Quantitative magnetic resonance imaging in the assessment of degenerative disc disease

Can axial loading restore in vivo disc geometry, opening pressure, and T2 relaxation time?

Background

Cadaveric intervertebral discs are often studied for a variety of research questions, and outcomes are interpreted in the in vivo context. Unfortunately, the cadaveric disc does not inherently represent the LIVE condition, such that the disc structure (geometry), composition (T2 relaxation time), and mechanical function (opening pressure, OP) measured in the cadaver do not necessarily represent the in vivo disc.

Methods

We conducted serial evaluations in the Yucatan minipig of disc geometry, T2 relaxation time, and OP to quantify the changes that occur with progressive dissection and used axial loading to restore the in vivo condition.

Results

We found no difference in any parameter from LIVE to TORSO; thus, within 2 h of sacrifice, the TORSO disc can represent the LIVE condition. With serial dissection and sample preparation the disc height increased (SEGMENT height 18% higher than TORSO), OP decreased (POTTED was 67% lower than TORSO), and T2 time was unchanged. With axial loading, an imposed stress of 0.20-0.33 MPa returned the disc to in vivo, LIVE disc geometry and OP, although T2 time was decreased. There was a linear correlation between applied stress and OP, and this was conserved across multiple studies and species.

Conclusion

To restore the LIVE disc state in human studies or other animal models, we recommend measuring the OP/stress relationship and using this relationship to select the applied stress necessary to recover the in vivo condition.

Intervertebral Disc Elastography to Relate Shear Modulus and Relaxometry in Compression and Bending

Intervertebral disc degeneration is the most recognized cause of low back pain, characterized by the decline of tissue structure and mechanics. Image-based mechanical parameters (e.g., strain, stiffness) may provide an ideal assessment of disc function that is lost with degeneration but unfortunately remains underdeveloped. Moreover, it is unknown whether strain or stiffness of the disc may be predicted by MRI relaxometry (e.g. T1 or T2), an increasingly accepted quantitative measure of disc structure. In this study, we quantified T1 and T2 relaxation times and in-plane strains using displacement-encoded MRI within the disc under physiological levels of compression and bending. We then estimated shear modulus in orthogonal image planes and compared these values to relaxation times and strains within regions of the disc. Intratissue strain depended on the loading mode, and shear modulus in the nucleus pulposus was typically an order of magnitude lower than the annulus fibrosis, except in bending, where the apparent stiffness depended on the loading. Relative shear moduli estimated from strain data derived under compression generally did not correspond with those from bending experiments, with no correlations in the sagittal plane and only 4 of 15 regions correlated in the coronal plane, suggesting that future inverse models should incorporate multiple loading conditions. Strain imaging and strain-based estimation of material properties may serve as imaging biomarkers to distinguish healthy and diseased discs. Additionally, image-based elastography and relaxometry may be viewed as complementary measures of disc structure and function to assess degeneration in longitudinal studies.

Variable flip angle T1 mapping and multi-echo T2 and T2* mapping magnetic resonance imaging sequences allow quantitative assessment of canine lumbar disc degeneration

Magnetic resonance imaging is the gold standard for diagnosing intervertebral disc (IVD) degeneration in dogs. However, published methods for quantifying severity or progression of IVD degeneration are currently limited. Mapping MRI sequences are used in humans for quantifying IVD degeneration but have rarely been applied in dogs. The objective of this prospective, method comparison study was to evaluate variable flip angle T1 mapping and multiecho T2 and T2* mapping as methods for quantifying canine lumbar IVD degeneration in twenty canine patients without clinical signs of spinal disease. Ventral and dorsal lumbar IVD widths were measured on radiographs, and lumbar IVDs were assigned a qualitative Pfirrmann grade based on standard T2-weighted sequences. T1, T2, and T2* relaxation times of the nucleus pulposus (NP) were measured on corresponding maps using manual-drawn ROIs. Strong intra- and interrater agreements were found (P < 0.01) for NP relaxation times. Radiographic IVD widths and T1, T2, and T2* mapping NP relaxation times were negatively correlated with Pfirrmann grading (P < 0.01). Significant differences in T1 NP relaxation times were found between Pfirrmann grade I and the other grades (P < 0.01). Significant differences in T2 and T2* NP relaxation times were found between grade I and the other grades and between grades II and III (P < 0.01). Findings indicated that T1, T2, and T2* MRI mapping sequences are feasible in dogs. Measured NP relaxation times were repeatable and decreased when Pfirrmann grades increased. These methods may be useful for quantifying the effects of regenerative treatment interventions in future longitudinal studies.

A bovine nucleus pulposus explant culture model

Low back pain is a global health problem that is frequently caused by intervertebral disc degeneration (IVDD). Sulfated glycosaminoglycans (sGAGs) give the healthy nucleus pulposus (NP) a high fixed charge density (FCD), which creates an osmotic pressure that enables the disc to withstand high compressive forces. However, during IVDD sGAG reduction in the NP compromises biomechanical function. The aim of this study was to develop an ex vivo NP explant model with reduced sGAG content and subsequently investigate biomechanical restoration via injection of proteoglycan-containing notochordal cell-derived matrix (NCM). Bovine coccygeal NP explants were cultured in a bioreactor chamber and sGAG loss was induced by chondroitinase ABC (chABC) and cultured for up to 14 days. Afterwards, diurnal loading was studied, and explant restoration was investigated via injection of NCM. Explants were analyzed via histology, biochemistry, and biomechanical testing via stress relaxation tests and height measurements. ChABC injection induced dose-dependent sGAG reduction on Day 3, however, no dosing effects were detected after 7 and 14 days. Diurnal loading reduced sGAG loss after injection of chABC. NCM did not show an instant biomechanical (equilibrium pressure) or biochemical (FCD) restoration, as the injected fixed charges leached into the medium, however, NCM stimulated proliferation and increased Alcian blue staining intensity and matrix organization. NCM has biological repair potential and biomaterial/NCM combinations, which could better entrap NCM within the NP tissue, should be investigated in future studies. Concluding, chABC induced progressive, time-, dose- and loading-dependent sGAG reduction that led to a loss of biomechanical function. Keywords biomechanics | intervertebral disc | matrix degradation | low back pain | proteoglycans.

Delineation of Inner Annulus Fibrosus and Nucleus Pulposus on Routine T2-weighted MR Images

STUDY DESIGN

Retrospective study of 150 IVDs.

OBJECTIVE

Assessment of costume algorithm ability to delineate the IAF and NP on routine T2 images.

SUMMARY OF BACKGROUND DATA

Central hyperintense region on T2-weighted MR images of normal lumbar IVDs represents a combination of IAF and NP. Ability to identify NP as distinct from IAF can help improve our understanding of IVD morphology in-vivo.

METHODS

Sagittal T2-weighted TSE MR images of 150 lumbar IVDs from 25 patients were analyzed. MR images were processed using a custom algorithm that markedly increased the signal intensity of structures with inherent signal intensity within 2 defined intensity thresholds. Signal intensity and contrast-to- noise ratio between outer annulus fibrosus, IAF, and NP were assessed at baseline and after processing. To assess consistency of underlying T2 differences, similar analysis was done on 108 discs from 18 patients in whom additional sagittal T2-weighted STIR images were available.

RESULTS

Following image processing, apparent IAF and NP were rendered visible in 86% and 84.3% IVDs on T2-weighted TSE and STIR images respectively. While signal intensity of these 2 regions was inherently different (P< 0.001) before processing on TSE and STIR images, their visualization was facilitated by a significant increase (P<0.001) in contrast-to-noise ratio after processing. Nonvisualization of NP was associated with disc degeneration (P<0.001).

CONCLUSION

Inherent differences exist in signal intensities of normal NP and IAF on T2-weighted MR images. Accentuating these differences using image postprocessing techniques can render these 2 structures visible.

Impact of Variations in Water Concentration on the Nanomechanical Behavior of Type I Collagen Microfibrils in Annulus Fibrosus

Radial variation in water concentration from outer to inner lamellae is one of the characteristic features of annulus fibrosus (AF). In addition, water concentration changes are also associated with intervertebral disc (IVD) degeneration. Such changes alter the chemo-mechanical interactions among the biomolecular constituents at molecular level, affecting the load-bearing nature of IVD. This study investigates mechanistic impacts of water concentration on the collagen type I microfibrils in AF using molecular dynamics simulations. Results show, in axial tension, that increase in water concentration (WC) from 0% to 50% increases the elastic modulus from 2.7 GPa to 3.9 GPa. This is attributed to combination of shift in deformation from backbone straightening to combined backbone stretching- intermolecular sliding and subsequent strengthening of tropocollagen-water (TC-water-TC) interfaces through water bridges and intermolecular electrostatic attractions. Further increase in WC to 75% reduces the modulus to 1.8 GPa due to shift in deformation to polypeptide straightening and weakening of TC-water-TC interface due to reduced electrostatic attraction and increase in the number of water molecules in a water bridge. During axial compression, increase in WC to 50% results in increase in modulus from 0.8 GPa to 4.5 GPa. This is attributed to the combination of the development of hydrostatic pressure and strengthening of the TC-water-TC interface. Further increase in WC to 75% shifts load-bearing characteristic from collagen to water, resulting in a decrease in elastic modulus to 2.8 GPa. Such water-mediated alteration in load-bearing properties acts as foundations toward AF mechanics and provides insights toward understanding degeneration-mediated altered spinal stiffness.

Intradiscal injection of monosodium iodoacetate induces intervertebral disc degeneration in an experimental rabbit model

Background

Establishing an optimal animal model for intervertebral disc (IVD) degeneration is essential for developing new IVD therapies. The intra-articular injection of monosodium iodoacetate (MIA), which is commonly used in animal models of osteoarthritis, induces cartilage degeneration and progressive arthritis in a dose- and time-dependent manner. The purpose of this study was to determine the effect of MIA injections into rabbit IVDs on the progression of IVD degeneration evaluated by radiographic, micro-computerized tomography (micro-CT), magnetic resonance imaging (MRI), and histological analyses.

