Sodium and T1rho MRI for molecular and diagnostic imaging of articular cartilage

Biologically aggressive regions within glioblastoma identified by spin-lock contrast T1 relaxation in the rotating frame (T1ρ) MRI

Spin-lattice relaxation in the rotating frame magnetic resonance imaging allows for the quantitative assessment of spin-lock contrast within tissues. We describe the utility of spin-lattice relaxation in the rotating frame metrics in characterizing glioblastoma biological heterogeneity. A 84-year-old man presented to our institution with a right frontal temporal mass. Prior tissue sampling from a peripheral nonenhancing lesion was nondiagnostic. Stereotactic image-guided tissue sampling of the nonenhancing T2-fluid-attenuated inversion recovery hyperintense region involving the anterior cingulate gyrus with elevated spin-lattice relaxation in the rotating frame metrics provided a pathologic diagnosis of glioblastoma. This case illustrates the utility of spin-lattice relaxation in the rotating frame magnetic resonance imaging in identifying biologically aggressive regions within glioblastoma.

Orientation anisotropy of quantitative MRI relaxation parameters in ordered tissue

In highly organized tissues, such as cartilage, tendons and white matter, several quantitative MRI parameters exhibit dependence on the orientation of the tissue constituents with respect to the main imaging magnetic field (B0). In this study, we investigated the dependence of multiple relaxation parameters on the orientation of articular cartilage specimens in the B0. Bovine patellar cartilage-bone samples (n = 4) were investigated ex vivo at 9.4 Tesla at seven different orientations, and the MRI results were compared with polarized light microscopy findings on specimen structure. Dependences of T2 and continuous wave (CW)-T1ρ relaxation times on cartilage orientation were confirmed. T2 (and T2*) had the highest sensitivity to orientation, followed by TRAFF2 and adiabatic T2ρ. The highest dependence was seen in the highly organized deep cartilage and the smallest in the least organized transitional layer. Increasing spin-lock amplitude decreased the orientation dependence of CW-T1ρ. T1 was found practically orientation-independent and was closely followed by adiabatic T1ρ. The results suggest that T1 and adiabatic T1ρ should be preferred for orientation-independent quantitative assessment of organized tissues such as articular cartilage. On the other hand, based on the literature, parameters with higher orientation anisotropy appear to be more sensitive to degenerative changes in cartilage.

R1ρ dispersion and sodium imaging in human calf muscle

PURPOSE

To evaluate the magnitude of chemical exchange effects and R_1ρ dispersion in muscle and their relationship to tissue sodium levels with aging.

METHODS

Seven healthy volunteers (aged 24 to 87years, median age 47) underwent MRI to assess tissue sodium levels and water T_1ρ values at different spin-locking frequencies in calf muscles. T_1ρ values at each locking field were computed based on a three-parameter mono-exponential model to fit signals obtained at different locking times, and R_1ρ (=1/T_1ρ) rates were compared at different locking fields. In particular, the dispersion of R_1ρ (ΔR_1ρ=R_1ρ(0Hz)-R_1ρ(500Hz)) was examined as a function of subject age. Muscle sodium content was calculated by comparing signal intensities between tissues and reference standards within the same image. The variations of ΔR_1ρ with age and sodium were analyzed by linear regression.

RESULTS

T_1ρ values and sodium content both increased with age. R_1ρ dispersion also increased with age and showed a strong linear correlation (correlation coefficient r=0.98, P=0.000578) with sodium content.

CONCLUSION

ΔR_1ρ reports on the contribution of labile protons such as hydroxyls which may be associated with macromolecule accumulation in the extracellular matrix (ECM). An increase of sodium signal suggests an enlarged ECM volume fraction and/or an increase in sodium concentration, which occurs during normal aging. The strong correlation between ΔR_1ρ and sodium is likely the consequence of increased ECM and density of total charged sites within the matrix from molecules such as collagens and proteoglycans. The results from this study show the potential use of R_1ρ dispersion and sodium imaging in the assessment of pathological changes in muscle such as fibrosis.

Longitudinal study of sodium MRI of articular cartilage in patients with knee osteoarthritis: initial experience with 16-month follow-up

OBJECTIVES

To evaluate the potential of sodium MRI to detect changes over time of apparent sodium concentration (ASC) in articular cartilage in patients with knee osteoarthritis (OA).

METHODS

The cartilage of 12 patients with knee OA were scanned twice over a period of approximately 16 months with two sodium MRI sequences at 7 T: without fluid suppression (radial 3D) and with fluid suppression by adiabatic inversion recovery (IR). Changes between baseline and follow-up of mean and standard deviation of ASC (in mM), and their rate of change (in mM/day), were measured in the patellar, femorotibial medial and lateral cartilage regions for each subject. A matched-pair Wilcoxon signed rank test was used to assess significance of the changes.

RESULTS

Changes in mean and in standard deviation of ASC, and in their respective rate of change over time, were only statistically different when data was acquired with the fluid-suppressed sequence. A significant decrease (p = 0.001) of approximately 70 mM in mean ASC was measured between the two IR scans.

CONCLUSION

Quantitative sodium MRI with fluid suppression by adiabatic IR at 7 T has the potential to detect a decrease of ASC over time in articular cartilage of patients with knee osteoarthritis.

KEY POINTS

• Sodium MRI can detect apparent sodium concentration (ASC) in cartilage • Longitudinal study: sodium MRI can detect changes in ASC over time • Potential for follow-up studies of cartilage degradation in knee osteoarthritis.

Differentiation of brain tumor-related edema based on 3D T1rho imaging

BACKGROUND AND PURPOSE

Cerebral edema associated with brain tumors is an important source of morbidity. Its type depends largely on the capillary ultra-structures of the histopathologic subtype of underlying brain tumor. The purpose of our study was to differentiate vasogenic edema associated with brain metastases and infiltrative edema related to diffuse gliomas using quantitative 3D T1 rho (T1ρ) imaging.

MATERIALS AND METHODS

Preoperative MR examination including whole brain 3D T1ρ imaging was performed in 23 patients with newly diagnosed brain tumors (9 with metastasis, 8 with lower grade glioma, LGG, 6 with glioblastoma, GBM). Mean T1ρ values were measured in regions of peritumoral non-enhancing T2 signal hyperintensity, excluding both enhancing and necrotic or cystic component, and normal-appearing white matter.

RESULTS

Mean T1ρ values were significantly elevated in the vasogenic edema surrounding intracranial metastases when compared to the infiltrative edema associated with either LGG or GBM (p=0.02 and <0.01, respectively). No significant difference was noted between T1ρ values of infiltrative edema between LGG and GBM (p=0.84 and 0.96, respectively).

CONCLUSION

Our study demonstrates the feasibility and potential diagnostic role of T1ρ in the quantitative differentiation between edema related to intracranial metastases and gliomas and as a potentially complementary tool to standard MR techniques in further characterizing pathophysiology of vasogenic and infiltrative edema.

MRI and biomechanics multidimensional data analysis reveals R2 -R1ρ as an early predictor of cartilage lesion progression in knee osteoarthritis

PURPOSE

To couple quantitative compositional MRI, gait analysis, and machine learning multidimensional data analysis to study osteoarthritis (OA). OA is a multifactorial disorder accompanied by biochemical and morphological changes in the articular cartilage, modulated by skeletal biomechanics and gait. While we can now acquire detailed information about the knee joint structure and function, we are not yet able to leverage the multifactorial factors for diagnosis and disease management of knee OA.

MATERIALS AND METHODS

We mapped 178 subjects in a multidimensional space integrating: demographic, clinical information, gait kinematics and kinetics, cartilage compositional T_1ρ and T₂ and R₂ -R_1ρ (1/T₂ -1/T_1ρ ) acquired at 3T and whole-organ magnetic resonance imaging score morphological grading. Topological data analysis (TDA) and Kolmogorov-Smirnov test were adopted for data integration, analysis, and hypothesis generation. Regression models were used for hypothesis testing.

RESULTS

The results of the TDA showed a network composed of three main patient subpopulations, thus potentially identifying new phenotypes. T₂ and T_1ρ values (T₂ lateral femur P = 1.45*10^-8 , T_1ρ medial tibia P = 1.05*10^-5 ), the presence of femoral cartilage defects (P = 0.0013), lesions in the meniscus body (P = 0.0035), and race (P = 2.44*10^-4 ) were key markers in the subpopulation classification. Within one of the subpopulations we observed an association between the composite metric R₂ -R_1ρ and the longitudinal progression of cartilage lesions.

