Study type: Medical/biological study (experimental study)

Normal brain response after interstitial microwave hyperthermia. med./bio.

Published in: Int J Hyperthermia 1991; 7 (5): 795-808

Aim of study (acc. to author)

To assess the extent and time course of radiographic changes induced in dog brain after a single 30 min hyperthermia application (at temperatures of 40, 41, 42, 43 and 44°C). A helical coil microwave antenna was used to induce a small focal lesion in the frontal white matter, and the volumes of necrosis and contrast enhancement were measured weekly for 6 weeks using computed tomography.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 2.45 GHz
Modulation type: CW
Exposure duration: 30 min
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Exposure 1

Main characteristics
Frequency 2.45 GHz
Type
Waveform
Exposure duration 30 min
Modulation
Modulation type CW
Exposure setup
Exposure source
Distance between measurement device and exposed object 5 m
Distance between exposed object and exposure source 0.0135 m
Setup microwave antenna inserted inside the skull
Additional info CT scans for 0.1s at 130 kVp and exposures of 63mAs.
Parameters

No parameters are specified for this exposure.

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)

Heat lesions were characterized by rapid development and resolution and consisted of an area of focal low density surrounded by a ring of contrast enhancement. Histologically, the focus of low density corresponded to regions of tissue necrosis, whereas the ring enhancement showed local reactive changes (including endothelial cell proliferation and infiltration with macrophages).
Tissue necrosis was found at temperatures greater than 43.9 +/- 1.5°C, and volumes of necrosis and ring enhancement were at a maximum 1 week following application. Relative to the contralateral, unheated hemisphere, regional cerebral blood flow in the heated brain appeared to be reduced for the first 3 weeks after application but approached normal by week 4. The mean transit time of blood was increased for weeks 1-3 compared to the untreated hemisphere, and tissue vascularity reached a maximum, 3 weeks after application.
The rapid computed tomography changes together with ultrafast computed tomography and histopathological findings suggest that focal heat lesions in the brain stimulate a significant and rapid vascular response.

Study character:

Study funded by