Methods

In total, 24 New Zealand White (NZW) rabbits were used in this study. Under general anesthesia, lumbar discs from L1–L2 to L4–L5 had a posterolateral percutaneous injection of MIA in contrast agent (CA) (L1–L2: CA only; L2–L3: MIA 0.01 mg; L3–L4: 0.1 mg; L4–L5: 1.0 mg; L5–L6: non-injection (NI) control). Disc height was radiographically monitored biweekly until 12 weeks after injection. Six rabbits were sacrificed at 2, 4, 8, and 12 weeks post-injection and processed for micro-CT, MRI (T2-mapping), and histological analyses. Three-dimensional (3D) disc height in five anatomical zones was evaluated by 3D reconstruction of micro-CT data.

Results

Disc height of MIA-injected discs (L2–L3 to L4–L5) gradually decreased time-dependently (P < 0.0001). The disc height of MIA 0.01 mg-injected discs was significantly higher than those of MIA 0.1 and 1.0 mg-injected discs (P < 0.01, respectively). 3D micro-CT analysis showed the dose- and time-dependent decrease of 3D disc height of MIA-injected discs predominantly in the posterior annulus fibrosus (AF) zone. MRI T2 values of MIA 0.1 and 1.0 mg-injected discs were significantly decreased compared to those of CA and/or NI controls (P < 0.05). Histological analyses showed progressive time- and dose-degenerative changes in the discs injected with MIA (P < 0.01). MIA induced cell death in the rabbit nucleus pulposus with a high percentage, while the percentage of cell clones was low.

Conclusions

The results of this study showed, for the first time, that the intradiscal injection of MIA induced degenerative changes of rabbit IVDs in a time- and dose-dependent manner. This study suggests that MIA injection into rabbit IVDs could be used as an animal model of IVD degeneration for developing future treatments.

Association between spinal alignment and biochemical composition of lumbar intervertebral discs assessed by quantitative magnetic resonance imaging

Background

To evaluate potential associations between spinopelvic parameters and the biochemical composition of lumbar intervertebral discs using quantitative magnetic resonance imaging in asymptomatic young adults.

Methods

Our study group comprised 93 asymptomatic volunteers aged 20-40 years (49 women and 44 men). Lumbar spine T2-weighted images and T2 relaxometry were acquired on a 1.5T MRI scanner. Spinopelvic parameters including sacral slope, pelvic tilt, pelvic incidence, lumbar lordosis, thoracic kyphosis, thoracolumbar alignment, sagittal vertical axis, spinosacral angle, C2 pelvic angle, and T1S1 and L1S1 length were measured on panoramic spine radiographs.

Results

Lumbar lordosis decrease correlates with discrete dehydration of nucleus pulposus at all lumbar levels. Also low values of sacral slope, pelvic tilt, pelvic incidence, thoracic kyphosis and spinosacral angle were associated with decrease of T2 relaxation times on annulus fibrosus.

Conclusions

In conclusion, spinopelvic parameters presented a discrete association with lumbar disc composition and water content.

Quantitative assessment of the lumbar intervertebral disc via T2 shows excellent long-term reliability

Methodologies for the quantitative assessment of the spine tissues, in particular the intervertebral disc (IVD), have not been well established in terms of long-term reliability. This is required for designing prospective studies. ¹H water T₂ in the IVD (“T₂”) has attained wider use in assessment of the lumbar intervertebral discs via magnetic resonance imaging. The reliability of IVD T₂ measurements are yet to be established. IVD T₂ was assessed nine times at regular intervals over 368 days on six anatomical slices centred at the lumbar spine using a spin-echo multi-echo sequence in 12 men. To assess repeatability, intra-class correlation co-efficients (ICCs), standard error of the measurement, minimal detectable difference and co-efficients of variation (CVs) were calculated along with their 95% confidence intervals. Bland-Altman analysis was also performed. ICCs were above 0.93, with the exception of nuclear T₂ at L5/S1, where the ICC was 0.88. CVs of the central-slice nucleus sub-region ranged from 4.3% (average of all levels) to 10.1% for L5/S1 and between 2.2% to 3.2% for whole IVD T₂ (1.8% for the average of all levels). Averaging between vertebral levels improved reliability. Reliability of measurements was least at L5/S1. ICCs of degenerated IVDs were lower. Test-retest reliability was excellent for whole IVD and good to excellent for IVD subregions. The findings help to establish the long-term repeatability of lumbar IVD T₂ for the implementation of prospective studies and determination of significant changes within individuals.

Variability of T2-Relaxation Times of Healthy Lumbar Intervertebral Discs is More Homogeneous within an Individual Than across Healthy Individuals

BACKGROUND AND PURPOSE

When one uses T2 relaxometry to classify lumbar intervertebral discs as degenerated, it is unclear whether the normative data should be based on other intervertebral discs from the same individual or from a pool of extraneous controls. This study aimed to explore the extent of intra- versus intersubject variation in the T2 times of healthy intervertebral discs.

MATERIALS AND METHODS

Using prospectively acquired T2-relaxometry data from 606 intervertebral discs in 101 volunteers without back pain (47 men, 54 women) in a narrow age range (25-35 years), we calculated intra- and intersubject variation in T2 times of intervertebral discs graded by 2 neuroradiologists on the Pfirrmann scale. Intrasubject variation of intervertebral discs was assessed relative to other healthy intervertebral discs (Pfirrmann grade, ≤2) in the same individual. Multiple intersubject variability measures were calculated using healthy extraneous references ranging from a single randomly selected intervertebral disc to all healthy extraneous intervertebral discs, without and with segmental stratification. These variability measures were compared for healthy and degenerated (Pfirrmann grade ≥3) intervertebral discs.

RESULTS

The mean T2 values of healthy (493/606, 81.3%) and degenerated intervertebral discs were 121.1 ± 22.5 ms and 91.5 ± 18.6 ms, respectively (P < .001). The mean intrasubject variability for healthy intervertebral discs was 9.8 ± 10.7 ms, lower than all intersubject variability measures (P < .001), and provided the most pronounced separation for healthy and degenerated intervertebral discs. Among intersubject variability measures, using all segment-matched healthy discs as references provided the lowest variability (P < .001).

CONCLUSIONS

Normative measures based on the T2 times of healthy intervertebral discs from the same individual are likely to provide the most discriminating means of identifying degenerated intervertebral discs on the basis of T2 relaxometry.

Quantifying the effect of posterior spinal instrumentation on the MRI signal of adjacent intervertebral discs

STUDY DESIGN

Ex vivo porcine imaging study.

OBJECTIVES

Quantitatively evaluate change in MRI signal at the discs caudal to spinal fusion instrumentation. Individuals who receive posterior spinal instrumentation are at risk of developing accelerated disc degeneration at adjacent levels. Degeneration is associated with a loss of biochemical composition and mechanical integrity of the disc, which can be noninvasively assessed through quantitative T2* (qT2*) MRI techniques. However, qT2* is sensitive to magnetic susceptibility introduced by metal.

METHODS

Nine ex vivo porcine lumbar specimens were imaged with 3 T MRI. Fast spin-echo T2-weighted (T2w) images and gradient-echo qT2* maps were acquired, both without and with posterior spinal fusion instrumentation. Average T2* relaxation times of the nuclei pulposi (NP) were measured at the adjacent and sub-adjacent discs and measurements were compared using t tests before and after instrumentation. The size of the signal void and metal artifact were determined (modified ASTM F2119-07) within the vertebral body and spinal cord for both MRI sequences. The relationship between T2* signal loss and distance from the instrumentation was evaluated using Pearson's correlation.

RESULTS

There was no significant difference between adjacent and sub-adjacent NP T2* relaxation time prior to instrumentation (p = 0.86). Following instrumentation, there was a significant decrease in the T2* relaxation time at the adjacent NP (average = 20%, p = 0.02), and no significant difference at the sub-adjacent NP (average = - 3%, p = 0.30). Furthermore, there was a significant negative correlation between signal loss and distance to disc (r = - 0.61, p < 0.01).

CONCLUSIONS

Spinal fusion instrumentation interferes with T2* relaxation time measurements at the adjacent disc but not at the sub-adjacent discs. However, there is sufficient signal at the adjacent disc to quantify changes in the T2* relaxation time following spinal fusion. Hence, baseline MRI scan following spinal fusion surgery are required to interpret and track changes in disc health at the caudal discs.

LEVEL OF EVIDENCE

N/A.

Diurnal T2-changes of the intervertebral discs of the entire spine and the influence of weightlifting

The purpose was to study if (1) diurnal changes occur in the entire spine and if (2) intervertebral discs (IVDs) of weightlifters (WL) have decreased baseline T2-values in the morning as well as (3) increased diurnal changes throughout the day. This prospective cohort study investigated healthy volunteers between 2015 and 2017. WL were required to have participated in weightlifting ≥ 4×/week for ≥ 5 years, while non-weightlifters (NWL) were limited to < 2×/week for ≥ 5 years. Both groups underwent magnetic resonance imaging (MRI) of the entire spine in the morning and evening. WL were requested to perform weightlifting in-between imaging. IVD regions of interest (nucleus pulposus) were defined and T2-maps were measured. Analysis consisted of unpaired t-test, paired t-test, propensity-score matching (adjusting for age and sex), and Pearson correlation. Twenty-five individuals (15 [60.0%] males) with a mean age of 29.6 (standard deviation [SD 6.9]) years were analyzed. Both groups (WL: n = 12 versus [vs.] NWL: n = 13) did not differ demographic characteristics. Mean IVD T2-values of all participants significantly decreased throughout the day (95.7 [SD 15.7] vs. 86.4 [SD 13.9] milliseconds [ms]) in IVDs of the cervical (71.8 [SD 13.4] vs. 64.4 [SD 14.1] ms), thoracic (98.8 [SD 19.9] vs. 88.6 [SD 16.3] ms), and lumbar (117.0 [SD 23.7] vs. 107.5 [SD 21.6] ms) spine (P < 0.001 each). There were no differences between both groups in the morning (P = 0.635) and throughout the day (P = 0.681), even after adjusting for confounders. It can be concluded that diurnal changes of the IVDs occurred in the entire (including cervical and thoracic) spine. WL and NWL showed similar morning baseline T2-values and diurnal changes. Weightlifting may not negatively affect IVDs chronically or acutely.

