Short-term bioeffects of an infrared pulsed laser device on burned rat skin monitored by transverse relaxation times (NMR)

Background and Objective: The aim of this study was to determine whether th e application of an infrared pulsed laser device (IPLD) on the burned skin of rats induced significant changes in the water dynamics of the burned tis sues as measured by nuclear magnetic resonance (NMR) at a proton frequency of 90 MHz by using transverse relaxation times (T-2, I/T-2). Study Design/Materials and Methods: Seven groups (GI-GVII), each consisting of four albino rats (Sprague-Dawley), of 12-14 weeks of age were used in t he experiment. Rats in GI-GVI were anesthetized and burned with a hot tip. GI, GIII, GV were not irradiated. GII, GIV, GVI were irradiated at 0 hours; 0 and 24 hours; and 0, 24, and 48 hours, respectively. Rats in GVII served as controls and were neither burned nor irradiated. Samples from all group s were obtained and monitored by NMR by using transverse relaxation times ( T-2 and 1/T-2). An unpaired Student's t-test and a one-way analysis of vari ance (ANOVA I) were preformed on the mean values obtained (T-2, 1/T-2). The statistical design was chosen to give a 95% power of contrast 1-beta (1/T- 2). The modulated beam of the IPLD used is composed of two superposed waves ; a carrier wave (3 MHz), and a drive force wave in the near infrared (904 nm, f = 10(14) Hz) A dose of 1.5 x 10(3) J/M-2 per session was applied by p lacing the IPLD directly over the burned tissue by using a top-hat distribu tion. Results: The results of a t-test on the T-2 and 1/T-2 values did not show s tatistically significant differences at 0 and 24 hours between the irradiat ed groups, the nonirradiated groups, and the nonburned nonirradiated (contr ol) group. Nonetheless, at 48 hours after the burn, we found a statisticall y significant difference in the 1/T-2 values for the irradiated specimens c ompared with the nonirradiated specimens and the control group. Furthermore , the variance of the 1/T-2 values as a function of time showed a tendency to decrease significantly only for the irradiated specimens. Conclusion: These findings show possible effects on the water dynamics of b urned rat tissue in a short term as a result of the IPLD's application. Las ers Surg. Med. 27:411-419, 2000. (C) 2000 Wiley-Liss, Inc.