Consecutive assessment of recovery after peripheral nerve injury of the sciatic nerve within the same rat using PET/MRI

Background: Positron emission tomography (PET) has been reported as effective in diagnosing peripheral nerve injury (PNI). However, there is a lack of studies evaluating different degrees of PNI using PET within the same individual to reduce errors due to interindividual differences. Purpose: To evaluate the recovery process in the same rat after sciatic nerve injury using PET/magnetic resonance imaging (MRI). Material and Methods: Crushing nerve injuries were induced in the left sciatic nerves of six male rats, preserving the right ones. The degree of nerve damage was measured at one, two, three, four, and five weeks postoperatively using three assessment methods: paw withdrawal threshold test (RevWT); PET (SUVR); and MRI (MRSIR). All the representing values of each method are presented as ratio values of the right and left sides in each rat. Results: Significant gradual recovery of all rats was observed over time in all the methods. No significant differences in RevWT and MRSIR were observed between before and more than four weeks after injury, whereas a significant difference in SUVR was still observed between before and five weeks after injury (P = 0.0007). The parameters of all methods decreased significantly over time (P = 0.000, all), and the explanatory power was significant in RevWT, SUVR, and MRSIR. Conclusion: PET and MRI could be valuable non-invasive techniques for diagnosing neuropathic pain resulting from PNI. PET/MRI would be expected to be a more accurate and informative diagnostic tool for PNI than MRI alone.