CONCLUSION

The analysis presented demonstrates some of the complex multitissue biochemical and biomechanical interactions that define joint degeneration and OA using a multidimensional approach, and potentially indicates that R₂ -R_1ρ may be an imaging biomarker for early OA.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:78-90.

Both 3-T dGEMRIC and Acetabular-Femoral T2 Difference May Detect Cartilage Damage at the Chondrolabral Junction

BACKGROUND

In addition to case reports of gadolinium-related toxicities, there are increasing theoretical concerns about the use of gadolinium for MR imaging. As a result, there is increasing interest in noncontrast imaging techniques for biochemical cartilage assessment. Among them, T2 mapping holds promise because of its simplicity, but its biophysical interpretation has been controversial.

QUESTIONS/PURPOSES

We sought to determine whether (1) 3-T delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) and T2 mapping are both capable of detecting cartilage damage at the chondrolabral junction in patients with femoroacetabular impingement (FAI); and (2) whether there is a correlation between these two techniques for acetabular and femoral head cartilage assessment.

METHODS

Thirty-one patients with hip-related symptoms resulting from FAI underwent a preoperative 3-T MRI of their hip that included dGEMRIC and T2 mapping (symptomatic group, 16 women, 15 men; mean age, 27 ± 8 years). Ten volunteers with no symptoms according to the WOMAC served as a control (asymptomatic group, seven women, three men; mean age, 28 ± 3 years). After morphologic cartilage assessment, acetabular and femoral head cartilages were graded according to the modified Outerbridge grading criteria. In the midsagittal plane, single-observer analyses of precontrast T1 values (volunteers), the dGEMRIC index (T1_Gd, patients), and T2 mapping values (everyone) were compared in acetabular and corresponding femoral head cartilage at the chondrolabral junction of each hip by region-of-interest analysis.

RESULTS

In the symptomatic group, T1_Gd and T2 values were lower in the acetabular cartilage compared with corresponding femoral head cartilage (T1_Gd: 515 ± 165 ms versus 650 ± 191 ms, p < 0.001; T2: 39 ± 8 ms versus 46 ± 10 ms, p < 0.001). In contrast, the asymptomatic group demonstrated no differences in T1 and T2 values for the acetabular and femoral cartilages with the numbers available (T1: 861 ± 130 ms versus 860 ± 182 ms, p = 0.98; T2: 43 ± 7 ms versus 42 ± 6 ms, p = 0.73). No correlation with the numbers available was noted between the modified Outerbridge grade and T1, T1_Gd, or T2 as well as between T2 and either T1 or T1_Gd.

CONCLUSIONS

Without the need for contrast media application, T2 mapping may be a viable alternative to dGEMRIC when assessing hip cartilage at the chondrolabral junction. However, acquisition-related phenomena as well as regional variations in the microstructure of hip cartilage necessitate an internal femoral head cartilage control when interpreting these results.

LEVEL OF EVIDENCE

Level IV, diagnostic study.

Composite metric R2 - R1ρ (1/T2 - 1/T1ρ ) as a potential MR imaging biomarker associated with changes in pain after ACL reconstruction: A six-month follow-up

This study looked to investigate a new quantitative metric, R₂  - R_1ρ (1/T₂  - 1/T_1ρ ), using magnetic resonance (MR) images and voxel-based relaxometry (VBR) for detecting early cartilage degeneration and explore the association with patient-reported outcomes measures (PROMs) in patients 6 months after ACL reconstruction. Sixty-four patients from three sites were bilaterally scanned on a 3T MR with a combined T_1ρ /T₂ protocol to calculate R_1ρ (1/T_1ρ ) and R₂ (1/T₂ ) values at baseline and 6 months after reconstructive surgery. Non-rigid registration was applied to align images onto a template, allowing VBR to determine VBR rate differences and explore cross-sectional and longitudinal differences between injured and uninjured knees, generating Statistical Parametric Maps (SPMs). Baseline R₂  - R_1ρ differences were further correlated with change in PROMs from the Knee Injury and Osteoarthritis Outcome Score (KOOS) from baseline to 6 months. Cross-sectional results demonstrated low relaxation rate differences in the injured patella (baseline: 21%, p = 0.01; 6-months: 18%, p = 0.02), lateral tibia (baseline: 25%, p = 0.01; 6-months: 24%, p = 0.01), and weight-bearing regions of the tibia and femur. The uninjured patella showed significant longitudinal changes (17%, p = 0.02). R₂  - R_1ρ differences showed significant correlations with KOOS PROMs, particularly in the lateral tibia, patella, and trochlea. R₂  - R_1ρ difference VBR analyses provide new and highly sensitive parameters for assessing early cartilage degeneration in patients after ACL injury by integrating findings from both T_1ρ and T₂ , commonly used relaxation time parameters, into a single metric. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:718-729, 2017.

Use of Saline as a Placebo in Intra-articular Injections in Osteoarthritis: Potential Contributions to Nociceptive Pain Relief

Background:

Osteoarthritis of the knee (OAK) is a severe debilitating condition characterized by joint pain, stiffness, and resultant limited mobility. In recent years, intra-articular (IA) injections have been used to relieve symptoms and have succeeded to varying degrees either with sodium hyaluronate preparations or with a biologic.

Objective:

The objective of this review is to evaluate multiple studies that demonstrate some relief from the symptoms of OAK in the saline arm of various clinical trials.

Method:

A thorough literature search (PubMed) was performed assessing the pain efficacy of various compounds compared to saline injections in clinical trials. A total of 73 studies were identified in the literature search including a total of 5,816 patients. These clinical trials all involved the IA injection of a viscosupplement (hyaluronate, platelet rich plasma (PRP), etc.) or a biologic (the low molecular weight fraction (< 5kDa) of human serum albumin (LMWF-5A)). For all of these studies, the control arm was injection of sterile physiological saline that approximates the salt concentration and total solute concentration of blood and most tissues.

Results:

Based on our review of the current literature, the tested compounds performed with mixed results when compared to saline injections. Moreover, OAK is a variable disease, with severity measured on the Kellgren and Lawrence (KL) scale where various hyaluronate preparations have a therapeutic effect mostly on KL 2-3 patients while a biologic works best on KL 3-4 patients.

Conclusion:

Since the effect of saline injection is always greater than no treatment, the evaluations of these treatments can be confounded in clinical trials. Therefore, the question of whether there are known therapeutic effects of saline injections might explain these results.

Elevated adiabatic T1ρ and T2ρ in articular cartilage are associated with cartilage and bone lesions in early osteoarthritis: A preliminary study

PURPOSE

To evaluate adiabatic T_1ρ and T_2ρ of articular cartilage in symptomatic osteoarthritis (OA) patients and asymptomatic volunteers, and to determine their association with magnetic resonance imaging (MRI)-based structural abnormalities in cartilage and bone.

MATERIALS AND METHODS

A total of 24 subjects (age range: 50-68 years; 12 female) were enrolled, including 12 early OA patients and 12 volunteers with normal joint function. Patients and volunteers underwent 3T MRI. T₂ , adiabatic T_1ρ , and T_2ρ relaxation times of knee articular cartilage were measured. Proton density (PD)- and T₁ -weighted MR image series were also obtained and separately evaluated for morphological changes using the MRI OA Knee Scoring (MOAKS) system. Comparisons using the Mann-Whitney nonparametric test were performed after dividing the study participants according to physical symptoms as determined by Western Ontario and McMaster Universities (WOMAC) score or presence of cartilage lesions, bone marrow lesions, or osteophytes.

RESULTS

Elevated adiabatic T_1ρ and T_2ρ relaxation times of articular cartilage were associated with cartilage loss (P = 0.024-0.047), physical symptoms (0.0068-0.035), and osteophytes (0.0039-0.027). Elevated adiabatic T_1ρ was also associated with bone marrow lesions (0.033).

CONCLUSION

Preliminary data suggest that elevated adiabatic T_1ρ and T_2ρ of cartilage are associated with morphological abnormalities of cartilage and bone, and thus may be applicable for in vivo OA research and diagnostics.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:678-689.

Changes in Cartilage and Tendon Composition of Patients With Type I Diabetes Mellitus: Identification by Quantitative Sodium Magnetic Resonance Imaging at 7 T

OBJECTIVE

The aim of this study was to investigate possible biochemical alterations in tendons and cartilage caused by type 1 diabetes mellitus (DM1), using quantitative in vivo 7 T sodium magnetic resonance (MR) imaging.

