Identification of motor and sensory fascicles in peripheral nerve trunk using micro-Raman spectroscopy

BACKGROUND: A variety of methods have been used to identify and distinguish motor and sensory nerves. However, their application is limited clinically due to the complex operation, time consumption, and subjectivity. Raman spectroscopy is a minimally invasive method that provides information about molecular structure and constitutions and has been frequently used for tissue identification. OBJECTIVE: To explore a time-efficient method of identifying motor and sensory fascicles in peripheral nerve trunk using laser micro-Raman spectroscopy. DESIGN, TIME AND SETTING: A comparative observation was performed at the Key Laboratory of Excited States Physics in Chinese Academy of Science, Changchun Branch, from October 2004 to October 2005. MATERIALS: JY-HR800 laser confocal micro-Raman spectrometer was purchased from Jobin-Yvon, France; 2060-10 argon ion laser was purchased from Spectra-Physics, USA. METHODS: A total of 32 New Zealand rabbits were selected and sacrificed. The roots of spinal nerves were exposed under an operating microscope, and the anterior and posterior roots, approximately 3-5 mm, were dissociated, and frozen as transverse sections of 30 mu m thickness. The sections were examined by micro-Raman spectroscopy. MAIN OUTCOME MEASURES: The specific spectral features of motor and sensory fascicles in the Raman spectra. RESULTS: Sections of the same type of nerve fascicle showed reproducibility with similar spectral features. Significant differences in the spectral properties, such as the intensity and breadth of the peak, were found between motor and sensory fascicles in the frequency regions of 1 088, 1 276, 1 439, 1 579, and 1 659 cm(-1). With the peak intensity ratio of 1.06 (I-1 276/I-1 439) as a standard, we could identify motor fascicles with a sensitivity of 88%, specificity of 94%, positive predictive value of 93% and negative predictive value of 88%. In the range of 2 700-3 500 cm(-1), the half-peak width of the motor fascicles was narrow and sharp, while that of the sensory fascicles was relatively wider. A total of 91% of the peak features were in accordance with the identification standard. CONCLUSION: Motor and sensory fascicles exhibit different characteristics in Raman spectra, which are constant and reliable. Therefore, it is an effective method to identify nerve fascicles according to the specific spectrum.