Intervertebral disk degeneration: T1ρ MR imaging of human and animal models

Deep Learning Assisted Classification of T1ρ-MR Based Intervertebral Disc Degeneration Phases

BACKGROUND

According to the T1ρ value of nucleus pulposus, our previous study has found that intervertebral disc degeneration (IDD) can be divided into three phases based on T1ρ-MR, which is helpful for the selection of biomaterial treatment timing. However, the routine MR sequences for patients with IDD are T1- and T2-MR, T1ρ-MR is not commonly used due to long scanning time and extra expenses, which limits the application of T1ρ-MR based IDD phases.

PURPOSE

To build a deep learning model to achieve the classification of T1ρ-MR based IDD phases from routine T1-MR images.

STUDY TYPE

Retrospective.

POPULATION

Sixty (M/F: 35/25) patients with low back pain or lower limb radiculopathy are randomly divided into training (N = 50) and test (N = 10) sets.

FIELD STRENGTH/SEQUENCES

1.5 T MR scanner; T1-, T2-, and T1ρ-MR sequence (spin echo).

ASSESSMENT

The T1ρ values of the nucleus pulposus in intervertebral discs (IVDs) were measured. IVDs were divided into three phases based on the mean T1ρ value: pre-degeneration phase (mean T1ρ value >110 msec), rapid degeneration phase (mean T1ρ value: 80-110 msec), and late degeneration phase (mean T1ρ value <80 msec). After measurement, the T1ρ values, phases, and levels of IVDs were input into the model as labels.

STATISTICAL TESTS

Intraclass correlation coefficient, area under the receiver operating characteristic curve (AUC), F1-score, accuracy, precision, and recall (P < 0.05 was considered significant).

RESULTS

In the test dataset, the model achieved a mean average precision of 0.996 for detecting IVD levels. The diagnostic accuracy of the T1ρ-MR based IDD phases was 0.840 and the AUC was 0.871, the average AUC of 5-folds cross validation was 0.843.

DATA CONCLUSION

The proposed deep learning model achieved the classification of T1ρ-MR based IDD phases from routine T1-MR images, which may provide a method to facilitate the application of T1ρ-MR in IDD.

EVIDENCE LEVEL

4 TECHNICAL EFFICACY: Stage 2.

Parathyroid hormone treatment partially reverses endplate remodeling and attenuates low back pain in animal models of spine degeneration

Low back pain (LBP) is one of the most prevalent diseases affecting quality of life, with no disease-modifying therapy. During aging and spinal degeneration, the balance between the normal endplate (EP) bilayers of cartilage and bone shifts to more bone. The aged/degenerated bony EP has increased porosity because of osteoclastic remodeling activity and may be a source of LBP due to aberrant sensory innervation within the pores. We used two mouse models of spinal degeneration to show that parathyroid hormone (PTH) treatment induced osteogenesis and angiogenesis and reduced the porosity of bony EPs. PTH increased the cartilaginous volume and improved the mechanical properties of EPs, which was accompanied by a reduction of the inflammatory factors cyclooxygenase-2 and prostaglandin E2. PTH treatment furthermore partially reversed the innervation of porous EPs and reversed LBP-related behaviors. Conditional knockout of PTH 1 receptors in the nucleus pulposus (NP) did not abolish the treatment effects of PTH, suggesting that the NP is not the primary source of LBP in our mouse models. Last, we showed that aged rhesus macaques with spontaneous spinal degeneration also had decreased EP porosity and sensory innervation when treated with PTH, demonstrating a similar mechanism of PTH action on EP sclerosis between mice and macaques. In summary, our results suggest that PTH treatment could partially reverse EP restructuring during spinal regeneration and support further investigation into this potentially disease-modifying treatment strategy for LBP.

Multifunctional injectable hydrogels with controlled delivery of bioactive factors for efficient repair of intervertebral disc degeneration

Millions of people worldwide suffer from intervertebral disc degeneration (IVDD), which imposes a significant socioeconomic burden on society. There is an urgent clinical demand for more effective treatments for IVDD because conventional treatments can only alleviate the symptoms rather than preventing the progression of IVDD. Hydrogels, a class of elastic biomaterials with good biocompatibility, are promising candidates for intervertebral disc repair and regeneration. In recent years, various hydrogels have been investigated in vitro and in vivo for the repair of intervertebral discs, some of which are ready for clinical testing. This review summarizes the latest findings and developments in using bioactive factors-released bioactive injectable hydrogels for the repair and regeneration of intervertebral discs. It focuses on the analysis and summary of the use of multifunctional injectable hydrogels to delivery bioactive factors (cells, exosomes, growth factors, genes, drugs) for disc regeneration, providing guidance for future study. Finally, we discussed and analyzed the optimal timing for the application of controlled-release hydrogels in the treatment of IVDD to meet the high standards required for intervertebral disc regeneration and precision medicine.

An Automatized Deep Segmentation and Classification Model for Lumbar Disk Degeneration and Clarification of Its Impact on Clinical Decisions

STUDY DESIGN

Cross-sectional database study.

