Glycosaminoglycan chemical exchange saturation transfer of lumbar intervertebral discs in patients with spondyloarthritis

Sodium MRI of the Lumbar Intervertebral Discs of the Human Spine: An Ex Vivo Study

BACKGROUND

Lower back pain affects 75%-85% of people at some point in their lives. The detection of biochemical changes with sodium (23Na) MRI has potential to enable an earlier and more accurate diagnosis.

PURPOSE

To measure 23Na relaxation times and apparent tissue sodium concentration (aTSC) in ex-vivo intervertebral discs (IVDs), and to investigate the relationship between aTSC and histological Thompson grade.

STUDY TYPE

Ex-vivo.

SPECIMEN

Thirty IVDs from the lumbar spines of 11 human body donors (4 female, 7 male, mean age 86 ± 8 years).

FIELD STRENGTH/SEQUENCE

3 T; density-adapted 3D radial sequence (DA-3D-RAD).

ASSESSMENT

IVD 23Na longitudinal (T1), short and long transverse (T2s* and T2l*) relaxation times and the proportion of the short transverse relaxation (ps) were calculated for one IVD per spine sample (11 IVDs). Furthermore, aTSCs were calculated for all IVDs. The degradation of the IVDs was assessed via histological Thompson grading.

STATISTICAL TESTS

A Kendall Tau correlation (τ) test was performed between the aTSCs and the Thompson grades. The significance level was set to P < 0.05.

RESULTS

Mean 23Na relaxation parameters of a subset of 11 IVDs were T1 = 9.8 ± 1.3 msec, T2s* = 0.7 ± 0.1 msec, T2l* = 7.3 ± 1.1 msec, and ps = 32.7 ± 4.0%. A total of 30 IVDs were examined, of which 3 had Thompson grade 1, 4 had grade 2, 5 had grade 3, 5 had grade 4, and 13 had grade 5. The aTSC decreased with increasing degradation, being 274.6 ± 18.9 mM for Thompson grade 1 and 190.5 ± 29.5 mM for Thompson grade 5. The correlation between whole IVD aTSC and Thompson grade was significant and strongly negative (τ = -0.56).

DATA CONCLUSION

This study showed a significant correlation between aTSC and degenerative IVD changes. Consequently, aTSC has potential to be useful as an indicator of degenerative spinal changes.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 1.

Biogenic Imaging Contrast Agents

Imaging contrast agents are widely investigated in preclinical and clinical studies, among which biogenic imaging contrast agents (BICAs) are developing rapidly and playing an increasingly important role in biomedical research ranging from subcellular level to individual level. The unique properties of BICAs, including expression by cells as reporters and specific genetic modification, facilitate various in vitro and in vivo studies, such as quantification of gene expression, observation of protein interactions, visualization of cellular proliferation, monitoring of metabolism, and detection of dysfunctions. Furthermore, in human body, BICAs are remarkably helpful for disease diagnosis when the dysregulation of these agents occurs and can be detected through imaging techniques. There are various BICAs matched with a set of imaging techniques, including fluorescent proteins for fluorescence imaging, gas vesicles for ultrasound imaging, and ferritin for magnetic resonance imaging. In addition, bimodal and multimodal imaging can be realized through combining the functions of different BICAs, which helps overcome the limitations of monomodal imaging. In this review, the focus is on the properties, mechanisms, applications, and future directions of BICAs.

Bioinformatics Analysis of Immune Cell Infiltration and Diagnostic Biomarkers between Ankylosing Spondylitis and Inflammatory Bowel Disease

Background

Ankylosing spondylitis (AS) and inflammatory bowel disease (IBD) are both autoimmune diseases, and they often occur together in clinical practice, but the pathogenesis is unclear. This study is aimed at identifying the hub genes and explore the related immune molecular mechanisms between AS and IBD by bioinformatics analysis.

Methods

From the public Gene Expression Omnibus (GEO) database, the AS and IBD datasets (GSE73754, GSE59071, GSE25101, and GSE36807) were obtained. The immune cell infiltration in the peripheral blood tissues of GSE73754 and GSE59071 was assessed using the CIBERSORT algorithm. Then, we used the Weighted Gene Coexpression Network Analysis (WGCNA) to identify the Differentially Expressed Genes (DEGs) related to AS and IBD. Then, the immune genes from the ImmPort database intersected with the DEGs to obtain hub genes. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyzed the functional correlation of hub genes. Then, hub genes were verified in GSE25101 and GSE36807. The clusterProfiler software and Gene Set Enrichment Analysis (GSEA) were used to conduct functional enrichment and pathway enrichment studies. Finally, the diagnostic efficacy was assessed using Receiver Operating Characteristic (ROC) curve analysis.

