T2* mapping of ovine intervertebral discs: Normative data for cervical and lumbar spine

Morphometric, Biomechanical and Histologic Assessment of Physiologic Ovine Cervical Intervertebral Disc: An Experimental Study and Brief Literature Review

The ovine cervical spine model has been established as a representative model of the human cervical spine in the current literature, and is the most commonly used large animal model in studies investigating pathogenesis and treatment strategies for intervertebral disc (IVD) degeneration. However, existing data regarding morphometry, biomechanical profiles and the microscopic features of a physiological ovine cervical IVD remain scarce. Hence, the aim of this study was to perform a multimodal morphometric, biomechanical and histologic evaluation of a normal ovine cervical IVD. For this purpose, nine ovine cervical IVDs were harvested from three female sheep, and subjected to morphometrical, biomechanical and histologic analyses. The biomechanical assessment included the performance of cyclic compression, creepand compressive strength tests in a controlledlaboratory environment. Histological evaluation was performed using hematoxylin-eosin, Masson's trichrome and Alcian blue staining. The results from the morphometric analysis showed that the range of disc heights was 4-9 mm in all surfaces, featuring a constant increase from cranial to caudal levels. Biomechanical evaluation revealed that cyclic loading for 20 cycles was necessary for preconditioning so that the repeatability of the force-displacement hysteresis response is present. The critical failure point was defined at 15.5 MPa, whereas Young's modulus of elasticity was 1.2 MPa. The histologic assessment demonstrated the presence of a concentric arrangement of collagen lamellae in external annulus fibrosus, along with the sparsely organized internal nucleus pulposus. Ovine cervical IVD represents a complex structure with distinct features that should be considered by researchers in this field in order to optimize the reliability and validity of testing results.

Preclinical in vivo animal models of intervertebral disc degeneration. Part 1: A systematic review

Intervertebral disc degeneration (IVDD), a widely recognized cause of lower back pain, is the leading cause of disability worldwide. A myriad of preclinical in vivo animal models of IVDD have been described in the literature. There is a need for critical evaluation of these models to better inform researchers and clinicians to optimize study design and ultimately, enhance experimental outcomes. The purpose of this study was to conduct an extensive systematic literature review to report the variability of animal species, IVDD induction method, and experimental timepoints and endpoints used in in vivo IVDD preclinical research. A systematic literature review of peer-reviewed manuscripts featured on PubMed and EMBASE databases was conducted in accordance with PRISMA guidelines. Studies were included if they reported an in vivo animal model of IVDD and included details of the species used, how disc degeneration was induced, and the experimental endpoints used for analysis. Two-hundred and fifty-nine (259) studies were reviewed. The most common species, IVDD induction method and experimental endpoint used was rodents(140/259, 54.05%), surgery (168/259, 64.86%) and histology (217/259, 83.78%), respectively. Experimental timepoint varied greatly between studies, ranging from 1 week (dog and rodent models), to >104 weeks in dog, horse, monkey, rabbit, and sheep models. The two most common timepoints used across all species were 4 weeks (49 manuscripts) and 12 weeks (44 manuscripts). A comprehensive discussion of the species, methods of IVDD induction and experimental endpoints is presented. There was great variability across all categories: animal species, method of IVDD induction, timepoints and experimental endpoints. While no animal model can replicate the human scenario, the most appropriate model should be selected in line with the study objectives to optimize experimental design, outcomes and improve comparisons between studies.

Ultrashort time-to-echo T2* and T2* relaxometry for evaluation of lumbar disc degeneration: a comparative study

Background

To compare potential of ultrashort time-to-echo (UTE) T2* mapping and T2* values from T2*-weighted imaging for assessing lumbar intervertebral disc degeneration (IVDD),with Pfirrmann grading as a reference standard.

Methods

UTE-T2* and T2* values of 366 lumbar discs (L1/2-L5/S1) in 76 subjects were measured in 3 segmented regions: anterior annulus fibrosus, nucleus pulposus (NP), and posterior annulus fibrosus. Lumbar intervertebral discs were divided into 3 categories based on 5-level Pfirrmann grading: normal (Pfirrmann grade I),early disc degeneration (Pfirrmann grades II-III), and advanced disc degeneration (Pfirrmann grades IV-V). Regional differences between UTE-T2* and T2* relaxometry and correlation with degeneration were statistically analyzed.