MATERIALS AND METHODS

The institutional review board approved this prospective study, and written informed consent was obtained. Eight DM1 patients with no history of knee trauma and 9 healthy age- and weight-matched volunteers were examined at 7 T using dedicated knee coils.All participants underwent morphological and sodium MR imaging. Region-of-interest analysis was performed manually for the non-weight-bearing area of the femoral condyle cartilage and for the patella tendon. Two readers read the image data sets independently, twice, for intrareader and interreader agreement. Normalized mean sodium signal intensity (NMSI) values were compared between patients and volunteers for each reader using analysis of variance.

RESULTS

On morphological images, cartilage in the non-weight-bearing area and the patellar tendon was intact in all patients. On sodium MR imaging, bivariate analysis of variance showed significantly lower mean NMSI values in the cartilage (P = 0.008) and significantly higher values in the tendons (P = 0.025) of patients compared with those of volunteers.

CONCLUSION

Our study showed significantly different NMSI values between DM1 patients and matched volunteers. Differences observed in the cartilage and tendon might be associated with a DM1-related alteration of biochemical composition that occurs before it can be visualized on morphological MR sequences.

Potential of PET-MRI for imaging of non-oncologic musculoskeletal disease

Early detection of musculoskeletal disease leads to improved therapies and patient outcomes, and would benefit greatly from imaging at the cellular and molecular level. As it becomes clear that assessment of multiple tissues and functional processes are often necessary to study the complex pathogenesis of musculoskeletal disorders, the role of multi-modality molecular imaging becomes increasingly important. New positron emission tomography-magnetic resonance imaging (PET-MRI) systems offer to combine high-resolution MRI with simultaneous molecular information from PET to study the multifaceted processes involved in numerous musculoskeletal disorders. In this article, we aim to outline the potential clinical utility of hybrid PET-MRI to these non-oncologic musculoskeletal diseases. We summarize current applications of PET molecular imaging in osteoarthritis (OA), rheumatoid arthritis (RA), metabolic bone diseases and neuropathic peripheral pain. Advanced MRI approaches that reveal biochemical and functional information offer complementary assessment in soft tissues. Additionally, we discuss technical considerations for hybrid PET-MR imaging including MR attenuation correction, workflow, radiation dose, and quantification.

T1ρ Magnetic Resonance Imaging to Assess Cartilage Damage After Primary Shoulder Dislocation

BACKGROUND

Patients who suffer anterior shoulder dislocations are at higher risk of developing glenohumeral arthropathy, but little is known about the initial cartilage damage after a primary shoulder dislocation. T1ρ is a magnetic resonance imaging (MRI) technique that allows quantification of cartilage proteoglycan content and can detect physiologic changes in articular cartilage.

PURPOSE

This study aimed to establish baseline T1ρ MRI values for glenoid and humeral head cartilage, determine whether T1ρ MRI can detect glenohumeral cartilage damage after traumatic primary shoulder dislocation, and assess for patterns in cartilage damage in anterior shoulder dislocation.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Nine male patients (mean age, 32.0 years; range, 20-59 years) who sustained first-time anterior shoulder dislocations underwent 3T T1ρ MRI. Five healthy controls (mean age, 27.4 years; range, 24-30 years) without prior dislocation or glenohumeral arthritis also underwent 3T T1ρ MRI. The T1ρ relaxation constant was determined for the entire glenoid and humeral head for patients with a dislocation and for healthy controls. The glenoid and humeral head were divided into 9 zones, and T1ρ values were determined for each zone in dislocated and control shoulders to identify patterns in cartilage damage in dislocated shoulders.

RESULTS

Average overall T1ρ values for humeral head cartilage in dislocated shoulders were significantly greater than in controls (41.7 ± 3.9 ms vs 38.4 ± 0.6 ms, respectively; P = .03). However, average overall T1ρ values for glenoid cartilage were not significantly different in dislocated shoulders compared with controls (44.0 ± 3.3 ms vs 44.6 ± 2.4 ms, respectively; P = .40), suggesting worse damage to humeral head cartilage. T1ρ values in the posterior-middle humeral head were higher in patients with a dislocation compared with controls (41.5 ± 3.8 ms vs 38.2 ± 2.2 ms, respectively; P = .021) and trended toward significance in the posterior-superior and middle-superior zones (35.2 ± 4.9 ms vs 31.3 ± 1.0 ms and 33.7 ± 5.0 ms vs 30.5 ± 1.3 ms, respectively; P = .056). These 3 humeral head zones are where Hill-Sachs lesions predominate. T1ρ values in the anterior-inferior glenoid zone trended toward significance in patients with a dislocation compared with controls (47.4 ± 5.0 ms vs 43.5 ± 3.5 ms, respectively; P = .073).

CONCLUSION

Humeral head cartilage sustained greater damage than glenoid cartilage in primary dislocation. T1ρ values were higher in glenohumeral zones associated with Bankart and Hill-Sachs lesions. Widespread initial cartilage damage may predispose patients to glenohumeral arthropathy.

Effect of collagen cross-linking on quantitative MRI parameters of articular cartilage

OBJECTIVE

To investigate the sensitivity of quantitative magnetic resonance imaging (MRI) parameters to increase of collagen cross-linking in articular cartilage, a factor possibly contributing to the aging-related development of osteoarthritis (OA). The issue has not been widely studied although collagen cross-links may significantly affect the evaluation of cartilage imaging outcome.

DESIGN

Osteochondral samples (n = 14) were prepared from seven bovine patellae. To induce cross-linking, seven samples were incubated in threose while the other seven served as non-treated controls. The specimens were scanned at 9.4 T for T1, T1Gd (dGEMRIC), T2, adiabatic and continuous wave (CW) T1ρ, adiabatic T2ρ and T1sat relaxation times. Specimens from adjacent tissue were identically treated and used for reference to determine biomechanical properties, collagen, proteoglycan and cross-link contents, fixed charge density (FCD), collagen fibril anisotropy and water concentration of cartilage.

RESULTS

In the threose-treated sample group, cross-links (pentosidine, lysyl pyridinoline (LP)), FCD and equilibrium modulus were significantly (P < 0.05) higher as compared to the non-treated group. Threose treatment resulted in significantly greater T1Gd relaxation time constant (+26%, P < 0.05), although proteoglycan content was not altered. Adiabatic and CW-T1ρ were also significantly increased (+16%, +28%, P < 0.05) while pre-contrast T1 was significantly decreased (-10%, P < 0.05) in the threose group. T2, T2ρ and T1sat did not change significantly.

CONCLUSION

Threose treatment induced collagen cross-linking and changes in the properties of articular cartilage, which were detected by T1, T1Gd and T1ρ relaxation time constants. Cross-linking should be considered especially when interpreting the outcome of contrast-enhanced MRI in aging populations.

MR Parametric Mapping as a Biomarker of Early Joint Degeneration

Context:

Osteoarthritis (OA) is a common, worldwide disorder. Magnetic resonance (MR) imaging can directly and noninvasively evaluate articular cartilage and has emerged as an essential tool in the study of OA.

Evidence Acquisition:

A PubMed search was performed using the keywords quantitative MRI and cartilage. No limits were set on the range of years searched. Articles were reviewed for relevance with an emphasis on in vivo studies performed at 3 tesla.

Study Design:

Clinical review.

Level of Evidence:

Level 4.

Results:

T2, T2*, T1 (particularly when measured after exogenous contrast administration, such as with the delayed gadolinium-enhanced MR imaging of cartilage [dGEMRIC] technique), and T1ρ are among the most widely utilized quantitative MR imaging techniques to evaluate cartilage and have been implemented in various patient cohorts. Existing challenges include reproducibility of results, insufficient consensus regarding optimal sequences and parameters, and interpretation of values.

Conclusion:

Quantitative assessment of cartilage using MR imaging techniques likely represents the best opportunity to identify early cartilage degeneration and to follow patients after treatment. Despite existing challenges, ongoing work and unique approaches have shown exciting and promising results.

Paired self-compensated spin-lock preparation for improved T1ρ quantification

PURPOSE

Spin-lock (SL) imaging allows quantification of the spin-lattice relaxation time in the rotating frame (T1ρ). B0 and B1 inhomogeneities impact T1ρ quantification because the preparatory block in SL imaging is sensitive to the field heterogeneities. Here, a modified preparatory block (PSC-SL) is proposed that attempts to alleviate SL sensitivity to field inhomogeneities in scenarios where existing approaches fail, i.e. high SL frequencies.