Characterization of Intervertebral Disc Changes in Asymptomatic Individuals with Distinct Physical Activity Histories Using Three Different Quantitative MRI Techniques

(1) Background: Assessments of intervertebral disc (IVD) changes, and IVD tissue adaptations due to physical activity, for example, remains challenging. Newer magnetic resonance imaging techniques can quantify detailed features of the IVD, where T2-mapping and T2-weighted (T2w) and Dixon imaging are potential candidates. Yet, their relative utility has not been examined. The performances of these techniques were investigated to characterize IVD differences in asymptomatic individuals with distinct physical activity histories. (2) Methods: In total, 101 participants (54 women) aged 25–35 years with distinct physical activity histories but without histories of spinal disease were included. T11/12 to L5/S1 IVDs were examined with sagittal T2-mapping, T2w and Dixon imaging. (3) Results: T2-mapping differentiated Pfirrmann grade-1 from all other grades (p < 0.001). Most importantly, T2-mapping was able to characterize IVD differences in individuals with different training histories (p < 0.005). Dixon displayed weak correlations with the Pfirrmann scale, but presented significantly higher water content in the IVDs of the long-distance runners (p < 0.005). (4) Conclusions: Findings suggested that T2-mapping best reflects IVD differences in asymptomatic individuals with distinct physical activity histories changes. Dixon characterized new aspects of IVD, probably associated with IVD hypertrophy. This complementary information may help us to better understand the biological function of the disc.

Whey protein supplementation with vibration exercise ameliorates lumbar paraspinal muscle atrophy in prolonged bed rest

We examined the impact of adding protein supplementation to exercise (resistive vibration exercise) as a countermeasure against changes in the spine during spaceflight simulation. We found that adding the protein supplementation reduced spine muscle atrophy more than exercise alone. Neither countermeasure approach prevented changes in the disks in the spine or impacted back pain reports.

Exercise for the intervertebral disc: a 6-month randomised controlled trial in chronic low back pain

BACKGROUND CONTEXT

Muscle, bone and tendon respond anabolically to mechanical forces. Whether the intervertebral disc (IVD) can benefit from exercise is unclear.

PURPOSE

To examine whether exercise can beneficially affect IVD characteristics.

STUDY DESIGN/SETTING

This is a single-blinded 6-month randomised controlled trial (ACTRN12615001270505) in an exercise and physiotherapy clinic.

PATIENT SAMPLE

Forty patients with chronic non-specific low back pain (NSCLBP) are included in this study.

OUTCOME MEASURES

The primary outcome was lumbar IVD T2 time (MRI). Secondary outcomes included IVD diffusion coefficient and IVD expansion with short-duration lying.

METHODS

Twenty patients progressively loaded their lumbar IVDs (exercise) via an exercise programme involving progressive upright aerobic and resistance exercises targeting the trunk and major muscle groups and were compared to twenty patients who performed motor control training and manual therapy (control). Testing occurred at baseline, 3 months and 6 months.

RESULTS

Seventeen exercise and fifteen control patients completed the interventions. There were no group-by-time differences in T2 time of the entire IVD (exercise 94.1 ± 10.0 ms vs. control 96.5 ± 9.3 ms, p = 0.549). Exercise patients had shorter T2 time in the posterior annulus at 6 months (82.7 ± 6.8 ms vs. 85.1 ± 8.0 ms, p = 0.028). Exercise patients showed higher L5/S1 apparent diffusion coefficients and decreased IVD height at 3 months (both p ≤ 0.050). After adjustments for multiple comparisons, differences lost statistical significance. Per-protocol and intent-to-treat analyses yielded similar findings.

CONCLUSIONS

This trial found that 6 months of exercise did not benefit the IVD of people with NSCLBP. Based on this index study, future studies could investigate the effect of exercise on IVD in different populations, with different types, durations and/or intensities of exercise, and using different IVD markers. These slides can be retrieved under Electronic Supplementary Material.

Quantifying deformations and strains in human intervertebral discs using Digital Volume Correlation combined with MRI (DVC-MRI)

Physical disruptions to intervertebral discs (IVDs) can cause mechanical changes that lead to degeneration and to low back pain which affects 75% of us in our lifetimes. Quantifying the effects of these changes on internal IVD strains may lead to better preventative strategies and treatments. Digital Volume Correlation (DVC) is a non-invasive technique that divides volumetric images into subsets, and measures strains by tracking the internal patterns within them under load. Applying DVC to MRIs may allow non-invasive strain measurements. However, DVC-MRI for strain measurements in IVDs has not been used previously. The purpose of this study was to quantify the strain and deformation errors associated with DVC-MRI for measurements in human IVDs. Eight human lumbar IVDs were MRI scanned (9.4 T) for a 'zero-strain study' (multiple unloaded scans to quantify noise within the system), and a loaded study (2 mm axial compression). Three DVC methodologies: Fast-Fourier transform (FFT), direct correlation (DC), and a combination of both FFT and DC approaches were compared with subset sizes ranging from 8 to 88 voxels to establish the optimal DVC methodology and settings which were then used in the loaded study. FFT + DC was the optimal method and a subset size of 56 voxels (2520 µm) was found to be a good compromise between errors and spatial resolution. Displacement and strain errors did not exceed 28 µm and 3000 microstrain, respectively. These findings demonstrate that DVC-MRI can quantify internal strains within IVDs non-invasively and accurately. The method has unique potential for assessing IVD strains within patients.

Multiscale and multimodal structure-function analysis of intervertebral disc degeneration in a rabbit model

OBJECTIVES

The objective of this study was to perform a quantitative analysis of the structural and functional alterations in the intervertebral disc during in vivo degeneration, using emerging tools that enable rigorous assessment from the microscale to the macroscale, as well as to correlate these outcomes with noninvasive, clinically relevant imaging parameters.

DESIGN

Degeneration was induced in a rabbit model by puncturing the annulus fibrosus (AF) with a 16-gauge needle. 2, 4, 8, and 12 weeks following puncture, degenerative changes in the discs were evaluated via magnetic resonance imaging (MRI), whole motion segment biomechanics, atomic force microscopy, histology and polarized light microscopy, immunohistochemistry, biochemical content, and second harmonic generation imaging.

RESULTS

Following puncture, degeneration was evident through marked changes in whole disc structure and mechanics. Puncture acutely compromised disc macro and microscale mechanics, followed by progressive stiffening and remodeling. Histological analysis showed substantial anterior fibrotic remodeling and osteophyte formation, as well as an overall reduction in disc height, and disorganization and infolding of the AF lamellae into the NP space. Increases in NP collagen content and aggrecan breakdown products were also noted within 4 weeks. On MRI, NP T2 was reduced at all post-puncture time points and correlated significantly with microscale indentation modulus.

CONCLUSION

This study defined the time dependent changes in disc structure-function relationships during IVD degeneration in a rabbit annular injury model and correlated degeneration severity with clinical imaging parameters. Our findings identified AF infolding and occupancy of the space as a principle mechanism of disc degeneration in response to needle puncture, and provide new insights to direct the development of novel therapeutics.

Effect of diminished flow in rabbit lumbar arteries on intervertebral disc matrix changes using MRI T2-mapping and histology

Background

Impaired lumbar artery flow has been reported in clinical and epidemiological studies to be associated with low back pain and lumbar disc degeneration. However, it has not been experimentally demonstrated that impaired lumbar artery flow directly induces intervertebral disc (IVD) degeneration by affecting IVD matrix metabolism. The purpose of this study was to evaluate whether ligation of the lumbar artery can affect degenerative changes in the rabbit IVD.

Methods

New Zealand White rabbits (n = 20) were used in this study. Under general anesthesia, the third and fourth lumbar arteries were double-ligated using vascular clips. The blood flow to the L3/L4 disc (cranial disc) was reduced by ligation of the third lumbar artery and that of the L5/L6 disc (caudal disc) by ligation of the fourth lumbar artery. The blood flow to the L4/L5 disc (bilateral disc) was decreased by ligation of both the third and fourth lumbar arteries. The L2/L3 disc was used as the control. Disc height was radiographically monitored biweekly until 12 weeks after surgery. The rabbits were sacrificed at 4, 8, and 12 weeks after surgery and magnetic resonance imaging (MRI) T2-mapping, histology and immunohistochemistry were assessed.

Results

Lumbar artery ligation did not induce significant changes in disc height between control and ischemic discs (cranial, bilateral and caudal discs) during the 12-week experimental period. T2-values of ischemic discs had no significant trend to be lower than those of the control L2/L3 discs. Histologically, Safranin-O staining changed following ligation of corresponding IVD lumbar arteries. Histological grading scores for disc degeneration, which correlated significantly with MRI T2-values, had significant changes after the surgery. Immunohistochemical analysis showed that the ligation of lumbar arteries significantly affected a change in the percentage of HIF-1α immunoreactive cells of ischemia discs compared to that of control discs four weeks after the surgery (p < 0.05).