Results

The analysis of immune characteristics showed that both AS and IBD were related to immunity, and neutrophils were positively correlated in both diseases. Nine coexpressed genes, including FCGRT, S100A11, IFNGR1, NFKBIZ, JAK2, LYN, PLAUR, ADM, and IL1RN, were linked to immune cells. The GO and KEGG analyses results showed that enrichment analysis was mainly related to cell transport and migration. Finally, the ROC curve was verified with the validation set, and it was found that PLAUR has clinical diagnostic significance and the most excellent specificity and sensitivity, respectively.

Conclusions

PLAUR (uPAR) is a promising biomarker and will be an underlying genetic biomarker for diagnosing AS comorbid IBD. Inflammation and immunological modulation mediated by neutrophil infiltration were important in the development of AS and IBD and may be diagnostic and therapeutic targets.

Imaging of exercise-induced spinal remodeling in elite rowers

OBJECTIVES

As in-vivo knowledge of training-induced remodeling of intervertebral discs (IVD) is scarce, this study assessed how lumbar IVDs change as a function of long-term training in elite athletes and age-matched controls using compositional Magnetic Resonance Imaging (MRI).

DESIGN

Prospective case-control study.

METHODS

Prospectively, lumbar spines of 17 elite rowers (ERs) of the German national rowing team (mean age: 23.9 ± 3.3 years) were imaged on a clinical 3.0 T MRI scanner. ERs were imaged twice during the annual training cycle, i.e., at training intensive preseason preparations (t₀) and 6 months later during post-competition recovery (t₁). Controls (n = 22, mean age: 26.3 ± 1.9 years) were imaged once at corresponding time points (t₀: n = 11; t₁: n = 11). Segment-wise, the glycosaminoglycan (GAG) content of lumbar IVDs (n = 195) was determined using glycosaminoglycan chemical exchange saturation transfer (gagCEST). Linear mixed models were set up to assess the influence of cohort and other variables on GAG content.

RESULTS

During preseason, IVD GAG values of ERs were significantly higher than those of controls (ERs(t₀): 2.58 ± 0.27% (mean ± standard deviations); controls(t₀): 1.43 ± 0.36%; p ≤ 0.001), while during post-competition recovery, such differences were not present anymore (ERs(t₁): 2.11 ± 0.18%; controls(t₁): 1.89 ± 0.24%; p = 0.362).

CONCLUSIONS

Professional elite-level rowing is transiently associated with significantly higher gagCEST values, which indicate increased lumbar IVD-GAG content and strong remodeling effects in response to training. Beyond professional rowing, core-strengthening full-body exercise may help to enhance the resilience of the lumbar spine as a potential therapeutic target in treating back pain.

Non-Specific Low Back Pain and Lumbar Radiculopathy: Comparison of Morphologic and Compositional MRI as Assessed by gagCEST Imaging at 3T

Using glycosaminoglycan Chemical Exchange Saturation Transfer (gagCEST) magnetic resonance imaging (MRI), this study comparatively evaluated the GAG contents of lumbar intervertebral disks (IVDs) of patients with non-specific low back pain (nsLBP), radiculopathy, and asymptomatic volunteers to elucidate the association of clinical manifestation and compositional correlate. A total of 18 patients (mean age 57.5 ± 22.5 years) with radiculopathy, 16 age-matched patients with chronic nsLBP and 20 age-matched volunteers underwent standard morphologic and compositional gagCEST MRI on a 3T scanner. In all cohorts, GAG contents of lumbar IVDs were determined using gagCEST MRI. An assessment of morphologic IVD degeneration based on the Pfirrmann classification and T2-weighted sequences served as a reference. A linear mixed model adjusted for multiple confounders was used for statistical evaluation. IVDs of patients with nsLBP showed lower gagCEST values than those of volunteers (nsLBP: 1.3% [99% confidence intervals (CI): 1.0; 1.6] vs. volunteers: 1.9% [99% CI: 1.6; 2.2]). Yet, IVDs of patients with radiculopathy (1.8% [99% CI: 1.4; 2.1]) were not different from patients with nsLBP or volunteers. In patients with radiculopathy, IVDs directly adjacent to IVD extrusions demonstrated lower gagCEST values than distant IVDs (adjacent: 0.9% [99% CI: 0.3; 1.5], distant: 2.1% [99% CI: 1.7; 2.5]). Advanced GAG depletion in nsLBP and directly adjacent to IVD extrusions in radiculopathy indicates close interrelatedness of clinical pathology and compositional degeneration.

Effectiveness of fat suppression using a water-selective binomial-pulse excitation in chemical exchange saturation transfer (CEST) magnetic resonance imaging

PURPOSE

The purpose of this study was to characterize the individual contribution of multiple fat peaks to the measured chemical exchange saturation transfer (CEST) signal when using water-selective binomial-pulse excitation and to determine the effects of multiple fat peaks in the presence of B₀ inhomogeneity.

METHODS

The excitation profiles of multiple binomial pulses were simulated. A CEST sequence with binomial-pulse excitation and modified point-resolved spectroscopy localization was then applied to the in vivo lumbar spinal vertebrae to determine the signal contributions of three distinct groups of lipid resonances. These confounding signal contributions were measured as a function of the irradiation frequency offset to determine the effect of the multi-peak nature of the fat signal on CEST imaging of exchange sites (at 1.0, 2.0 and 3.5 ppm) and robustness in the presence of B₀ inhomogeneity.

