Raman laser damage threshold of rat pial cortex
Noh T, Felicella M, Poisson L, Zakaria HM, DeCarvalho A, Broadbent B, Auner G, and Kalkanis S. Raman laser damage threshold of rat pial cortex. Neuro-Oncology 2017; 19:vi239.
INTRODUCTION: Raman spectroscopy utilizes a label-free modality of optical imaging that measures scattered photon shifts to give a unique biochemical signature. Its diagnostic capabilities are currently being explored including its applications to intraoperatively identify tissue and oncologic surgical margins. The goal of the present safety study was to assess the threshold at which a 785nM raman laser damages rat pial cortex. METHODS: Sprague Dawley Rats underwent a craniotomy/durotomy and were randomly assigned to either a sham surgery or exposed to a 785nM raman laser. Initial experiments at 100mW failed to show any damage, and the laser was maximally increased to 180mW and exposure time increased to 10 minutes. Animals were then sacrificed immediately, 3 days and 7 days postoperatively and brains processed for pathologic analysis by 2 neuropathologists using H&E, NFAP, GFAP and Luxol fast blue staining. RESULTS: Two neuropathologists examined all slides and did not detect any changes on sham or exposed brains, thus the laser power was increased to 180mW and exposure time to 10 minutes. Even at the increased power and exposure time, there were no observed differences. CONCLUSION: A 785nM 180mW raman laser does not cause thermal damage to the rat pial cortical surface even with 10 minutes of exposure time. Current diagnostic lasers utilize much lower powers and exposure times. Since the absorption of cerebral components is similar in rat and human tissue, these diagnostic tools are likely safe to use intraoperatively. Further studies are needed at higher laser powers, increasing survival times and human tissue to observe delayed changes that may be detected by stains such as NFAP, GFAP and luxol blue.