.4 T. The measured qMRI parameters included T1 , T2 , continuous-wave T1ρ (CWT1ρ ), adiabatic T1ρ (AdT1ρ ), and T2ρ (AdT2ρ ) and relaxation along a fictitious field (TRAFF ). For reference, cartilage equilibrium and dynamic moduli, proteoglycan content and collagen fiber orientation were determined. Mean values and profiles from full-thickness cartilage regions of interest, at increasing distances from the lesions, were used to compare experimental against control and to correlate qMRI with the references. Significant alterations were detected by qMRI parameters, including prolonged T1 , CWT1ρ , and AdT1ρ in the regions adjacent to the lesions. The changes were confirmed by the reference methods. CWT1ρ was more strongly associated with the reference measurements and prolonged in the affected regions at lower spin-locking amplitudes. Moderate to strong correlations were found between all qMRI parameters and the reference parameters (ρ = -0.531 to -0.757). T1 , low spin-lock amplitude CWT1ρ , and AdT1ρ were most responsive to changes in visually intact cartilage adjacent to the lesions. In the context of PTOA, these findings highlight the potential of T1 , CWT1ρ , and AdT1ρ in evaluation of compositional and structural changes in cartilage.

Multiparametric MR imaging reveals early cartilage degeneration at 2 and 8 weeks after ACL transection in a rabbit model.

In this study, the rabbit model with anterior cruciate ligament transection (ACLT) was used to investigate early degenerative changes in cartilage using multiparametric quantitative magnetic resonance imaging (qMRI). ACLT was surgically induced in the knees of skeletally mature New Zealand White rabbits (n = 14). ACL transected and contralateral knee compartments-medial femur, lateral femur, medial tibia, and lateral tibia-were harvested 2 (n = 8) and 8 weeks (n = 6) postsurgery. Twelve age-matched nonoperated rabbits served as control. qMRI was conducted at 9.4 T and included relaxation times T1 , T2 , continuous-wave T1ρ (CWT1ρ ), adiabatic T1ρ (AdT1ρ ), adiabatic T2ρ (AdT2ρ ), and relaxation along a fictitious field (TRAFF ). For reference, quantitative histology and biomechanical measurements were carried out. Posttraumatic changes were primarily noted in the superficial half of the cartilage. Prolonged T1 , T2 , CWT1ρ , and AdT1ρ were observed in the lateral femur 2 and 8 weeks post-ACLT, compared with the corresponding control and contralateral groups (P < .05). Collagen orientation was significantly altered in the lateral femur at 2 weeks post-ACLT compared with the corresponding control group. In the medial femur, all the studied relaxation time parameters, except TRAFF , were increased 8 weeks post-ACLT, as compared with the corresponding contralateral and control groups (P < .05). Similarly, significant proteoglycan loss was observed in the medial femur at 8 weeks following surgery (P < .05). Multiparametric MRI demonstrated early degenerative changes primarily in the superficial cartilage with T1 , T2 , CWT1ρ , and AdT1ρ sensitive to cartilage changes at 2 weeks after surgery.