Results

UTE-T2* and T2*value correlated negatively with Pfirrmann grades (P < 0.001). In NP, correlations with Pfirrmann grade were high with UTE-T2* values (r =  − 0.733; P < 0.001) and moderate with T2* values (r = -0.654; P < 0.001). Diagnostic accuracy of detecting early IVDD was better with UTE-T2* mapping than T2* mapping (P < 0.05),with receiver operating characteristic analysis area under the curve of 0.715–0.876.

Conclusions

UTE-T2* relaxometry provides another promising magnetic resonance imaging sequence for quantitatively evaluate lumbar IVDD and was more accurate than T2*mapping in the earlier stage degenerative process.

Different responses of cervical intervertebral disc caused by low and high virulence bacterial infection: a comparative study in rats

The aims of this study were to investigate the outcomes of low- and high-virulence bacterial cervical intervertebral discs (IVDs) infection and its association with cervical IVDs degeneration in rats. A total of 75 clean grade male rats were used to establish the corresponding animal models of low and high virulent bacterial cervical disc infection via an anterior cervical approach, with injection of Propionibacterium acnes (P. acnes) and Staphylococcus epidermidis (S. epidermidis) with a 29 G needle to cervical IVDs. Specimens were collected for evaluation of Blood routine (Blood-RT), histological staining, and gene expression assays after a magnetic resonance imaging (MRI) scan. There were no statistical differences in all groups in white blood cells (WBC) at 2 and 6 weeks postoperatively (P = 0.136). The highest percentage of neutrophils was found in the S. epidermidis group at 2 weeks postoperatively (P = 0.043). MRI and histology showed that at 6 weeks postoperatively, the puncture group and P. acnes group had similar disc degeneration. In the S. epidermidis group, the disc and subchondral bone structure had been destroyed and bony fusion had occurred after the discitis. The upregulation of pro-inflammatory factor expression had the strongest effect of S. epidermidis on the early stage, while the upregulation in the puncture and P. acnes groups was more persistent. P. acnes infection of the cervical IVDs can lead to degenerative changes, whereas S. epidermidis infection leads to the manifestation of septic discitis. The correlation between P. acnes infection and cervical IVDs degeneration found in clinical studies was confirmed.

Patterns of Intervertebral Disk Alteration in Asymptomatic Elite Rowers: A T2* MRI Mapping Study

Background:

Repetitive loading of the back puts elite rowers at risk for acute and chronic back injuries.

Hypothesis:

That asymptomatic elite rowers would demonstrate characteristic intervertebral disk (IVD) alterations on T2* magnetic resonance imaging (MRI) mapping compared with asymptomatic nonrowers.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

This study included 20 asymptomatic elite rowers (mean age, 23.4 ± 3.03 years; 9 women, 11 men) studied at 2 different times, once before (t₁) and once after (t₂) the competition phase. MRI including T2* mapping was performed on a 3-T scanner. The authors derived normative T2* data from a previous study on 40 asymptomatic volunteers (20 men, 20 women) who were not competitive rowers; based on complete T2* data sets, 37 controls were included. T2* values were compared between groups in 4 lumbar IVDs, and midsagittal T2* values were compared in 5 zones: anterior annulus fibrosus (AF), anterior nucleus pulposus (NP), central NP, posterior NP, and posterior AF. The Pfirrmann grade was used for morphological assessment of disk degeneration. Statistical analysis was conducted using the Mann-Whitney U test, Wilcoxon matched-pairs test, and Spearman rank correlation coefficient.

Results:

Lower T2* values were noted in the rower group compared with the controls (37.08 ± 33.63 vs 45.59 ± 35.73 ms, respectively; P < .001). The intersegmental comparison revealed lower mean T2* values among rowers (P ≤ .027 for all). The interzonal comparison indicated significantly lower mean T2* values for the rowers in all zones except for the anterior NP (P ≤ .008 for all). Lower mean T2* values were observed for the rowers at t₁ versus t₂ (39.25 ± 36.19 vs 43.97 ± 38.67 ms, respectively; P = .008). The authors noted a higher level of IVD damage according to Pfirrmann assessment in the rower cohort (P < .001); the Pfirrmann grade distributions of rowers versus controls, respectively, were as follows: 51.3% versus 73.7% (grade 1), 20.5% versus 19.5% (grade 2), 21.8% versus 6.8% (grade 3), 5.1% versus 0% (grade 4), and 1.3% versus 0% (grade 5). The authors also noted a correlation between low T2* and high Pfirrmann grade at t₁ (r =–0.48; P < .001) and t₂ (r =–0.71; P < .001).