METHODS

Computer simulations, phantom and in vivo experiments were used to determine the effect of field inhomogeneities on T1ρ quantification. Existing SL preparations were compared with PSC-SL in different conditions to assess the advantages and disadvantages of each method.

RESULTS

Phantom experiments and computer modeling demonstrate that PSC-SL provides superior T1ρ quantification at high SL frequencies in situations where the existing SL preparation methods fail. This result has been confirmed in pre-clinical neuro and body imaging at 7T.

CONCLUSION

PSC-SL complements existing methods by increasing the accuracy of T1ρ quantification at high spin-lock frequencies when large field inhomogeneities are present. A-priory information about the experimental conditions such, as field distribution and spinlock frequency are useful for selecting an appropriate spin-lock preparation for specific applications.

Multi-parametric MRI characterization of enzymatically degraded articular cartilage

Several laboratory and rotating frame quantitative MRI parameters were evaluated and compared for detection of changes in articular cartilage following selective enzymatic digestion. Bovine osteochondral specimens were subjected to 44 h incubation in control medium or in collagenase or chondroitinase ABC to induce superficial collagen or proteoglycan (glycosaminoglycan) alterations. The samples were scanned at 9.4 T for T1 , T1 Gd (dGEMRIC), T2 , adiabatic T1 ρ , adiabatic T2 ρ , continuous-wave T1 ρ , TRAFF2 , and T1 sat relaxation times and for magnetization transfer ratio (MTR). For reference, glycosaminoglycan content, collagen fibril orientation and biomechanical properties were determined. Changes primarily in the superficial cartilage were noted after enzymatic degradation. Most of the studied parameters were sensitive to the destruction of collagen network, whereas glycosaminoglycan depletion was detected only by native T1 and T1 Gd relaxation time constants throughout the tissue and by MTR superficially. T1 , adiabatic T1 ρ , adiabatic T2 ρ , continuous-wave T1 ρ , and T1 sat correlated significantly with the biomechanical properties while T1 Gd correlated with glycosaminoglycan staining. The findings indicated that most of the studied MRI parameters were sensitive to both glycosaminoglycan content and collagen network integrity, with changes due to enzymatic treatment detected primarily in the superficial tissue. Strong correlation of T1 , adiabatic T1ρ , adiabatic T2 ρ , continuous-wave T1 ρ , and T1 sat with the altered biomechanical properties, reflects that these parameters were sensitive to critical functional properties of cartilage. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1111-1120, 2016.

Endogenous assessment of diffuse myocardial fibrosis in patients with T1ρ -mapping

PURPOSE

Recently, it was shown that a significantly higher T_1ρ is found in compact myocardial fibrosis after chronic myocardial infarction. In this study, we investigated the feasibility of native T_1ρ -mapping for the detection of diffuse myocardial fibrosis in patients with dilated cardiomyopathy (DCM).

MATERIALS AND METHODS

T_1ρ -mapping was performed on three explanted hearts from DCM patients at 3 Tesla (T). Histological fibrosis quantification was performed, and compared with the T_1ρ -relaxation times in the heart. Furthermore, twenty DCM patients underwent an MRI at 1.5T. Native T_1ρ -maps, native T₁ -maps, and extracellular volume (ECV)-maps were acquired. Additionally, eight healthy volunteers were scanned for reference values.

RESULTS

A significant correlation (Pearson r = 0.49; P = 0.005) was found between ex vivo T_1ρ -values and fibrosis fraction from histology. Additionally, a significantly higher T_1ρ -relaxation time (55.2 ± 2.7 ms) was found in DCM patients compared with healthy control subjects (51.5 ± 1.2 ms) (P = 0.0024). The relation between in vivo T_1ρ -values and ECV-values was significant (Pearson r = 0.66). No significant relation was found between native T₁ - and ECV-values in this study (P = 0.89).

CONCLUSION

This study showed proof of principle for the endogenous detection of diffuse myocardial fibrosis with T_1ρ -MRI. Ex vivo and in vivo experiments showed promising results that T_1ρ -MRI can be used to measure the extent of diffuse myocardial fibrosis in the myocardium.

LEVEL OF EVIDENCE

2 J. Magn. Reson. Imaging 2017;45:132-138.

The influences of different spatial resolutions on the characteristics of T2 relaxation times in articular cartilage: A coarse-graining study of the microscopic magnetic resonance imaging data

Microscopic magnetic resonance imaging (µMRI) T2 data from canine cartilage at different tibial locations were analyzed to investigate the influences of spatial resolution and pixel position on the T2 sensitivity to osteoarthritis (OA). Five experimental factors were investigated: inaccurate pixel position, different pixel resolutions, different specimen orientations in the magnetic field, topographical variations over the tibial surface, and different OA stages. A number of significant trends were identified in this analysis, which shows the subtle but substantial influences to our abilities of detecting OA due to T2 changes. In particular, any deviation in locating the cartilage pixels may result in erratic values near the cartilage surface. Significant differences were found in T2 values between nearly any two comparison-groups under all resolutions both in the meniscus-covered and -uncovered areas, which were also showed interaction between the OA degradation stages. This multiresolution project should help to improve the detection sensitivities of MRI toward cartilage degeneration. Microsc. Res. Tech. 79:754-765, 2016. © 2016 Wiley Periodicals, Inc.

Optimized cartilage visualization using 7-T sodium ((23)Na) imaging after patella dislocation

PURPOSE

Retropatellar cartilage lesions often occur in the course of recurrent patella dislocation. Aim of this study was to develop a more detailed method for examining cartilage tissue, in order to reduce patient discomfort and time of care.

METHODS

For detailed diagnosing, a 7-T MRI of the knee joint and patella was performed in nine patients, with mean age of 26.4 years, after patella dislocation to measure the cartilage content in three different regions of interest of the patella. Axial sodium ((23)Na) images were derived from an optimized 3D GRE sequence on a 7-T MR scanner. Morphological cartilage grading was performed, and sodium signal-to-noise ratio (SNR) values were calculated. Mean global sodium values and SNR were compared between patients and volunteers.

RESULTS

Two out of nine patients showed a maximum cartilage defect of International Cartilage Repair Society (ICRS) grade 3, three of grade 2, three of  grade 1, and one patient showed no cartilage defect. The mean SNR in sodium images for cartilage was 13.4 ± 2.5 in patients and 14.6 ± 3.7 in volunteers (n.s.). A significant negative correlation between age and global sodium SNR for cartilage was found in the medial facet (R = -0.512; R (2) = 0.26; p = 0.030). Mixed-model ANOVA yielded a marked decrease of the sodium SNR, with increasing grade of cartilage lesions (p < 0.001).

CONCLUSIONS

Utilization of the (23)Na MR imaging will make earlier detection of alterations to the patella cartilage after dislocation possible and will help prevent subsequent disease due to start adequate therapy earlier in the rehabilitation process.

LEVEL OF EVIDENCE

II.

Capturing fast relaxing spins with SWIFT adiabatic rotating frame spin-lattice relaxation (T1ρ) mapping

Rotating frame spin-lattice relaxation, with the characteristic time constant T1ρ, provides a means to access motion-restricted (slow) spin dynamics in MRI. As a result of their restricted motion, these spins are sometimes characterized by a short transverse relaxation time constant T2 and thus can be difficult to detect directly with conventional image acquisition techniques. Here, we introduce an approach for three-dimensional adiabatic T1ρ mapping based on a magnetization-prepared sweep imaging with Fourier transformation (MP-SWIFT) sequence, which captures signal from almost all water spin populations, including the extremely fast relaxing pool. A semi-analytical procedure for T1ρ mapping is described. Experiments on phantoms and musculoskeletal tissue specimens (tendon, articular and epiphyseal cartilages) were performed at 9.4 T for both the MP-SWIFT and fast spin echo (FSE) read outs. In the phantom with liquids having fast molecular tumbling and a single-valued T1ρ time constant, the measured T1ρ values obtained with MP-SWIFT and FSE were similar. Conversely, in normal musculoskeletal tissues, T1ρ values measured with MP-SWIFT were much shorter than the values obtained with FSE. Studies of biological tissue specimens demonstrated that T1ρ-weighted SWIFT provides higher contrast between normal and diseased tissues relative to conventional acquisitions. Adiabatic T1ρ mapping with SWIFT readout captures contributions from the otherwise undetected fast relaxing spins, allowing more informative T1ρ measurements of normal and diseased states.

