Introduction The IVD cartilaginous endplate (CEP) is a 450 mm to 800 mm thick layer of hyaline cartilage,2 which functions as a mechanical barrier between the pressurized nucleus pulposus and the vertebral endplate, and as a gateway for nutrient diffusion to the avascular disk.1–3 With age and degeneration, the CEP becomes thinner, calcifies, and may have reduced porosity,4 and it has been implicated as a contributor to degeneration.1–3 As the CEP is not well imaged on MRI, key geometric parameters of the CEP have not been obtained noninvasively. Thus, the objective of this study was to measure geometric properties of the CEP with MRI. Materials and Methods Lumbar motion segments ( n = 24), from 11 human cadavers (age 64.9 ± 10.0 years) were imaged on a Siemens 7T MRI scanner using a custom RF coil. Disk degeneration was graded via mid-sagittal T2 mapping. Full volume imaging of each disk at 200 mm isotropic resolution was achieved via 3D FLASH (TR/TE = 9/3.7 ms) in 6 minutes (Fig. 1). Geometric parameters (area, circumference, anterior-posterior width, lateral width) were measured in the axial and mid-sagittal planes for both the CEP and the entire disk using OsiriX software. Disk height was measured using custom-written Matlab code.5 Evaluation of CEP thickness was done on a mid-sagittal image of each disc. Semiautomated image analysis was conducted using custom-written Matlab code in which signal intensity profiles across the CEP thickness were captured at the center of the CEP and at ± ¼ and ± ¾ of its A-P length. Comparisons between superior and inferior CEP geometry were established using paired, two-tailed t-tests ( p < 0.05). Data, except thickness, was normalized by dividing CEP geometry by its corresponding disk geometry to account for differences in disk sizes between levels. A one-way ANOVA was used to evaluate differences between disk level and CEP geometry. CEP thickness measurements were evaluated using a two-way ANOVA with repeated measures, where the factors were disk level and anterior-posterior disk location. A posthoc Bonferonni test was performed when significance was detected. Linear regression analysis was performed to compare CEP geometry with T2 mapping values and subject age. Results Directly measured whole disk and CEP geometry for each level are provided in the Table. The mean CEP thickness in the mid-sagittal plane across all disk levels and locations was 0.50 ± 0.20 mm. No significant differences were found in CEP thickness with respect to the superior or inferior endplate or disk level ( p > 0.2). There was no significant difference in CEP A-P width, lateral width, or circumference area with respect to superior/inferior location ( p > 0.7) or disk level ( p > 0.6) except between L1-L2 and L4-L5 ( p < 0.05) (Fig. 2A-C). L1-L2 A-P width, lateral width, and circumference area were larger than in L4-L5 by 14, 18, and 28%, respectively. CEP thickness varied significantly with respect to anterior-posterior location for every level ( p < 0.005) (Fig. 2D). The minimum thickness was at the center of the disk (superior = 0.39 ± 0.10 mm, inferior = 0.38 ± 0.11 mm). The thickness at the center was 19.9 and 42.4% less than that of the ± ¼ and ± ¾ A-P locations. In the linear regression analysis, no correlation was found between CEP geometries and T2 mapping or age. Conclusion This study noninvasively visualized the CEP morphology and quantified CEP circumference, area, A-P width, lateral width, and thickness using an MRI 3D FLASH sequence. The measured disk geometries in this study agree well with previous literature.5,6 CEP geometries were not linearly correlated with age or T2 mapping, which is correlated with disk degenerative grade. The lack of correlation between CEP geometries and either age or T2 mapping as a marker of degeneration was not completely expected, since it has been discussed that CEP thickness decreases with degeneration.1–3 Additional data and increased sample size may provide more insight into the potential role of the CEP in the degenerative cascade. Acknowledgment NIH grant R01 AR050052. I confirm having declared any potential conflict of interest for all authors listed on this abstract Yes Disclosure of Interest None declared Urban JPG. Arthritis Research Therapy 2003;5:120 Roberts S. Spine 1989;14:166 Moore RJ. European Spine Journal 2000;9:92 Bernick S, Spine 1982;7:97 O'Connell GD. Spine 2007:32:328 Elliott DM. Spine 2004;29:713

The 3D shape of the intervertebral disc (IVD) is modeled in this work from a population of samples. Heretofore, 3D models of the disc have been created from individual samples only. L3/L4 discs were segmented from 14 magnetic resonance images. The mean shape was calculated using a signed distance function representation, and principal components analysis was used to re-express the residual variability with an orthonormal basis. The first basis vector, which represents lateral bulging of the disc, expresses the majority of the population's shape variation. This vector was also significantly correlated with Pfirrmann grade (p<;0.01), a measure of disc degeneration. The IVD shape model can thus be used to generate an average IVD shape for the population, as well as shapes for specific degenerative grades.

