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