OBJECTIVE

The purpose of this study was to develop a successful, reproducible, and reliable convolutional neural network (CNN) model capable of segmentation and classification for grading intervertebral disc degeneration (IVDD), as well as quantify the network's impact on doctors' clinical decision-making.

METHODS

5685 discs from 1137 patients were graded separately by four experienced doctors according to the Pfirrmann classification. A ground truth (GT) was established for each disc in accordance with the decision of the majority of doctors. The U-net model is used for segmentation. 1815 discs from 363 patients were used to train and test the U-net. The Inception V3 model is employed for classification. All discs were separated into two distinct sets: 90% in a training set and 10% in a test set. The performance metrics of these models were measured. Reliability tests were performed. The impact of CNN assistance on doctors was assessed.

RESULTS

Segmentation accuracy was .9597 with a .8717 Jaccard Index and a .9314 Sorensen Dice coefficient. Classification accuracy is .9346, and the F1 score is .9355. The intraclass correlation coefficient (ICC) and kappa values between CNN and GT were .95-.97. With CNN's assistance, the success rates of doctors increased by 7.9% to 22%.

CONCLUSIONS

The fully automated network outperformed doctors markedly in terms of accuracy and reliability. The results of CNN were comparable to those of other recent studies in the literature. It was determined that CNN's assistance had a substantial positive effect on the doctor's decision.

T1rho, T2, and T2* relaxation time based on grading of intervertebral disc degeneration

BACKGROUND

Previous studies have explored the biochemical changes of disc degeneration and its relevance in low back pain using various quantitative magnetic resonance imaging (MRI) techniques. However, quantitative evaluation of intervertebral disc (IVD) with MRI such as T1rho, T2, and T2* have not been previously analyzed and compared directly in the same patients.

PURPOSE

To investigate T1rho, T2, and T2* of IVD degeneration in the same patients, reveal the correlation coefficients of these values, and evaluate which values are more sensitive to detect the degree of IVD degeneration.

MATERIAL AND METHODS

The participants were 55 patients who underwent MRI examinations which the investigator classified the degree of IVD degeneration according to the Pfirrmann classification. The T1rho, T2, and T2* values of IVD were analyzed for their classification and were compared.

RESULTS

T1rho, T2, and T2* values were 74.3 ± 7.1, 61.2 ± 6.7, and 46.5 ± 16.3 ms (grade II); 61.6 ± 11.8, 48.9 ± 8.2, and 34.1 ± 11.8 ms (grade III); 50.8 ± 10.8, 38.9 ± 9.8, and 25.4 ± 8.1 ms, (grade IV); 44.5 ± 13.3, 34.8 ± 9.5, and 11.2 ± 6.6 ms (grade V), respectively. Those values significantly decreased with increasing grades, but T1rho and T2 values for grades IV and V were not different.

CONCLUSION

The T1rho and T2 values were excellent for the evaluation of initial to moderate IVD degeneration with water and proteoglycan content. In contrast, the T2* value was suitable for detailed evaluation of progressive IVD, even with poor water content.

Augmenting Intracellular Cargo Delivery of Extracellular Vesicles in Hypoxic Tissues through Inhibiting Hypoxia-Induced Endocytic Recycling

As mesenchymal stem-cell-derived small extracellular vesicles (MSC-sEVs) have been widely applied in treatment of degenerative diseases, it is essential to improve their cargo delivery efficiency in specific microenvironments of lesions. However, the interaction between the microenvironment of recipient cells and MSC-sEVs remains poorly understood. Herein, we find that the cargo delivery efficiency of MSC-sEVs was significantly reduced under hypoxia in inflammaging nucleus pulposus cells due to activated endocytic recycling of MSC-sEVs. Hypoxia-inducible factor-1 (HIF-1)-induced upregulated RCP (also known as RAB11FIP1) is shown to promote the Rab11a-dependent recycling of internalized MSC-sEVs under hypoxia via enhancing the interaction between Rab11a and MSC-sEV. Based on this finding, si-RCP is loaded into MSC-sEVs using electroporation to overcome the hypoxic microenvironment of intervertebral disks. The engineered MSC-sEVs significantly inhibit the endocytic recycling process and exhibit higher delivery efficiency under hypoxia. In a rat model of intervertebral disk degeneration (IDD), the si-RCP-loaded MSC-sEVs successfully treat IDD with improved regenerative capacity compared with natural MSC-sEV. Collectively, the findings illustrate the intracellular traffic mechanism of MSC-sEVs under hypoxia and demonstrate that the therapeutic capacity of MSC-sEVs can be improved via inhibiting endocytic recycling. This modifying strategy may further facilitate the application of extracellular vesicles in hypoxic tissues.