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.

High-resolution morphologic and ultrashort time-to-echo quantitative magnetic resonance imaging of the temporomandibular joint

OBJECTIVE

To implement high-resolution morphologic and quantitative magnetic resonance imaging (MRI) of the temporomandibular joint (TMJ) using ultrashort time-to-echo (UTE) techniques in cadavers and volunteers.

METHODS

This study was approved by the institutional review board. TMJs of cadavers and volunteers were imaged on a 3-T MR system. High-resolution morphologic and quantitative sequences using conventional and UTE techniques were performed in cadaveric TMJs. Morphologic and UTE quantitative sequences were performed in asymptomatic and symptomatic volunteers.

RESULTS

Morphologic evaluation demonstrated the TMJ structures in open- and closed-mouth position. UTE techniques facilitated the visualization of the disc and fibrocartilage. Quantitative UTE MRI was successfully performed ex vivo and in vivo, reflecting the degree of degeneration. There was a difference in the mean UTE T2* values between asymptomatic and symptomatic volunteers.

CONCLUSIONS

MRI evaluation of the TMJ using UTE techniques allows characterization of the internal structure and quantification of the MR properties of the disc. Quantitative UTE MRI can be performed in vivo with short scan times.

Volumetric multislice gagCEST imaging of articular cartilage: Optimization and comparison with T1rho

PURPOSE

To develop and optimize a multislice glycosaminoglycan (GAG) chemical exchange saturation transfer (GagCEST) sequence for volumetric imaging of articular cartilage, and to validate the sequence against T_1ρ relaxation times in whole joint imaging of tibiotalar cartilage.

METHODS

Ex vivo experiments were used to observe the effect of the number of partitions and shot TR on signal-to-noise ratio and measured GagCEST_asym . GagCEST imaging of the entire tibiotalar joint was also performed on 10 healthy subjects. The measured GagCEST_asym was compared and correlated with T_1ρ relaxation times.

RESULTS

Ex vivo studies showed a higher average GagCEST_asym from articular cartilage on multislice acquisitions acquired with two or more partitions than observed with a single-slice acquisition. In healthy human subjects, an average GagCEST_asym of 8.8 ± 0.7% was observed. A coefficient of variation of GagCEST_asym across slices of less than 15% was seen for all subjects. Across subjects, a Pearson correlation coefficient of -0.58 was observed between the measured gagCEST_asym and T_1ρ relaxation times.

CONCLUSIONS

We demonstrated the feasibility and optimization of multislice GagCEST mapping of articular cartilage. Volumetric analysis and decreased scan times will help to advance the clinical utility of GagCEST imaging of articular cartilage. Magn Reson Med 77:1134-1141, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Evaluation of cartilage repair and osteoarthritis with sodium MRI

The growing need for early diagnosis and higher specificity than that which can be achieved with morphological MRI is a driving force in the application of methods capable of probing the biochemical composition of cartilage tissue, such as sodium imaging. Unlike morphological imaging, sodium MRI is sensitive to even small changes in cartilage glycosaminoglycan content, which plays a key role in cartilage homeostasis. Recent advances in high- and ultrahigh-field MR systems, gradient technology, phase-array radiofrequency coils, parallel imaging approaches, MRI acquisition strategies and post-processing developments have resulted in many clinical in vivo sodium MRI studies of cartilage, even at 3 T. Sodium MRI has great promise as a non-invasive tool for cartilage evaluation. However, further hardware and software improvements are necessary to complete the translation of sodium MRI into a clinically feasible method for 3-T systems. This review is divided into three parts: (i) cartilage composition, pathology and treatment; (ii) sodium MRI; and (iii) clinical sodium MRI studies of cartilage with a focus on the evaluation of cartilage repair tissue and osteoarthritis.

High-Resolution Methods for Diagnosing Cartilage Damage In Vivo

Advances in current clinical modalities, including magnetic resonance imaging and computed tomography, allow for earlier diagnoses of cartilage damage that could mitigate progression to osteoarthritis. However, current imaging modalities do not detect submicrometer damage. Developments in in vivo or arthroscopic techniques, including optical coherence tomography, ultrasonography, bioelectricity including streaming potential measurement, noninvasive electroarthrography, and multiphoton microscopy can detect damage at an earlier time point, but they are limited by a lack of penetration and the ability to assess an entire joint. This article reviews current advancements in clinical and developing modalities that can aid in the early diagnosis of cartilage injury and facilitate studies of interventional therapeutics.

Sodium magnetic resonance imaging of ankle joint in cadaver specimens, volunteers, and patients after different cartilage repair techniques at 7 T: initial results

OBJECTIVES

The goal of cartilage repair techniques such as microfracture (MFX) or matrix-associated autologous chondrocyte transplantation (MACT) is to produce repair tissue (RT) with sufficient glycosaminoglycan (GAG) content. Sodium magnetic resonance imaging (MRI) offers a direct and noninvasive evaluation of the GAG content in native cartilage and RT. In the femoral cartilage, this method was able to distinguish between RTs produced by MFX and MACT having different GAG contents. However, it needs to be clarified whether sodium MRI can be useful for evaluating RT in thin ankle cartilage. Thus, the aims of this 7-T study were (1) to validate our sodium MRI protocol in cadaver ankle samples, (2) to evaluate the sodium corrected signal intensities (cSI) in cartilage of volunteers, (3) and to compare sodium values in RT between patients after MFX and MACT treatment.

MATERIALS AND METHODS

Five human cadaver ankle samples as well as ankles of 9 asymptomatic volunteers, 6 MFX patients and 6 MACT patients were measured in this 7-T study. Sodium values from the ankle samples were compared with histochemically evaluated GAG content. In the volunteers, sodium cSI values were calculated in the cartilages of ankle and subtalar joint. In the patients, sodium cSI in RT and reference cartilage were measured, morphological appearance of RT was evaluated using the magnetic resonance observation of cartilage repair tissue (MOCART) scoring system, and clinical outcome before and after surgery was assessed using the American Orthopaedic Foot and Ankle Society score and Modified Cincinnati Knee Scale. All regions of interest were defined on morphological images and subsequently transferred to the corresponding sodium images. Analysis of variance, t tests, and Pearson correlation coefficients were evaluated.

RESULTS

In the patients, significantly lower sodium cSI values were found in RT than in reference cartilage for the MFX (P = 0.007) and MACT patients (P = 0.008). Sodium cSI and MOCART scores in RT did not differ between the MFX and MACT patients (P = 0.185). No significant difference in sodium cSI was found between reference cartilage of the volunteers and the patients (P = 0.355). The patients showed significantly higher American Orthopaedic Foot and Ankle Society and Modified Cincinnati scores after treatment than they did before treatment. In the volunteers, sodium cSI was significantly higher in the tibial cartilage than in the talar cartilage of ankle joint (P = 0.002) and in the talar cartilage than in the calcaneal cartilage of subtalar joint (P < 0.001). Data from the cadaver ankle samples showed a strong linear relationship between the sodium values and the histochemically determined GAG content (r = 0.800; P < 0.001; R = 0.639).

CONCLUSIONS

This study demonstrates the feasibility of in vivo quantification of sodium cSI, which can be used for GAG content evaluation in thin cartilages of ankle and subtalar joints at 7 T. A strong correlation observed between the histochemically evaluated GAG content and the sodium values proved the sufficient sensitivity of sodium MRI to changes in the GAG content of cartilages in the ankle. Both MFX and MACT produced RT with lower sodium cSI and, thus, of lower quality compared with reference cartilage in the patients or in the volunteers. Our results suggest that MFX and MACT produce RT with similar GAG content and similar morphological appearance in patients with similar surgery outcome. Sodium MRI at 7 T allows a quantitative evaluation of RT quality in the ankle and may thus be useful in the noninvasive assessment of new cartilage repair procedures.

Comparison of multiple quantitative MRI parameters for characterization of the goat cartilage in an ongoing osteoarthritis: dGEMRIC, T1ρ and sodium

RATIONALE AND OBJECTIVES

Osteoarthritis (OA) is a degenerative joint disease leading to cartilage deterioration by loss of matrix, fibrillation, formation of fissures, and ultimately complete loss of the cartilage surface. Here, three magnetic resonance imaging (MRI) techniques, dGEMRIC (delayed Gadolinium enhanced MRI of cartilage; dG1=T1,post; dG2=1/T1,post-1/T1,pre), T1ρ,and sodium MRI, are compared in a preclinical in vivo study to evaluate the differences in their potential for cartilage characterization and to establish an examination protocol for a following clinical study.