Conclusions

The MRI and histology results suggest that diminished flow in lumbar arteries induce mild changes in the extracellular matrix metabolism of rabbit IVDs. These matrix changes, however, were not progressive and differed from the degenerative disc changes seen in the process of human IVD degeneration.

Diffusion based MR measurements correlates with age-related changes in human intervertebral disks

BACKGROUND

Understanding the association between MR parameters and age related deterioration in human intervertebral disks forms an important step in the development of clinical diagnostic protocols for disk disease.

METHODS

Ten unfixed thoracic and lumbar cadaver disk joints, age 37-81 years were imaged at 9.4 T using T2 relaxation (CPMG) and ADC (DWI spin echo) MR protocols. For each MR parameter, spatial maps were computed from the axial images, with the AF and NP segmented based on the T2 maps. Linear regression tested for the correlation between mean and variance (COV) of T2 and ADC with age in the disk, nucleus and annulus, and the effect of thoracic vs. lumbar spine on these correlations.

FINDINGS

In the disk, age negatively correlated with mean ADC (P < 0.001) and positively with COV of ADC (P < 0.001) and T2 (P < 0.05). Age was negatively correlated with mean T2 (P < 0.01), mean ADC (P < 0.001) and positively with COV of ADC (P < 0.001) and T2 (P < 0.05) in the NP and positively correlated with mean T2 (P < 0.05), COV of ADC (P < 0.01) and T2 (P < 0.05) and negatively with mean ADC (P < 0.05) in the AF. Compared to thoracic disks, lumbar disks showed higher mean ADC (P < 0.05), lower mean T2 (P < 0.001) and higher COV of ADC (P < 0.01) and T2 (P < 0.05).

INTERPRETATION

Compared to T2, MR diffusion was a more sensitive measure of age mediated changes in disk tissues. Strong differences in the association of MR parameters with age between the lumbar and thoracic suggest that mechanical environment effects tissue specific MR parameters' association with age.

Quantitative MRI in early intervertebral disc degeneration: T1rho correlates better than T2 and ADC with biomechanics, histology and matrix content

Introduction

Low-back pain (LBP) has been correlated to the presence of intervertebral disc (IVD) degeneration on T2-weighted (T2w) MRI. It remains challenging, however, to accurately stage degenerative disc disease (DDD) based on T2w MRI and measurements of IVD height, particularly for early DDD. Several quantitative MRI techniques have been introduced to detect changes in matrix composition signifying early DDD. In this study, we correlated quantitative T2, T1rho and Apparent Diffusion Coefficient (ADC) values to disc mechanical behavior and gold standard early DDD markers in a graded degenerated lumbar IVD caprine model, to assess their potential for early DDD detection.

Methods

Lumbar caprine IVDs were injected with either 0.25 U/ml or 0.5 U/ml Chondroïtinase ABC (Cabc) to trigger early DDD-like degeneration. Injection with phosphate-buffered saline (PBS) served as control. IVDs were cultured in a bioreactor for 20 days under axial physiological loading. High-resolution 9.4 T MR images were obtained prior to intervention and after culture. Quantitative MR results were correlated to recovery behavior, histological degeneration grading, and the content of glycosaminoglycans (GAGs) and water.

Results

Cabc-injected IVDs showed aberrancies in biomechanics and loss of GAGs without changes in water-content. All MR sequences detected changes in matrix composition, with T1rho showing largest changes pre-to-post in the nucleus, and significantly more than T2 and ADC. Histologically, degeneration due to Cabc injection was mild. T1rho nucleus values correlated strongest with altered biomechanics, histological degeneration score, and loss of GAGs.

Conclusions

T2- and T1rho quantitative MR-mapping detected early DDD changes. T1rho nucleus values correlated better than T2 and ADC with biomechanical, histological, and GAG changes. Clinical implementation of quantitative MRI, T1rho particularly, could aid in distinguishing DDD more reliably at an earlier stage in the degenerative process.

Inflammatory biomarkers of low back pain and disc degeneration: a review

Biomarkers are biological characteristics that can be used to indicate health or disease. This paper reviews studies on biomarkers of low back pain (LBP) in human subjects. LBP is the leading cause of disability, caused by various spine-related disorders, including intervertebral disc degeneration, disc herniation, spinal stenosis, and facet arthritis. The focus of these studies is inflammatory mediators, because inflammation contributes to the pathogenesis of disc degeneration and associated pain mechanisms. Increasingly, studies suggest that the presence of inflammatory mediators can be measured systemically in the blood. These biomarkers may serve as novel tools for directing patient care. Currently, patient response to treatment is unpredictable with a significant rate of recurrence, and, while surgical treatments may provide anatomical correction and pain relief, they are invasive and costly. The review covers studies performed on populations with specific diagnoses and undefined origins of LBP. Since the natural history of LBP is progressive, the temporal nature of studies is categorized by duration of symptomology/disease. Related studies on changes in biomarkers with treatment are also reviewed. Ultimately, diagnostic biomarkers of LBP and spinal degeneration have the potential to shepherd an era of individualized spine medicine for personalized therapeutics in the treatment of LBP.

Knockout of Apolipoprotein E in rabbit promotes premature intervertebral disc degeneration: A new in vivo model for therapeutic approaches of spinal disc disorders

Intervertebral disc (IVD) degeneration that accelerates the loss of disc structural and functional integrities is recognized as one of the major factors of chronic back pain. Cardiovascular risk factors, such as deficits of apolipoproteins that elevate the levels of cholesterol and triglycerides, are considered critical for the progress of atherosclerosis; notably in the abdominal aorta and its lumbar branching arteries that supply lumbar vertebrae and IVDs. Obstruction of the lumbar arteries by atherosclerosis is presumed to promote lumbar disc degeneration and low back pain. APOE-knockout rabbits have recently been shown to generate hyperlipidemia with increased levels of cholesterol and triglycerides that mimic the symptoms of atherosclerosis in humans. Here, we analysed IVD degeneration in the lumbar spines of ten homozygous APOE-knockout and four wild-type New Zealand White rabbits of matching age to prove accelerated IVD degeneration in APOE-knockout rabbits, since APOE-knockout rabbits could be a beneficial model for therapeutic approaches of degenerative IVD disorders. Experiments were performed using T1/T2-weighted magnetic resonance imaging, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, glucose-oxidase assay, enzyme-linked immunosorbent assay, quantitative reverse transcription PCR and western blot. APOE-knockout lumbar spines showed more advanced IVD degeneration, obstructed lumbar arteries and lower enhancement of contrast agent in IVDs. Moreover, lower concentration of glucose, lower number of viable cells and lower concentrations of aggrecan, collagen II and higher concentration of collagen I were detected in APOE-knockout IVDs (p < 0.0001). APOE-knockout in rabbits could induce structurally deteriorating premature IVD degeneration that mimics the symptoms of accelerated IVD degeneration in humans. APOE-knockout rabbits could be used as beneficial model, as they can bypass the standard surgical interventions that are commonly applied in research animals for the induction of enhanced IVD degeneration. Their parallel use in therapeutic approaches of IVD disorders and atherosclerosis could reduce the number of research animals to be used and contribute to the principles of 3Rs (Replacement, Reduction and Refinement).

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.

Can Exercise Positively Influence the Intervertebral Disc?

To better understand what kinds of sports and exercise could be beneficial for the intervertebral disc (IVD), we performed a review to synthesise the literature on IVD adaptation with loading and exercise. The state of the literature did not permit a systematic review; therefore, we performed a narrative review. The majority of the available data come from cell or whole-disc loading models and animal exercise models. However, some studies have examined the impact of specific sports on IVD degeneration in humans and acute exercise on disc size. Based on the data available in the literature, loading types that are likely beneficial to the IVD are dynamic, axial, at slow to moderate movement speeds, and of a magnitude experienced in walking and jogging. Static loading, torsional loading, flexion with compression, rapid loading, high-impact loading and explosive tasks are likely detrimental for the IVD. Reduced physical activity and disuse appear to be detrimental for the IVD. We also consider the impact of genetics and the likelihood of a 'critical period' for the effect of exercise in IVD development. The current review summarises the literature to increase awareness amongst exercise, rehabilitation and ergonomic professionals regarding IVD health and provides recommendations on future directions in research.

Quantitative chemical exchange saturation transfer MRI of intervertebral disc in a porcine model

PURPOSE

Previous studies have associated low pH in intervertebral discs (IVDs) with discogenic back pain. The purpose of this study was to determine whether quantitative CEST (qCEST) MRI can be used to detect pH changes in IVDs in vivo.

METHODS

The exchange rate k_sw between glycosaminoglycan (GAG) protons and water protons was determined from qCEST analysis. Its dependence on pH value was investigated in GAG phantoms with varying pH and concentrations. The relationship between k_sw and pH was studied further in vivo in a porcine model on a 3T MR scanner and validated using a pH meter. Sodium lactate was injected into the IVDs to induce various pH values within the discs ranging from 5 to 7.

RESULTS

Phantom and animal results revealed that k_sw measured using qCEST MRI is highly correlated with pH level. In the animal studies, the relationship can be described as k_sw  =9.2 × 10⁶ × 10^-pH + 196.9, R²  = 0.7883.

CONCLUSION

The exchange rate between GAG and water protons determined from qCEST MRI is closely correlated with pH value. This technique has the potential to noninvasively measure pH in the IVDs of patients with discogenic pain. Magn Reson Med 76:1677-1683, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Review of the fluid flow within intervertebral discs - How could in vitro measurements replicate in vivo?