Quiescence preconditioned nucleus pulposus stem cells alleviate intervertebral disc degeneration by enhancing cell survival via adaptive metabolism pattern in rats

Quiescence is a cellular state of reversible growth arrest required to maintain homeostasis and self-renewal. Entering quiescence allows the cells to remain in the non-dividing stage for an extended period of time and enact mechanisms to protect themselves from damage. Due to the extreme nutrient-deficient microenvironment in the intervertebral disc (IVD), the therapeutic effect of cell transplantation is limited. In this study, nucleus pulposus stem cells (NPSCs) were preconditioned into quiescence through serum starvation in vitro and transplanted to repair intervertebral disc degeneration (IDD). In vitro, we investigated apoptosis and survival of quiescent NPSCs in a glucose-free medium without fetal bovine serum. Non-preconditioned proliferating NPSCs served as controls. In vivo, the cells were transplanted into a rat model of IDD induced by acupuncture, and the intervertebral disc height, histological changes, and extracellular matrix synthesis were observed. Finally, to elucidate the mechanisms underlying the quiescent state of NPSCs, the metabolic patterns of the cells were investigated through metabolomics. The results revealed that quiescent NPSCs decreased apoptosis and increased cell survival when compared to proliferating NPSCs both in vitro and in vivo, as well as maintained the disc height and histological structure significantly better than that by proliferating NPSCs. Furthermore, quiescent NPSCs have generally downregulated metabolism and reduced energy requirements in response to a switch to a nutrient-deficient environment. These findings support that quiescence preconditioning maintains the proliferation and biological function potential of NPSCs, increases cell survival under the extreme environment of IVD, and further alleviates IDD via adaptive metabolic patterns.

T1ρ, T2 and T2* mapping of lumbar intervertebral disc degeneration: a comparison study

BACKGROUND

Early and accurate assessment of lumbar intervertebral disc degeneration (IVDD) is very important to therapeutic strategy. This study aims to correlate and compare the performances of T1ρ, T2 and T2* mapping for Pfirrmann grades and morphologic changes in the IVDD.

METHODS

This prospective study included 39 subjects with 195 lumbar discs. T1ρ, T2 and T2* mapping were performed, and T1ρ, T2 and T2* values of nucleus pulposus (NP), and anterior and posterior annulus fibrosus were measured. IVDD was assessed with Pfirrmann grading and morphologic changes (normal, bulging, herniation and annular fissure). The performances of T1ρ, T2 and T2* relaxation times were compared for detecting early (Pfirrmann grade II-III) and advanced degeneration (Pfirrmann grade IV-V), as well as for morphologic changes.

RESULTS

T2 relaxation times was strongly corelated with T1ρ and T2* relaxation times. Areas under the curves (AUCs) of T1ρ, T2 and T2* relaxation times of NP were 0.70, 0.87 and 0.80 for early degeneration, and 0.91, 0.95 and 0.82 for advanced degeneration, respectively. AUCs of T1ρ, T2 and T2* relaxation times of NP were 0.78, 0.83 and 0.64 for bulging discs, 0.87, 0.89 and 0.69 for herniated discs, and 0.79, 0.82 and 0.69 for annular tearing, respectively. The AUC of T2 relaxation time was significantly higher than those of T1ρ relaxation times (both P < 0.01) for early IVDD, and the AUCs of T1ρ and T2 relaxation times for assessing advanced degeneration and morphologic changes were similar (P > 0.05) but significantly higher than that of T2*relaxation time (P < 0.01).

CONCLUSIONS

T2 mapping performed better than T1ρ mapping for the detection of early IVDD. T1ρ and T2 mapping performed similarly but better than T2* mapping for advanced degeneration and morphologic changes of IVDD.

Oxidative Stress and Intervertebral Disc Degeneration: Pathophysiology, Signaling Pathway, and Therapy

Intervertebral disc degeneration (IDD), characterized as decreased proteoglycan content, ossification of endplate, and decreased intervertebral height, is one of the major reasons of low back pain, which seriously affects the quality of life and also brings heavy economic burden. However, the mechanisms leading to IDD and its therapeutic targets have not been fully elucidated. Oxidative stress refers to the imbalance between oxidation and antioxidant systems, between too many products of reactive oxygen species (ROS) and the insufficient scavenging function. Excessive ROS can damage cell lipids, nucleic acids and proteins, which has been proved to be related to the development of a variety of diseases. In recent years, an increasing number of studies have reported that oxidative stress is involved in the pathological process of IDD. Excessive ROS can accelerate the IDD process via inducing the pathological activities, such as inflammation, apoptosis, and senescence. In this review, we focused on pathophysiology and molecular mechanisms of oxidative stress-induced IDD. Moreover, the present review also summarized the possible ideas for the future therapy strategies of oxidative stress-related IDD.

Magnetic resonance imaging R2* sequences can better detect microstructural cartilage changes than T2 mapping in cynomolgus monkeys with limited knee kinematics: preliminary imaging findings

BACKGROUND

The difference between MRI (Magnetic resonance imaging)-R2* and T2 mapping sequences regarding their superiority in the detection of microstructural cartilage changes in knees with limited ROM (range of motion) was unknown.

METHODS

Twenty male cynomolgus monkeys (mean age: 10.65 ± 0.97 years) underwent knee ROM evaluations and were divided into three groups: Group A (n = 10), with similar left and right knee ROM; Group B (n = 5), with left knee ROM superior to right; and Group C (n = 5), with left knee ROM inferior to right. Twenty-eight ROIs (regions of interest) in the cartilage of the lateral (L) and medial (M) femoral trochlea (FT), anterior (A)/central (C)/posterior (P) femoral condyle (FC) and tibial plateau (TP) of both knees were identified in each monkey. The corresponding ROI values in R2* and T2 mapping sequences were recorded for analysis. One-way ANOVA, Chi-square tests and Pearson's correlation analysis were used for statistical analyses.

