Gray-scale contrast-enhanced ultrasonography for quantitative evaluation of the blood perfusion of the sciatic nerves with crush injury.

RATIONALE AND OBJECTIVES

Blood perfusion of peripheral nerves plays an important role in regeneration after nerve injury. Functional recovery after a peripheral nerve injury depends not only on the survival of the affected neurons but also on the recovered blood perfusion. Previous studies have shown that it is possible to quantitatively assess blood perfusion of tissue using contrast-enhanced ultrasound (CEUS). The aim of this study was to evaluate the usefulness of CEUS for the quantitative evaluation of blood perfusion of the sciatic nerves with crush injury.

MATERIALS AND METHODS

Crush injuries were created in the left sciatic nerve of 30 New Zealand white rabbits. CEUS of the bilateral sciatic nerves was performed in six experimental rabbits at 3 days, 1 week, 2 weeks, 4 weeks, and 8 weeks after injury. Pulse-inversion harmonic imaging was used for real-time CEUS. The other six rabbits were used as a control group. Serial laser Doppler measurements of blood flow and quantitative histologic evaluation were performed parallel to CEUS on all animals.

RESULTS

Quantitative analysis of CEUS showed that the perfusion index of the crushed sciatic nerves was increased at 3 days after injury, with a peak at 1 week after injury (P = .000). The area under the curve for the crushed sites was increased at 3 days after injury, with a peak at 2 weeks after injury (P = .000). The mean transit time and maximum intensity of the crushed site of the left sciatic nerves were not significantly changed during the 2 months after injury (P = .335 and P = .157 respectively). The perfusion indices measured by CEUS correlated well with those measured by laser Doppler (r = 0.791, P = .000). Marked Wallerian degeneration was found at the crushed site of sciatic nerves at 3 days after injury. The percentage of degenerated myelinated axons was increased during the first 2 weeks after injury and then decreased during the following period. Regenerated axons with small diameter and thin myelin sheaths were found at 2 weeks after injury and during the following period.

CONCLUSIONS

CEUS may provide a new imaging method to quantitatively analyze blood perfusion of injured peripheral nerves.