By maintaining a balance between external mechanical loads and internal osmotic pressure, fluid content of intervertebral discs constantly alters causing fluctuations in disc hydration, height, diameter and pressure that govern disc temporal response. This paper reviews and discusses the relevant findings of earlier studies on the disc fluid flow with the aim to understand and remedy discrepancies between in vivo and in vitro observations. New results of finite element model studies are also exploited in order to help identify the likely causes for such differences and underlying mechanisms observed in vitro. In vivo measurements of changes in spinal height and disc fluid content/pressure via stadiometry, magnetic resonance imaging and intradiscal pressure measurements have been carried out. They have demonstrated that the disc volume, fluid content, height and nucleus pressure alter depending to a large extent on prior-current external load conditions. Although the diurnal loading lasts on average nearly twice longer than the subsequent resting (16 vs. 8h), the disc completely recovers its height and volume during the latter period through fluid inflow. In view of much longer periods required to recover disc height and pressure in vitro in ovine, porcine, caprine, bovine and rat discs, concerns have been raised on the fluid inflow through the endplates that might be hampered by clogged blood vessels post mortem. Analyses of discrepancies in the flow-dependent recoveries in vivo and in vitro highlight an excessive fluid content in the latter as a likely cause. To replicate in vivo conditions as closely as possible in vitro, preparation and preconditioning of specimens and/or pressure and osmolarity of the culture media in which specimens are immersed should hence be designed in a manner as to diminish disc hydration level and/or fluid transport.

Correlations between quantitative T2 and T1ρ MRI, mechanical properties and biochemical composition in a rabbit lumbar intervertebral disc degeneration model

Improved diagnostic measures for intervertebral disc degeneration are necessary to facilitate early detection and treatment. The aim of this study was to correlate changes in mechanical and biochemical properties with the quantitative MRI parameters T2 and T1ρ in rabbit lumbar discs using an ex vivo chymopapain digestion model. Rabbit lumbar spinal motion segments from animals less than 6 months of age were injected with 100 μl of saline (control) or chymopapain at 3, 15, or 100 U/ml (n = 5 per group). T2 and T1ρ MRI series were obtained at 4.7T. Specimens were mechanically tested in tension-compression and creep. Normalized nucleus pulposus (NP) water and GAG contents were quantified. Stepwise multiple linear regression was performed to determine which parameters contributed significantly to changes in NP T2 and T1ρ. When all groups were included, multiple regression yielded a model with GAG, compressive modulus, and the creep time constants as variables significantly impacting T2 (multiple r(2)  = 0.64, p = 0.006). GAG and neutral zone (NZ) modulus were identified as variables contributing to T1ρ (multiple r(2)  = 0.28, p = 0.08). When specimens with advanced degeneration were excluded from the multiple regression analysis, T2 was significantly predicted by compressive modulus, τ1, and water content (multiple r(2)  = 0.71, p = 0.009), while no variables were significant predictors in the model for T1ρ. These results indicate that quantitative MRI can detect changes in the mechanical and biochemical properties of the degenerated disc. T2 may be more sensitive to early stage degenerative changes than T1ρ, while both quantitative MRI parameters are sensitive to advanced degeneration. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1382-1388, 2016.

Sensitivity of MRI parameters within intervertebral discs to the severity of adolescent idiopathic scoliosis

PURPOSE

To measure magnetic resonance imaging (MRI) parameters including relaxation times (T₁ ρ, T₂ ), magnetization transfer (MT) and diffusion parameters (mean diffusivity [MD], fractional anisotropy [FA]) of intervertebral discs in adolescents with idiopathic scoliosis, and to investigate the sensitivity of these MR parameters to the severity of the spine deformities.

MATERIALS AND METHODS

Thirteen patients with adolescent idiopathic scoliosis and three control volunteers with no history of spine disease underwent an MRI acquisition at 3T including the mapping of T₁ ρ, T₂ , MT, MD, and FA. The apical zone included all discs within the scoliotic curve while the control zone was composed of other discs. The severity was analyzed through low (<32°) versus high (>40°) Cobb angles. One-way analysis of variance (ANOVA) and agglomerative hierarchical clustering (AHC) were performed.

RESULTS

Significant differences were found between the apical zone and the control zone for T₂ (P = 0.047), and between low and high Cobb angles for T₂ (P = 0.014) and MT (P = 0.002). AHC showed two distinct clusters, one with mainly low Cobb angles and one with mainly high Cobb angles, for the MRI parameters measured within the apical zone, with an accuracy of 0.9 and a Matthews correlation coefficient (MCC) of 0.8. Within the control zone, the AHC showed no clear classification (accuracy of 0.6 and MCC of 0.2).

CONCLUSION

We successfully performed an in vivo multiparametric MRI investigation of young patients with adolescent idiopathic scoliosis. The MRI parameters measured within the intervertebral discs were found to be sensitive to intervertebral disc degeneration occurring with scoliosis and to the severity of scoliosis. J. Magn. Reson. Imaging 2016;44:1123-1131.

Intervertebral disc internal deformation measured by displacements under applied loading with MRI at 3T

PURPOSE

Noninvasive assessment of tissue mechanical behavior could enable insights into tissue function in healthy and diseased conditions and permit the development of effective tissue repair treatments. Measurement of displacements under applied loading with MRI (dualMRI) has the potential for such biomechanical characterization on a clinical MRI system.

METHODS

dualMRI was translated from high-field research systems to a 3T clinical system. Precision was calculated using repeated tests of a silicone phantom. dualMRI was demonstrated by visualizing displacements and strains in an intervertebral disc and compared to T2 measured during cyclic loading.

RESULTS

The displacement and strain precisions were 24 µm and 0.3% strain, respectively, under the imaging parameters used in this study. Displacements and strains were measured within the intervertebral disc, but no correlations were found with the T2 values.

CONCLUSION

The translation of dualMRI to a 3T system unveils the potential for in vivo studies in a myriad of tissue and organ systems. Because of the importance of mechanical behavior to the function of a variety of tissues, it's expected that dualMRI implemented on a clinical system will be a powerful tool in assessing the interlinked roles of structure, mechanics, and function in both healthy and diseased tissues.

T1ρ and T2 mapping of the intervertebral disk: comparison of different methods of segmentation

BACKGROUND AND PURPOSE

Intervertebral disk biochemical composition could be accessed in vivo by T1ρ and T2 relaxometry. We found no studies in the literature comparing different segmentation methods for data extraction using these techniques. Our aim was to compare different manual segmentation methods used to extract T1ρ and T2 relaxation times of intervertebral disks from MR imaging. Seven different methods of partial-disk segmentation techniques were compared with whole-disk segmentation as the reference standard.

MATERIALS AND METHODS

Sagittal T1ρ and T2 maps were generated by using a 1.5T MR imaging scanner in 57 asymptomatic volunteers 20-40 years of age. Two hundred eighty-five lumbar disks were separated into 2 groups: nondegenerated disk (Pfirrmann I and II) and degenerated disk (Pfirrmann III and IV). In whole-disk segmentation, the disk was segmented in its entirety on all sections. Partial-disk segmentation methods included segmentation of the disk into 6, 5, 4, 3, and 1 sagittal sections. Circular ROIs positioned in the nucleus pulposus and annulus fibrosus were also used to extract T1ρ and T2, and data were compared with whole-disk segmentation

RESULTS

In the nondegenerated group, segmentation of ≥5 sagittal sections showed no statistical difference with whole-disk segmentation. All the remaining partial-disk segmentation methods and circular ROIs showed different results from whole-disk segmentation (P < .001). In the degenerated disk group, all methods were statistically similar to whole-disk segmentation. All partial-segmentation methods, including circular ROIs, showed strong linear correlation with whole-disk segmentation in both the degenerated and nondegenerated disk groups.

CONCLUSIONS

Manual segmentation showed strong reproducibility for T1ρ and T2 and strong linear correlation between partial- and whole-disk segmentation. Absolute T1ρ and T2 values extracted from different segmentation techniques were statistically different in disks with Pfirrmann grades I and II.

MR diffusion is sensitive to mechanical loading in human intervertebral disks ex vivo

PURPOSE

To use T2 and diffusion MR to determine the change in the mechanical function of human disks with increased degenerative state.

MATERIALS AND METHODS

Spatial changes in T2 and diffusion were quantified in five cadaveric human lumbar disks under compressive loads. Regression models were used to investigate the relationship between the change in MR parameters and the disk's dynamic and viscoelastic properties.

RESULTS

Compressive loading caused a significant reduction in the disk's mean diffusivity ([11.3 versus 9.7].10(-4) .mm(2) /s, P < 0.001) but little change in T2 (P < 0.05). Diffusivity and T2 were correlated with the disk's dynamic (P < 0.01 and P < 0.05) and long-term viscoelastic (P < 0.05 and P < 0.05) stiffness. Diffusivity but not T2, was correlated with its viscoelastic dampening (r(2) = 0.45, P < 0.01) and instantaneous stiffness (r(2) = 0.44, P < 0.05). Nucleus diffusivity was significantly higher than the annulus's (-21% to -4%, P < 0.01). MR-estimated hydration was correlated with the instantaneous viscoelastic stiffness of the nucleus (r(2) = 0.35, P < 0.05) and the dynamic (r(2) = 0.44, P < 0.05) and long-term viscoelastic (r(2) = 0.42, P < 0.05) stiffness in the annulus. T2 correlated with diffusivity at low load (r(2) = 0.66, P < 0.05), but not at high load.

CONCLUSION

The strong correlations between diffusivity and the rheological assessments of disk mechanics suggest that MR might permit quantitative assessment of disk functional status and structural integrity.

Evaluation of intervertebral disc regeneration with implantation of bone marrow mesenchymal stem cells (BMSCs) using quantitative T2 mapping: a study in rabbits

PURPOSE

The aim of the study was to investigate the curative effects of transplantation of bone marrow mesenchymal stem cells (BMSCs) on intervertebral disc regeneration and to investigate the feasibility of the quantitative T2 mapping method for evaluating repair of the nucleus pulposus after implantation of BMSCs.