MATERIALS AND METHODS

OA was induced in 12 caprine knees (6 control, 6 therapy). Adipose derived stem cells were injected afterwards as a treatment. The animals were examined healthy, 3 and 16 weeks postoperatively with all three MRI methods. Using statistical analysis, the OA development and the degree of correlation between the different MRI methods were determined.

RESULTS

A strong correlation was observed between the dGEMRIC indices dG1 and dG2 (r=-0.87) which differ only in considering or not considering the T1 baseline. Moderate correlations were found between T1ρ and dG1 (r=0.55), T1ρ and dG2 (r=0.47) and at last, sodium and dG1 (r=0.45). The correlations found in this study match to the biomarkers which the methods are sensitive to.

CONCLUSION

Even though the goat cartilage is significantly thinner than the human cartilage and even more in a degenerated cartilage, all three methods were able to characterize the cartilage over the whole period of time during an ongoing OA. Due to measurement and post processing optimizations, as well as the correlations detected in this work, the overall measurement time in future goat studies can be minimized. Moreover, an examination protocol for characterizing the cartilage in a clinical study was established.

Magnetic resonance spectroscopy and imaging can differentiate between engineered bone and engineered cartilage

In the situation when both cartilage and its underlying bone are damaged, osteochondral tissue engineering is being developed to provide a solution. In such cases, the ability to non-invasively monitor and differentiate the development of both cartilage and bone tissues is important. Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) have been widely used to non-invasively assess tissue-engineered cartilage and tissue-engineered bone. The purpose of this work is to assess differences in MR properties of tissue-engineered bone and tissue-engineered cartilage generated from the same cell-plus-scaffold combination at the early stage of tissue growth. We developed cartilage and bone tissue constructs by seeding human marrow stromal cells (HMSCs, 2 million/ml) in 1:1 collagen/chitosan gel for four weeks. The chondrogenic or osteogenic differentiation of cells was directed with the aid of a culture medium containing chondrogenic or osteogenic growth factors, respectively. The proton and sodium NMR and waterproton T1, T2 and diffusion MRI experiments were performed on these constructs and the control collagen/chitosan gel using a 9.4 T ((1)H freq. = 400 MHz) and a 11.7 T ((1)H freq. = 500 MHz) NMR spectrometers. In all cases, the development of bone and cartilage was found to be clearly distinguishable using NMR and MRI. We conclude that MRS and MRI are powerful tools to assess growing osteochondral tissue regeneration.

A flexible nested sodium and proton coil array with wideband matching for knee cartilage MRI at 3T

PURPOSE

We describe a 2 × 6 channel sodium/proton array for knee MRI at 3T. Multielement coil arrays are desirable because of well-known signal-to-noise ratio advantages over volume and single-element coils. However, low tissue-coil coupling that is characteristic of coils operating at low frequency can make the potential gains from a phased array difficult to realize.

METHODS

The issue of low tissue-coil coupling in the developed six-channel sodium receive array was addressed by implementing 1) a mechanically flexible former to minimize the coil-to-tissue distance and reduce the overall diameter of the array and 2) a wideband matching scheme that counteracts preamplifier noise degradation caused by coil coupling and a high-quality factor. The sodium array was complemented with a nested proton array to enable standard MRI.

RESULTS

The wideband matching scheme and tight-fitting mechanical design contributed to >30% central signal-to-noise ratio gain on the sodium module over a mononuclear sodium birdcage coil, and the performance of the proton module was sufficient for clinical imaging.

CONCLUSION

We expect the strategies presented in this study to be generally relevant in high-density receive arrays, particularly in x-nuclei or small animal applications. Magn Reson Med 76:1325-1334, 2016. © 2015 Wiley Periodicals, Inc.

Multiparametric MRI of Epiphyseal Cartilage Necrosis (Osteochondrosis) with Histological Validation in a Goat Model

PURPOSE

To evaluate multiple MRI parameters in a surgical model of osteochondrosis (OC) in goats.

METHODS

Focal ischemic lesions of two different sizes were induced in the epiphyseal cartilage of the medial femoral condyles of goats at 4 days of age by surgical transection of cartilage canal blood vessels. Goats were euthanized and specimens harvested 3, 4, 5, 6, 9 and 10 weeks post-op. Ex vivo MRI scans were conducted at 9.4 Tesla for mapping the T1, T2, T1ρ, adiabatic T1ρ and TRAFF relaxation times of articular cartilage, unaffected epiphyseal cartilage, and epiphyseal cartilage within the area of the induced lesion. After MRI scans, safranin O staining was conducted to validate areas of ischemic necrosis induced in the medial femoral condyles of six goats, and to allow comparison of MRI findings with the semi-quantitative proteoglycan assessment in corresponding safranin O-stained histological sections.

RESULTS

All relaxation time constants differentiated normal epiphyseal cartilage from lesions of ischemic cartilage necrosis, and the histological staining results confirmed the proteoglycan (PG) loss in the areas of ischemia. In the scanned specimens, all of the measured relaxation time constants were higher in the articular than in the normal epiphyseal cartilage, consistently allowing differentiation between these two tissues.

CONCLUSIONS

Multiparametric MRI provided a sensitive approach to discriminate between necrotic and viable epiphyseal cartilage and between articular and epiphyseal cartilage, which may be useful for diagnosing and monitoring OC lesions and, potentially, for assessing effectiveness of treatment interventions.

T2* mapping and delayed gadolinium-enhanced magnetic resonance imaging in cartilage (dGEMRIC) of humeral articular cartilage--a histologically controlled study

BACKGROUND

Cartilage biochemical imaging modalities that include the magnetic resonance imaging (MRI) techniques of T2* mapping (sensitive to water content and collagen fiber network) and delayed gadolinium-enhanced MRI of cartilage (dGEMRIC, sensitive to the glycosaminoglycan content) can be effective instruments for early diagnosis and reliable follow-up of cartilage damage. The purpose of this study was to provide T2* mapping and dGEMRIC values in various histologic grades of cartilage degeneration in humeral articular cartilage.

METHODS

A histologically controlled in vitro study was conducted that included human humeral head cartilage specimens with various histologic grades of cartilage degeneration. High-resolution, 3-dimensional (3D) T2* mapping and dGEMRIC were performed that enabled the correlation of MRI and histology data. Cartilage degeneration was graded according to the Mankin score, which evaluates surface morphology, cellularity, toluidine blue staining, and tidemark integrity. SPSS software was used for statistical analyses.

RESULTS

Both MRI mapping values decreased significantly (P < .001) with increasing cartilage degeneration. Spearman rank analysis revealed a significant correlation (correlation coefficients ranging from -0.315 to 0.784; P < .001) between the various histologic parameters and the T2* and T1Gd mapping values.

CONCLUSION

This study demonstrates the feasibility of 3D T2* and dGEMRIC to identify various histologic grades of cartilage damage of humeral articular cartilage. With regard to the advantages of these mapping techniques with high image resolution and the ability to accomplish a 3D biochemically sensitive imaging, we consider that these imaging techniques can make a positive contribution to the currently evolving science and practice of cartilage biochemical imaging.

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.

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.

Advanced Imaging in Femoroacetabular Impingement: Current State and Future Prospects

Symptomatic femoroacetabular impingement (FAI) is now a known precursor of early osteoarthritis (OA) of the hip. In terms of clinical intervention, the decision between joint preservation and joint replacement hinges on the severity of articular cartilage degeneration. The exact threshold during the course of disease progression when the cartilage damage is irreparable remains elusive. The intention behind radiographic imaging is to accurately identify the morphology of osseous structural abnormalities and to accurately characterize the chondrolabral damage as much as possible. However, both plain radiographs and computed tomography (CT) are insensitive for articular cartilage anatomy and pathology. Advanced magnetic resonance imaging (MRI) techniques include magnetic resonance arthrography and biochemically sensitive techniques of delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T1rho (T1ρ), T2/T2* mapping, and several others. The diagnostic performance of these techniques to evaluate cartilage degeneration could improve the ability to predict an individual patient-specific outcome with non-surgical and surgical care. This review discusses the facts and current applications of biochemical MRI for hip joint cartilage assessment covering the roles of dGEMRIC, T2/T2*, and T1ρ mapping. The basics of each technique and their specific role in FAI assessment are outlined. Current limitations and potential pitfalls as well as future directions of biochemical imaging are also outlined.