RESULTS

Numerical simulations and in vivo experiments showed that water excitation (WE) using a 1-3-3-1 (WE-4) pulse provided the broadest signal suppression, which provided partial robustness against B₀ inhomogeneity effects. Confounding fat signal contributions to the CEST contrasts at 1.0, 2.0 and 3.5 ppm were unavoidable due to the multi-peak nature of the fat signal. However, these CEST sites only suffer from small lipid artifacts with ∆B₀ spanning roughly from  - 50 to 50 Hz. Especially for the CEST site at 3.5 ppm, the lipid artifacts are smaller than 1% with ∆B₀ in this range.

CONCLUSION

In WE-4-based CEST magnetic resonance imaging, B₀ inhomogeneity is the limiting factor for fat suppression. The CEST sites at 1.0, 2.0 ppm and 3.5 ppm unavoidably suffer from lipid artifacts. However, when the ∆B₀ is confined to a limited range, these CEST sites are only affected by small lipid artifacts, which may be ignorable in some cases of clinical applications.

Functional MR imaging beyond structure and inflammation-radiographic axial spondyloarthritis is associated with proteoglycan depletion of the lumbar spine

BACKGROUND

To compare the glycosaminoglycan (GAG) content of lumbar intervertebral disks (IVDs) of patients with ankylosing spondylitis (AS) and healthy volunteers and to investigate the association of GAG depletion and disease-related clinical and imaging features.

METHODS

Lumbar spines of 50 AS patients (mean age 50 ± 10.5 years) and 30 age-matched volunteers were studied with 3-T magnetic resonance imaging (MRI) and conventional radiographs (CR). The MRI protocol included high-resolution morphological sequences and the compositional GAG chemical exchange saturation transfer imaging technique (gagCEST). Morphological images were analyzed by three raters for inflammatory activity, fat deposition, disk degeneration, and structural changes on CR. Clinical and serological measures included the Bath AS Disease Activity (BASDAI) and Bath AS Function (BASFI) Indices and C-reactive protein (CRP) levels. GagCEST values of both groups were compared using a linear mixed model. Kendall-Tau correlation analyses were performed.

RESULTS

GagCEST values were significantly lower in AS patients (2.0 ± 1.7%) vs. healthy volunteers (2.4 ± 1.8%), p = 0.001. Small, yet significant correlations were found between gagCEST values and CRP levels (τ = - 0.14, p = 0.007), BASFI (τ = - 0.18, p < 0.001) and presence of syndesmophytes (τ = - 0.17, p = 0.001). No significant correlations were found with BASDAI, inflammation, and fat deposition MRI scores.

CONCLUSIONS

Lumbar spines of r-AS patients undergo significant GAG depletion, independently associated with syndesmophyte formation, functional disability, and increased serological inflammation markers. Beyond establishing a pathophysiological role of the cartilage in AS, these findings suggest that gagCEST imaging may have an adjunct confirmatory role in the assessment of disease-related pathological MRI findings in axial spondyloarthritis.

TRIAL REGISTRATION

3980 ( https://studienregister.med.uni-duesseldorf.de ).

The role of cartilage glycosaminoglycan structure in gagCEST

Glycosaminoglycan (GAG) chemical exchange saturation transfer (gagCEST) is a potential method for cartilage quality assessment. The aim of this study was to investigate how the gagCEST effect depends on the types and molecular organization of GAG typically found in articular cartilage. gagCEST was performed on different concentrations of GAG in various forms: free chains of chondroitin sulfate (CS) of different types (-A and -C) and GAG bound to protein in aggregated and nonaggregated aggrecan extracted from calf articular cartilage. The measured magnetization transfer ratio asymmetry (MTR_asym ) was compared with known GAG concentrations or GAG concentrations determined through biochemical analysis. The gagCEST effect was assessed through the linear regression coefficient with 95% confidence interval of MTR_asym per GAG concentration. We observed a lower gagCEST effect in phantoms containing a mixture of CS-A and CS-C compared with phantoms containing mainly CS-A. The difference in response corresponds well to the difference in CS-A concentration. GAG bound in aggrecan from calf articular cartilage, where CS-A is assumed to be the major type of GAG, produed a similar gagCEST effect as that observed for free CS-A. The effect was also similar for aggregated (ie, bound to hyaluronic acid) and nonaggregated aggrecan. In conclusion, our results indicate that the aggrecan structure in itself does not impact the gagCEST effect, but that the effect is strongly dependent on GAG type. In phantoms, the current implementation of gagCEST is sensitive to CS-A while for CS-C, the main GAG component in mature human articular cartilage, the sensitivity is limited. This difference in gagCEST sensitivity between GAG types detected in phantoms is a strong motivation to also explore the possibility of a similar effect in vivo.