METHODS

Forty-eight New Zealand white rabbits were used to establish the lumber disc degenerative model by stabbing the annulus fibrosus and then randomly divided into four groups, i.e. two weeks afterwards, BMSCs or phosphate-buffered saline (PBS) were transplanted into degenerative discs (BMSCs group and PBS group), while the operated rabbits without implantation of BMSCs or PBS served as the sham group and the rabbits without operation were used as the control group. At weeks two, six and ten after operation, the T2 values and disc height indices (DHI) were calculated by magnetic resonance imaging (MRI 3.0 T), and the gene expressions of type II collagen (COL2) and aggrecan (ACAN) in degenerative discs were evaluated by real-time reverse transcription polymerase chain reaction (RT-PCR). T2 values for the nucleus pulposus were correlated with ACAN or COL2 expression by regression analysis.

RESULTS

Cell clusters, disorganised fibres, interlamellar glycosaminoglycan (GAG) matrix and vascularisation were observed in lumber degenerative discs. BMSCs could be found to survive in intervertebral discs and differentiate into nucleus pulposus-like cells expressing COL2 and ACAN. The gene expression of COL2 and ACAN increased during ten weeks after transplantation as well as the T2 signal intensity and T2 value. The DHI in the BMSCs group decreased more slowly than that in PBS and sham groups. The T2 value correlated significantly with the gene expression of ACAN and COL2 in the nucleus pulposus.

CONCLUSIONS

Transplantation of BMSCs was able to promote the regeneration of degenerative discs. Quantitative and non-invasive T2 mapping could be used to evaluate the regeneration of the nucleus pulposus with good sensitivity.

Characterization of metabolites determined by means of 1H HR MAS NMR in intervertebral disc degeneration

Object

The objective of this study is the identification of metabolites by means of ¹H high resolution magic angle spinning nuclear magnetic resonance (¹H HR MAS NMR) spectroscopy and the evaluation of their applicability in distinguishing between healthy and degenerated disc tissues.

Materials and methods

Differences between the metabolic profiles of healthy and degenerated disc tissues were studied by means of ¹H HR MAS NMR. Analysis was performed for 81 disc tissue samples (control samples n = 21, degenerated disc tissue samples n = 60). Twenty six metabolites (amino acids, carbohydrates, and alcohols) were identified and quantified.

Results

The results indicate that the metabolic profile of degenerated discs is characterized by the presence of 2-propanol and the absence of scyllo-inositol and taurine. The concentrations of 2-propanol and lactate increase with age.

Conclusion

PCA analysis of ex vivo ¹H HR MAS NMR data revealed the occurrence of two groups: healthy and degenerative disc tissues. The effects of insufficient nutrient supply of discs, leading to their degeneration and back pain, are discussed.

Electronic supplementary material

The online version of this article (doi:10.1007/s10334-014-0457-0) contains supplementary material, which is available to authorized users.

Screening of hyaluronic acid-poly(ethylene glycol) composite hydrogels to support intervertebral disc cell biosynthesis using artificial neural network analysis

Hyaluronic acid (HA)-poly(ethylene glycol) (PEG) composite hydrogels have been widely studied for both cell delivery and soft tissue regeneration applications. A very broad range of physical and biological properties have been engineered into HA-PEG hydrogels that may differentially affect cellular "outcomes" of survival, synthesis and metabolism. The objective of this study was to rapidly screen multiple HA-PEG composite hydrogel formulations for an effect on matrix synthesis and behaviors of nucleus pulposus (NP) and annulus fibrosus (AF) cells of the intervertebral disc (IVD). A secondary objective was to apply artificial neural network analysis to identify relationships between HA-PEG composite hydrogel formulation parameters and biological outcome measures for each cell type of the IVD. Eight different hydrogels were developed from preparations of thiolated HA (HA-SH) and PEG vinylsulfone (PEG-VS) macromers, and used as substrates for NP and AF cell culture in vitro. Hydrogel mechanical properties ranged from 70 to 489kPa depending on HA molecular weight, and measures of matrix synthesis, metabolite consumption and production and cell morphology were obtained to study relationships to hydrogel parameters. Results showed that NP and AF cell numbers were highest upon the HA-PEG hydrogels formed from the lower-molecular-weight HA, with evidence of higher sulfated glycosaminoglycan production also upon lower-HA-molecular-weight composite gels. All cells formed more multi-cell clusters upon any HA-PEG composite hydrogel as compared to gelatin substrates. Formulations were clustered into neurons based largely on their HA molecular weight, with few effects of PEG molecular weight observed on any measured parameters.

Percutaneous single-fiber reflectance spectroscopy of canine intervertebral disc: is there a potential for in situ probing of mineral degeneration?

BACKGROUND AND OBJECTIVES

Intervertebral disc herniation is a common disease in chondrodystrophic dogs, and a similar neurologic condition also occurs in humans. Percutaneous laser disc ablation (PLDA) is a minimally invasive procedure used increasingly for prevention of disc herniation. Currently, PLDA is performed on thoracolumbar discs with the same laser energy applied regardless of the differing extent of degeneration among mineralized discs. In a previous study performed on 15 normal and 6 degenerated intervertebral discs in chondrodystrophoid canine species, it was demonstrated that percutaneous single-fiber reflectance spectroscopy (SfRS) detected increased light scattering from mineralized intervertebral discs when comparing to normal discs. The objective of this study is to evaluate how SfRS evaluation of mineralized discs in situ fairs with X-ray radiography and computed tomography (CT) diagnoses and if SfRS sensing of the scattering changes correlates with the level of mineral degeneration in nucleus pulposus.

MATERIALS AND METHODS

Percutaneous SfRS was performed on a total of 28 intervertebral discs of three dogs post-mortem, through a 20 gauge spinal needle standard to PLDA. The raw SfRS measurement was normalized to extract a dimension-less spectral intensity profile, from which the average over 600-900 nm was used as the SfRS intensity index to compare among the measured discs. The discs were imaged prior to percutaneous SfRS by radiography and CT, and harvested after percutaneous SfRS for histopathologic examinations.

RESULTS

Five among 10 discs of dog #1, six among 9 discs of dog #2, and nine out of 9 discs of dog #3 were determined by histopathology to have central focal or multi-focal areas of mineralization occupying 5-75% of the examined area of nucleus pulposus. The overall numbers of discs with detectable and undetectable central mineralization were 20 and 8, respectively. CT resulted in one false positive (FP) and four false negative (FN) diagnoses for dog #1, three FP and zero FN diagnoses for dog #2, and zero FP and one FN diagnosis for dog #3. Of the total 28 discs the CT had an overall positive predictive value (PPV) of 78.8% and an overall negative predictive value (NPV) of 44.4%. X-ray radiography gave five FN diagnoses for dog #1, two FN diagnoses for dog #2, and eight FN diagnoses for dog #3. Of the total 28 discs the radiography had an overall PPV of 100% and an overall NPV of 30.4%. The receiver-operating-characteristic analysis of the SfRS measurement was performed on 24 discs that had a central mineralization not greater than 50%. An area-under-curve of 0.6758 infers that the SfRS intensity weakly indicates the level of mineralization.

CONCLUSIONS

Percutaneous SfRS may be useful as an in situ sensing tool for assessing the level of mineral degeneration in intervertebral discs for the prospect of disc-specific dosage adjustment in PLDA.

Detection of extracellular matrix degradation in intervertebral disc degeneration by diffusion magnetic resonance spectroscopy

PURPOSE

To investigate whether diffusion magnetic resonance spectroscopy (MRS) can detect the extracellular matrix (ECM) degradation during intervertebral disc degeneration (IVDD) by the increased mobility of ECM macromolecules such as proteoglycans and collagens.

METHODS

Fresh bovine intervertebral discs were injected with papain solution to induce ECM degradation. The apparent diffusion coefficients (ADCs), T2 values, and contents of ECM macromolecules and water resonances were measured longitudinally in the nucleus pulposus.

RESULTS

The macromolecule ADCs increased drastically at day 1 after papain injection, and continued increasing for 5 days. In contrast, the proteoglycan content exhibited a small and slow decrease after injection while the macromolecule T2 values, water T2, ADC, and content showed slight increase or no change. The protein gel electrophoresis analysis confirmed the gradually increased ECM fragmentation in accordance with the observed macromolecule ADC increases.

CONCLUSION

Diffusion MRS provides a new method to characterize the ECM degradation processes directly and sensitively. Macromolecule ADCs offer a potentially more sensitive and earlier marker for ECM degradation than the proteoglycan content and T2, and water MR properties during early IVDD. Such diffusion approach offers the possibility to directly monitor ECM integrity and degradation processes in vivo at molecular and microstructural levels in both preclinical and clinical settings.

Does normalized signal intensity of cervical discs on T2 weighted MRI images change in whiplash patients?

PURPOSE

We tested the hypothesis that whiplash trauma leads to changes of the signal intensity of cervical discs in T2-weighted images.

METHODS AND MATERIALS

50 whiplash patients (18-65 years) were examined within 48h after motor vehicle accident, and again after 3 and 6 months and compared to 50 age- and sex-matched controls. Signal intensity in ROI's of the discs at the levels C2/3 to C7/T1 and the adjacent vertebral bodies were measured on sagittal T2 weighted MR images and normalized using the average of ROI's in fat tissue. The contrast between discs and both adjacent vertebrae was calculated and disc degeneration was graded by the Pfirrmann-grading system.

RESULTS

Whiplash trauma did not have a significant effect on the normalized signals from discs and vertebrae, on the contrast between discs and adjacent vertebrae, or on the Pfirrmann grading. However, the contrast between discs and adjacent vertebrae and the Pfirrmann grading showed a strong correlation. In healthy volunteers, the contrast between discs and adjacent vertebrae and Pfirrmann grading increased with age and was dependent on the disc level.

