Temperature-time profile in rats subjected to selective microwave irradiation of the brain med./bio.

To measure real-time cortical and colonic temperature changes in rats irradiated for 20 min by a 2450 MHz contact radiator at the animals head.

• animal
• rat/Wistar
• partial body: head

Lower power densities (up to 0.7 mW/cm²) yielded a small cortical temperature increase below that for the body core whereas higher power densities produced a greater temperature rise of the cortex (the rise in cortical temperature surpassed that for the colonic temperature). Even at an incident power density as high as 875 mW/cm² (that resulted in a SAR of 70 mW/g in the brain) the cortical temperature increased by less than 3.0°C while the colonic temperature rose by 0.5°C. The temperature of the cortex rapidly rose during the initial transient period of exposure. It soon became nonlinear and achieved a steady-state level around 39°C. From these observations the authors concluded that the brain temperature was lowered by thermoregulatory processes involving blood circulation, temperature, and mass differences between the brain and the non-exposed body of the animals, and furthermore, the exposed brain received significant protection from the nonirradiated body.