Conclusion:

The cohort of elite rowers revealed more degenerative IVD changes compared with controls. The T2* values suggest that repetitive loading of the spine has demonstrable short-term and possibly permanent effects on the lumbar IVD.

Comparison of MRI T1, T2, and T2* mapping with histology for assessment of intervertebral disc degeneration in an ovine model

An easy, reliable, and time-efficient standardized approach for assessing lumbar intervertebral disc (IVD) degeneration with relaxation times measurements in pre-clinical and clinical studies is lacking. This prospective study aims to determine the most appropriate method for lumbar IVD degeneration (IDD) assessment in sheep by comparing three quantitative MRI sequences (variable-flip-angle T1 mapping, and multi-echo T2 and T2* mapping), correlating them with Pfirrmann grading and histology. Strong intra- and interrater agreements were found for Nucleus pulposus (NP) regions-of-interest (ROI). T1, T2, and T2* mapping correlated with Pfirrmann grading and histological scoring (p < 0.05) except for the most ventral rectangular ROI on T2 maps. Correlations were excellent for all of the T1 ROIs and the T2* NP ROIs. Highly significant differences in T1 values were found between all Pfirrmann grades except between grades I/II and between grades III/IV. Significant differences were identified in the T2 and the T2* values between all grades except between grades I/III. T1, T2, and T2* relaxation times measurements of the NP are an accurate and time-efficient tool to assess lumbar IDD in sheep. Variable-flip-angle T1 mapping may be further considered as a valuable method to investigate IDD and to assess the efficacy of regenerative treatments in longitudinal studies.

A comprehensive tool box for large animal studies of intervertebral disc degeneration

Preclinical studies involving large animal models aim to recapitulate the clinical situation as much as possible and bridge the gap from benchtop to bedside. To date, studies investigating intervertebral disc (IVD) degeneration and regeneration in large animal models have utilized a wide spectrum of methodologies for outcome evaluation. This paper aims to consolidate available knowledge, expertise, and experience in large animal preclinical models of IVD degeneration to create a comprehensive tool box of anatomical and functional outcomes. Herein, we present a Large Animal IVD Scoring Algorithm based on three scales: macroscopic (gross morphology, imaging, and biomechanics), microscopic (histological, biochemical, and biomolecular analyses), and clinical (neurologic state, mobility, and pain). The proposed algorithm encompasses a stepwise evaluation on all three scales, including spinal pain assessment, and relevant structural and functional components of IVD health and disease. This comprehensive tool box was designed for four commonly used preclinical large animal models (dog, pig, goat, and sheep) in order to facilitate standardization and applicability. Furthermore, it is intended to facilitate comparison across studies while discerning relevant differences between species within the context of outcomes with the goal to enhance veterinary clinical relevance as well. Current major challenges in pre-clinical large animal models for IVD regeneration are highlighted and insights into future directions that may improve the understanding of the underlying pathologies are discussed. As such, the IVD research community can deepen its exploration of the molecular, cellular, structural, and biomechanical changes that occur with IVD degeneration and regeneration, paving the path for clinically relevant therapeutic strategies.