CONCLUSION

We could not find any trauma related changes of cervical disc signal intensities. Normalized signals of discs and Pfirrmann grading changed with age and varied between disc levels with the used MR sequence.

Identification of intervertebral disc regeneration with magnetic resonance imaging after a long-term follow-up in patients treated with percutaneous diode laser nucleoplasty: a retrospective clinical and radiological analysis of 14 patients

PURPOSE

The aim of this study was to demonstrate regeneration of intervertebral discs undergoing laser therapy with sagittal relaxation time (T2) mapping after a long-term follow-up.

MATERIALS AND METHODS

Fourteen patients (9 men, 5 women; age range 20-57 years; mean age 36.5 years) treated with percutaneous 908-nm wave-length diode laser nucleoplasty for lumbar disc prolapsus at our clinic between January 2006 and June 2009 were studied. For the application of laser nucleoplasty in the past, patients who did not have central canal stenosis and/or lateral stenosis, sequestered disc fragment, operation scars and bleeding disorders were selected. The intervertebral disc levels undergoing laser therapy were L3-L4 (n = 2) or L4-L5 (n = 12). Patients were called for follow-up visits after a maximum 6-years (n = 2) or a minimum 3 years (n = 3) with a mean of 4.4 years. The patients' clinical status for leg pain was evaluated according to the visual analog scale (VAS) and subsequently, a lumbar magnetic resonance imaging was performed. Sagittal T2 mapping was performed for the intervertebral discs undergoing laser nucleoplasty. We analyzed the relationship between T2 in the regions of interest (ROIs), which is known to correlate with changes in the composition of intervertebral discs, and the degree of degeneration determined using the Pfirrmann grading system and VAS of patients.

RESULTS

On the basis of the evaluation of the results of intervertebral discs in all patients, there was a significant increase in T2 in the anterior NP (ROI 2, +10.3 ms; p < 0.05). A significant increase was noted in T2 in the middle NP (ROI 3, +24.6 ms; p < 0.001). The most significant increase was recorded for the posterior NP (ROI 4, +28.6 ms; p < 0.001). No significant decrease was found in T2 in the anterior and posterior AF (ROI 1, -1.5 ms; p = 0.925; ROI 5, -0.1 ms; p = 0.683). According to the Pfirrmann grading system, disc degeneration grades before laser therapy were recorded as grade III (n = 6) and grade IV (n = 8) whereas disc degeneration grades after laser therapy were found to be grade I (n = 6) and II (n = 8). A significant decrease was noted in Pfirrmann grades of disc degeneration after laser therapy (p < 0.0005).

CONCLUSIONS

In this study, there was a prolongation of T2 indicating regeneration in the nucleus pulposus after laser therapy and these results were found to be consistent with VAS measurements after a long-term follow-up. This study, which demonstrates the quantitative efficacy of laser therapy, indicates that MRG can be more effectively used in the future.

In vivo quantification of T1ρ in lumbar spine disk spaces at 3 T using parallel transmission MRI

OBJECTIVE

T1ρ MRI is an emerging, quantitative imaging modality that has been shown to correlate with proteoglycan content of disk material in vitro at 1.5 T. The purpose of this study is to quantify T1ρ values at all lumbar spine disk space levels at 3 T with parallel-transmission MRI in healthy adult volunteers.

SUBJECTS AND METHODS

Thirty-four subjects (15 men, ages 21-60 years [mean age, 38.4 years]; and 19 women, ages 20-56 years [mean age, 36.5 years]) with no history of back pain or surgery underwent T1ρ MRI of the lumbar spine at 3 T with parallel transmission and sagittal T2-weighted imaging. Mean T1ρ values of all lumbar spine disk space levels were quantified. Linear regression analysis and Spearman rank correlation were performed on age, sex, degenerative grade (Pfirrmann scores), and T1ρ with significance set at p < 0.05 and correlations considered strong for r > 0.7 and moderate for r = 0.5-0.7.

RESULTS

There was a statistically significant moderate negative correlation between T1ρ and subject age at disk space levels L1-2 through L4-5 (inclusive) (p < 0.001) and L5-S1 (p < 0.01). There was a statistically significant difference in T1ρ between all age groups sampled (p < 0.01) and a significant difference between T1ρ and Pfirrmann grades 1-3 (p < 0.01).

CONCLUSION

T1ρ MRI in the lumbar spine with parallel transmission shows signifi-cant negative correlations with age at all disk space levels, which lends support to a potential role for T1ρ as a quantitative, in vivo biomarker of disk degeneration.

MRI signal distribution within the intervertebral disc as a biomarker of adolescent idiopathic scoliosis and spondylolisthesis

Background

Early stages of scoliosis and spondylolisthesis entail changes in the intervertebral disc (IVD) structure and biochemistry. The current clinical use of MR T2-weighted images is limited to visual inspection. Our hypothesis is that the distribution of the MRI signal intensity within the IVD in T2-weighted images depends on the spinal pathology and on its severity. Therefore, this study aims to develop the AMRSID (analysis of MR signal intensity distribution) method to analyze the 3D distribution of the MR signal intensity within the IVD and to evaluate their sensitivity to scoliosis and spondylolisthesis and their severities.

Methods

This study was realized on 79 adolescents who underwent a MRI acquisition (sagittal T2-weighted images) before their orthopedic or surgical treatment. Five groups were considered: low severity scoliosis (Cobb angle ≤50°), high severity scoliosis (Cobb angles >50°), low severity spondylolisthesis (Meyerding grades I and II), high severity spondylolisthesis (Meyerding grades III, IV and V) and control. The distribution of the MRI signal intensity within the IVD was analyzed using the descriptive statistics of histograms normalized by either cerebrospinal fluid or bone signal intensity, weighted centers and volume ratios. Differences between pathology and severity groups were assessed using one- and two-way ANOVAs.

Results

There were significant (p < 0.05) variations of indices between scoliosis, spondylolithesis and control groups and between low and high severity groups. The cerebrospinal fluid normalization was able to detect differences between healthy and pathologic IVDs whereas the bone normalization, which reflects both bone and IVD health, detected more differences between the severities of these pathologies.

Conclusions

This study proves for the first time that changes in the intervertebral disc, non visible to the naked eye on sagittal T2-weighted MR images of the spine, can be detected from specific indices describing the distribution of the MR signal intensity. Moreover, these indices are able to discriminate between scoliosis and spondylolisthesis and their severities, and provide essential information on the composition and structure of the discs whatever the pathology considered. The AMRSID method may have the potential to complement the current diagnostic tools available in clinics to improve the diagnostic with earlier biomarkers, the prognosis of evolution and the treatment options of scoliosis and spondylolisthesis.

Assessment of mechanical properties of isolated bovine intervertebral discs from multi-parametric magnetic resonance imaging

BACKGROUND

The treatment planning of spine pathologies requires information on the rigidity and permeability of the intervertebral discs (IVDs). Magnetic resonance imaging (MRI) offers great potential as a sensitive and non-invasive technique for describing the mechanical properties of IVDs. However, the literature reported small correlation coefficients between mechanical properties and MRI parameters. Our hypothesis is that the compressive modulus and the permeability of the IVD can be predicted by a linear combination of MRI parameters.

METHODS

Sixty IVDs were harvested from bovine tails, and randomly separated in four groups (in-situ, digested-6h, digested-18h, digested-24h). Multi-parametric MRI acquisitions were used to quantify the relaxation times T1 and T2, the magnetization transfer ratio MTR, the apparent diffusion coefficient ADC and the fractional anisotropy FA. Unconfined compression, confined compression and direct permeability measurements were performed to quantify the compressive moduli and the hydraulic permeabilities. Differences between groups were evaluated from a one way ANOVA. Multi linear regressions were performed between dependent mechanical properties and independent MRI parameters to verify our hypothesis. A principal component analysis was used to convert the set of possibly correlated variables into a set of linearly uncorrelated variables. Agglomerative Hierarchical Clustering was performed on the 3 principal components.

RESULTS

Multilinear regressions showed that 45 to 80% of the Young's modulus E, the aggregate modulus in absence of deformation HA0, the radial permeability kr and the axial permeability in absence of deformation k0 can be explained by the MRI parameters within both the nucleus pulposus and the annulus pulposus. The principal component analysis reduced our variables to two principal components with a cumulative variability of 52-65%, which increased to 70-82% when considering the third principal component. The dendograms showed a natural division into four clusters for the nucleus pulposus and into three or four clusters for the annulus fibrosus.

CONCLUSIONS

The compressive moduli and the permeabilities of isolated IVDs can be assessed mostly by MT and diffusion sequences. However, the relationships have to be improved with the inclusion of MRI parameters more sensitive to IVD degeneration. Before the use of this technique to quantify the mechanical properties of IVDs in vivo on patients suffering from various diseases, the relationships have to be defined for each degeneration state of the tissue that mimics the pathology. Our MRI protocol associated to principal component analysis and agglomerative hierarchical clustering are promising tools to classify the degenerated intervertebral discs and further find biomarkers and predictive factors of the evolution of the pathologies.

New treatments and imaging strategies in degenerative disease of the intervertebral disks

Magnetic resonance (MR) imaging in patients with persistent low back pain and sciatica effectively demonstrates spine anatomy and the relationship of nerve roots and intervertebral disks. Except in cases with nerve root compression, disk extrusion, or central stenosis, conventional anatomic MR images do not help distinguish effectively between painful and nonpainful degenerating disks. Hypoxia, inflammation, innervation, accelerated catabolism, and reduced water and glycosaminoglycan content characterize degenerated disks, the extent of which may distinguish nonpainful from painful ones. Applied to the spine, "functional" imaging techniques such as MR spectroscopy, T1ρ calculation, T2 relaxation time measurement, diffusion quantitative imaging, and radio nucleotide imaging provide measurements of some of these degenerative features. Novel minimally invasive therapies, with injected growth factors or genetic materials, target these processes in the disk and effectively reverse degeneration in controlled laboratory conditions. Functional imaging has applications in clinical trials to evaluate the efficacy of these therapies and eventually to select patients for treatment. This report summarizes the biochemical processes in disk degeneration, the application of advanced disk imaging techniques, and the novel biologic therapies that presently have the most clinical promise.

