Purchase this article with an account.
Y. Yamashiro, K. Sato, A. Hirata, M. Kojima, T. Sakai, S. Watanabe, M. Taki, Y. Suzuki, K. Sasaki, H. Sasaki; Normalized Temperature Elevation Velocity in Ocular Tissues by 18-40 GHz Radio- Frequency Exposure. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2390.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Temperature in ocular tissues may be a threshold for injury by radio-frequency exposure. Here, normalized temperature elevation velocity (NTEV) was employed as an indicator to evaluate frequency characteristics of temperature elevation from 18 to 40 GHz.
Anesthetized rabbit eyes were irradiated by radio-frequency through a horn antenna in the frequency range 18, 22, 26.5 GHz (k band), or 26.5, 35, 40 GHz (ka band), at incident power density of 200mW/cm2 for 3 minutes. During the duration, changes in temperature of the cornea, lens, and vitreous were recorded by three thermometer (Fluoroptic thermometer) probes inserted into the center of the respective tissues. Obtained temperatures were compared with frequencies as temperature elevation velocity (TEV) or NTEV in two phases; early phase; 30- 60 seconds, and late phase; 60-180 seconds. Quite-variable first 30 seconds of exposure were eliminated. TEV was calculated as the average temperature elevation value per second, and NTEV as its ratio to the maximum temperature elevation value in each phase. ANOVA and the least-squares method were employed for statistical analysis.
TEV significantly increased linearly in all ocular tissues in both phases except in the vitreous where the effect was only evident in the late phase. NTEV showed no significant effect by frequencies in any tissue during any phase. Comparing TEV and NTEV in the early phase with that in the late phase, both were significantly higher in the early phase for the cornea (p<0.0001), whereas higher in late for the vitreous (p = 0.028), no significant difference was found for the lens.
Dependency of TEV on frequency suggests that the power absorption by ocular tissues may increase temperature with higher frequency. In contrast, NTEV was almost constant regardless of frequency. From this result, the heat conduction is thought to be the major factor for inducing temperature elevation, and the mechanism was not specific to frequency.
This PDF is available to Subscribers Only