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Proceedings Paper

Effects of polarization in low-level laser therapy of spinal cord injury in rats
Author(s): Takahiro Ando; Shunichi Sato; Hiroaki Kobayashi; Hiroshi Nawashiro; Hiroshi Ashida; Michael R. Hamblin; Minoru Obara
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Paper Abstract

Low-level laser therapy (LLLT) is a promising approach to treat the spinal cord injury (SCI). Since nerve fibers have optical anisotropy, propagation of light in the spinal tissue might be affected by its polarization direction. However, the effect of polarization on the efficacy of LLLT has not been elucidated. In the present study, we investigated the effect of polarization on the efficacy of near-infrared LLLT for SCI. Rat spinal cord was injured with a weight-drop device. The lesion site was irradiated with an 808-nm diode laser beam that was transmitted through a polarizing filter immediately after injury and daily for five consecutive days. The laser power at the injured spinal cord surface was 25 mW, and the dosage per day was 9.6 J/cm2 (spot diameter, 2 cm; irradiation duration, 1200 s). Functional recovery was assessed daily by an open-field test. The results showed that the functional scores of the SCI rats that were treated with 808-nm laser irradiation were significantly higher than those of the SCI alone group (Group 1) from day 5 after injury, regardless of the polarization direction. Importantly, as compared to the locomotive function of the SCI rats that were treated with the perpendicularly-polarized laser parallel to the spinal column (Group 2), that of the SCI rats that were irradiated with the linearly aligned polarization (Group 3) was significantly improved from day 10 after injury. In addition, the ATP contents in the injured spinal tissue of Group 3, which were measured immediately after laser irradiation, were moderately higher than those of Group 2. These observations are attributable to the deeper penetration of the parallelpolarized light in the anisotropic spinal tissue, suggesting that polarization direction significantly affects the efficacy of LLLT for SCI.

Paper Details

Date Published: 9 March 2012
PDF: 7 pages
Proc. SPIE 8211, Mechanisms for Low-Light Therapy VII, 82110B (9 March 2012); doi: 10.1117/12.906951
Show Author Affiliations
Takahiro Ando, Keio Univ. (Japan)
Shunichi Sato, National Defense Medical College Research Institute (Japan)
Hiroaki Kobayashi, National Defense Medical College (Japan)
Hiroshi Nawashiro, National Defense Medical College (Japan)
Hiroshi Ashida, National Defense Medical College Research Institute (Japan)
Michael R. Hamblin, Wellman Ctr. For Photomedicine, Masachusetts General Hospital (United States)
Harvard Medical School (United States)
Harvard-MIT Health Sciences and Technology (United States)
Minoru Obara, Keio Univ. (Japan)

Published in SPIE Proceedings Vol. 8211:
Mechanisms for Low-Light Therapy VII
Michael R. Hamblin; Juanita Anders; James D. Carroll, Editor(s)

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