High Field Sodium MRI Assessment of Stem Cell Chondrogenesis in a Tissue-Engineered Matrix

The development of non-invasive assessment techniques in vitro and in vivo is essential for monitoring and evaluating the growth of engineered cartilage tissues. Magnetic resonance imaging (MRI) is the leading non-invasive imaging modality used for assessing engineered cartilage. Typical MRI uses water proton relaxation times (T1 and T2) and apparent diffusion coefficient (ADC) to assess tissue growth. These techniques, while excellent in providing the first assurance of tissue growth, are unspecific to monitor the progress of engineered cartilage extracellular matrix components. In the current article, we present high field (11.7 T, (1)H freq. = 500 MHz) sodium MRI assessment of tissue-engineered cartilage at the early stage of tissue growth in vitro. We observed the chondrogenesis of human bone marrow derived stromal cells seeded in a gradient polymer-hydrogel matrix made out of poly(85 lactide-co-15 glycolide)--PuraMatrix™ for 4 weeks. We calculated the sodium concentration in the engineered constructs using a model of sodium MRI voxels that takes into account scaffold volume, cell density and amount of glycosaminoglycan (GAG). The sodium concentration was then converted to the fixed charge density (FCD) and compared with FCD derived from biochemical GAG analysis. Despite the small amount of GAG present in the engineered constructs, the sodium MRI derived FCD is found to be correlated (Pearson correlation coefficient R = 0.79) with the FCD derived from biochemical analysis. We conclude that sodium MRI could prove to be an invaluable tool in assessing engineered cartilage quantitatively during the repair or regeneration of cartilage defects.

T1rho Magnetic Resonance Imaging at 3T Detects Knee Cartilage Changes After Viscosupplementation

Viscosupplementation may affect cartilage. Changes in T1rho magnetic resonance imaging (MRI) relaxation times correlate with proteoglycan changes in cartilage. The authors hypothesized that T1rho MRI will show an improvement in proteoglycan content at 6 weeks and 3 months after viscosupplementation and that this improvement will correlate with functional outcome scores. Ten patients (mean age, 56 years; Kellgren-Lawrence grade 1 or 2) underwent T1rho MRI at baseline, 6 weeks, and 3 months after viscosupplementation. Volumetric T1rho means were calculated by depth and region. Visual analog scale (VAS), International Knee Documentation Committee (IKDC), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores were obtained. Mean T1rho values decreased in the superficial patella at 6 weeks (10.3%, P=.002) and 3 months (7.9%, P=.018) and in the middle patella at 6 weeks (7.0%, P=.014) compared with baseline values. Deep patella T1rho values increased at 3 months compared with 6 weeks (9.9%, P=.033), returning to values similar to baseline. Mean T1rho values increased in the deep tibia at 6 weeks (4.7%, P=.048) and in the middle tibia (5.2%, P=.004) and deep tibia (11.2%, P=.002) at 3 months compared with baseline. At 6 weeks, improvement was seen in VAS (5.9 to 3.9, P<.01), IKDC-9 (55.3 to 63.7, P=.03), and WOMAC (43.9 to 32.8, P=.03) scores. Functional VAS (4.0, P=.02), IKDC-9 (67.8, P=.04), and WOMAC (30.0, P=.04) scores remained better at 3 months. T1rho MRI is a feasible noninvasive method of studying molecular changes in cartilage. Some segments improved after viscosupplementation, and others worsened, possibly reflecting natural history or symptom relief and subsequent increase in activity-related wear.

Comparison of T1rho imaging between spoiled gradient echo (SPGR) and balanced steady state free precession (b-FFE) sequence of knee cartilage at 3T MRI

PURPOSE

To investigate the difference in T1rho profiles of the entire femoral cartilage between SPGR and b-FFE sequences at 3.0T.

MATERIALS AND METHODS

20 healthy volunteers were enrolled in this study. T1rho images of each subject were acquired with two types of pulse sequences: SPGR and b-FFE. Femoral cartilage segmentation was performed by two independent raters slice-by-slice using Matlab. Inter- and intra-observer reproducibility between the two imaging protocols was calculated. The relative signal intensity (SI) of cartilage, subchondral bone marrow, joint effusion, and the relative signal contrast between structures of the knee were quantitatively measured. The difference in T1rho values between SPGR and b-FFE sequences was statistically analyzed using the Wilcoxon signed-rank test.

RESULTS

The average T1rho value of the entire femoral cartilage with b-FFE was significantly higher compared to SPGR (p<0.05). The reproducibility of the segmented area and T1rho values was superior with SPGR compared to b-FFE. The inter-class correlation coefficient was 0.846 on SPGR and 0.824 on b-FFE. The intra-class correlation coefficient of T1rho values was 0.878 on SPGR and 0.836 on b-FFE. The two imaging techniques demonstrated different signal and contrast characteristics. The relative SI of fluid was significantly higher on SPGR, while the relative SI of subchondral bone was significantly higher on b-FFE (p<0.001). There were also significant differences in the relative contrast between fluid-cartilage, fluid-subchondral bone, and cartilage-subchondral bone between the two sequences (all p<0.001).

CONCLUSION

We need to pay attention to differences in T1rho values between SPGR and b-FFE in clinical applications.

Techniques and applications of in vivo diffusion imaging of articular cartilage

Early in the process of osteoarthritis (OA) the composition (water, proteoglycan [PG], and collagen) and structure of articular cartilage is altered leading to changes in its mechanical properties. A technique that can assess the composition and structure of the cartilage in vivo can provide insight in the mechanical integrity of articular cartilage and become a powerful tool for the early diagnosis of OA. Diffusion tensor imaging (DTI) has been proposed as a biomarker for cartilage composition and structure. DTI is sensitive to the PG content through the mean diffusivity and to the collagen architecture through the fractional anisotropy. However, the acquisition of DTI of articular cartilage in vivo is challenging due to the short T2 of articular cartilage (∼40 ms at 3 Tesla) and the high resolution needed (0.5-0.7 mm in plane) to depict the cartilage anatomy. We describe the pulse sequences used for in vivo DTI of articular cartilage and discus general strategies for protocol optimization. We provide a comprehensive review of measurements of DTI of articular cartilage from ex vivo validation experiments to its recent clinical applications.

Rotating frame relaxation imaging of prostate cancer: Repeatability, cancer detection, and Gleason score prediction

PURPOSE

To investigate relaxation along a fictitious field (RAFF) and continuous wave (cw) T1ρ imaging of prostate cancer (PCa) in the terms of repeatability, PCa detection, and characterization.

METHODS

Thirty-six patients (PSA 11.6 ± 7.6 ng/mL, mean ± standard deviation) with histologically confirmed PCa underwent two repeated 3T MR examinations using surface array coils before prostatectomy. Relaxation along fictitious field, cw T1ρ, and T2 relaxation times (TRAFF, T1ρcw, T2) were measured and averaged over regions of interest placed in PCa, normal peripheral zone (PZ), and normal central gland (CG) positioned using whole-mount prostatectomy sections and anatomical T2-weighted images. Receiver operating characteristic curve analysis with area under the curve (AUC) was calculated to distinguish PCa from PZ/CG and PCa with Gleason score (GS) of 3+3 from GS of 3+4/≥ 3+4.

RESULTS

TRAFF and T1ρcw relaxation times were repeatable with coefficients of repeatability as a percentage of median value in the range of 7.8-23.2%. AUC (mean, 95% confidence interval) in the differentiation of PCa with GS of 3+3 from PCa with CS of ≥ 3+4 were 0.88 (0.72-0.99), 0.69 (0.46-0.90), and 0.68 (0.45-0.88), for TRAFF, T1ρcw, and T2, respectively.

CONCLUSION

In quantitative region of interest based analysis, TRAFF outperformed T1ρcw and T2 in PCa detection and characterization.

Quantitative magnetic resonance imaging (MRI) evaluation of cartilage repair after microfracture treatment for full-thickness cartilage defect models in rabbit knee joints: correlations with histological findings

OBJECTIVE

To evaluate repair tissue (RT) after microfracture treatment for full-thickness cartilage defect models using quantitative MRI and investigate the correlations between MRI and histological findings.

