P 71 Optical coherence tomography – a future imaging technique of peripheral nerves?

Abstract

Object: Owing to their complex topography, their long courses and their small diameters peripheral nerves are challenging structures for radiological diagnostics. However, imaging techniques in the area of peripheral nerve diseases have undergone unexpected development in recent decades. They include magnetic-resonance imaging (MRI) and high-resolution sonography (HRS). Yet none of those imaging techniques reaches a resolution comparable to that of histological sections. Fascicles are the smallest discernable structure. Optical-coherence tomography (OCT) is the first imaging technique that is able to depict a nerve’s ultrastructure at micrometer resolution. Methods: OCT measurement was performed in 32 patients with different peripheral nerve pathologies, i.e. nerve compression syndromes. The nerves were examined during surgery after exposing. Only the sural nerve was twice examined ex vivo . The OCT systems Thorlabs Callisto and Thorlabs Ganymede were used. For intra-operative use, a hand probe was covered with a sterile foil. Different post-processing imaging techniques were applied and evaluated. Results: The intra-operative use of OCT is easy and intuitive. Image artifacts are mainly caused by motion and the sterile foil. If they are kept at a low level, the hyporeflecting bundles of nerve fascicles and their inner parts can be displayed. In the Haralick evaluation the second angular moment (SAM) is most suitable to depict the connective tissue. Conclusion: OCT is a new imaging technique which has shown to be promising in peripheral nerve surgery for particular questions. Its resolution exceeds that provided by recent radiological possibilities such as MRI and HRS. Since its field of view is relatively small, faster acquisition times would be highly desirable. Currently, the method resembles an optical biopsy and can be a supplement to intra-operative sonography, giving high-resolution insight into a suspect area which has been located by sonography in advance. This could be especially helpful in surgery of peripheral nerve lesions in continuity.