MRI-biochemical follow up measurements of lumbar intervertebral disc in patients with leg length discrepancy: Is it possible to alter cartilage damage with conservative therapy?

Objective

Effect of conservative therapy on intervertebral discs (IVD) in patients with leg-length-discrepancy (LLD).

M&M

Seventy lumbar IVDs of 14 participants (five with LLD 10-20 mm) were examined using a 3T-MRI-scanner. Morphological (Pfirrmann) and molecular (glycosaminoglycan-chemical-exchange-saturation-transfer, gagCEST) grading was assessed before and after a four-month therapy (physiotherapy and shoe inlays).

Results

Significantly lower GAG values in patients with LLD were found (L5/S1, p = 0.02). After therapy, a trend towards higher gagCEST values in patients with LLD was observed (2.48 ± 1.77% vs. 1.79 ± 0.79%; p > 0.05).

Conclusion

LLD represents a risk factor for molecular alterations of lumbar IVDs. Only minor effects of conservative therapy on these alterations could be found.

Chemical exchange saturation transfer magnetic resonance imaging and its main and potential applications in pre-clinical and clinical studies

Chemical exchange saturation transfer (CEST) imaging is a novel contrast mechanism, relying on the exchange between mobile protons in amide (-NH), amine (-NH2) and hydroxyl (-OH) groups and bulk water. Due to the targeted protons present in endogenous molecules or exogenous compounds applied externally, CEST imaging can respectively, generate endogenous or exogenous contrast. Nowadays, CEST imaging for endogenous contrast has been explored in pre-clinical and clinical studies. Amide CEST, also called amide proton transfer weighted (APT) imaging, generates CEST effect at 3.5 ppm away from the water signal and has been widely investigated. Given the sensitivity to amide proton concentration and pH level, APT imaging has shown robust performance in the assessment of ischemia, brain tumors, breast and prostate cancer as well as neurodegenerative diseases. With advanced methods proposed, pure APT and Nuclear Overhauser Effect (NOE) mediated CEST effects were separately fitted from original APT signal. Using both effects, early but promising results were obtained for glioma patients in the evaluation of tumor response to therapy and patient survival. Compared to amide CEST, amine CEST is also mobile proton concentration and pH dependent, but has a faster exchange rate between amine protons and water. The resultant CEST effect is usually introduced at 1.8-3 ppm. Glutamate and creatine, as two main metabolites with amine groups for CEST imaging, have been applied to quantitatively assess diseases in the central nervous system and muscle system, respectively. Glycosaminoglycan (Gag) as a representative metabolite with hydroxyl groups has also been measured to evaluate the cartilage of knee or intervertebral discs in CEST MRI. Due to limited frequency difference between hydroxyl protons and water, 7T for better spectral separation is preferred over 3T for GagCEST measurement. The applications of CEST MRI with exogenous contrast agents are still quite limited in clinic. While certain diamagnetic CEST agents, such as dynamic-glucose, have been tried in human for brain tumor or neck cancer assessment, most exogenous agents, i.e., paramagnetic CEST agents, are still tested in the pre-clinical stage, mainly due to potential toxicity. Engineered tissues for tissue regeneration and drug delivery have also shown a great potential in CEST imaging, as many of them, such as hydrogel and polyamide materials, contain mobile protons or can be incorporated with CEST specific chemical compounds. These engineered tissues can thus generate CEST effect in vivo, allowing a possibility to understand the fate of them in vivo longitudinally. Although the CEST MRI with engineered tissues has only been established in early stage, the obtained first evidence is crucial for further optimizing these biomaterials and finally accomplishing the translation into clinical use.

[MRI diagnostics in inflammatory joint and spinal diseases: protocols and special sequences: when and for what?]

Magnetic resonance imaging (MRI) is an important component in rheumatology for imaging diagnostics and therapy monitoring of inflammatory and non-inflammatory diseases of the spine and peripheral joints. The correct selection of suitable and practical MRI protocols and sequences represents a great challenge for physicians with respect to requesting and interpreting the indications for MRI investigations. This review article provides recommendations and suggestions for MRI investigation protocols for clinical utilization and practice. New sequences are evaluated and assessed in order to generate the best possible standardized and comparable examinations for rheumatology in the future and therefore optimize the quality of radiological interventions.

Assessment of glycosaminoglycan content in intervertebral discs of patients with leg length discrepancy: A pilot study

OBJECTIVE

Leg length discrepancy (LLD) could be a predisposing factor for early degeneration of lumbar intervertebral discs (IVD). The purpose of this study was to elucidate the molecular effect of LLD on IVDs.

METHODS

IVDs of Eleven patients (25.6 ± 4.3years) with LLD (>10 mm) and 14 control subjects (23.9 ± 3.5years) were compared using a 3T-MR scanner. Morphological T2-weighted and glycosaminoglycan-chemical-exchange-saturation-transfer (gagCEST) sequences were performed.