MATERIALS AND METHODS

The animal experiment was approved by the Animal Care and Use Committee of our college. Thirty-six full-thickness cartilage defect models in rabbit knee joints were assigned to the microfracture or joint debridement group (as control). Each group consisted of 3-week, 5-week, and 7-week subgroups. MR imaging, including a three-dimensional double-echo steady-state sequence (3D-DESS), and T2 mapping were performed at 3, 5, and 7 weeks postoperatively. The thickness and T2 indices of RT were calculated. After MRI scans at each time point, operation sites were removed to make hematoxylin-eosin (H&E)-stained sections. Histological results were evaluated using the modified O'Driscoll score system. Comparisons were made between the two groups with respect to the MRI and histological findings, and correlation analysis was performed within each group.

RESULTS

The thickness index and histological O'Driscoll score of RT in the two groups increased over time, while the T2 index decreased. The thickness index and histological O'Driscoll score of the microfracture group were higher than in the joint debridement group at each time point. The T2 index of the microfracture group was lower than in the joint debridement group at 3 weeks (P = 0.006), while it was higher than in the joint debridement group at 5 and 7 weeks (P = 0.025 and 0.025). The thickness index was positively correlated with the histological O'Driscoll score in both groups (microfracture: r s = 0.745, P < 0.001; joint debridement: r s = 0.680, P = 0.002). The T2 index was negatively correlated with the histological O'Driscoll score in both groups (microfracture: r s = -0.715, P = 0.002; joint debridement: r s = -0.826, P < 0.001).

CONCLUSION

Significant improvement over time after microfracture can be expected on the basis of the quantitative MRI finding and histological O'Driscoll score. MRI was correlated with the histological O'Driscoll score, which indicated that quantitative MRI 3D-DESS and T2 mapping could evaluate cartilage repair after microfracture as an effective noninvasive tool.

T1rho MRI and CSF biomarkers in diagnosis of Alzheimer's disease

In the current study, we have evaluated the performance of magnetic resonance (MR) T1rho (T_1ρ) imaging and CSF biomarkers (T-tau, P-tau and Aβ-42) in characterization of Alzheimer's disease (AD) patients from mild cognitive impairment (MCI) and control subjects. With informed consent, AD (n = 27), MCI (n = 17) and control (n = 17) subjects underwent a standardized clinical assessment and brain MRI on a 1.5-T clinical-scanner. T_1ρ images were obtained at four different spin-lock pulse duration (10, 20, 30 and 40 ms). T_1ρ maps were generated by pixel-wise fitting of signal intensity as a function of the spin-lock pulse duration. T_1ρ values from gray matter (GM) and white matter (WM) of medial temporal lobe were calculated. The binary logistic regression using T_1ρ and CSF biomarkers as variables was performed to classify each group. T_1ρ was able to predict 77.3% controls and 40.0% MCI while CSF biomarkers predicted 81.8% controls and 46.7% MCI. T_1ρ and CSF biomarkers in combination predicted 86.4% controls and 66.7% MCI. When comparing controls with AD, T_1ρ predicted 68.2% controls and 73.9% AD, while CSF biomarkers predicted 77.3% controls and 78.3% for AD. Combination of T_1ρ and CSF biomarkers improved the prediction rate to 81.8% for controls and 82.6% for AD. Similarly, on comparing MCI with AD, T_1ρ predicted 35.3% MCI and 81.9% AD, whereas CSF biomarkers predicted 53.3% MCI and 83.0% AD. Collectively CSF biomarkers and T_1ρ were able to predict 59.3% MCI and 84.6% AD. On receiver operating characteristic analysis T_1ρ showed higher sensitivity while CSF biomarkers showed greater specificity in delineating MCI and AD from controls. No significant correlation between T_1ρ and CSF biomarkers, between T_1ρ and age, and between CSF biomarkers and age was observed. The combined use of T_1ρ and CSF biomarkers have promise to improve the early and specific diagnosis of AD. Furthermore, disease progression form MCI to AD might be easily tracked using these two parameters in combination.

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Increased T1rho was observed in MCI and AD compared to controls.

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Increased T-tau and P-tau and decreased Aβ1-42 were observed in MCI and AD.

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Combined biomarkers have promise to improve early and specific diagnosis of AD.

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MCI to AD progression might be tracked using these two biomarkers in combination.

Zonal T2* and T1Gd assessment of knee joint cartilage in various histological grades of cartilage degeneration: an observational in vitro study

OBJECTIVES

Accurate assessment of cartilage status is increasingly becoming important to clinicians for offering joint preservation surgeries versus joint replacements. The goal of this study was to evaluate the validity of three-dimensional (3D), gradient-echo (GRE)-based T2* and T1Gd mapping for the assessment of various histological severities of degeneration in knee joint cartilage with potential implications for clinical management.

METHODS

MRI and histological assessment were conducted in 36 ex vivo lateral femoral condyle specimens. The MRI protocol included a 3D GRE multiecho data image combination sequence in order to assess the T2* decay, a 3D double-echo steady-state sequence for assessment of cartilage morphology, and a dual flip angle 3D GRE sequence with volumetric interpolated breathhold examination for the T1Gd assessment. The histological sample analysis was performed according to the Mankin system. The data were then analysed statistically and correlated.

RESULTS

We observed a significant decrease in the T2* and T1Gd values with increasing grades of cartilage degeneration (p<0.001) and a moderate correlation between T2* (r=0.514)/T1Gd (r=0.556) and the histological grading of cartilage degeneration (p<0.001). In addition, we noted a zonal variation in the T2* and T1Gd values reflecting characteristic zonal differences in the biochemical composition of hyaline cartilage.

CONCLUSIONS

This study outlines the potential of GRE-based T2* and T1Gd mapping to identify various grades of cartilage damage. Early changes in specific zones may assist clinicians in identifying methods of early intervention involving the targeted joint preservation approach versus moving forward with unicompartmental, bicompartmental or tricompartmental joint replacement procedures.

TRIAL REGISTRATION NUMBER

DRKS00000729.

Utility of T2 mapping and dGEMRIC for evaluation of cartilage repair after allograft chondrocyte implantation in a rabbit model

OBJECTIVE

To investigate the effectiveness of quantitative Magnetic resonance imaging (MRI) for evaluating the quality of cartilage repair over time following allograft chondrocyte implantation using a three-dimensional scaffold for osteochondral lesions.

DESIGN

Thirty knees from 15 rabbits were analyzed. An osteochondral defect (diameter, 4 mm; depth, 1 mm) was created on the patellar groove of the femur in both legs. The defects were filled with a chondrocyte-seeded scaffold in the right knee and an empty scaffold in the left knee. Five rabbits each were euthanized at 4, 8, and 12 weeks and their knees were examined via macroscopic inspection, histological and biochemical analysis, and quantitative MRI (T2 mapping and dGEMRIC) to assess the state of tissue repair following allograft chondrocyte implantation with a three-dimensional scaffold for osteochondral lesions.

RESULTS

Comparatively good regenerative cartilage was observed both macroscopically and histologically. In both chondrocyte-seeded and control knees, the T2 values of repair tissues were highest at 4 weeks and showed a tendency to decrease with time. ΔR1 values of dGEMRIC also tended to decrease with time in both groups, and the mean ΔR1 was significantly lower in the CS-scaffold group than in the control group at all time points. ΔR1 = 1/r (R1post - R1pre), where r is the relaxivity of Gd-DTPA(2-), R1 = 1/T1 (longitudinal relaxation time).

CONCLUSION

T2 mapping and dGEMRIC were both effective for evaluating tissue repair after allograft chondrocyte implantation. ΔR1 values of dGEMRIC represented good correlation with histologically and biochemically even at early stages after the implantation.

Investigation of regional influence of magic-angle effect on t2 in human articular cartilage with osteoarthritis at 3 T

RATIONALE AND OBJECTIVES

The objectives of this research study were to determine the magic-angle effect on different subregions of in vivo human femoral cartilage through the quantitative assessment of the effect of static magnetic field orientation (B0) on transverse (T2) relaxation time at 3.0 T.

MATERIALS AND METHODS

Healthy volunteers (n = 5; mean age, 36.4 years) and clinical patients (n = 5; mean age, 64 years) with early osteoarthritis (OA) were scanned at 3.0-T magnetic resonance using an 8-channel phased-array knee coil (transmit-receive).

RESULTS

The T2 maps revealed significantly greater values in anterior than in posterior regions. When the cartilage regions were oriented at 55° to B0 (magic angle), the longest T2 values were detected in comparison with the neighboring regions oriented 90° and 180° (0°) to B0. The subregions oriented 180° (0°) to B0 showed the lowest T2 values.

CONCLUSIONS

The differences in T2 values of different subregions suggest that magic-angle effect needs to be considered when interpreting cartilage abnormalities in OA patients.