RESULTS

Among the total 1120 ROIs, significant differences in R2* values among the three groups existed in two ROIs: cartilage of the right MPTP (F = 5.216, P = 0.017) and left MAFC (F = 4.919, P = 0.021). However, the T2 mapping values of all ROIs were similar among the three groups. Microstructural cartilage changes occurred more frequently in the medial (40 ROIs) than in the lateral (0 ROIs) knee compartment (χ² = 43.077, P < 0.001). The Group B cartilage R2* value of the right MPTP increased with the difference in bilateral knee ROM (r = 0.913, P = 0.030).

CONCLUSIONS

In knees with limited ROM, MRI-R2* sequence is superior to T2 mapping in the detection of microstructural cartilage changes, which the medial knee compartment was more susceptible to. Cartilage R2* values tend to increase with the amount of knee ROM loss.

Comprehensive assessment of in vivo lumbar spine intervertebral discs using a 3D adiabatic T1ρ prepared ultrashort echo time (UTE-Adiab-T1ρ) pulse sequence

BACKGROUND

T_1ρ has been extensively reported as a sensitive biomarker of biochemical changes in the nucleus pulposus (NP) and annulus fibrosis of intervertebral discs (IVDs). However, no T_1ρ study of cartilaginous endplates (CEPs) has yet been reported because the relatively long echo times (TEs) of conventional clinical T_1ρ sequences cannot effectively capture the fast-decaying magnetic resonance signals of CEPs, which have very short T₂/T₂*s. This can be overcome by using ultrashort echo time (UTE) T_1ρ acquisitions.

METHODS

Seventeen subjects underwent UTE with adiabatic T_1ρ preparation (UTE-Adiab-T_1ρ) and T₂-weighted fast spin echo imaging of their lumbar spines. Each IVD was manually segmented into seven regions (i.e., outer anterior annulus fibrosis, inner anterior annulus fibrosis, outer posterior annulus fibrosis, inner posterior annulus fibrosis, superior CEP, inferior CEP, and NP). T_1ρ values of these sub-regions were correlated with IVD modified Pfirrmann grades and subjects' ages. In addition, T_1ρ values were compared in subjects with and without low back pain (LBP).

RESULTS

Correlations of T_1ρ values of the outer posterior annulus fibrosis, superior CEP, inferior CEP, and NP with modified Pfirrmann grades were significant (P<0.05) with R values of 0.51, 0.36, 0.38, and -0.94, respectively. Correlations of T_1ρ values of the outer anterior annulus fibrosis, outer posterior annulus fibrosis, and NP with ages were significant with R equal to 0.52, 0.71, and -0.76, respectively. T_1ρ differences of the outer posterior annulus fibrosis, inferior CEP, and NP between the subjects with and without LBP were significant (P=0.005, 0.020, and 0.000, respectively).

CONCLUSIONS

The UTE-Adiab-T_1ρ sequence can quantify T_1ρ of whole IVDs including CEPs. This is an advance, and of value for comprehensive assessment of IVD degeneration.

Establishing an in vitro model of MR-T1ρ imaging technology to quantify nucleus pulposus tissue proteoglycans: a preliminary study

Background

The aim of the present study was to construct an in vitro model of degenerated nucleus pulposus with different combinations of biochemical components, and to find an in vitro model for the early degeneration of nucleus pulposus suitable for the detection of magnetic resonance T1rho (MR-T1ρ) sequence for the early diagnosis of degeneration of lumbar intervertebral disc.

Methods

The proteoglycan concentration gradient in the first experimental group was 5%, with a concentration range of 7 samples in vitro models from 5% to 35%. The second experimental group had 15 samples with a 1% concentration gradient of proteoglycan (range, 10–24%), with a higher water content compared with the first group. The third experimental group contained 20 samples with a concentration gradient of 1% proteoglycan (range, 10–29%), with 75% water content. All of the in vitro models were scanned using a 3.0T GE MR. To analyze the correlation between the proteoglycan content of the in vitro model and the T1ρ value, we investigated the feasibility and stability of modeling.

Results

There was no correlation between the in vitro model proteoglycan concentration and T1ρ value in the first experimental group; however, there was a significant negative correlation between the proteoglycan concentration and T1ρ value in the second experimental group (Y=–3.02X+131.8, R²=0.852, P<0.05). In the third experimental group, the proteoglycan concentration was significantly positively correlated with T1ρ value (Y=3.05X+11.99, R²=0.834, P<0.05). The comparison of the T1ρ values in the third experimental group before and 3 months after yielded an intraclass correlation coefficient value of 0.980, indicating that the biochemical components in the third experimental group were still stable after 3 months of storage. The slope of the regression equation between the Pfirrmann grading and T1ρ value in the third experimental group was not statistically different from the volunteer group (F=0.54, P=0.814), suggesting that the lumbar disc nucleus pulposus tissue of in vitro model samples fitted well with the volunteer group.

Conclusions

In this experiment, we successfully constructed an in vitro model of nucleus pulposus tissue proteoglycan that can be used for the quantitative evaluation of the MR-T1ρ imaging.