RESULTS

No differences in morphological Pfirrmann grading were found (p > 0.05). In contrast, nucleus-pulposus-gagCEST-values of L5/S1 were significantly lower (p = 0.0008).

CONCLUSION

Our results suggest that LLD is a predisposing factor for molecular IVD alterations, which are detectable even before morphological pathologies could be found.

Imaging of the spine: Where do we stand?

The number of patients presenting with spine-related problems has globally increased, with an enormous growing demand for the use of medical imaging to address this problem. The last three decades witnessed great leaps for diagnostic imaging modalities, including those exploited for imaging the spine. These developments improved our diagnostic capabilities in different spinal pathologies, especially with multi-detector computed tomography and magnetic resonance imaging, via both hardware and software improvisations. Nowadays, imaging may depict subtle spinal instability caused by various osseous and ligamentous failures, and could elucidate dynamic instabilities. Consequently, recent diagnostic modalities can discern clinically relevant spinal canal stenosis. Likewise, improvement in diagnostic imaging capabilities revolutionized our understanding of spinal degenerative diseases via quantitative biomarkers rather than mere subjective perspectives. Furthermore, prognostication of spinal cord injury has become feasible, and this is expected to be translated into better effective patient tailoring to management plans with better clinical outcomes. Meanwhile, our confidence in diagnosing spinal infections and assessing the different spinal instrumentation has greatly improved over the past few last decades. Overall, revolutions in diagnostic imaging over the past few decades have upgraded spinal imaging from simple subjective and qualitative indices into a more sophisticated yet precise era of objective metrics via deploying quantitative imaging biomarkers.

A Qualitative and Quantitative Correlation Study of Lumbar Intervertebral Disc Degeneration Using Glycosaminoglycan Chemical Exchange Saturation Transfer, Pfirrmann Grade, and T1-ρ

BACKGROUND AND PURPOSE

Glycosaminoglycan chemical exchange saturation transfer (gagCEST) imaging allows the direct measurement and mapping of glycosaminoglycans. In this study, we aimed to evaluate the usefulness of gagCEST imaging in the quantitative assessment of intervertebral disc degeneration in a comparison with Pfirrmann grade and T1-ρ measurements.

MATERIALS AND METHODS

Ninety-six lumbar intervertebral discs in 24 volunteers (36.0 ± 8.5 years of age, 21 men and 3 women) were examined with both gagCEST imaging and T1-ρ measurements. The gagCEST imaging was performed at 3T with a saturation pulse with 1.0-second duration and the B₁ amplitude of 0.8 μT followed by imaging by a 2D fast spin-echo sequence. The Z-spectra were obtained at 25 frequency offsets from -3 to +3 ppm (step, 0.25 ppm). A point-by-point B₀ correction was performed with a B₀ map. The gagCEST signal and T1-ρ values were measured in the nucleus pulposus in each intervertebral disc. The Pfirrmann grades were assessed on T2-weighted images.

RESULTS

The gagCEST signal at grade I (5.36% ± 2.79%) was significantly higher than those at Pfirrmann grade II (3.15% ± 1.40%, P = .0006), grade III (0.14% ± 1.03%, P < .0001), grade IV (-1.75% ± 2.82%, P < .0001), and grade V (-1.47% ± 0.36%, P < .0001). The gagCEST signal at grade II was significantly higher than those of grade III (P < .0001), grade IV (P < .0001), and grade V (P < .0001). The gagCEST signal was significantly correlated negatively with Pfirrmann grade (P < .0001) and positively correlated with T1-ρ (P < .0001).

CONCLUSIONS

GagCEST imaging could be a reliable and quantitative technique for assessing intervertebral disc degeneration.

Clinical applications of chemical exchange saturation transfer (CEST) MRI

Chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) has been developed and employed in multiple clinical imaging research centers worldwide. Selective radiofrequency (RF) saturation pulses with standard 2D and 3D MRI acquisition schemes are now routinely performed, and CEST MRI can produce semiquantitative results using magnetization transfer ratio asymmetry (MTR_asym ) analysis while accounting for B₀ inhomogeneity. Faster clinical CEST MRI acquisition methods and more quantitative acquisition and analysis routines are under development. Endogenous biomolecules with amide, amine, and hydroxyl groups have been detected during clinical CEST MRI studies, and exogenous CEST agents have also been administered to patients. These CEST MRI tools show promise for contributing to assessments of cerebral ischemia, neurological disorders, lymphedema, osteoarthritis, muscle physiology, and solid tumors. This review summarizes the salient features of clinical CEST MRI protocols and critically evaluates the utility of CEST MRI for these clinical imaging applications.

LEVEL OF EVIDENCE

5 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:11-27.

