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A quantitative and clinical evaluation of nerve root in lumbosacral radiculopathy using diffusion tensor imaging1The First Affiliated Hospital With Nanjing Medical University, NanJing, China, 2GE Healthcare, MR Research China, Beijing, China
Synopsis
In this study, we aimed to investigate if diffusion tensor imaging technique can quantitatively evaluate nerve root in lumbosacral radiculopathy by measuring MR fractional anisotropy (FA) values. By measuring 34 patients with unilateral disc related lumbosacral nerve root compression, we found that the mean FA value of nerve root correlate significantly with JOA score that is performed on the clinical function of the patients. Therefore, we can demonstrate that DTI can quantitatively and clinically evaluate nerve root by measuring FA values in disc related lumbosacral radiculopathy.
INTRODUCTION
Lumbosacral radiculopathy occurs in approximately 5–25% of the population in the world, and this disease mostly affects the working-age group between 35 and 55 years old1-4. Conventional magnetic resonance imaging (MRI), as an attractive noninvasive image technique for high resolution imaging, has been used to diagnose lumbosacral spinal diseases5. However, due to the lack of quantitative information, it may be limited for further application in the evaluation of lumbosacral radiculopathy. Diffusion tensor imaging (DTI), as a promising functional MRI method, can provide fractional anisotropy (FA) values reflecting the directionality of molecular diffusion, and thus has been used to image nerve fiber tracts in the central nervous system or peripheral nerves6-7. However, it remains unknown if DTI is also feasible to evaluate the nerve fibers in lumbosacral radiculopathy. Therefore, in this study the main aims were to firstly investigate if DTI technique can quantitatively evaluate nerve roots with FA values in lumbar intervertebral disc related compression of lumbosacral plexus nerve root, and secondly to evaluate the potential clinical value of DTI in preoperative diagnosis and prognosis evaluation of disc related lumbosacral nerve root compression.METHODS
Subjects
In total 34 patients (mean ages 47.2±10.2 years old) with unilateral disc related lumbosacral nerve root compression were recruited for DTI measurement in this study. JOA score8 was performed on the clinical function of the patients
MR experiments
All experiments were performed on a 3T clinical scanner (Discovery 750w, GE Healthcare, Milwaukee, WI, USA) equipped with a body coil. A diffusion tensor imaging technique was employed for lumbosacral plexus imaging with scan parameters of MPG, 11 directions; 800 s/mm2 for the b-value; 6000/80 ms for TR/TE; axial orientation, 4/0-mm slice thickness/gap; 420 mm × 420 mm FOV; 96 matrix × 128 matrix; 4.38 mm × 3.28 mm × 4.0 mm actual voxel size; 1.64 mm × 1.64 mm × 4.0 mm calculated voxel size; 4 excitations; 60 slices; and a scan time of 7 minutes 24 seconds.
Data analysis
All data were processed at a workstation (Advantage workstation 4.6; GE Medical Systems). GE Functool software was used for FA mapping and tractography. A log-linear fitting method was used to calculate the diffusion tensor. The regions of interest (ROIs) were placed at three levels for calculating FA values: proximal, medial, and distal to the lumbar foraminal zone9.SPSS software (version 18.0.0; SPSS Inc., Chicago, IL) was used to perform statistical analysis. The embedded paired-t test toolbox was used to compare the FA values of nerves between the symptomatic and asymptomatic sides at three levels. The Pearson correlation analysis was conducted for the correlation between the clinical JOA scores and the FA values of nerves at three levels. The significant threshold for data analysis was set as p=0.05.
RESULTS
As shown in Figure 1, tractograms showed distinct abnormalities in the symptomatic nerve tracts. On the symptomatic side of nerve roots, the mean FA values showed a significant declining trend from proximal to distal (mean FA value of three levels: proximal 0.227±0.047, medial 0.207±0.030, distal 0.183±0.024; p＜0.05; Fig.2). No significant differences were observed between the three levels for nerves on the asymptomatic side. The FA values of the symptomatic side of the nerve roots were significantly lower than those of the asymptomatic side at the proximal, medial and distal levels (in the asymptomatic side mean FA value of three levels: proximal 0.281±0.027, medial 0.291±0.030, distal 0.266±0.028; p＜0.05; Fig.3). The mean FA value of nerve root correlated significantly with JOA score (p＜0.05; Fig.4).DISCUSSION
In this study, an increase in diffusion perpendicular to the largest eigenvalue occurs leading to a decrease in FA values10-11. The decrease showed a correlation with the axonal degeneration which caused significant clinical symptoms. The mean FA values were statistically lower in the compressed nerve root9. Results showed a positive correlation between the JOA score and the mean FA values. JOA score was calculated clinically by the abnormal sensation and motion dysfunction symptoms in lumbosacral radiculopathy. Hence, the clinical changes of patients that suffer from lumbar intervertebral disc related radiculopathy can be quantitatively evaluated by measuring FA values.CONCLUSION
DTI imaging for nerve root in lumbosacral radiculopathy has demonstrated that lumbosacral radiculopathy can be evaluated quantitatively and clinically by measuring FA values of nerve roots.Acknowledgements
No acknowledgement found.References
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Figures
Fig.1 Diffusion tensor tractogram of lumbosacral plexus nerve.
A Tractograms showed abnormalities located as right L5 nerve root. B ractograms showed abnormalities located as right S1 nerve root. Tractograms distinctly showed abnormalities in the symptomatic nerve tracts, such as narrowing, rarefaction, emargination, and interruption in their route through the lumbar foramen (arrows)