Q-Dixon and GRAPPATINI T2 Mapping Parameters: A Whole Spinal Assessment of the Relationship Between Osteoporosis and Intervertebral Disc Degeneration

BACKGROUND

The relationship between osteoporosis and intervertebral disc (IVD) degeneration remains controversial. Novel quantitative Dixon (Q-Dixon) and GRAPPATINI T2 mapping techniques have shown potential for evaluating the biochemical components of the spine.

PURPOSE

To investigate the correlation of osteoporosis with IVD degeneration in postmenopausal women.

STUDY TYPE

Prospective.

SUBJECTS

A total of 105 postmenopausal females (mean age, 65 years; mean body mass index, 26 kg/m² ).

FIELD STRENGTH/SEQUENCE

3 T; sagittal; 6-echo Q-Dixon, multiecho spin-echo GRAPPATINI T2 mapping, turbo spin echo (TSE) T1-weighted and TSE T2-weighted sequences.

ASSESSMENT

The subjects were divided into normal (N = 47), osteopenia (N = 28), and osteoporosis (N = 30) groups according to quantitative computed tomography examination. The Pfirrmann grade of each IVD was obtained. Region of interest analysis was performed separately by two radiologists (X.L., with 10 years of experience, and S.C., with 20 years of experience) on a fat fraction map and T2 map to calculate the bone marrow fat fraction (BMFF) from the L1 to L5 vertebrae and the T2 values of each adjacent IVD separately.

STATISTICAL TESTS

One-way analysis of variance, post-hoc comparisons, and Kruskal-Wallis H tests were performed to evaluate the differences in the magnetic resonance imaging parameters between the groups. The relationships between BMFF and the IVD features were analyzed using the Spearman correlation analysis and linear regression models.

RESULTS

There were significant differences in BMFF among the three groups. The osteoporosis group had higher BMFF values (64.5 ± 5.9%). No significant correlation was found between BMFF and Pfirrmann grade (r = 0.251, P = 0.06). BMFF was significantly negatively correlated with the T2 of the adjacent IVD from L1 to L3 (r = -0.731; r = -0.637; r = -0.547), while significant weak correlations were found at the L4 to L5 levels (r = -0.337; r = -0.278).

DATA CONCLUSION

This study demonstrated that osteoporosis is associated with IVD degeneration.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 4.

Pathomechanism and Biomechanics of Degenerative Disc Disease: Features of Healthy and Degenerated Discs

The human intervertebral disc (IVD) is a complex organ composed of fibrous and cartilaginous connective tissues, and it serves as a boundary between 2 adjacent vertebrae. It provides a limited range of motion in the torso as well as stability during axial compression, rotation, and bending. Adult IVDs have poor innate healing potential due to low vascularity and cellularity. Degenerative disc disease (DDD) generally arises from the disruption of the homeostasis maintained by the structures of the IVD, and genetic and environmental factors can accelerate the progression of the disease. Impaired cell metabolism due to pH alteration and poor nutrition may lead to autophagy and disruption of the homeostasis within the IVD and thus plays a key role in DDD etiology. To develop regenerative therapies for degenerated discs, future studies must aim to restore both anatomical and biomechanical properties of the IVDs. The objective of this review is to give a detailed overview about anatomical, radiological, and biomechanical features of the IVDs as well as discuss the structural and functional changes that occur during the degeneration process.

The Optimal Timing of Hydrogel Injection for Treatment of Intervertebral Disc Degeneration: Quantitative Analysis Based on T1ρ MR Imaging

STUDY DESIGN

Animal experimental study.

OBJECTIVE

The aim of this study was to investigate the optimal time of hydrogel injection for regenerating intervertebral disc degeneration (IDD) based on T1ρ magnetic resonance imaging (MRI).

SUMMARY OF BACKGROUND DATA

Currently, different approaches are being pursued to regenerate the IDD. However, the optimal timing for the regenerative intervention is unclear.

METHODS

The slowly, progressive IDD models were established in 18 rhesus monkeys. On the basis of the MR T1ρ values of the discs, the rhesus monkeys were divided into severe (T1ρ values: <81 ms), moderate (T1ρ values: 81∼95 ms), and mild (T1ρ values: 96∼110 ms) degeneration groups. Biocompatible hydrogel was injected into the central part of the nucleus pulposus of the discs under fluoroscopic guidance. Treatment effects were investigated using radiography, T1ρ MRI, and histology until 12 months postoperatively.

RESULTS

After injection, the T1ρ values of all the discs increased significantly at 1 month postoperatively, and then remained at approximately 110 ms in the mild and moderate groups during the whole observation period, with no significant difference compared to the values at 1 month (P > 0.05). However, in the severe group, the T1ρ values decreased significantly after 1 month and leveled at approximately 70 ms after 6 months, with significant difference compared to the values at 1 month (P < 0.05). In the mild and moderate groups, there were no significant differences between preoperative histological scores and those at 12 months (P > 0.05). However, the histological score in the severe group at 12 months was significantly higher than the preoperative scores (P < 0.05).