Introduction: Advanced Normalization Tools (ANTs) is an image registration program that has been validated for analysis of several tissues, but not previously applied to the disc. The objectives of this study were to optimize ANTs for disc image registration and to validate ANTs strain measurements by comparison with Vic2D, a commercially available software previously applied to quantify disc strain, before and after nucleotomy. Methods: Human lumbar motion segments (n=5) underwent 1000 N compression before and after nucleotomy and MR images were acquired in a reference and deformed state. Image overlap statistics were used to select mapping parameters, and strain analysis was used to select the optimal number of splines. Once the optimal registration method was selected (elastic mapping, 0.01 outlier, 6×6 splines), axial and radial strains were measured in the AAF, PAF, and IVD. Results: Excellent overlap statistics were achieved. No significant differences were found for strains calculated with ANTs and Vic2D (p≥0.35). With nucleotomy, the axial compressive strain increased in the PAF (p=0.04) and there was a trend towards decrease in radial strain (p=0.07). Discussion: ANTs is an accurate and powerful tool to calculate disc strains from MR images.

INTRODUCTION Intervertebral disc degeneration is considered one of the key causes of back pain. The intervertebral disc has three major structural components: nucleus pulposus, annulus fibrosus, and cartilaginous endplates (CEP). Many studies have been reported on anatomy, mechanics, and chemistry of the nucleus and annulus [1-4] while very little is known about the MR characteristics of the CEP because it is very thin (~600μm) and difficult to image and recognize on routine MR exams (e.g., Fig. 3d: mid-sagittal T2-weighted scan for Pfirrmann grading). Functionally, the CEP is considered a gateway for nutrient transport from blood vessels into the central disc [2]. As degeneration progresses, the CEP becomes sclerotic and loses contact with blood vessels, providing less nutrition to the disc as well as to the CEP itself. As a result, proteoglycan content decreases within the disc, which in turn, causes a loss of hydration and osmotic pressure of the disc matrix [3,4]. The loss of the CEP is also associated with calcification and rupture (e. g. Schmorl’s nodes, a protrusion of disc into the adjacent vertebral body). Therefore, visualizing CEP or measuring water content of the CEP is important for the evaluation of disc degeneration. Recently, ex-vivo MR imaging of the CEP has been reported [5], however, imaging the CEP in-vivo is challenging due to the CEP’s thinness and low SNR, and is limited by the subject’s tolerance and movement. In this study, we have used a 3D FLASH sequence to visualize the CEP, first in specimens and then in volunteers, in order to assess the feasibility of MRI characterization of the CEP for in-vivo studies of disc degeneration.

INTRODUCTION The intervertebral disc (IVD) undergoes more extensive structural and compositional changes with age and degeneration than any other musculoskeletal tissue. With age and degeneration, tears appear within discs due to limiting diffusion of nutrients into the disc, alteration of chemical composition, and injuries. Disc tears are associated with low back pain [1,2]. The current clinical understanding of tears is that tears radiating to the outer third of the annulus fibrosis (AF) may cause low back pain [1]. However, detection of tears is difficult and quantification of their characteristics is not possible. Radial tears are often visualized under discography, however their location and orientation is difficult to determine [3]. Additionally, discography is an invasive procedure and involves exposure to radiation. The literature is replete with cadaveric studies using histology or gross sections showing a high incidence of AF tears [4,5]. However, shapes and sizes of tears are intricate, and even multiple histological sections cannot reconstruct the complex 3D tear geometry. As a result, quantitative characteristics of the 3D human AF tear remain largely unknown. The objective of this study is to provide a non-invasive MR technique for 3D visualization, measurement, and the ability to precisely locate disc tear orientation within a disc.