111 - Do fractional anisotropy and apparent diffusion coefficient from diffusion tensor imaging correlate to symptoms of radiculopathy? A case series from BACPAC MRI

Introduction
Quantitative diffusion tensor imaging (DTI) parameters such as fractional anisotropy (FA) and apparent diffusion coefficient (ADC) are used to detect axonal pathology in nerve injuries. This case series is among the first to provide consecutive quantitative DTI measurements of the lumbar plexus nerves and correlate the tractography with patient-reported symptoms in those with lumbar plexus radiculopathy in the Back Pain Consortium (BACPAC) cohort.

Methods
The ganglia of the lumbar plexus nerves (L1-5) were manually identified using the region of interest (ROI) method. The regions were input as seeds to track the nerve fibers using Constant Solid Angle reconstruction (CSA). Fiber tracts were extracted using ROIs and values of FA and ADC were extracted along the lumbar plexus nerve profiles. The average measurements were taken per level. Change in patient-reported symptoms in pain (VAS) and disability (ODI) after interlaminar epidural steroid injection at site of compression was compared to the changes in FA and ADC values.

Results
Five exams from three patients with bilateral L4-5 foraminal narrowing were included in this study. Two patients were imaged at two time points, three months apart. The average age of the cohort was 62.6±5.3 years. Mean FA values were lowest at L3 (left: 0.32±0.08; right: 0.35±0.05) and L4 (left: 0.39±0.06; right: 0.38±0.03). Correspondingly, mean ADC values were highest at L3 (left: 0.0017±0.0002; right: 0.0016±0.0001) and L4 (left: 0.0.0013±0.0001; right: 0.0015±0.0002). For one patient, pain did not change in severity and ODI improved from severe to moderate disability after steroid injection: FA increased (L5: 0.33±0.02 to 0.36±0.01; L4: 0.42±0.01 to 0.40±0.01) with no significant change in ADC (L5: 0.0015±0.0001 to 0.0017±0.0001; L4: 0.0013±0.00003 to 0.0013±0.0001). For another patient, pain increased from moderate to severe and ODI stayed the same after injection: FA decreased (L5: 0.41±0.02 to 0.29±0.01; L4: 0.41±0.02 to 0.36±0.02) and ADC did not significantly change (L5: 0.0015±0.0001 to 0.0013±0.0001; L4: 0.0016±0.0001 to 0.0014±0.0001).

Conclusion
The tractography generated from the segmentation model demonstrated lowest FA and highest ADC values corresponding to the level of compression. For patient outcomes, the FA values were observed to be more sensitive to changes in pain and disability compared to the ADC values.