A Histopathological Scheme for the Quantitative Scoring of Intervertebral Disc Degeneration and the Therapeutic Utility of Adult Mesenchymal Stem Cells for Intervertebral Disc Regeneration

The purpose of this study was to develop a quantitative histopathological scoring scheme to evaluate disc degeneration and regeneration using an ovine annular lesion model of experimental disc degeneration. Toluidine blue and Haematoxylin and Eosin (H&E) staining were used to evaluate cellular morphology: (i) disc structure/lesion morphology; (ii) proteoglycan depletion; (iii) cellular morphology; (iv) blood vessel in-growth; (v) cell influx into lesion; and (vi) cystic degeneration/chondroid metaplasia. Three study groups were examined: 5 × 5 mm lesion; 6 × 20 mm lesion; and 6 × 20 mm lesion plus mesenchymal stem cell (MSC) treatment. Lumbar intervertebral discs (IVDs) were scored under categories (i-vi) to provide a cumulative score, which underwent statistical analysis using STATA software. Focal proteoglycan depletion was associated with 5 × 5 mm annular rim lesions, bifurcations, annular delamellation, concentric and radial annular tears and an early influx of blood vessels and cells around remodeling lesions but the inner lesion did not heal. Similar features in 6 × 20 mm lesions occurred over a 3-6-month post operative period. MSCs induced a strong recovery in discal pathology with a reduction in cumulative histopathology degeneracy score from 15.2 to 2.7 (p = 0.001) over a three-month recovery period but no recovery in carrier injected discs.

A Phase I clinical trial of the knee to assess the correlation of gagCEST MRI, delayed gadolinium-enhanced MRI of cartilage and T2 mapping

PURPOSE

Osteoarthritis (OA) is associated with the loss of glycosaminoglycan (GAG) during disease progression, which can be detected by glycosaminoglycan chemical exchange-dependent saturation transfer (gagCEST) MRI. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) is considered one of the standard methods for GAG quantification in vivo. This Phase I study assessed the correlation between gagCEST MRI and dGEMRIC in determining cartilage GAG concentration. Standard T2 mapping was used as a comparator with the two other methods.

MATERIALS AND METHODS

Eight athletic volunteers with no known knee diseases were recruited in this study. The sagittal images of both knees in each volunteer were obtained by a 3T MRI system. GAG concentration was calculated based on fixed charge density (FCD) within articular cartilage as calculated by T1 values obtained from dGEMRIC sequences. Magnetization transfer ratio asymmetry (MTR_asym) of the CEST spectrum at 1ppm was determined with gagCEST MRI. T2 values were calculated using a multi-echo turbo spin echo (TSE) sequence. The Pearson correlations among MTR_asym were calculated from gagCEST analysis.

RESULTS

There was moderate correlation (correlation coefficient r=0.55) between dGEMRIC and gagCEST MRI results. T2 had a low correlation (r=-0.30) with gagCEST and no correlation with dGEMRIC (r=0.003). Both gagCEST and dGEMRIC were able to distinguish between high GAG concentration cartilage compartments (higher than 210mM) and low GAG cartilage compartments (lower than 210mM).

CONCLUSION

dGEMRIC was shown to be a more accurate and sensitive clinical imaging tool in evaluating cartilage GAG levels in vivo. While GagCEST showed less sensitivity to GAG concentration variations than dGEMRIC, further improvements may yet enable gagCEST to be a clinically robust methodology.

RNA Sequencing Reveals a Role of TonEBP Transcription Factor in Regulation of Pro-inflammatory Genes in Response to Hyperosmolarity in Healthy Nucleus Pulposus Cells: A HOMEOSTATIC RESPONSE?

Transcription factor tonicity-responsive enhancer-binding protein (TonEBP/NFAT5) is critical for osmo-adaptation and extracellular matrix homeostasis of nucleus pulposus (NP) cells in their hypertonic tissue niche. Recent studies implicate TonEBP signaling in inflammatory disease and rheumatoid arthritis pathogenesis. However, broader functions of TonEBP in the disc remain unknown. RNA sequencing was performed on NP cells with TonEBP knockdown under hypertonic conditions. 1140 TonEBP-dependent genes were identified and categorized using Ingenuity Pathway Analysis. Bioinformatic analysis showed enrichment of matrix homeostasis and cytokine/chemokine signaling pathways. C-C motif chemokine ligand 2 (CCL2), interleukin 6 (IL6), tumor necrosis factor (TNF), and nitric oxide synthase 2 (NOS2) were studied further. Knockdown experiments showed that TonEBP was necessary to maintain expression levels of these genes. Gain- and loss-of-function experiments and site-directed mutagenesis demonstrated that TonEBP binding to a specific site in the CCL2 promoter is required for hypertonic inducibility. Despite inhibition by dominant-negative TonEBP, IL6 and NOS2 promoters were not hypertonicity-inducible. Whole-disc response to hypertonicity was studied in an ex vivo organ culture model, using wild-type and haploinsufficient TonEBP mice. Pro-inflammatory targets were induced by hypertonicity in discs from wild-type but not TonEBP-haploinsufficient mice. Mechanistically, NF-κB activity increased with hypertonicity and was necessary for hypertonic induction of target genes IL6, TNF, and NOS2 but not CCL2 Although TonEBP maintains transcription of genes traditionally considered pro-inflammatory, it is important to note that some of these genes also serve anabolic and pro-survival roles. Therefore, in NP cells, this phenomenon may reflect a physiological adaptation to diurnal osmotic loading of the intervertebral disc.