CONCLUSION

This study suggested that the moderate degenerative stage of IDD (T1ρ values from 95 to 80 ms) could be the optimal time for hydrogel injection aimed at the regenerative intervention, based on T1ρ-MR imaging technique and quantitative analysis.

LEVEL OF EVIDENCE

N/A.

Changes of the end plate cartilage are associated with intervertebral disc degeneration: A quantitative magnetic resonance imaging study in rhesus monkeys and humans

Background

The end plate plays an important role in intervertebral disc degeneration progression. The aim of the study was to examine the compositional and structural changes of the end plate with age and to investigate the correlation between end plate and disc degeneration by T1ρ and T2 map magnetic resonance imaging.

Methods

There were 12 young monkeys (6-7 years old), 20 aged monkeys (14-17 years old) and 12 human participants (30-50 years old) in this study. T1ρ or T2 map values of the nucleus pulposus and end plate cartilage were analyzed according to Pfirrmann grades and age. Afterwards, micro computed tomography and histological analysis were used to confirm the end plate changes in monkeys. Pearson’s correlation was performed to investigate the relationship between end plate and disc degeneration.

Results

In monkeys, T1ρ (r=-0.794, P<0.001) and T2 map values (r=-0.8, P<0.001) of the nucleus pulposus were negatively associated with Pfirrmann grades. Moreover, the T2 map was more suitable than T1ρ for the evaluation of end plate degeneration. Age was an important influence factor of end plate and disc degeneration, which was confirmed by microcomputed tomography, Safranin O/fast green staining, and collagen II staining. The T2 map value of lower end plate degeneration positively correlated with that of the intervertebral discs in monkeys (R²=0.3133, P<0.001) and humans (R²=0.2092, P<0.001).

Conclusion

This study suggests that the compositional and structural changes of the end plate can be quantitatively evaluated by T2 map. Furthermore, cartilage end plate degeneration is associated with disc degeneration during ageing.

The translational potential of this article

A better understanding of how the cartilage end plate affects disc degeneration is needed, which may propose a new clinical application using T2 map to evaluate end plate degeneration.

Correlation study between facet joint cartilage and intervertebral discs in early lumbar vertebral degeneration using T2, T2* and T1ρ mapping

Recent advancements in magnetic resonance imaging have allowed for the early detection of biochemical changes in intervertebral discs and articular cartilage. Here, we assessed the feasibility of axial T2, T2* and T1ρ mapping of the lumbar facet joints (LFJs) to determine correlations between cartilage and intervertebral discs (IVDs) in early lumbar vertebral degeneration. We recruited 22 volunteers and examined 202 LFJs and 101 IVDs with morphological (sagittal and axial FSE T2-weighted imaging) and axial biochemical (T2, T2* and T1ρ mapping) sequences using a 3.0T MRI scanner. IVDs were graded using the Pfirrmann system. Mapping values of LFJs were recorded according to the degeneration grades of IVDs at the same level. The feasibility of T2, T2* and T1ρ in IVDs and LFJs were analyzed by comparing these mapping values across subjects with different rates of degeneration using Kruskal-Wallis tests. A Pearson's correlation analysis was used to compare T2, T2* and T1ρ values of discs and LFJs. We found excellent reproducibility in the T2, T2* and T1ρ values for the nucleus pulposus (NP), anterior and posterior annulus fibrosus (PAF), and LFJ cartilage (intraclass correlation coefficients 0.806-0.955). T2, T2* and T1ρ mapping (all P<0.01) had good Pfirrmann grade performances in the NP with IVD degeneration. LFJ T2* values were significantly different between grades I and IV (PL = 0.032, PR = 0.026), as were T1ρ values between grades II and III (PL = 0.002, PR = 0.006) and grades III and IV (PL = 0.006, PR = 0.001). Correlations were moderately negative for T1ρ values between LFJ cartilage and NP (rL = -0.574, rR = -0.551), and between LFJ cartilage and PAF (rL = -0.551, rR = -0.499). T1ρ values of LFJ cartilage was weakly correlated with T2 (r = 0.007) and T2* (r = -0.158) values. Overall, we show that axial T1ρ effectively assesses early LFJ cartilage degeneration. Using T1ρ analysis, we propose a link between LFJ degeneration and IVD NP or PAF changes.

Susceptibility-weighted imaging: current status and future directions

Susceptibility-weighted imaging (SWI) is a method that uses the intrinsic nature of local magnetic fields to enhance image contrast in order to improve the visibility of various susceptibility sources and to facilitate diagnostic interpretation. It is also the precursor to the concept of the use of phase for quantitative susceptibility mapping (QSM). Nowadays, SWI has become a widely used clinical tool to image deoxyhemoglobin in veins, iron deposition in the brain, hemorrhages, microbleeds and calcification. In this article, we review the basics of SWI, including data acquisition, data reconstruction and post-processing. In particular, the source of cusp artifacts in phase images is investigated in detail and an improved multi-channel phase data combination algorithm is provided. In addition, we show a few clinical applications of SWI for the imaging of stroke, traumatic brain injury, carotid vessel wall, siderotic nodules in cirrhotic liver, prostate cancer, prostatic calcification, spinal cord injury and intervertebral disc degeneration. As the clinical applications of SWI continue to expand both in and outside the brain, the improvement of SWI in conjunction with QSM is an important future direction of this technology. Copyright © 2016 John Wiley & Sons, Ltd.

