Study type: Medical/biological study (experimental study)

Blood-brain barrier alteration after microwave-induced hyperthermia is purely a thermal effect: I. Temperature and power measurements med./bio.

By: Moriyama E, Salcman M, Broadwell RD
Published in: Surg Neurol 1991; 35 (3): 177-182
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Aim of study (acc. to author)

To answer the following questions: Is there an effect of microwave-induced hyperthermia on blood-brain barrier function, and, if so, is the effect mediated by nonthermal means?

Endpoint

Exposure

Exposure Parameters
Exposure 1: 2.45 GHz
Modulation type: CW
Exposure duration: 30 or 60 min
  • power: 3 W minimum (4 W max value)
  • SAR: 404.2 mW/g maximum (partial body) (in the brain)

Exposure 1

Main characteristics
Frequency 2.45 GHz
Type
Exposure duration 30 or 60 min
Modulation
Modulation type CW
Exposure setup
Exposure source
Setup The head of the animal was fixed to a stereotactic frame. An antenna placed in the bony groove drilled 2 mm lateral to the midline.
Additional info The left hemicranium was covered with an aluminum sheet to prevent exposure to MW and served as control.
Parameters
Measurand Value Type Method Mass Remarks
power 3 W minimum - - 4 W max value
SAR 404.2 mW/g maximum calculated partial body in the brain
Measurement and calculation details

SAR was calculated from the slope of the time-temperature profile using cerebral specific heat and electrical conductivity.

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)

Increased permeability of blood-brain barrier was observed in brain tissue heated above 44.3°C for 30 minutes and at 42.5°C for 60 minutes. Microwave irradiation failed to open the blood-brain barrier when brain temperatures were sustained below 40.3°C by a local cooling system. Opening of blood-brain barrier occured at sites of maximal temperature elevation, even when these did not coincide with the site of maximum power density. The data suggest that microwave-induced increase in permeability of the blood-brain barrier is a thermal effect.

Study character:

Study funded by