Facet tropism and facet joint orientation: risk factors for the development of early biochemical alterations of lumbar intervertebral discs

OBJECTIVE

To assess the glycosaminoglycan (GAG) content of lumbar intervertebral discs (IVD) in healthy volunteers with facet tropism (FT) and sagittal facet joint (FJ) orientation using glycosaminoglycan chemical exchange saturation transfer imaging (gagCEST).

METHOD

Seventy-five lumbar IVDs of twenty-five young, healthy volunteers without any history of lumbar spine pathologies (13 female; 12 male; mean age: 28.0 ± 4.4 years; range: 21-35 years) were examined with a 3T MRI scanner. Orientation of FT and FJ were assessed for L3/4, L4/5 and L5/S1 using standard T2 weighted images. Biochemical gagCEST imaging was used to determine the GAG content of each nucleus pulposus (NP) and annulus fibrosus (AF).

RESULTS

Significantly higher gagCEST values of NP were found in volunteers without FT and normal FJ orientation compared to volunteers with FT and sagittal FJ orientation >45° (P < 0.0001). GagCEST values were significantly higher in volunteers without FT compared to volunteers with moderate or severe FT (moderate FT: P < 0.0001; severe FT: P = 0.0033). Volunteers with normal FJ orientation showed significantly higher gagCEST values compared to those with sagittal FJ orientation >45° (P < 0.001). We found a significant, negative correlation between gagCEST values and higher angels in sagittal FJ orientation (rho = -0.459; P < 0.0001).

CONCLUSION

GagCEST analysis indicated lower GAG values of NP in young volunteers with FT and sagittal orientated FJ, indicating that FT and sagittal orientation of the FJ represent risk factors for the development of early biochemical alterations of lumbar IVDs.

Strategies in regenerative medicine for intervertebral disc repair using mesenchymal stem cells and bioscaffolds

The intervertebral disc (IVD) is a major weight bearing structure that undergoes degenerative changes with aging limiting its ability to dissipate axial spinal loading in an efficient manner resulting in the generation of low back pain. Low back pain is a number one global musculoskeletal disorder with massive socioeconomic impact. The WHO has nominated development of mesenchymal stem cells and bioscaffolds to promote IVD repair as primary research objectives. There is a clear imperative for the development of strategies to effectively treat IVD defects. Early preclinical studies with mesenchymal stem cells in canine and ovine models have yielded impressive results in IVD repair. Combinatorial therapeutic approaches encompassing biomaterial and cell-based therapies promise significant breakthroughs in IVD repair in the near future.

Comparison of glycosaminoglycan chemical exchange saturation transfer using Gaussian-shaped and off-resonant spin-lock radiofrequency pulses in intervertebral disks

PURPOSE

To investigate, if a train of spin-lock pulses (chemical exchange saturation transfer with spin-lock pulses = CESL) improves biochemical glycosaminoglycan imaging compared with conventional chemical exchange saturation transfer with Gaussian-shaped pulses (CEST) in lumbar intervertebral discs.

METHODS

T₂ , CEST, and CESL imaging was performed in lumbar intervertebral discs of 15 healthy volunteers at 3 Tesla. Mean and standard deviation of the asymmetric magnetization transfer ratio (MTR_asym ), the asymmetric spin-lock ratio (SLR_asym ) and T₂ values were calculated for nucleus pulposus (NP) and annulus fibrosus (AF). Wilcoxon test was used to analyze differences between MTR_asym and SLR_asym . Pearson correlation was used to determine the relationship between MTR_asym , SLR_asym and T₂ .

RESULTS

Data showed no significant difference between MTR_asym and SLR_asym (NP: P = 0.35; AF: P = 0.34). MTR_asym and SLR_asym values differed significantly between NP and AF (MTR_asym : P = 0.014, SLR_asym : P = 0.005). T₂ values correlated significantly with MTR_asym (NP: ρ = 0.76, P < 0.001; AF: ρ = 0.60, P < 0.001) and SLR_asym (NP: ρ = 0.73, P < 0.001; AF: ρ = 0.47, P < 0.001).

CONCLUSION

CESL does not improve the chemical exchange asymmetry effect compared with conventional CEST, but leads to comparable results. Magn Reson Med 78:280-284, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Improvement of water saturation shift referencing by sequence and analysis optimization to enhance chemical exchange saturation transfer imaging

PURPOSE

To optimize B0-field inhomogeneity correction for chemical exchange saturation transfer (CEST) imaging by investigating different water saturation shift referencing (WASSR) Z-spectrum shapes and different frequency correction techniques.