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

Objective

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

Materials and Methods

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

Results

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

Conclusion

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

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

BACKGROUND

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Endogenous contrast T1rho cardiac magnetic resonance for myocardial fibrosis in hypertrophic cardiomyopathy patients

BACKGROUND

Late gadolinium enhancement (LGE) is a standard method to evaluate myocardial fibrosis, but restricted due to contrast agent contraindications. Non-contrast T1rho can generate endogenous contrast, and detect fibrosis in chronic myocardial infarction. However, T1rho for hypertrophic cardiomyopathy (HCM) patients is still unreported. The present study aimed to investigate T1rho for fibrotic assessment and the clinical implication in HCM patients.

METHODS

18 HCM patients and 8 controls underwent T1rho, cine, and LGE cardiac magnetic resonance (CMR). T1rho relaxation time maps were created. Left ventricular (LV) parameters assessed included wall thickness, wall thickening, chamber volumes, ejection function, and fibrotic size. New York Heart Association (NYHA) functional classification was conducted.

RESULTS

Hyper-T1rho value was identified in 12 HCM patients, consistent with LGE. The mean T1rho values of controls, LGE-negative patients, and remote myocardium of LGE-positive patients were 42.2±1.6ms, 43.9±2.5ms, and 42.5±1.2ms respectively, and these values showed no significant difference (all p>0.05). T1rho-3-SD and T1rho-4-SD fibrotic sizes (32.5±14.0% and 25.1±11.5%) did not differ from LGE fibrotic size (28.1±11.2%) (both p>0.05). For the fibrotic size, T1rho-3-SD method obtained the strongest correlation with LGE (r=0.88, p<0.001), and T1rho-4-SD obtained the minimal mean difference with LGE (-3.1%; -15.2 to 9.1%), compared with other SDs. All the fibrotic sizes assessed by both methods correlated directly with LV maximal end-diastolic thickness (all p<0.05). Negative correlation was found between T1rho-4-SD fibrotic size and LV ejection fraction (r=-0.49, p=0.11). T1rho-4-SD fibrotic size showed positive correlation with NYHA class (r=0.46, p=0.13).

CONCLUSIONS

T1rho CMR has potential to detect fibrosis in HCM patients. 4-SD may be the appropriate threshold for assessment.

Pingyangmycin-induced in vivo lumbar disc degeneration model of rhesus monkeys

STUDY DESIGN

Animal experimental study.

OBJECTIVE

To establish a slowly progressive and reproducible intervertebral disc degeneration model and determine the performance of T1ρ magnetic resonance imaging in the evaluation of disc degeneration.

SUMMARY OF BACKGROUND DATA

Recently, one of the hotspots of research efforts was related to management of early stage of disc degeneration. To our knowledge, a functional animal model that mimics ischemic and slowly progressive disc degeneration of humans does not exist.

METHODS

The subchondral bone adjacent to the lumbar intervertebral discs (from L3-L4 to L6-L7) of 8 rhesus monkeys was randomly injected with 4 mL of Pingyangmycin (PYM) solution (1.5 mg/mL, PYM), or 4 mL of phosphate buffered saline (Vehicle control), or exteriorized but not injected anything (Sham), respectively. The degenerative process was investigated by using radiography and T1ρ magnetic resonance imaging at 1, 3, 6, 9, 12, and 15 months postoperatively. Histological scoring, immunohistochemistry, and real-time polymerase chain reaction were performed at 15 months.

RESULTS

The mean T1ρ values of nucleus pulposus and annulus fibrosus in the PYM group significantly decreased after 3 and 6 months, respectively, followed by slow decrease, and the histological score was significantly higher at 15 months, compared with the control groups. The results of molecular analysis revealed a significant increase matrix metalloprotease-3, A disintegrin and metalloproteinase with thrombospondin motifs -5, tumor necrosis factor α, interleukin-1β, interleukin-6 expressions, and marked reduction in aggrecan, type II collagen, von Willebrand factor expressions at the messenger RNA levels in the PYM group. Spearman correlation analysis of Pfirrmann grades showed significantly inverse correlation with T1ρ values of nucleus pulposus and annulus fibrosus (r = -0.634, -0.617, respectively, P < 0.01).

CONCLUSION

Injection of PYM into the subchondral bone adjacent to the lumbar intervertebral discs of rhesus monkeys can results in mild, slowly progressive disc degeneration, which mimics the onset of human disc degeneration, and the T1ρ magnetic resonance imaging is suited for evaluating intervertebral disc degeneration.

LEVEL OF EVIDENCE

N/A.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

In vivo experimental intervertebral disc degeneration induced by bleomycin in the rhesus monkey

Background

Recently, biological therapies for early intervention of degenerative disc disease have been introduced and developed; however, a functional animal model that mimics slowly progressive disc degeneration of humans does not exist. The objective of this study was to establish a slowly progressive and reproducible intervertebral disc (IVD) degeneration model.

