Study type: Technical/dosimetric study (experimental study)

Changes in heating patterns due to perturbations by thermometer probes at 915 and 434 MHz tech./dosim.

Published in: Int J Hyperthermia 1988; 4 (4): 447-456

Aim of study (acc. to author)

To study the changes in heating patterns due to perturbations by thermometer probes in microwave fields in static phantoms (filled with muscle equivalent material) at 915 and 434 MHz.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 915 MHz
Exposure duration: 15 s, 30 s and 60 s
Exposure 2: 434 MHz
Exposure duration: 2, 4 and 6 min

Exposure 1

Main characteristics
Frequency 915 MHz
Exposure duration 15 s, 30 s and 60 s
Modulation
Modulation type unspecified
Exposure setup
Exposure source
Chamber Two phantom boxes made of Plexiglas, 7.5 cm deep and 30 cm² filled with muscle equivalent material
Setup The total spacing between the surface of the muscle phantom and the aperture of the applicator was 5/8 in.
Additional info The phantom material was held in place within the slabs or blocks with polyester screen and Plexiglas. Thermistors, thermocouples, Luxtron fibre optic probes and 17 gauge needle implants were placed either between one slab and the square block or on the surface of the block, at different orientations - either parallel, perpendicular or at 45 to the electrical field.
Parameters
Measurand Value Type Method Mass Remarks
power 500 W minimum unspecified - -
power 525 W maximum unspecified - -

Exposure 2

Main characteristics
Frequency 434 MHz
Exposure duration 2, 4 and 6 min
Additional info electric and magnetic fields are complicated at the near field of the applicator
Modulation
Modulation type unspecified
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
power 95 W minimum unspecified - -
power 100 W maximum unspecified - -

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • before exposure
  • after exposure

Main outcome of study (acc. to author)

Thermograms taken parallel to the plane of E (electric) and H (magnetic) fields, at depths of up to 2 cm, indicated heating changes of +25 to -45 per cent at 915 MHz and +/- 15 per cent at 434 MHz. The amount of disturbance is dependent on the length, size and location of the probes in the radiofrequency fields and their orientations to the electric field. Disturbance also varies with applicator designs and phantom geometry.
If thermistors and thermocouples are used, the effects of perturbation should be studied with individual applicators under applicable clinical conditions. Thermistors, thermometers, and thermocouples should be used with caution for hyperthermia treatment.

Study character:

Study funded by