METHODS

WASSR Z-spectra were simulated for different B1-fields and pulse durations (PD). Two parameter settings were used for further simulations and experiments (WASSR1: B1=0.1 μT, PD=50ms; WASSR2: B1=0.3 μT, PD=40ms). Four frequency correction techniques were investigated: 1) MinW: Minimum of the spline-interpolated WASSR-spectrum; 2) MSCF: maximum symmetry center frequency algorithm; 3) PMSCF: further development of MSCF algorithm; 4) BFit: fit with Bloch equations. Performance of frequency correction was assessed with Monte-Carlo simulations and in-vivo MR examinations in the brain and intervertebral disks.

RESULTS

Different shapes of WASSR-Z-spectra were obtained by changing B1 and PD including spectra with one (1-Peak) or two (2-Peak) minima. WASSR1 resulted in 1-Peak WASSR-spectrum, whereas WASSR2 resulted in 2-Peak WASSR-spectrum. Both Monte-Carlo simulations and in-vivo MR examinations revealed highest accuracy of field-inhomogeneity correction with WASSR1 combined with PMSCF or BFit.

CONCLUSION

Using a WASSR sequence, which results in a Z-spectrum with a single absorption peak, in combination with advanced postprocessing algorithms enables improved B0-field inhomogeneity correction for CEST imaging.

Biochemical imaging of cervical intervertebral discs with glycosaminoglycan chemical exchange saturation transfer magnetic resonance imaging: feasibility and initial results

OBJECTIVE

To evaluate glycosaminoglycan chemical exchange saturation transfer (gagCEST) imaging at 3T in the assessment of the GAG content of cervical IVDs in healthy volunteers.

MATERIALS AND METHODS

Forty-two cervical intervertebral discs of seven healthy volunteers (four females, three males; mean age: 21.4 ± 1.4 years; range: 19-24 years) were examined at a 3T MRI scanner in this prospective study. The MRI protocol comprised standard morphological, sagittal T2 weighted (T2w) images to assess the magnetic resonance imaging (MRI) based grading system for cervical intervertebral disc degeneration (IVD) and biochemical imaging with gagCEST to calculate a region-of-interest analysis of nucleus pulposus (NP) and annulus fibrosus (AF).

RESULTS

GagCEST of cervical IVDs was technically successful at 3T with significant higher gagCEST values in NP compared to AF (1.17% ± 1.03% vs. 0.79% ± 1.75%; p = 0.005). We found topological differences of gagCEST values of the cervical spine with significant higher gagCEST effects in lower IVDs (r = 1; p = 0). We could demonstrate a significant, negative correlation between gagCEST values and cervical disc degeneration of NP (r = -0.360; p = 0.019). Non-degenerated IVDs had significantly higher gagCEST effects compared to degenerated IVDs in NP (1.76% ± 0.92% vs. 0.52% ± 1.17%; p < 0.001).

CONCLUSION

Biochemical imaging of cervical IVDs is feasible at 3T. GagCEST analysis demonstrated a topological GAG distribution of the cervical spine. The depletion of GAG in the NP with increasing level of morphological degeneration can be assessed using gagCEST imaging.

Gender, BMI and T2 dependencies of glycosaminoglycan chemical exchange saturation transfer in intervertebral discs

PURPOSE

The purpose was to investigate the dependence of glycosaminoglycan chemical exchange saturation transfer (gagCEST) effect of lumbar intervertebral discs (IVD) on gender, body mass index and T2 value.

METHODS

T2 imaging and gagCEST imaging was performed in 34 healthy volunteers (17 males, 17 females) without low back pain at a 3T MRI system (Magnetom Trio, A Tim System, Siemens Healthcare, Erlangen, Germany). The body mass index was determined for each volunteer. The mean and standard deviation of MTRasym and T2 values were calculated for nucleus pulposus (NP) and annulus fibrosus (AF) as descriptive statistics for females and males. An unpaired student's t-test was applied in order to validate obtained differences. Pearson correlation was determined in order to reveal, if gagCEST effect and T2 values decrease with increasing body mass index (BMI). Pearson correlation analysis was additionally performed between gagCEST and T2 values.

RESULTS

GagCEST effect and T2 values were significantly higher in females compared to males [gagCEST effect (nucleus pulposus, females)=3.58±1.49%; gagCEST effect (nucleus pulosus, males)=3.01±1.63%, p-value (gagCEST effect, nucleus pulposus)=0.02); T2 (nucleus pulposus, females)=134.56±30.27 ms, T2 (nucleus pulposus, males)=122.35±27.64 ms, p-value (T2, nucleus pulposus)=0.01)]. Pearson correlation analysis showed a significant negative relation between BMI and gagCEST effect (nucleus pulposus: ρ=-0.16, p=0.03) and between BMI and T2 values (nucleus pulposus: ρ=-0.30, p<0.01). The correlation between gagCEST effect and T2-values was highly significant (nucleus pulposus: ρ=0.59, p<0.01).

CONCLUSIONS

Significantly lower gagCEST effects were found in males compared to females and with increased body mass index. The gagCEST effect was highly correlated with quantitative T2 imaging.