Methods

The subchondral bone adjacent to the lumbar IVDs (L3/4 and L5/6) of ten rhesus monkeys was randomly injected with 4 ml bleomycin solution (1.5 mg/ml), or 4 ml phosphate buffer saline (PBS) per segment as control, respectively. The degenerative process was investigated by using radiography and T1ρ MR imaging at 1, 3, 6, 9, 12 and 15 months postoperatively. Histological scoring, Sulfated Glycosaminoglycans (GAGs) analysis and real-time PCR were performed at 15 months. The correlation between histological score, GAGs and T1ρ values were also analyzed.

Results

The results showed that the mean T1ρ values of nucleus pulposus (NP) and annulus fibrosus (AF) in the bleomycin group significantly decreased after 3 and 6 months respectively, followed by slowly decrease until at 15 months. At 15 months, the histological scores was significantly higher, and the GAGs of NP was significantly lower in the bleomycin group, compared with the control group (P < 0.05). The results of real-time PCR revealed a significant increase in matrix metalloprotease (MMP)-3, A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-5, tumor necrosis factor α, interleukin-1β, interleukin-6 expressions, transforming growth factor (TGF-β1) and marked reduction in aggrecan, type II collagen, von willebrand factor (vWF) expressions at the mRNA levels in the bleomycin group. Spearman correlation analysis showed a strong positive correlation between GAGs and T1ρ values of NP (r =0.740, P < 0.01), and a significant inverse correlation between histological score and T1ρ values of NP and AF (r = -0.761, r = -0.729, respectively, P < 0.01).

Conclusions

Injection of bleomycin into the subchondral bone adjacent to the lumbar IVDs of rhesus monkeys can results in mild, slowly progressive disc degeneration, which mimics the onset of human disc degeneration. T1ρ MR imaging is an effective and noninvasive technique for assessment of early stage disc degeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-340) contains supplementary material, which is available to authorized users.

Erythropoietin administration alone or in combination with endurance training affects neither skeletal muscle morphology nor angiogenesis in healthy young men

The aim was to investigate the ability of an erythropoiesis-stimulating agent (ESA), alone or in combination with endurance training, to induce changes in human skeletal muscle fibre and vascular morphology. In a comparative study, 36 healthy untrained men were randomly dispersed into the following four groups: sedentary-placebo (SP, n = 9); sedentary-ESA (SE, n = 9); training-placebo (TP, n = 10); or training-ESA (TE, n = 8). The ESA or placebo was injected once weekly. Training consisted of progressive bicycling three times per week for 10 weeks. Before and after the intervention period, muscle biopsies and magnetic resonance images were collected from the thigh muscles, blood was collected, body composition measured and endurance exercise performance evaluated. The ESA treatment (SE and TE) led to elevated haematocrit, and both ESA treatment and training (SE, TP and TE) increased maximal O2 uptake. With regard to skeletal muscle morphology, TP alone exhibited increases in whole-muscle cross-sectional area and fibre diameter of all fibre types. Also exclusively for TP was an increase in type IIa fibres and a corresponding decrease in type IIx fibres. Furthermore, an overall training effect (TP and TE) was statistically demonstrated in whole-muscle cross-sectional area, muscle fibre diameter and type IIa and type IIx fibre distribution. With regard to muscle vascular morphology, TP and TE both promoted a rise in capillary to muscle fibre ratio, with no differences between the two groups. There were no effects of ESA treatment on any of the muscle morphological parameters. Despite the haematopoietic effects of ESA, we provide novel evidence that endurance training rather than ESA treatment induces adaptational changes in angiogenesis and muscle morphology.

Osteoarthritis year 2013 in review: imaging

PURPOSE

To review recent original research publications related to imaging of osteoarthritis (OA) and identify emerging trends and significant advances.

METHODS

Relevant articles were identified through a search of the PubMed database using the query terms "OA" in combination with "imaging", "radiography", "MRI", "ultrasound", "computed tomography", and "nuclear medicine"; either published or in press between March 2012 and March 2013. Abstracts were reviewed to exclude review articles, case reports, and studies not focused on imaging using routine clinical imaging measures.

RESULTS

Initial query yielded 932 references, which were reduced to 328 citations following the initial review. MRI (118 references) and radiography (129 refs) remain the primary imaging modalities in OA studies, with fewer reports using computed tomography (CT) (35 refs) and ultrasound (23 refs). MRI parametric mapping techniques remain an active research area (33 refs) with growth in T2*- and T1-rho mapping publications compared to prior years. Although the knee is the major joint studied (210 refs) there is interest in the hip (106 refs) and hand (29 refs). Imaging continues to focus on evaluation of cartilage (173 refs) and bone (119 refs).

CONCLUSION

Imaging plays a major role in OA research with publications continuing along traditional lines of investigation. Translational and clinical research application of compositional MRI techniques is becoming more common driven in part by the availability of T2 mapping data from the Osteoarthritis Initiative (OAI). New imaging techniques continue to be developed with a goal of identifying methods with greater specificity and responsiveness to changes in the joint, and novel functional neuroimaging techniques to study central pain. Publications related to imaging of OA continue to be heavily focused on quantitative and semiquantitative MRI evaluation of the knee with increasing application of compositional MRI techniques in the hip.