Purpose

Low back pain, which is induced by intervertebral disc degeneration in most cases, has seriously affected life quality of patients and the disc nutrient supply is closely related to intervertebral disc degeneration [1,2]. However, it is challenging to detect intervertebral disc generation in imaging, as the morphological changes usually take place at a very late stage. Endplates pathway was considered as a critical way for intervertebral disc main nutrition, and was believed to play an important role in intervertebral disc degeneration. In the past, contrast enhanced imaging has been used to assess the perfusion level of endplate, however only qualitative and semi-quantitative measurements were used [3,4]. In this work, quantitative metrics derived from dynamic susceptibility contrast (DSC) imaging are investigated in evaluating the relationship between endplate perfusion with intervertebral disc degeneration.

Method

A total of 18 patients were enrolled in this study. All participants fulfilled the following criteria: (a) have no scoliosis, acute and chronic trauma, no vertebral benign and malignant tumor and (b) have no blood system disease or other systemic diseases, diabetes, spinal surgery or radiotherapy history, body mass index <27 kg / m2. All the subjects underwent MRI exams including DCE-MRI, T2*mapping as well as conventional lumbar imaging on a 3.0T whole body scanner (MR750, GE, USA). Perfusion parametric maps including Ktrans, Kep, Ve were derived using the Omni Kinetics software (GE life science, USA), and region of interest measurements were made on cranial and caudal vertebral subchondral bone(VSB) and CEP by an experienced radiologist (illustrated in Fig.1). T2* map of nucleus pulposus (NP) of lumbar disc in median sagittal plane were obtained (Fig.2). T2-weighted imaging of lumbar median sagittal plane was used for Pfirrmann classification. One-way ANOVA was employed to judge the difference of the T2* value of different Pfirrmann grades. Pearson correlation analysis were performed between DCE–MRI perfusion parameters and T2* values. One-way ANOVA with post-hoc tests (Newman-Keuls Multiple Comparison Test) was used to judge the difference of the perfusion metrics among these grades.

Results

The derived perfusion parametric maps and T2* of a typical patient are shown in Fig. 2 and Fig.3 respectively. Statistically significant difference was observed in T2* values of different Pfirrmann groups (F=24.34, P<0.0001, Fig. 4), however no correlation between perfusion parameters and T2* values(all r <0.3,P >0.05) was obtained. The perfusion increased at Pfirrmann grade 1-2,decreased at grade 2-3, and then increased at grade 4-5, decreased finally at grade 5(Fig. 5). The cranial VSB Ktrans, Kep, caudal VSB Kep and cranial CEP Kep were statistically significant in different Pfirrmann grades by One-way ANOVA (F=2.701, 5.036, 2.724, 2.714, all P<0.05). Except for the cranial VSB perfusion parameters Kep of Pfirrmann grade 1 and 2, Pfirrmann grade 1 and 4, Pfirrmann grade 3 and 2, Pfirrmann grade 3 and 4, the caudal VSB perfusion parameters Kep of Pfirrmann grade 1 and 4, the cranial CEP Kep of Pfirrmann grade 3 and 2 (q=4.560, 5.059, 3.425, 4.305, 3.996, 4.256, all P<0.05), the other two different grades of perfusion parameters showed no significant difference observed in VSB and CEP.

Discussion

In this study, it was found that T2* showed a negative correlation with the Pfirrmann grades, while showed no correlation with the perfusion parameters. This indicates that not only endplate perfusion but also many other factors may impact the intervertebral disc degeneration process. Muftuler LT et al [3,4] found that Pfirrmann grading and endplate perfusion was positively correlated in their semi quantitative DCE-MRI study, however a variation was observed in this study: the endplate perfusion increased in Pfirrmann grade 2, decreased in Pfirrmann grade 3, then increased in Pfirrmann grade 4 and 5, finally decreased in Pfirrmann grade 5. This difference may be due to the fact that quantitative perfusion metrics may better reveal the pathological process of intervertebral disc degeneration at different stages : at early stage the self-repair metabolism lead to increased blood flow [5]; in following stage their synthetic capacity may deteriorate causing the perfusion level to drop[6]; and vertebral endplate osteochondritis or CEP defect may cause perfusion in discs to raise up again at grade 4 and 5; finally because of complete ossification or loss of the endplate structure and the decrease of vascular structures[7], perfusion return to normal level in the end.

Conclusion

Hence based on this study, it can be concluded that intervertebral disc degeneration had no direct correlation with endplate perfusion level.

References

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