Purpose The cartilaginous endplate (CEP) is a thin layer of hyaline cartilage positioned between the vertebral endplate and nucleus pulposus (NP) that functions both as a mechanical barrier and as a gateway for nutrient transport into the disc. Despite its critical role in disc nutrition and degeneration, the morphology of the CEP has not been well characterized. The objective of this study was to visualize and report observations of the CEP three-dimensional morphology, and quantify CEP thickness using an MRI FLASH (fast low-angle shot) pulse sequence. Methods MR imaging of ex vivo human cadaveric lumbar spine segments (N = 17) was performed in a 7T MRI scanner with sequence parameters that were selected by utilizing highresolution T1 mapping, and an analytical MRI signal model to optimize image contrast between CEP and NP. The CEP thickness at five locations along the mid-sagittal AP direction (center, 5 mm, 10 mm off-center towards anterior and posterior) was measured, and analyzed using two-way ANOVA and a post hoc Bonferonni test. For further investigation, six in vivo volunteers were imaged with a similar sequence in a 3T MRI scanner. In addition, decalcified and undecalcified histology was performed, which confirmed that the FLASH sequence successfully detected the CEP. Results CEP thickness determined by MRI in the midsagittal plane across all lumbar disc levels and locations was 0.77 ± 0.24 mm ex vivo. The CEP thickness was not different across disc levels, but was thinner toward the center of the disc. Conclusions This study demonstrates the potential of MRI FLASH imaging for structural quantification of the CEP geometry, which may be developed as a technique to evaluate changes in the CEP with disc degeneration in future applications.
Study Design Prospective MRI study of LBP patients requiring discography as part of their routine clinical diagnoses and asymptomatic age-matched volunteers. Objective To determine whether T1ρ MRI and discography opening pressure are quantitative biomarkers of disc degeneration in LBP patients and in asymptomatic volunteers. Summary of Background Data Disc degenerative disease (DDD), a common cause of low back pain (LBP), is related to the patient’s prognosis and serves as a target for therapeutic interventions. However, there are few quantitative measures in the clinical setting. Discography opening pressure (OP) and T1ρ MRI are potential biomarkers of DDD related to biochemical composition the intervertebral disc (IVD). Methods The Institutional Review Board approved all experiments and informed consent was provided by each subject. Patients being treated for LBP (n=17, 68 levels, mean age 44±6 years, range 30–53) and control (CTL) subjects (n=11, 44 levels, mean age 43±17, range 22–76) underwent T1ρ and T2 MRI on a Siemens 3T Tim Trio clinical scanner. The LBP patients also received multi-level provocative discography before their MRI. Opening Pressure (OP) was recorded as the pressure when fluid first enters the nucleus of the IVD. Results T1ρ was significantly lower in the painful discs (55.3ms±3.0 ms, mean ± std. error) from control (92.0±4.9 ms, p<0.001) and non-painful discs (83.6±3.2 ms, p<0.001). Mean OP for the painful discs (11.8±1.0 psi, mean ± std. error) was significantly lower than non-painful discs (19.1±0.7 psi, p<0.001). Both T1ρ and OP correlated moderately with Pfirrmann degenerative grade. ROC area under the curve was 0.91 for T1ρ MRI and 0.84 for OP for predicting painful discs. Conclusions T1ρ and OP are quantitative measures of degeneration that are consistent across both control subjects and LBP patients. A significant and strong correlation exists between T1ρ values and in vivo OP measurements obtained by discography in LBP patients.
Study objectives were to develop, validate, and apply a method to measure threedimensional (3D) internal strains in intact human discs under axial compression. A custom-built loading device applied compression and permitted load-relaxation outside of the magnet while also maintaining compression and hydration during imaging. Strain was measured through registration of 300 lm isotropic resolution images. Excellent registration accuracy was achieved, with 94% and 65% overlap of disc volume and lamellae compared to manual segmentation, and an average Hausdorff, a measure of distance error, of 0.03 and 0.12 mm for disc volume and lamellae boundaries, respectively. Strain maps enabled qualitative visualization and quantitative regional annulus fibrosus (AF) strain analysis. Axial and circumferential strains were highest in the lateral AF and lowest in the anterior and posterior AF. Radial strains were lowest in the lateral AF, but highly variable. Overall, this study provided new methods that will be valuable in the design and evaluation surgical procedures and therapeutic interventions.
Intervertebral disc mechanics are affected by both disc shape and disc degeneration, which in turn each affect the other; disc mechanics additionally have a role in the etiology of disc degeneration. Finite element analysis (FEA) is a favored tool to investigate these relationships, but limited data for intervertebral disc 3D shape has forced the use of simplified or single-subject geometries, with the effect of inter-individual shape variation investigated only in specialized studies. Similarly, most data on disc shape variation with degeneration is based on 2D mid-sagittal images, which incompletely define 3D shape changes. Therefore, the objective of this study was to quantify inter-individual disc shape variation in 3D, classify this variation into independently-occurring modes using a statistical shape model, and identify correlations between disc shape and degeneration. Three-dimensional disc shapes were obtained from MRI of 13 human male cadaver L3L4 discs. An average disc shape and four major modes of shape variation (representing 90% of the variance) were identified. The first mode represented disc axial area and was significantly correlated to degeneration (R2 = 0.44), indicating larger axial area in degenerate discs. Disc height variation occurred in three distinct modes, each also involving non-height variation. The statistical shape model provides an average L3L4 disc shape for FEA that is fully defined in 3D, and makes it convenient to generate a set of shapes with which to represent aggregate inter-individual variation. Degeneration grade-specific shapes can also be generated. To facilitate application, the model is included in this paper’s supplemental content.
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