Part 1: Dual-tuned proton/sodium magnetic resonance imaging of the lumbar spine in a rabbit model

STUDY DESIGN

Development of a dual-tuned proton/sodium radiofrequency (RF) coil for magnetic resonance imaging (MRI) of the rabbit spine and quantification of sodium concentration in intervertebral discs.

OBJECTIVE

To develop the dual-tuned proton/sodium MRI of rabbit lumbar spine to investigate proteoglycan matrix content and intervertebral disc degeneration (IDD).

SUMMARY OF BACKGROUND DATA

IDD is a common chronic condition that may lead to back pain, limited activity, and disability. Early-stage IDD involves the loss of proteoglycan matrix and water content in the disc. Sodium MRI is a promising noninvasive technique for quantitative measurement of proteoglycan changes associated with IDD. The combined structural (proton) and biochemical (sodium) MRI facilitates the investigation of morphological and molecular changes associated with degeneration of discs.

METHODS

Multichannel dual-tuned proton/sodium transceiver RF coil of the rabbit spine was developed and optimized at 3T human scanner-8 channels allocated for the sodium coil and 4 channels for the proton coil. High-resolution anatomy proton images of the discs were acquired using turbo spin echo and dual echo steady state sequence. Sodium concentration of the discs was quantified from sodium magnetic resonance (MR) images that were calibrated for signal attenuation because of RF field inhomogeneity, sodium MR relaxation times, and disc thickness. Twelve rabbits (~1-yr old, female, 5.2 ± 0.4 kg) were used for measuring disc sodium concentration.

RESULTS

High-resolution in vivo proton and sodium MR images of rabbit discs (≤2-mm thickness) were successfully obtained using an in-house dual-tuned proton/sodium RF coil at 3T. The total acquisition time for each set of images was approximately 40 minutes. Sodium concentration of normal rabbit lumbar discs was measured at 269.7 ± 6.3 mM, and this measurement was highly reproducible, with 5.3% of coefficient of variation.

CONCLUSION

Sodium concentrations of rabbit lumbar discs were reliably measured using our newly developed dual-tuned multichannel proton/sodium RF coil at 3T.

Part 2: Quantitative proton T2 and sodium magnetic resonance imaging to assess intervertebral disc degeneration in a rabbit model

STUDY DESIGN

Comparison of sodium concentration ([Na]) and proton T2 relaxation time between normal and degenerated discs in a rabbit model.

OBJECTIVE

The purpose of this article was to evaluate quantitative [Na] and T2 characteristics of discs associated with degenerative changes.

SUMMARY OF BACKGROUND DATA

Intervertebral disc degeneration is a common chronic condition that may lead to back pain, limited activity, and disability. Noninvasive imaging method to detect early intervertebral disc degeneration is vital to follow disease progression and guide clinical treatment and management.

METHODS

Dual-tuned magnetic resonance imaging of rabbit discs was performed using 3T. Thirteen rabbits were included in the study; 6 control rabbits (24 normal discs) and 7 rabbits with annular puncture-induced disc degeneration (9 degenerated discs, 19 intact internal-control discs). Dual-tuned magnetic resonance imaging of discs was performed at baseline and 12-week poststab. [Na] and T2 were measured and compared among 3 groups of discs.

RESULTS

The mean [Na] were 274.8 ± 40.2 mM for the normal discs, 247.2 ± 27.7 mM for the internal-control discs, and 190.6 ± 19.1 mM for the degenerated discs. The corresponding T2 for 3 groups were 97.1 ± 12.1 ms, 93.7 ± 11.9 ms, and 79.0 ± 9.1 ms, respectively. The [Na] is highly correlated with the T2 in the degenerated discs (r = 0.90, P < 0.01). The mean percent decreases from the normal to degenerated discs were in 30.6% in [Na] and 18.6% in T2, whereas those from the internal-control to degenerated discs were 22.9% in [Na] and 15.6% in T2.

CONCLUSION

Although both [Na] and T2 changes in discs were associated with the disc-punctured rabbits, greater change in [Na] is observed at 12-week poststab compared with T2 change. Because T2 and [Na] reflect different disc properties, performing both imaging under same condition will be helpful in the evaluation of disc degeneration.

Quantitative analysis of lumbar intervertebral disc abnormalities at 3.0 Tesla: value of T(2) texture features and geometric parameters

T(2) relaxation time mapping provides information about the biochemical status of intervertebral discs. The present study aimed to determine whether texture features extracted from T(2) maps or geometric parameters are sensitive to the presence of abnormalities at the posterior aspect of lumbar intervertebral discs, i.e. bulging and herniation. Thirty-one patients (21 women and 10 men; age range 18-51 years) with low back pain were enrolled. MRI of the lumbar spine at 3.0 Tesla included morphological T(1) - and T(2) -weighted fast spin-echo sequences, and multi-echo spin-echo sequences that were used to construct T(2) maps. On morphological MRI, discs were visually graded into 'normal', 'bulging' or 'herniation'. On T(2) maps, texture analysis (based on the co-occurrence matrix and wavelet transform) and geometry analysis of the discs were performed. The three T(2) texture features and geometric parameters best-suited for distinguishing between normal discs and discs with bulging or herniation were determined using Fisher coefficients. Statistical analysis comprised ANCOVA and post hoc t-tests. Eighty-two discs were classified as 'normal', 49 as 'bulging' and 20 showed 'herniation.' The T(2) texture features Entropy and Difference Variance, and all three pre-selected geometric parameters differed significantly between normal and bulging, normal and herniated, and bulging and herniated discs (p < 0.05). These findings suggest that T(2) texture features and geometric parameters are sensitive to the presence of abnormalities at the posterior aspect of lumbar intervertebral discs, and may thus be useful as quantitative biomarkers that predict disease.

Assessment of glycosaminoglycan distribution in human lumbar intervertebral discs using chemical exchange saturation transfer at 3 T: feasibility and initial experience

Recent studies have proposed that glycosaminoglycan chemical exchange saturation transfer (gagCEST) is associated with a loss of glycosaminoglycans (GAGs), which may be an initiating factor in intervertebral disc (IVD) degeneration. Despite its promising potential, this application has not been reported in human in vivo IVD studies because of the challenges of B(0) magnetic field inhomogeneity in gagCEST. This study aimed to evaluate the feasibility of quantifying CEST values in IVDs of healthy volunteers using a clinical 3 T scanner. A single-slice turbo spin echo sequence was used to quantify the CEST effect in various GAG phantoms and in IVDs of 12 volunteers. The phantom results indicated high correlation between gagCEST and GAG concentrations (R(2)  = 0.95). With optimal B(0) inhomogeneity correction, in vivo CEST maps of IVDs showed robust contrast between the nucleus pulposus (NP) and the annulus fibrosus (AF) (p < 0.01), as well as higher signal in the central relative to the peripheral NP. In addition, a trend of decreasing CEST values from upper to lower disc levels was evident in NP. Our results demonstrate that in vivo gagCEST quantification in human lumbar IVDs is feasible at 3 T in combination with successful B(0) inhomogeneity correction, but without significant hardware modifications. Our initial findings suggest that it would be worthwhile to perform direct correlation studies between CEST and GAGs using cadaver samples, and to extend this novel technique to studies on patients with degenerative discs to better understand its distinct imaging features relative to conventional techniques.

Quantitative T2 evaluation at 3.0T compared to morphological grading of the lumbar intervertebral disc: a standardized evaluation approach in patients with low back pain

BACKGROUND

The purpose of our investigation was to compare quantitative T2 relaxation time measurement evaluation of lumbar intervertebral discs with morphological grading in young to middle-aged patients with low back pain, using a standardized region-of-interest evaluation approach.

PATIENTS AND METHODS

Three hundred thirty lumbar discs from 66 patients (mean age, 39 years) with low back pain were examined on a 3.0T MR unit. Sagittal T1-FSE, sagittal, coronal, and axial T2-weighted FSE for morphological MRI, as well as a multi-echo spin-echo sequence for T2 mapping, were performed. Morphologically, all discs were classified according to Pfirrmann et al. Equally sized rectangular regions of interest (ROIs) for the annulus fibrosus were selected anteriorly and posteriorly in the outermost 20% of the disc. The space between was defined as the nucleus pulposus. To assess the reproducibility of this evaluation, inter- and intraobserver statistics were performed.

RESULTS

The Pfirrmann scoring of 330 discs showed the following results: grade I: six discs (1.8%); grade II: 189 (57.3%); grade III: 96 (29.1%); grade IV: 38 (11.5%); and grade V: one (0.3%). The mean T2 values (in milliseconds) for the anterior and the posterior annulus, and the nucleus pulposus for the respective Pfirrmann groups were: I: 57/30/239; II: 44/67/129; III: 42/51/82; and IV: 42/44/56. The nucleus pulposus T2 values showed a stepwise decrease from Pfirrmann grade I to IV. The posterior annulus showed the highest T2 values in Pfirrmann group II, while the anterior annulus showed relatively constant T2 values in all Pfirrmann groups. The inter- and intraobserver analysis yielded intraclass correlation coefficients (ICC) for average measures in a range from 0.82 (anterior annulus) to 0.99 (nucleus).

CONCLUSIONS

Our standardized method of region-specific quantitative T2 relaxation time evaluation seems to be able to characterize different degrees of disc degeneration quantitatively. The reproducibility of our ROI measurements is sufficient to encourage the use of this method in future investigations, particularly for longitudinal studies.