T2* Mapping of the Adult Intervertebral Lumbar Disc: Normative Data and Analysis of Diurnal Effects

In this prospective study, we sought to establish normative data for T2* analysis of lumbar intervertebral discs (IVDs). Further, potential diurnal effects regarding T2* relaxometry of the lower spine were examined. Lumbar IVDs of young, healthy, adult men (n = 20) and women (n = 20; mean age = 24.5 ± 2.9 years) were assessed. Magnetic resonance imaging including T2* mapping was performed on a 3-T scanner. Mid-sagittal T2* values were obtained in five regions: anterior annulus fibrosus (AF), anterior nucleus pulposus (NP), central NP, posterior NP, and posterior AF. Zonal and segmental differences, as well as diurnal variations between the T2* analysis in the morning and the evening and effects of unloading, were analyzed. Discs with signs of degeneration on morphological images or imaging artifacts were excluded. We noted a zonal and segmental T2* distribution with high values in the NP, low T2* values in the AF and a T2* increase towards the caudal NP. We observed no diurnal differences between the mean T2* values in the morning and in the evening (p = 0.748). The effect of unloading the spine was low (maximum T2* difference between four measurements = 13.6 ms; significant difference noted only between the 0 and 15-min measurement). The T2* values obtained in this study will serve as normative values for future T2* measurements. There are no diurnal influences, and we suggest that unloading of the spine has no demonstrable effect after 30 min on the T2* results. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1956-1962, 2019.

A comparative study of diffusion kurtosis imaging and T2* mapping in quantitative detection of lumbar intervertebral disk degeneration

PURPOSE

To assess the feasibility of diffusion kurtosis imaging (DKI) for diagnosing lumbar intervertebral disk degeneration (IDD) and to compare the potential of DKI and T2* mapping in the diagnosis of early IDD.

METHODS

Sagittal T2WI, DKI, and T2* mapping were performed in 75 subjects with 375 lumbar intervertebral disks at a 3.0-T MRI. DKI-related parameters including mean kurtosis (MK), mean diffusivity (MD), fractional anisotropy (FA), and T2* values were calculated for each disk which was segmented into three regions: nucleus pulposus (NP), anterior annulus fibrosus (AAF), and posterior annulus fibrosus (PAF).

RESULTS

MK and FA were positively correlated with Pfirrmann grade (all P < 0.001). MD and T2* were negatively correlated with Pfirrmann grade (all P < 0.001) except for T2* value of AAF (r = 0.087, P > 0.05). MK and FA values increased, while MD and T2* values decreased with age. No statistical significance was found between men and women (P > 0.05). Cephalic lumbar disks (L1/L2 and L2/L3) got lower MK and FA values than caudal lumbar disks (L4/L5 and L5/S1) (all P < 0.05), while cephalic lumbar disks got higher MD value than caudal lumbar disks (all P < 0.05). ROC analysis demonstrated that MK, MD, and FA showed significantly higher diagnostic accuracies than T2*, especially in NP and PAF.

CONCLUSIONS

DKI can be used to assess human lumbar IDD. And DKI was more sensitive to the quantitative detection of early lumbar IDD than T2* mapping. These slides can be retrieved under Electronic Supplementary Material.

Correlation between T2* (T2 star) relaxation time and cervical intervertebral disc degeneration: An observational study

PURPOSE

To demonstrate the potential benefits of T2 relaxation time of intervertebral discs (IVDs) regarding the detection and grading of degenerative disc disease using 3.0-T magnetic resonance imaging (MRI) in a clinical setting.

MATERIALS AND METHODS

Cervical sagittal T2-weighted, T2 relaxation MRI was performed at 3.0-T in 61 subjects, covering discs C2-3 to C6-7. All discs were morphologically assessed based on the Pfirrmann grade, and regions of interests (ROIs) were drawn over the T2 mapping. Receiver operating characteristic (ROC) analysis was performed among grades to determine the cut-off values.

RESULTS

Cervical intervertebral discs (IVDs) of patients were commonly determined to be at Pfirrmann grades III to V. The nucleus pulposus (NP) values did not differ significantly between sexes at the same anatomic level (P > 0.05). In the NP, the T2 values tended to decrease with increasing grade (P < 0.000), and a significant difference was found in the T2 values between grades I to V (P < 0.05). T2 values based on disc degeneration level classification were as follows: grade I (>30 milliseconds), grade II (24.55-29.99 milliseconds), grade III (21.65-24.54 milliseconds), grade IV (18.35-21.64 milliseconds), and grade V (<18.34 milliseconds).

CONCLUSION

Our standardized method of region-specific quantitative T2 relaxation time evaluation seems capable of characterizing different degrees of disc degeneration quantitatively. The T2 values obtained in these cervical IVDs may serve as baseline values for future T2 measurements in both healthy and degenerated cervical discs.