Since the dosimetry of this irradiation system is well documented, and the power density of exposure can be adjusted to give different whole-body averaged SARs in the exposed animals, the system provides a reliable means to investigate the dose (SAR)-response relationship of microwave irradiation. This preliminary report describes the effect of varying the power density of microwave exposure on choline uptake in different regions of the brain.
|Exposure duration||continuous for 45 min|
|Pulse width||2 µs|
|Repetition frequency||500 Hz|
|Chamber||The cylindrical waveguide system [Guy et al., 1979] consisted of eight individual exposure tubes consisting of a section of circular waveguide made of galvanized wire screen. The circularly polarised field in TE11 mode propagated from one end of the waveguide to the other end. The rat was housed in a plastic chamber with a floor of glass rods.|
|Sham exposure||A sham exposure was conducted.|
The results show a dose-response relationship of central choline uptake with microwave irradiation. However, different brain areas have different sensitivities to the exposure. Decrease in choline uptake was observed in the striatum at a SAR of 0.75 W/kg and above. For the frontal cortex and hippocampus, decreases in choline uptake were observed at a SAR of 0.45 W/kg and above. No significant effect was observed in the hypothalamus at the irradiation power densities studied. The probit analysis was used to determine the SAR50 in each brain area (i.e. the SAR at which 50% of maximum response was elicited). SAR50 for the striatum, frontal cortex, and hippocampus were 0.65, 0.38, and 0.44 W/kg, respectively.