| Co-Investigator(Kenkyū-buntansha) |
MORITA Kiyoshi OKAYAMA UNIVERSITY, Graduate School of Medicine and Dentistry, Professor, 大学院・医歯学総合研究科, 教授 (40108171)
TAKEDA Yoshimasa OKAYAMA UNIVERSITY, University hospital, Assistant professor, 医学部・歯学部附属病院, 助手 (30294466)
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| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2003: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2002: ¥2,700,000 (Direct Cost: ¥2,700,000)
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| Research Abstract |
Although recent surgical microscopes for neurosurgery are equipped with xenon light sources to obtain bright fields of vision, the safety of a xenon beam, which has a strong spectral peak in 365-nm ultraviolet light, for cortical neurons has not been evaluated. Cranial windows were made in the parietal bones of gerbils. The skull of each gerbil was covered with warmed saline (0.5 mm in depth) to maintain the brain temperature. Ultraviolet irradiation (365-nm) was performed for 30 minutes at the energy levels of 9.6, 4.4, 1.3 and 0.3 mwatts/cm^2, and neuronal damage was observed in 90±4%, 42±23%, 9±6% and O±0% of pyramidal cells in the parietal cortex 24 hours later. With use of logistic regression curve, the energy level causing 50% of neuronal damage was estimated to be 5.4 mwatts/cm^2. By increasing the thickness of saline layer over the skull surface (1 and 2mm), neuronal damages were significantly attenuated (21±18% and l0±8%, respectively, 4.4 mwatts/cm^2). Since the highest energy levels of 365-nm ultraviolet rays emitted from surgical microscopes measured in the present study (0.379 mwatts/cm^2) was much closer to the dose causing 0% damage than to the dose causing 9% damage, the risk of neuronal injury occurring during microsurgery could be negligible. However, care should be taken to patients who take medicine classified as photosensitizing agents, such as diphenylhydantoin, which are thought to concentrate ultraviolet energy. The use of saline over the cortical surface may be beneficial for reducing the detrimental effects of 365-nm ultraviolet light.
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