Effects of Lumbar Disc Degeneration at the Cartilaginous End Plate and the Annulus Fibrosus on Off-Resonant Saturation Ratios Assessed by a 3D Ultrashort Echo Time Sequence at 3 T
Authors: Gebhard H. , Martirosian P. , Springer F. , Grosse U. , Schick F. , Stoeckle U. , Syah R. 
Published: May 2014

Introduction Biological disc replacement demands a distinct understanding of referring pathologies and states of degeneration. Clinical imaging modalities are needed to apply such measurements to potential patients. The introduction of UTE sequences to whole body magnetic resonance imaging (MRI) allows for quantitative characterization of tissue consisting of components with fast signal decay. We hypothesize that UTE will enable us to differentiate states of degeneration within the EP and the AF. The aim of this study was to investigate effects of LDD on ORS ratios in the cartilaginous EP and the AF. Materials and Methods A total of 20 human lumbar motion segments of seven fresh-frozen cadaveric specimens (median age 66, range 49-66 years) were assessed using a whole-body MRI scanner. A sagittal 3D UTE sequence with an isotropic submillimeter resolution of 0.7 mm (TE 0.07 ms, TR 10.3 ms, FoV 128 mm, FA 10 degrees) with and without off-resonant saturation preparation pulse at 3 T was used. The off-resonance frequency was varied between 1 and 5 kHz. OSRs of images with and without preparation pulse were calculated for the upper and the lower EP as well as for the AF. Intervertebral discs were classified healthy (CO, n = 9), mildly degenerated (MIL, n = 6) and severely degenerated (SEV, n = 8) concerning morphology and signal alteration in conventional MR sequences. A nonparametric U-test was performed to report the level of significance. The relationship between OSR and grade of degeneration was estimated using multiple regression analysis in respect to age and body mass index (BMI). Results Upper and lower EP as well as AF in controls revealed no significant differences concerning OSR from 1 to 5 kHz. Regarding all regions (EPs and AF), the SEV group showed significantly increased OSRs ranging from 0.37 ± 0.01 (1 kHz) to 0.22 ± 0.01 (5 kHz), compared with the CO group, ranging from 0.33 ± 0.01 (1 kHz) to 0.2 ± 0.01 (5 kHz), and the MIL group, ranging from 0.32 ± 0.01 (1 kHz) to 0.2 ± 0.01 (5 kHz) ( p < 0.05). The MIL group showed a tendency toward lower OSR compared with the CO group. This was underlined by the results of multiple regression analysis after adjusting for age (Table A). [Table: see text] Conclusion UTE sequences reveal clear images of human lumbar EP and AF and allow for quantitative assessment of free water. EP and AF of lumbar discs with major degeneration showed a loss of free water content compared with healthy and slightly degenerated discs, indicating a change toward a more condensed structure. EP and AF of slightly degenerated discs, however, showed a tendency to higher OSR, indicating an increase of free water. This might have occurred due to edema or focal destruction of EP and AF in early stages. Focused repair strategies and potential outcome predictors may result from this imaging modality. Disclosure of Interest None declared