Study type: Medical/biological study (experimental study)

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

Published in: IEEE Trans Biomed Eng 1981; 28 (1): 29-31

Aim of study (acc. to author)

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.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 2.45 GHz
Modulation type: pulsed
Exposure duration: 20 min
Exposure 2: 2.45 GHz
Modulation type: pulsed
Exposure duration: 20 min
Exposure 3: 2.45 GHz
Modulation type: pulsed
Exposure duration: 20 min
Exposure 4: 2.45 GHz
Modulation type: pulsed
Exposure duration: 20 min
Exposure 5: 2.45 GHz
Modulation type: pulsed
Exposure duration: 20 min

Exposure 1

Main characteristics
Frequency 2.45 GHz
Type
Exposure duration 20 min
Modulation
Modulation type pulsed
Pulse width 10 µs
Repetition frequency 25 Hz
Exposure setup
Exposure source
  • Radiator (aperture 14 mm diameter)
Setup Anethetized animals were placed prone over a Polyfoam stand or body holder with the top of the head in horizontal position. The radiator was in contact with left side of the rats head irradiating only the left hemisphere of the brain.
Parameters
Measurand Value Type Method Mass Remarks
power density 1.8 W/m² mean calculated - -

Exposure 2

Main characteristics
Frequency 2.45 GHz
Type
Exposure duration 20 min
Modulation
Modulation type pulsed
Pulse width 10 µs
Repetition frequency 50 Hz
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power density 3.5 W/m² mean calculated - -

Exposure 3

Main characteristics
Frequency 2.45 GHz
Type
Exposure duration 20 min
Modulation
Modulation type pulsed
Pulse width 10 µs
Repetition frequency 100 Hz
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power density 7 W/m² mean calculated - -

Exposure 4

Main characteristics
Frequency 2.45 GHz
Type
Exposure duration 20 min
Modulation
Modulation type pulsed
Pulse width 10 µs
Repetition frequency 500 Hz
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power density 35 W/m² mean calculated - -

Exposure 5

Main characteristics
Frequency 2.45 GHz
Type
Exposure duration 20 min
Modulation
Modulation type pulsed
Pulse width 10 µs
Repetition frequency 500 Hz
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
SAR 70 mW/g unspecified unspecified partial body in the rat brain.
power density 875 W/m² mean calculated - -

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

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.

Study character:

Study funded by

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